subject:( Massive Stars )

Queens University

1. David-Uraz, Alexandre. Investigating the potential magnetic origin of wind variability in OB stars .

Degree: Physics, Engineering Physics and Astronomy, 2016, Queens University

URL: http://hdl.handle.net/1974/14445

► In this thesis, the origin of large-scale structures in hot star winds, believed to be responsible for the presence of discrete absorption components (DACs) in… (more)

▼ In this thesis, the origin of large-scale structures in hot star winds, believed to be responsible for the presence of discrete absorption components (DACs) in the absorption troughs of ultraviolet resonance lines, is constrained using both observations and numerical simulations. These structures are understood as arising from bright regions on the stellar surface, although their physical cause remains unknown. First, we use high quality circular spectropolarimetric observations of 13 well-studied OB stars to evaluate the potential role of dipolar magnetic fields in producing DACs. We perform longitudinal field measurements and place limits on the field strength using Bayesian inference, assuming that it is dipolar. No magnetic field was detected within this sample. The derived constraints statistically refute any significant dynamical influence from a magnetic dipole on the wind for all of these stars, ruling out such fields as a cause for DACs. Second, we perform numerical simulations using bright spots constrained by broadband optical photometric observations. We calculate hydrodynamical wind models using three sets of spot sizes and strengths. Co-rotating interaction regions are yielded in each model, and radiative transfer shows that the properties of the variations in the UV resonance lines synthesized from these models are consistent with those found in observed UV spectra, establishing the first consistent link between UV spectroscopic line profile variability and photometric variations and thus supporting the bright spot paradigm (BSP). Finally, we develop and apply a phenomenological model to quantify the measurable effects co-rotating bright spots would have on broadband optical photometry and on the profiles of photopheric lines in optical spectra. This model can be used to evaluate the existence of these spots, and, in the event of their detection, characterize them. Furthermore, a tentative spot evolution model is presented. A preliminary analysis of its output, compared to the observed photometric variations of xi Persei, suggests the possible existence of “active longitudes” on the surface of this star. Future work will expand the range of observational diagnostics that can be interpreted within the BSP, and link phenomenology (bright spots) to physical processes (magnetic spots or non-radial pulsations).

Subjects/Keywords: astrophysics ; stellar winds ; massive stars

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APA (6^th Edition):

David-Uraz, A. (2016). Investigating the potential magnetic origin of wind variability in OB stars . (Thesis). Queens University. Retrieved from http://hdl.handle.net/1974/14445

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

David-Uraz, Alexandre. “Investigating the potential magnetic origin of wind variability in OB stars .” 2016. Thesis, Queens University. Accessed March 05, 2021. http://hdl.handle.net/1974/14445.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

David-Uraz, Alexandre. “Investigating the potential magnetic origin of wind variability in OB stars .” 2016. Web. 05 Mar 2021.

Vancouver:

David-Uraz A. Investigating the potential magnetic origin of wind variability in OB stars . [Internet] [Thesis]. Queens University; 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1974/14445.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

David-Uraz A. Investigating the potential magnetic origin of wind variability in OB stars . [Thesis]. Queens University; 2016. Available from: http://hdl.handle.net/1974/14445

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Queens University

2. Grunhut, Jason. A detailed observational analysis of magnetism in three B and O stars observed within the context of the MiMeS project .

Degree: Physics, Engineering Physics and Astronomy, 2012, Queens University

URL: http://hdl.handle.net/1974/7546

► The detailed observational analysis of three massive B- and O-type stars was carried out in this study in order to characterize their fundamental, magnetic, and… (more)

▼ The detailed observational analysis of three massive B- and O-type stars was carried out in this study in order to characterize their fundamental, magnetic, and variability properties. The bulk of the data acquired were obtained with the high-resolution ESPaDOnS spectropolarimeter at the Canada-France-Hawaii telescope, within the context of the Magnetism in Massive Stars (MiMeS) project. Two of these stars (HR5907 and HD57682) are newly detected magnetic stars, discovered from observations acquired as part of the broader survey component of the MiMeS program, while the last star, ω Ori, was previously reported as magnetic in the literature. The rotation periods of HR5907 and HD57682 were inferred from photometric, Hα emission and longitudinal field variations. A period of 0.508276 was inferred for HR5907, making this the shortest period, non-degenerate, magnetic massive star identified to date. Furthermore, ultraviolet and optical spectroscopy were combined to infer the fundamental properties of HR5907 and HD57682. Direct modelling of the Least-Squares Deconvolved line profiles and the longitudinal magnetic field measurements were used to infer the magnetic properties of HR5907, HD57682, and ω Ori. A detailed investigation of the newly obtained and archival polarimetric data of ω Ori revealed no convincing evidence for a magnetic field, despite evidence of variability in some emission quantities in this dataset, which had been previously attributed to a large-scale magnetic field. The strength and variability of the optical photospheric helium lines of HR5907 suggests that this star is He-rich, with a non-uniform distribution of its surface chemistry. Lastly, the emission variations in the hydrogen lines of HR5907 suggest this star hosts a highly-structured, rigidly-rotating, centrifugally supported magnetosphere. Similarly, line profile variations throughout the optical spectrum of HD57682 are attributed to emission variations caused by a rotationally-modulated, dynamical magnetosphere. As magnetism in massive stars is a relatively rare and poorly-studied phenomenon, these studies comprise the bulk of the detailed investigations of magnetic massive stars carried out to date. The results of these investigations are also discussed in the context of addressing the current outstanding issues related to magnetism in massive stars.

Subjects/Keywords: Magnetism ; Magnetosphere ; Magnetometry ; Massive Stars

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APA (6^th Edition):

Grunhut, J. (2012). A detailed observational analysis of magnetism in three B and O stars observed within the context of the MiMeS project . (Thesis). Queens University. Retrieved from http://hdl.handle.net/1974/7546

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Grunhut, Jason. “A detailed observational analysis of magnetism in three B and O stars observed within the context of the MiMeS project .” 2012. Thesis, Queens University. Accessed March 05, 2021. http://hdl.handle.net/1974/7546.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Grunhut, Jason. “A detailed observational analysis of magnetism in three B and O stars observed within the context of the MiMeS project .” 2012. Web. 05 Mar 2021.

Vancouver:

Grunhut J. A detailed observational analysis of magnetism in three B and O stars observed within the context of the MiMeS project . [Internet] [Thesis]. Queens University; 2012. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1974/7546.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Grunhut J. A detailed observational analysis of magnetism in three B and O stars observed within the context of the MiMeS project . [Thesis]. Queens University; 2012. Available from: http://hdl.handle.net/1974/7546

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

3. BOIAN, IOANA. Connecting evolved massive stars to interacting supernovae.

Degree: School of Physics. Discipline of Physics, 2021, Trinity College Dublin

URL: http://hdl.handle.net/2262/94297

► Massive stars and supernovae are not only remarkable objects on their own but they are closely related to many other topics in Astrophysics, such as… (more)

▼ Massive stars and supernovae are not only remarkable objects on their own but they are closely related to many other topics in Astrophysics, such as nucleosynthesis, star formation, and gravitational waves. However the properties of massive stars at late stages and their links to supernovae are not well understood.In our work we aim to improve the knowledge on these topics, by studying the spectra of evolved massive stars and the early spectra of supernovae that interact with the winds/atmospheres of massive stars, as they provide valuable information about supernova progenitors, such as mass-loss rates, wind velocities, and surface abundances.We use the radiative transfer code for expanding atmospheres in non-local thermodynamic equilibrium, CMFGEN. The code makes no assumptions for the source of radiative energy at the inner boundary and hence can be employed in modelling both stars with dense atmospheres/winds and eject a from explosive events interacting with the circumstellar material. Supernova progenitors are usually constrained from post-explosion data, but in exceptional cases they have been directly observed, mainly photometrically, and on even rarer occasions spectroscopically. Such is the case of SN 2015bh,a transient whose post-explosion fate is unknown, with a spectrum taken 1.5 yrs pre-explosion. In the first part of this thesis we aim to determine the progenitor properties of SN 2015bh using CMFGEN. Modelling the pre-explosion spectrum of SN 2015bh shows that the star had an effective temperature between8 700 and 10 000 K, luminosity of 1.8?4.74?106L, mass-loss rate of 0.6?1.5?10?3Myr?1, a wind terminal velocity of 1000 km s?1, and contained at least 25% H in mass at the surface, and half-solar Fe abundances. Therefore we conclude that the progenitor of SN 2015bh was a warm luminous blue variable star with an extended wind. Given the high wind velocity there is also the possibility the star was an inflated Wolf-Rayet star. If SN 2015bh was an impostor, we expect late-time spectroscopy to reveal either a similar luminous blue variable star or a Wolf-Rayet star, depending on how much H it retained in its envelope. If it was a genuine supernova, its minimum mass of 35M at the pre-supernova stage makes it a remarkable case of a successful explosion with black-hole formation.In the second part of this thesis, we investigate the post-explosion proper-ties of massive stars. We built an extensive library of spectra simulating the interaction of supernovae with their progenitor?s circumstellar medium at early times. We considered a range of progenitor mass-loss rates ( ?M=5?10?4to10?2Myr?1), abundances (solar-like, CNO-processed, and He-rich), and explosion luminosities (L=1.9?108to 2.5?1010L). The diversity of massive star properties at the pre-supernova stage causes a variety of early-time interacting supernovae. We recognise three main classes of early-time spectra based on the ionisation stages of the species present, i.e. high (e.g. HeIIand OVI), medium(e.g. CIIIand… Advisors/Committee Members: Groh, Jose.

Subjects/Keywords: astrophysics; supernovae; massive stars

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APA (6^th Edition):

BOIAN, I. (2021). Connecting evolved massive stars to interacting supernovae. (Thesis). Trinity College Dublin. Retrieved from http://hdl.handle.net/2262/94297

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

BOIAN, IOANA. “Connecting evolved massive stars to interacting supernovae.” 2021. Thesis, Trinity College Dublin. Accessed March 05, 2021. http://hdl.handle.net/2262/94297.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

BOIAN, IOANA. “Connecting evolved massive stars to interacting supernovae.” 2021. Web. 05 Mar 2021.

Vancouver:

BOIAN I. Connecting evolved massive stars to interacting supernovae. [Internet] [Thesis]. Trinity College Dublin; 2021. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2262/94297.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

BOIAN I. Connecting evolved massive stars to interacting supernovae. [Thesis]. Trinity College Dublin; 2021. Available from: http://hdl.handle.net/2262/94297

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Illinois – Urbana-Champaign

4. Lee, I-Jen. Understanding star formation at early stages in the filamentary era.

Degree: PhD, 0333, 2013, University of Illinois – Urbana-Champaign

URL: http://hdl.handle.net/2142/44802

► This thesis presents a study of star formation at early stages in the filamentary era with a special focus on massive star and cluster formation.… (more)

▼ This thesis presents a study of star formation at early stages in the filamentary era with a special focus on massive star and cluster formation. We first investigate the importance of filamentary structures in star formation and propose an observationally driven scenario for the evolution of filamentary structures from large-scale molecular clouds to small-scale circumstellar envelopes. In addition, as theories of star formation have gradually shifted from individual, isolated objects to the formation of clusters over the decade, we study the environment in the protocluster IRAS 05345+3157 to better understand the initial conditions for cluster formation. With CS(2-1) observations using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) observatory, we have identified seven dense gas cores in this region and discussed the role of initial turbulence. The gas cores require an external pressure of 10⁸ K cm^-3 to be bound to form possible seeds for future protostars. Furthermore, to understand massive star formation, we study the structure and kinematics of nine starless cores in Orion. As two main models about massive star formation, the turbulent core model and the competitive accretion model, predict different level of fragmentation in massive starless cores, our results from high angular resolution observations with CS(2-1) using CARMA show three to five fragments associated with each core, in a broad consistency with the models involving turbulent fragmentation. The number of fragments suggest that magnetic fields may be playing a role in suppressing the fragmentation. Also, the spectral data from the IRAM CS(2-1) observations of several cores show consistency with a picture of converging flows along a filament toward the core center; these flows may be important in massive and cluster formation. Our result does not fully support either the turbulent core scenario or the competitive accretion scenario. Finally, we present the first results from the CARMA Large Area Star Formation Survey (CLASSy) toward Serpens Main, NGC 1333, and Barnard 1. The project provides an unique opportunity to study cold, dense gas structure at millimeter wavelengths from 1500 AU to a few parsecs. The data reveal some exciting properties in morphological and kinematic structures for the first time, and will be unveiling more underlying physics in the star formation process in the future. Advisors/Committee Members: Looney, Leslie W. (advisor), Looney, Leslie W. (Committee Chair), Crutcher, Richard M. (committee member), Mouschovias, T. Ch. (committee member), Wong, Tony (committee member).

Subjects/Keywords: Star formation; Massive stars; Protocluster formation

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APA (6^th Edition):

Lee, I. (2013). Understanding star formation at early stages in the filamentary era. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/44802

Chicago Manual of Style (16^th Edition):

Lee, I-Jen. “Understanding star formation at early stages in the filamentary era.” 2013. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed March 05, 2021. http://hdl.handle.net/2142/44802.

MLA Handbook (7^th Edition):

Lee, I-Jen. “Understanding star formation at early stages in the filamentary era.” 2013. Web. 05 Mar 2021.

Vancouver:

Lee I. Understanding star formation at early stages in the filamentary era. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2013. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2142/44802.

Council of Science Editors:

Lee I. Understanding star formation at early stages in the filamentary era. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2013. Available from: http://hdl.handle.net/2142/44802

University of Minnesota

5. Grammer, Skyler. The massive Star Population in M101.

Degree: PhD, 2014, University of Minnesota

URL: http://hdl.handle.net/11299/167865

► An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. Very little is known about the origin of these… (more)

▼ An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. Very little is known about the origin of these giant eruptions and their progenitors which are presumably very-massive, evolved stars such as luminous blue variables, hypergiants, and supergiants. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the luminous and evolved massive star populations in several nearby galaxies. We aim to identify the likely progenitors of the giant eruptions, study the spatial variations in the stellar populations, and examine the relationship between massive star populations and their environment.The work presented here is focused on stellar populations in the relatively nearby, giant, spiral galaxy M101 from sixteen archival BVI HST/ACS images. We create a catalog of stars in the direction to M101 with photometric errors < 10% for V < 24.5 and 50% completeness down to V = 26.5 even in regions of high stellar crowding. Using color and magnitude criteria we have identified candidate luminous OB type stars and blue supergiants, yellow supergiants, and red supergiants for future observation. We examine their spatial distributions across the face of M101 and find that the ratio of blue to red supergiants decreases by two orders of magnitude over the radial extent.From our catalog, we derive the the star formation history (SFH) for the stellar populations in five 2' wide annuli by fitting the color-magnitude diagrams. Binning the SFH into time frames corresponding to populations traced by Halpha, far ultraviolet (FUV), and near ultraviolet (NUV) emission, we show that the fraction of stellar populations young enough to contribute in Halpha is 15% " 35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of Halpha emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into the modeled ratios, we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant. Though photometry has proven to be a powerful tool to identify candidate evolved massive stars and their effects on their host galaxy, spectroscopy is necessary to study the physical properties of individual stars. We observed moderate-resolution optical spectra for 56 of the brightest stars in the direction to M101 using the Multiple Mirror Telescope. We also created light curves for each target using multi-epoch UBV R images from the Large Binocular Telescope. We separate the spectroscopially confirmed members of M101 into four groups: hot…

Subjects/Keywords: Galaxies; Massive Stars; Stellar evolution; Astrophysics

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APA (6^th Edition):

Grammer, S. (2014). The massive Star Population in M101. (Doctoral Dissertation). University of Minnesota. Retrieved from http://hdl.handle.net/11299/167865

Chicago Manual of Style (16^th Edition):

Grammer, Skyler. “The massive Star Population in M101.” 2014. Doctoral Dissertation, University of Minnesota. Accessed March 05, 2021. http://hdl.handle.net/11299/167865.

MLA Handbook (7^th Edition):

Grammer, Skyler. “The massive Star Population in M101.” 2014. Web. 05 Mar 2021.

Vancouver:

Grammer S. The massive Star Population in M101. [Internet] [Doctoral dissertation]. University of Minnesota; 2014. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/11299/167865.

Council of Science Editors:

Grammer S. The massive Star Population in M101. [Doctoral Dissertation]. University of Minnesota; 2014. Available from: http://hdl.handle.net/11299/167865

University of St. Andrews

6. Johnston, Katharine G. Observational signatures of massive star formation : an investigation of the environments in which they form, and the applicability of the paradigm of low-mass star formation .

Degree: 2011, University of St. Andrews

URL: http://hdl.handle.net/10023/1895

► This thesis presents both a study of the cluster-scale environments in which massive stars form, investigating in particular how the ionized gas in these regions… (more)

▼ This thesis presents both a study of the cluster-scale environments in which massive stars form, investigating in particular how the ionized gas in these regions relates to the molecular star-forming material, as well as detailed studies of two luminous forming stars, AFGL 2591 and IRAS 20126+4104, to determine whether they are forming similarly to their low-mass counterparts. The results of this work include the identification of 35 HII regions (20 newly discovered) via a radio continuum survey of ionized gas towards 31 molecular cluster-forming clumps. The observed ionized gas was found to be preferentially associated with the clumps, which were shown to have a range of evolutionary stages. The massive star formation efficiency was determined for the clumps with associated ionized gas, and a relationship was found between the mass of the clumps and the mass of their embedded massive stars. By modelling the SEDs and images of AFGL 2591 and IRAS 20126+4104, it was found that the geometry of their circumstellar material was generally consistent with an envelope plus disk, similar to that expected for low-mass protostars. However, within the central ~1800 AU, the mid-IR images of IRAS 20126+4104 were better described by only a flattened envelope, suggesting that the radiation from IRAS 20126+4104 may be affecting the regions closest to the star. Observations of the ionized and molecular gas towards AFGL 2591 were carried out, and a photoionization code was developed to interpret these observations. The results showed that the observed 3.6 cm emission is likely to be produced by both a shock-ionized jet and a hypercompact HII region that does not appear to have disrupted the jet or the large-scale circumstellar environment. In addition, the C¹⁸O(1-0) emission observed towards AFGL2591 traces the densest parts of the outflow, with the blue-shifted emission exhibiting many of the properties of the outflows from low-mass protostars. Advisors/Committee Members: Wood, Kenny (advisor).

Subjects/Keywords: Astronomy; Star formation; Massive stars; Modelling; Observations; Young stars

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APA (6^th Edition):

Johnston, K. G. (2011). Observational signatures of massive star formation : an investigation of the environments in which they form, and the applicability of the paradigm of low-mass star formation . (Thesis). University of St. Andrews. Retrieved from http://hdl.handle.net/10023/1895

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Johnston, Katharine G. “Observational signatures of massive star formation : an investigation of the environments in which they form, and the applicability of the paradigm of low-mass star formation .” 2011. Thesis, University of St. Andrews. Accessed March 05, 2021. http://hdl.handle.net/10023/1895.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Johnston, Katharine G. “Observational signatures of massive star formation : an investigation of the environments in which they form, and the applicability of the paradigm of low-mass star formation .” 2011. Web. 05 Mar 2021.

Vancouver:

Johnston KG. Observational signatures of massive star formation : an investigation of the environments in which they form, and the applicability of the paradigm of low-mass star formation . [Internet] [Thesis]. University of St. Andrews; 2011. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10023/1895.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Johnston KG. Observational signatures of massive star formation : an investigation of the environments in which they form, and the applicability of the paradigm of low-mass star formation . [Thesis]. University of St. Andrews; 2011. Available from: http://hdl.handle.net/10023/1895

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Queens University

7. Shultz, Matthew. The Rotational Evolution and Magnetospheric Emission of the Magnetic Early B-type Stars .

Degree: Physics, Engineering Physics and Astronomy, 2016, Queens University

URL: http://hdl.handle.net/1974/14691

► How do the magnetic fields of massive stars evolve over time? Are their gyrochronological ages consistent with ages inferred from evolutionary tracks? Why do most… (more)

▼ How do the magnetic fields of massive stars evolve over time? Are their gyrochronological ages consistent with ages inferred from evolutionary tracks? Why do most stars predicted to host Centrifugal Magnetospheres (CMs) display no Hα emission? Does plasma escape from CMs via centrifugal breakout events, or by a steady-state leakage mechanism? This thesis investigates these questions via a population study with a sample of 51 magnetic early B-type stars. The longitudinal magnetic field \bz~was measured from Least Squares Deconvolution profiles extracted from high-resolution spectropolarimetric data. New rotational periods P_rot were determined for 15 stars from \bz, leaving only 3 stars for which P_rot is unknown. Projected rotational velocities \vsini~were measured from multiple spectral lines. Effective temperatures and surface gravities were measured via ionization balances and line profile fitting of H Balmer lines. Fundamental physical parameters, \bz, \vsini, and P_rot were then used to determine radii, masses, ages, dipole oblique rotator model, stellar wind, magnetospheric, and spindown parameters using a Monte Carlo approach that self-consistently calculates all parameters while accounting for all available constraints on stellar properties. Dipole magnetic field strengths B_d follow a log-normal distribution similar to that of Ap stars, and decline over time in a fashion consistent with the expected conservation of fossil magnetic flux. P_rot increases with fractional main sequence age, mass, and B_d, as expected from magnetospheric braking. However, comparison of evolutionary track ages to maximum spindown ages t_S,max shows that initial rotation fractions may be far below critical for stars with M_*>10 M_\odot. Computing t_S,max with different mass-loss prescriptions indicates that the mass-loss rates of B-type stars are likely much lower than expected from extrapolation from O-type stars. Stars with Hα in emission and absorption occupy distinct regions in the updated rotation-magnetic confinement diagram: Hα-bright stars are found to be younger, more rapidly rotating, and more strongly magnetized than the general population. Emission strength is sensitive both to the volume of the CM and to the mass-loss rate, favouring leakage over centrifugal breakout.

Subjects/Keywords: Stellar Winds ; Binary Stars ; Magnetospheres ; Massive Stars ; Magnetic Braking ; Stellar Magnetism ; Spectropolarimetry

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APA (6^th Edition):

Shultz, M. (2016). The Rotational Evolution and Magnetospheric Emission of the Magnetic Early B-type Stars . (Thesis). Queens University. Retrieved from http://hdl.handle.net/1974/14691

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Shultz, Matthew. “The Rotational Evolution and Magnetospheric Emission of the Magnetic Early B-type Stars .” 2016. Thesis, Queens University. Accessed March 05, 2021. http://hdl.handle.net/1974/14691.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Shultz, Matthew. “The Rotational Evolution and Magnetospheric Emission of the Magnetic Early B-type Stars .” 2016. Web. 05 Mar 2021.

Vancouver:

Shultz M. The Rotational Evolution and Magnetospheric Emission of the Magnetic Early B-type Stars . [Internet] [Thesis]. Queens University; 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1974/14691.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Shultz M. The Rotational Evolution and Magnetospheric Emission of the Magnetic Early B-type Stars . [Thesis]. Queens University; 2016. Available from: http://hdl.handle.net/1974/14691

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Washington

8. Choi, Yumi. Resolved Stars' Insights into Galaxy Physics.

Degree: PhD, 2016, University of Washington

URL: http://hdl.handle.net/1773/37021

► The history of a galaxy is encoded in its individual stars, and resolved stellar populations in nearby galaxies provide a wealth of information about star… (more)

▼ The history of a galaxy is encoded in its individual stars, and resolved stellar populations in nearby galaxies provide a wealth of information about star formation history (SFH), its relation to the interstellar medium, and galactic dynamics/structures. Using the power of resolved stars, imaged in multiple wavelengths by the Hubble Space Telescope, I investigate different types of galactic physics in three nearby galaxies: (1) measuring the escape fraction of ionizing photons from NGC 4214 and discussing its implications for cosmic reionization, (2) testing the density wave theory in M81 and understanding the origin of its spiral arms, and (3) tracing stellar overdensity features in M31 using red giant branch (RGB) stars and studying potential causes of the overdensities. In each of these studies, I developed and tested new methodology. First, I develop a new approach to measure the escape fraction of ionizing photons from a galaxy, and apply the technique to the nearest starburst dwarf galaxy NGC 4214. This new technique includes inferring the intrinsic ionizing fluxes from individual stars within a galaxy as well as the amount of absorption by the intervening dust by modeling the observed individual stars’ spectral energy distributions (SEDs), constructed from multi-wavelength HST observations, using the probabilistic SED fitting tool, called BEAST (Bayesian Ex- tinction And Stellar Tool). By combining these measurements with the estimates of the amount of consumed ionizing photons by photoionization using the Hα luminosity, I present the escape fraction map for NGC 4214 with unprecedented spatial resolution. I found a significant spatial variation in the escape fraction across the galaxy, and a ∼60 times higher global escape fraction (∼12%) than the previous measurement. Second, I use resolved stellar populations to trace prominent spiral structures in M81, which are highlighted by blue, young stars, and to understand the underlying dynamical mechanisms between star formation and these galactic structures. The origin of grand-design spiral patterns has been extensively explored observationally. However, the conclusions from different studies have often conflicted even for the same galaxies. The discrepancies mainly result from estimating the age gradient using discontinuous tracers, such as star clusters and gas/dust emissions including Hi, 24μm, CO and Hα. Instead of using discontinuous tracers, I model color-magnitude diagram that are constructed from resolved stars in M81 to derive spatially resolved SFHs around one of M81’s spiral arms and com- pare with the star formation propagation predicted by the density wave theory. I find that the grand-design spiral arms in M81 are likely induced by tidal interaction with companion galaxies about 200–300 Myr ago, not by the density waves. Finally, I use resolved stellar populations to investigate the global structures of the M31’s disk. Specifically, I make use of old RGB stars, selected based on their near-IR color and magnitude from the Panchromatic Hubble Andromeda… Advisors/Committee Members: Dalcanton, Julianne J (advisor).

Subjects/Keywords: cosmic reionization; galactic structures; individual galaxies; massive stars; resolved stars; star formation; Astronomy; astronomy

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APA (6^th Edition):

Choi, Y. (2016). Resolved Stars' Insights into Galaxy Physics. (Doctoral Dissertation). University of Washington. Retrieved from http://hdl.handle.net/1773/37021

Chicago Manual of Style (16^th Edition):

Choi, Yumi. “Resolved Stars' Insights into Galaxy Physics.” 2016. Doctoral Dissertation, University of Washington. Accessed March 05, 2021. http://hdl.handle.net/1773/37021.

MLA Handbook (7^th Edition):

Choi, Yumi. “Resolved Stars' Insights into Galaxy Physics.” 2016. Web. 05 Mar 2021.

Vancouver:

Choi Y. Resolved Stars' Insights into Galaxy Physics. [Internet] [Doctoral dissertation]. University of Washington; 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1773/37021.

Council of Science Editors:

Choi Y. Resolved Stars' Insights into Galaxy Physics. [Doctoral Dissertation]. University of Washington; 2016. Available from: http://hdl.handle.net/1773/37021

9. Smith, Michael. Mining the obscured OB star population in Carina.

Degree: PhD, 2017, University of Hertfordshire

URL: http://hdl.handle.net/2299/17469

► Massive OB stars are very influential objects in the ecology of galaxies like our own. Current catalogues of Galactic OB stars are heavily biased towards… (more)

▼ Massive OB stars are very influential objects in the ecology of galaxies like our own. Current catalogues of Galactic OB stars are heavily biased towards bright (g < 13) objects, only typically including fainter objects when found in prominent star clusters (Garmany et al., 1982; Reed, 2003; Maíz-Apellániz et al., 2004). Exploitation of the VST Photometric Hα Survey (VPHAS+) allows us to build a robust catalogue of photometrically-selected OB stars across the entire Southern Galactic plane, both within clusters and in the field, down to ~20th magnitude in g. For the first time, a complete accounting of the OB star runaway phenomenon becomes possible. Along with making the primary selection using VPHAS+ colours, I have performed Markov-Chain Monte Carlo fitting of the spectral energy distributions of the selected stars by combining VPHAS+ u, g, r, i with published J, H, K photometry. This gives rough constraints on effective temperature and distance, whilst delivering much more precise reddening parameters A0 and RV - allowing us to build a much richer picture of how extinction and extinction laws vary across the Galactic Plane. My thesis begins with a description of the method of photometric selection of OB star candidates and its validation across a 2 square degree field including the well- known young massive star cluster Westerlund 2 (Mohr-Smith et al., 2015)1. Following on from this I present spectroscopy with AAOmega of 283 candidates identified by our method, which confirms that ~ 94% of the sample are the expected O and early B stars. I then develop this method further and apply it to a Galactic Plane strip of 42 square-degrees that runs from the Carina Arm tangent region to the much studied massive cluster in NGC 3603. A new aspect I attend to in this expansion of method is tightening up the uniform photometric calibration of the data, paying particular attention to the always-challenging u band. This leads to a new and reliable catalogue of 5915 OB stars. As well as increasing the numbers of identified massive stars in this large region of the sky by nearly an order of magnitude, a more complete picture of massive star formation in the Carina Arm has emerged. I have found a broad over-density of O stars around the highly luminous cluster NGC 3603 and have uncovered two new candidate OB clusters/associations. I have also paired up the ionization sources of a number of HII regions catalogued by the RMS survey. It is also shown that the OB star scale- height can serve as a roughly standard ruler, leading to the result that the OB star layer shows the onset of warping at RG ~ 10kpc. My results confirm that this entire region requires a non-standard (3.5 < RV < 4.0) reddening law for distances greater than ~2kpc. The methods developed in this study are ready to roll out across the rest of the VPHAS+ footprint that has been observed to date. This extension will take in a strip ~ ±2 degrees across the entire Southern Galactic mid-plane (a sky area of over 700 square degrees), within which we expect to find the…

Subjects/Keywords: 523.1; Massive stars; OB stars; Carina; Milky Way; Dust; Extinction; Open clusters; VPHAS+

11 more images…

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APA (6^th Edition):

Smith, M. (2017). Mining the obscured OB star population in Carina. (Doctoral Dissertation). University of Hertfordshire. Retrieved from http://hdl.handle.net/2299/17469

Chicago Manual of Style (16^th Edition):

Smith, Michael. “Mining the obscured OB star population in Carina.” 2017. Doctoral Dissertation, University of Hertfordshire. Accessed March 05, 2021. http://hdl.handle.net/2299/17469.

MLA Handbook (7^th Edition):

Smith, Michael. “Mining the obscured OB star population in Carina.” 2017. Web. 05 Mar 2021.

Vancouver:

Smith M. Mining the obscured OB star population in Carina. [Internet] [Doctoral dissertation]. University of Hertfordshire; 2017. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2299/17469.

Council of Science Editors:

Smith M. Mining the obscured OB star population in Carina. [Doctoral Dissertation]. University of Hertfordshire; 2017. Available from: http://hdl.handle.net/2299/17469

University of California – Santa Cruz

10. Rosen, Anna Lorraine. The Destructive Birth of Massive Stars and Massive Star Clusters.

Degree: Astronomy & Astrophysics, 2017, University of California – Santa Cruz

URL: http://www.escholarship.org/uc/item/3wr3b49z

► The injection of energy and momentum into the interstellar medium by young massive stars’ intense radiation fields and their fast, radiatively driven winds can have… (more)

▼ The injection of energy and momentum into the interstellar medium by young massive stars’ intense radiation fields and their fast, radiatively driven winds can have a profound influence on their formation and environment. Massive star forming regions are rare and highly obscured, making the early moments of their formation difficult to observe. Instead, we must turn to theory to elucidate the physics involved in the formation of massive stars and massive star clusters (MSCs), which can host thousands of massive stars. In my thesis, I developed analytical and numerical techniques to study the formation of massive stars and how stellar wind feedback affects the dynamics of gas that surrounds MSCs. To estimate the initial rotation rates of massive stars at birth, I developed a protostellar angular momentum evolution model for accreting protostars to determine if magnetic torques can spin down massive stars during their formation. I found that magnetic torques are insufficient to spin down massive stars due to their short formation times and high accretion rates. Radiation pressure is likely the dominate feedback mechanism regulating massive star formation. Therefore detailed simulation of the formation of massive stars requires an accurate treatment of radiation. For this purpose, I developed a new, highly accurate radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. With this new tool, I performed a suite of three-dimensional adaptive mesh refinement radiation-hydrodynamic simulations of the formation of massive stars from collapsing massive pre-stellar cores. I found that mass is channeled to the massive star via dense infalling filaments that are uninhibited by radiation pressure and gravitational and Rayleigh-Taylor instabilities. To determine the importance of stellar wind feedback in young MSCs, I used observations to constrain a range of kinetic energy loss channels for the hot gas produced by the shock-heating of stellar winds to explain the low X-ray luminosities observed in Hii regions. I demonstrated that the energy injected by stellar winds is not a significant contributor to stellar feedback in young MSCs.

Subjects/Keywords: Astrophysics; computational astrophysics; massive stars; star formation; stellar feedback; theory

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APA (6^th Edition):

Rosen, A. L. (2017). The Destructive Birth of Massive Stars and Massive Star Clusters. (Thesis). University of California – Santa Cruz. Retrieved from http://www.escholarship.org/uc/item/3wr3b49z

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Rosen, Anna Lorraine. “The Destructive Birth of Massive Stars and Massive Star Clusters.” 2017. Thesis, University of California – Santa Cruz. Accessed March 05, 2021. http://www.escholarship.org/uc/item/3wr3b49z.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Rosen, Anna Lorraine. “The Destructive Birth of Massive Stars and Massive Star Clusters.” 2017. Web. 05 Mar 2021.

Vancouver:

Rosen AL. The Destructive Birth of Massive Stars and Massive Star Clusters. [Internet] [Thesis]. University of California – Santa Cruz; 2017. [cited 2021 Mar 05]. Available from: http://www.escholarship.org/uc/item/3wr3b49z.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Rosen AL. The Destructive Birth of Massive Stars and Massive Star Clusters. [Thesis]. University of California – Santa Cruz; 2017. Available from: http://www.escholarship.org/uc/item/3wr3b49z

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of California – Berkeley

11. SHIODE, JOSHUA HAJIME. The Evolution and Stability of Massive Stars.

Degree: Astrophysics, 2013, University of California – Berkeley

URL: http://www.escholarship.org/uc/item/5112z6xz

► Massive stars are the ultimate source for nearly all the elements necessary for life. The first stars forge these elements from the sparse set of… (more)

▼ Massive stars are the ultimate source for nearly all the elements necessary for life. The first stars forge these elements from the sparse set of ingredients supplied by the Big Bang, and distribute enriched ashes throughout their galactic homes via their winds and explosive deaths. Subsequent generations follow suit, assembling from the enriched ashes of their predecessors. Over the last several decades, the astrophysics community has developed a sophisticated theoretical picture of the evolution of these stars, but it remains an incomplete accounting of the rich set of observations. Using state of the art models of massive stars, I have investigated the internal processes taking place throughout the life-cycles of stars spanning those from the first generation (“Population III”) to the present-day (“Population I”). I will argue that early-generation stars were not highly unstable to perturbations, contrary to a host of past investigations, if a correct accounting is made for the viscous effect of convection. For later generations, those with near solar metallicity, I find that this very same convection may excite gravity-mode oscillations that produce observable brightness variations at the stellar surface when the stars are near the main sequence. If confirmed with modern high-precision monitoring experiments, like Kepler and CoRoT, the properties of observed gravity modes in massive stars could provide a direct probe of the poorly constrained physics of gravity mode excitation by convection. Finally, jumping forward in stellar evolutionary time, I propose and explore an entirely new mechanism to explain the giant eruptions observed and inferred to occur during the final phases of massive stellar evolution. This mechanism taps into the vast nuclear fusion luminosity, and accompanying convective luminosity, in the stellar core to excite waves capable of carrying a super-Eddington luminosity out to the stellar envelope. This energy transfer from the core to the envelope has the potential to unbind a significant amount of mass in close proximity to a star's eventual explosion as a core collapse supernova.

Subjects/Keywords: Astrophysics; Massive stars; Stellar astrophysics; Stellar Mass Loss; Supernovae

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APA (6^th Edition):

SHIODE, J. H. (2013). The Evolution and Stability of Massive Stars. (Thesis). University of California – Berkeley. Retrieved from http://www.escholarship.org/uc/item/5112z6xz

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

SHIODE, JOSHUA HAJIME. “The Evolution and Stability of Massive Stars.” 2013. Thesis, University of California – Berkeley. Accessed March 05, 2021. http://www.escholarship.org/uc/item/5112z6xz.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

SHIODE, JOSHUA HAJIME. “The Evolution and Stability of Massive Stars.” 2013. Web. 05 Mar 2021.

Vancouver:

SHIODE JH. The Evolution and Stability of Massive Stars. [Internet] [Thesis]. University of California – Berkeley; 2013. [cited 2021 Mar 05]. Available from: http://www.escholarship.org/uc/item/5112z6xz.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

SHIODE JH. The Evolution and Stability of Massive Stars. [Thesis]. University of California – Berkeley; 2013. Available from: http://www.escholarship.org/uc/item/5112z6xz

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Rochester Institute of Technology

12. Trombley, Christine. Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters.

Degree: PhD, School of Physics and Astronomy (COS), 2013, Rochester Institute of Technology

URL: https://scholarworks.rit.edu/theses/43

► Young stellar clusters serve as powerful natural laboratories for studying the intermediate to high mass end of the initial mass function. The purpose of this… (more)

Subjects/Keywords: Initial mass function; Massive stars; Near-infrared; Stellar clusters - open

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APA (6^th Edition):

Trombley, C. (2013). Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters. (Doctoral Dissertation). Rochester Institute of Technology. Retrieved from https://scholarworks.rit.edu/theses/43

Chicago Manual of Style (16^th Edition):

Trombley, Christine. “Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters.” 2013. Doctoral Dissertation, Rochester Institute of Technology. Accessed March 05, 2021. https://scholarworks.rit.edu/theses/43.

MLA Handbook (7^th Edition):

Trombley, Christine. “Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters.” 2013. Web. 05 Mar 2021.

Vancouver:

Trombley C. Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters. [Internet] [Doctoral dissertation]. Rochester Institute of Technology; 2013. [cited 2021 Mar 05]. Available from: https://scholarworks.rit.edu/theses/43.

Council of Science Editors:

Trombley C. Investigation of the intermediate and high end initial mass function as probed by near-infrared selected stellar clusters. [Doctoral Dissertation]. Rochester Institute of Technology; 2013. Available from: https://scholarworks.rit.edu/theses/43

13. Teodoro, Mairan Macedo. Análise multi-espectral dos eventos cíclicos de Carinae.

Degree: PhD, Astronomia, 2009, University of São Paulo

URL: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-14012010-140113/ ;

►

Nesta tese foi feito um estudo dos eventos cíclicos em Carinae em diversas faixas espectrais. A presença de um buraco na região polar do Homúnculo… (more)

▼

Nesta tese foi feito um estudo dos eventos cíclicos em Carinae em diversas faixas espectrais. A presença de um buraco na região polar do Homúnculo foi confirmada pelos mapas de velocidade da linha do [Fe II] 12567. A componente em emissão da linha do He I 10830, detectada na linha de visada do lóbulo NW e que apresenta velocidades negativas, foi mapeada e está contida no plano equatorial. Foi observado que durante um período de 206 dias, centrado na fase zero, a linha do He I 10830 apresenta um aumento na velocidade máxima da componente em absorção, atingindo 1800 km/s. Tal comportamento favorece orientações orbitais onde a passagem pelo periastro ocorre próximo à oposição. O Pequeno Homúnculo apresenta a mesma distribuição espacial da emissão em rádio e, considerando que esta seja proveniente principalmente da secundária, o fluxo de fótons no contínuo de Lyman é compatível com uma estrela de tipo espectral O5.5O7. A variabilidade das componentes largas e estreitas das linhas em diversas faixas espectrais apresenta um período bem definido (2022.1±0.6 dias) e extremamente estável ao longo dos últimos 60 anos, sendo que as variações observadas no período são devido aos erros nas medidas. Utilizando a componente estreita da linha do He I 6678 foi possível determinar a fase zero do ciclo11 (T0=2452819.8). Os eventos espectroscópicos são compostos de dois regimes: um de variações lentas e outro de colapso. A primeira é revelada por variações lentas no nível de ionização do meio circunstelar ao longo de todo o ciclo e está associada a variações graduais no cone de choque dos ventos (abertura angular e conteúdo). O regime de colapso é observado ao redor do mínimo e é causado por um colapso temporário do cone de choque. Os fenômenos de alta energia são sensíveis somente ao regime de colapso, enquanto os de baixa energia, ao de variação lenta. Os fenômenos que envolvem energias intermediárias, respondem aos dois regimes. Foi observado uma anti-correlação entre a linha do Fe II 6455 e a do He I 7065, indicando que a primeira é formada nas regiões mais externas do vento da primária e a segunda, na secundária ou no cone de choque dos ventos. A curva de luz do He II 4686 apresenta dois picos antes da fase zero e outro logo após. Os dois picos antes do mínimo apresentam uma correlação com os picos na faixa dos raios-X, porém estes ocorrem 16.5 dias antes daqueles. O mecanismo mais provável para explicar a luminosidade observada do He II 4686 é a produção de fótons com 1215 Å através do fluxo de fótons na faixa do ultra-violeta extremo/raios-X moles produzidos na região próxima ao ápex do cone de colisão dos ventos. Como este mecanismo é extremamente sensível à densidade do meio, a região mais favorável para produzir a luminosidade observada do He II 4686 é a região do cone de choque voltada para a primária.

In this thesis, a multi-wavelength study on the cyclic events of Eta Carinae was performed. The presence of a hole in the polar region of the Homunculus was confirmed by the velocity maps of the [Fe II] 12567 line. The…

Advisors/Committee Members: Damineli Neto, Augusto.

Subjects/Keywords: espectroscopia; estrelas massivas; Eta Carinae; Eta Carinae; massive stars; spectroscopy

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APA (6^th Edition):

Teodoro, M. M. (2009). Análise multi-espectral dos eventos cíclicos de Carinae. (Doctoral Dissertation). University of São Paulo. Retrieved from http://www.teses.usp.br/teses/disponiveis/14/14131/tde-14012010-140113/ ;

Chicago Manual of Style (16^th Edition):

Teodoro, Mairan Macedo. “Análise multi-espectral dos eventos cíclicos de Carinae.” 2009. Doctoral Dissertation, University of São Paulo. Accessed March 05, 2021. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-14012010-140113/ ;.

MLA Handbook (7^th Edition):

Teodoro, Mairan Macedo. “Análise multi-espectral dos eventos cíclicos de Carinae.” 2009. Web. 05 Mar 2021.

Vancouver:

Teodoro MM. Análise multi-espectral dos eventos cíclicos de Carinae. [Internet] [Doctoral dissertation]. University of São Paulo; 2009. [cited 2021 Mar 05]. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-14012010-140113/ ;.

Council of Science Editors:

Teodoro MM. Análise multi-espectral dos eventos cíclicos de Carinae. [Doctoral Dissertation]. University of São Paulo; 2009. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-14012010-140113/ ;

14. Shivvers, Isaac Steven. The Deaths of Massive Stars: Core-Collapse Supernovae and Pre-Explosion Mass Loss.

Degree: Astrophysics, 2017, University of California – Berkeley

URL: http://www.escholarship.org/uc/item/172293nb

► This thesis addresses some of the gaps in our current understanding of the deaths of massive stars using observations of supernovae (SNe) obtained at frequencies… (more)

Subjects/Keywords: Astronomy; Massive Stars; Supernovae

…when massive stars die, they seed their environments with a variety of heavy elements fused… …explosions from massive stars are triggered by the collapse of the stellar core, giving these… …THE PHYSICS OF MASSIVE STARS 2 1.1 The Physics of Massive Stars Stars spend most of their… …interaction with their companion). Somewhat more massive stars (0.5 . M . 8M )… …interstellar medium and therefore cannot be recycled into new stars. More massive stars undergo…

10 more images…

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APA (6^th Edition):

Shivvers, I. S. (2017). The Deaths of Massive Stars: Core-Collapse Supernovae and Pre-Explosion Mass Loss. (Thesis). University of California – Berkeley. Retrieved from http://www.escholarship.org/uc/item/172293nb

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Shivvers, Isaac Steven. “The Deaths of Massive Stars: Core-Collapse Supernovae and Pre-Explosion Mass Loss.” 2017. Thesis, University of California – Berkeley. Accessed March 05, 2021. http://www.escholarship.org/uc/item/172293nb.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Shivvers, Isaac Steven. “The Deaths of Massive Stars: Core-Collapse Supernovae and Pre-Explosion Mass Loss.” 2017. Web. 05 Mar 2021.

Vancouver:

Shivvers IS. The Deaths of Massive Stars: Core-Collapse Supernovae and Pre-Explosion Mass Loss. [Internet] [Thesis]. University of California – Berkeley; 2017. [cited 2021 Mar 05]. Available from: http://www.escholarship.org/uc/item/172293nb.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Shivvers IS. The Deaths of Massive Stars: Core-Collapse Supernovae and Pre-Explosion Mass Loss. [Thesis]. University of California – Berkeley; 2017. Available from: http://www.escholarship.org/uc/item/172293nb

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Exeter

15. Ali, Ahmad. Formation and feedback processes of massive stars in clusters.

Degree: PhD, 2018, University of Exeter

URL: http://hdl.handle.net/10871/34339

► Many uncertainties remain as to how the most massive stars are formed and how they interact with their environment via radiative and mechanical processes. This… (more)

▼ Many uncertainties remain as to how the most massive stars are formed and how they interact with their environment via radiative and mechanical processes. This feedback may affect future generations of star formation – triggering it by compressing gas, or hindering it by dispersing reservoirs. These scenarios can be simulated by solving the equations of hydrodynamics and radiative transfer. However, the latter is usually simplified due to its computational expense, despite its importance in determining the dynamics. In this thesis, I describe how I increased the efficiency of the radiation hydrodynamics code, TORUS, which uses a Monte Carlo approach to solving the radiative transfer. Tens of millions of energy packets are propagated through a domain split over hundreds of processors running in parallel with Message Passing Interface (MPI). By re-examining and improving communication algorithms, I lowered the radiation run time by about a factor of ten, making it tractable to run three-dimensional simulations of massive star feedback in clusters. This includes both the stellar and diffuse radiation fields, with multiple atomic species and silicate dust grains. The full ionization states and temperatures can then be fed in to produce self-consistent synthetic observations. I applied this to clouds of 1000 and 10,000 solar masses with surface density 0.01 g/cm², containing a 34 solar mass star, with photoionization and radiation pressure feedback. Photoionization is efficient at shaping and dispersing clouds. The expanding ionization front forms dense, spherical knots with pillars pointing away from the emitting star. These resemble the Pillars of Creation in the Eagle Nebula, and the proplyds observed in the Orion Nebula. In the lower-mass model, almost all material is removed from the (15.5 pc)³ grid within 1.6 Myr; the higher mass cloud is somewhat more resistant, with 25 per cent remaining inside (32.3 pc)³ after 4.3 Myr. Radiation pressure has a negligible effect, but will be more important for denser clouds or higher luminosities.

Subjects/Keywords: 500; physics; astronomy; star formation; massive stars; hydrodynamics; radiative transfer

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Ali, A. (2018). Formation and feedback processes of massive stars in clusters. (Doctoral Dissertation). University of Exeter. Retrieved from http://hdl.handle.net/10871/34339

Chicago Manual of Style (16^th Edition):

Ali, Ahmad. “Formation and feedback processes of massive stars in clusters.” 2018. Doctoral Dissertation, University of Exeter. Accessed March 05, 2021. http://hdl.handle.net/10871/34339.

MLA Handbook (7^th Edition):

Ali, Ahmad. “Formation and feedback processes of massive stars in clusters.” 2018. Web. 05 Mar 2021.

Vancouver:

Ali A. Formation and feedback processes of massive stars in clusters. [Internet] [Doctoral dissertation]. University of Exeter; 2018. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10871/34339.

Council of Science Editors:

Ali A. Formation and feedback processes of massive stars in clusters. [Doctoral Dissertation]. University of Exeter; 2018. Available from: http://hdl.handle.net/10871/34339

University of Washington

16. Garofali, Kristen Elise. X-ray Insights into Massive Star Evolution: the X-ray Source Population of M33 as seen by XMM-Newton, Chandra, and the Hubble Space Telescope.

Degree: PhD, 2018, University of Washington

URL: http://hdl.handle.net/1773/42954

► Massive stars are key drivers in the cycle of star formation and overall galactic chemical evolution, but many aspects of the evolution of high-mass stars,… (more)

▼ Massive stars are key drivers in the cycle of star formation and overall galactic chemical evolution, but many aspects of the evolution of high-mass stars, in particular the end stages of their lifetimes, are difficult to constrain observationally. High-mass X-ray binaries (HMXBs) and supernova remnants (SNRs) are observable at a broad range of wavelengths and are unique probes into how massive stars evolve, die and subsequently interact with and enrich their environments. Previous studies of HMXB and SNR populations, both galactic and extragalactic, have demonstrated the wealth of knowledge to be gleaned from X-ray observations of these objects. However, these studies have been limited in the range of galactic host environments (metallicities and star formation rates) probed, as well as suffering from distance, extinction and X-ray positional uncertainties. M33, a late-type Sc spiral, is ideal for X-ray studies of both HMXBs and SNRs. It's proximity to the Milky Way makes both HMXBs and SNRs resolvable for study, and its low foreground extinction and close to face-on inclination make it easier to study such objects as populations. Furthermore, it has deep, and wide coverage from Chandra, which affords high spatial resolution, and XMM-Newton, which offers high soft sensitivity, in conjunction with considerable archival Hubble Space Telescope (HST) coverage. In this thesis, I probe the X-ray source population of M33 with a particular emphasis on massive stars and their end products, which are well-characterized using the available multiwavelength coverage. I characterize the large X-ray point source population of M33 from deep XMM-Newton observations, from which I identify a sizable number of new soft sources, and produce a deep X-ray luminosity function indicative of a substantial population of HMXBs. The source population from this catalog forms the backbone for studying M33's massive star population from the X-ray perspective. From this source population, I also identify a large number of SNRs newly detected in X-rays in M33. With this large sample of SNRs I examine the effect of host galaxy properties, such as metallicity and star formation rate, on SNR characteristics and detectability. I further study the massive star population of M33 through identification and characterization of a new sample of candidate HMXBs in M33 found using archival HST and Chandra imaging. I use the HST photometric data to model the color-magnitude diagrams in the vicinity of each candidate HMXB to measure a resolved recent star formation history, and thus a formation time-scale, or age for each source. For a subset of these HMXBs, I present an in-depth source classification on the basis of available X-ray and optical spectra and colors. I discuss these results in the context of massive star, and massive binary evolution and their connection to host galaxy environment as seen through the lens of M33. Studying large samples of massive star end products in a nearby galaxy such as M33 paves the way towards understanding massive star and… Advisors/Committee Members: Williams, Benjamin F (advisor).

Subjects/Keywords: massive stars; supernova remnants; X-ray binaries; Astronomy; Astrophysics; Astronomy

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APA (6^th Edition):

Garofali, K. E. (2018). X-ray Insights into Massive Star Evolution: the X-ray Source Population of M33 as seen by XMM-Newton, Chandra, and the Hubble Space Telescope. (Doctoral Dissertation). University of Washington. Retrieved from http://hdl.handle.net/1773/42954

Chicago Manual of Style (16^th Edition):

Garofali, Kristen Elise. “X-ray Insights into Massive Star Evolution: the X-ray Source Population of M33 as seen by XMM-Newton, Chandra, and the Hubble Space Telescope.” 2018. Doctoral Dissertation, University of Washington. Accessed March 05, 2021. http://hdl.handle.net/1773/42954.

MLA Handbook (7^th Edition):

Garofali, Kristen Elise. “X-ray Insights into Massive Star Evolution: the X-ray Source Population of M33 as seen by XMM-Newton, Chandra, and the Hubble Space Telescope.” 2018. Web. 05 Mar 2021.

Vancouver:

Garofali KE. X-ray Insights into Massive Star Evolution: the X-ray Source Population of M33 as seen by XMM-Newton, Chandra, and the Hubble Space Telescope. [Internet] [Doctoral dissertation]. University of Washington; 2018. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1773/42954.

Council of Science Editors:

Garofali KE. X-ray Insights into Massive Star Evolution: the X-ray Source Population of M33 as seen by XMM-Newton, Chandra, and the Hubble Space Telescope. [Doctoral Dissertation]. University of Washington; 2018. Available from: http://hdl.handle.net/1773/42954

University of Toronto

17. Ro, Stephen S. On the Launching of Optically Thick Outflows from Massive Stars.

Degree: PhD, 2017, University of Toronto

URL: http://hdl.handle.net/1807/80892

► For decades, massive stars have been seen to lose mass at every stage of evolution. In recent years, detections of outbursts and circumstellar relics uncover… (more)

▼ For decades, massive stars have been seen to lose mass at every stage of evolution. In recent years, detections of outbursts and circumstellar relics uncover transient modes emerging moments before the supernova. The goal of this thesis is to bring theoretical attention into how massive stars launch outflows. In this thesis, we study two modes of mass loss seen during rare, but critical, phases of stellar evolution. The first considers dense, steady outflows from Wolf-Rayet stars. The second considers the eruptions and explosions seen from luminous blue variables (LBVs) and Type IIn supernova (SN) progenitors. Outflows from both systems are optically thick but either radiative or adiabatic in nature. Wolf-Rayet winds are driven by strong radiative pressure on metal lines. Suppressing the outflow is shown to drastically alter the stellar structure with peculiar features including an extended radiative cavity encased in a massive shell. We construct outflow models and conclude the galactic WR population does not harbour such structures. We derive a minimum mass loss rate to launch a transonic, optically thick outflow and find the iron opacity bump to be responsible for launching WR winds. LBVs and Type IIn SN progenitors are seen to abruptly expel mass. Observational inferences suggest the rates are both exceptional and unsustainable with durations exceeding the outer envelope dynamical time. Yet, these outflows are occasionally preceded by fast motions indicative of shock acceleration. In this thesis, we explain how waves can be responsible for these dynamics. We derive an analytic solution wave steepening and shock formation for an inhomogeneous medium. The results suggest that any super-Eddington phenomenon driven by waves it{must} involve shocks. Shocks form deep in the star where they are initially weak. We show how weak shocks are capable of accelerating to become strong, breakout, and produce fast ejecta using a revived semi-analytical approximation. We discuss how a train of shocks can heat a large volume of the envelope and eject significant mass. Advisors/Committee Members: Matzner, Christopher D, Astronomy and Astrophysics.

Subjects/Keywords: Acoustic waves; hydrodynamics; Massive Stars; Shocks; supernova; Winds; 0596

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APA (6^th Edition):

Ro, S. S. (2017). On the Launching of Optically Thick Outflows from Massive Stars. (Doctoral Dissertation). University of Toronto. Retrieved from http://hdl.handle.net/1807/80892

Chicago Manual of Style (16^th Edition):

Ro, Stephen S. “On the Launching of Optically Thick Outflows from Massive Stars.” 2017. Doctoral Dissertation, University of Toronto. Accessed March 05, 2021. http://hdl.handle.net/1807/80892.

MLA Handbook (7^th Edition):

Ro, Stephen S. “On the Launching of Optically Thick Outflows from Massive Stars.” 2017. Web. 05 Mar 2021.

Vancouver:

Ro SS. On the Launching of Optically Thick Outflows from Massive Stars. [Internet] [Doctoral dissertation]. University of Toronto; 2017. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1807/80892.

Council of Science Editors:

Ro SS. On the Launching of Optically Thick Outflows from Massive Stars. [Doctoral Dissertation]. University of Toronto; 2017. Available from: http://hdl.handle.net/1807/80892

University of Minnesota

18. West, Christopher James. Metallicity-dependent isotopic abundances and the impact of helium rate uncertainties in massive stars.

Degree: PhD, Physics, 2013, University of Minnesota

URL: http://hdl.handle.net/11299/162703

► All stellar evolution models for nucleosynthesis require an initial isotopic abundance set to use as a starting point, because nuclear reactions occur between isotopes. Generally,… (more)

▼ All stellar evolution models for nucleosynthesis require an initial isotopic abundance set to use as a starting point, because nuclear reactions occur between isotopes. Generally, our knowledge of isotopic abundances of stars is fairly incomplete except for the Solar System. We develop a first model for a complete average isotopic decomposition as a function of metallicity. Our model is based on the underlying nuclear astrophysics processes, and is fitted to observational data, rather than traditional forward galactic chemical evolution modeling which integrates stellar yields beginning from big bang nucleosynthesis. We first decompose the isotopic solar abundance pattern into contributions from astrophysical sources. Each contribution is then assumed to scale as a function of metallicity. The resulting total isotopic abundances are summed into elemental abundances and fitted to available halo and disk stellar data to constrain the model's free parameter values. This procedure allows us to use available elemental observational data to reconstruct and constrain both the much needed complete isotopic evolution that is not accessible to current observations, and the underlying astrophysical processes. Our model finds a best fit for Type Ia supernovae contributing ∼0.7 to the solar Fe abundance, and Type Ia onset occurring at [Fe/H]∼−1.2, in agreement with typical values. The completed model can be used in future nucleosynthesis studies. We also perform a preliminary analysis to assess the impact of our isotopic scaling model on the resulting nucleosynthesis of massive stars, compared to a linear interpolation method. Using these two input methods we compute a limited grid of stellar models, and compare the final nucleosynthesis to observations. The compactness parameter was first used to assess which models would likely explode as successful supernovae, and contribute explosive nucleosynthesis yields. We find a better agreement to solar observations using the scaling model compared to the linear interpolation method, for the six s–only isotopes along the weak s–process path. As a second project, we study the sensitivity of presupernova evolution and supernova nucleosynthesis yields of massive stars to variations of the helium-burning reaction rates within the range of their uncertainties. The current solar abundances from Lodders (2010) are used for the initial stellar composition. We compute a grid of 12 initial stellar masses and 176 models per stellar mass to explore the effects of independently varying the ¹²C(α,γ)¹⁶O</and 3α reaction rates, denoted R_α,12 and R_3α, respectively. The production factors of both the intermediate-mass elements (A=16–40) and the s–only isotopes along the weak s–process path (⁷⁰Ge, ⁷⁶Se, ⁸⁰Kr, ⁸²Kr, ⁸⁶Sr, and ⁸⁷Sr) were found to be in reasonable agreement with predictions for variations of R_3α and R_α,12 of ±25%;…

Subjects/Keywords: Galactic abundances; Massive stars; Nuclear reactions; Nucleosynthesis; Stellar abundances

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APA (6^th Edition):

West, C. J. (2013). Metallicity-dependent isotopic abundances and the impact of helium rate uncertainties in massive stars. (Doctoral Dissertation). University of Minnesota. Retrieved from http://hdl.handle.net/11299/162703

Chicago Manual of Style (16^th Edition):

West, Christopher James. “Metallicity-dependent isotopic abundances and the impact of helium rate uncertainties in massive stars.” 2013. Doctoral Dissertation, University of Minnesota. Accessed March 05, 2021. http://hdl.handle.net/11299/162703.

MLA Handbook (7^th Edition):

West, Christopher James. “Metallicity-dependent isotopic abundances and the impact of helium rate uncertainties in massive stars.” 2013. Web. 05 Mar 2021.

Vancouver:

West CJ. Metallicity-dependent isotopic abundances and the impact of helium rate uncertainties in massive stars. [Internet] [Doctoral dissertation]. University of Minnesota; 2013. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/11299/162703.

Council of Science Editors:

West CJ. Metallicity-dependent isotopic abundances and the impact of helium rate uncertainties in massive stars. [Doctoral Dissertation]. University of Minnesota; 2013. Available from: http://hdl.handle.net/11299/162703

19. Mutale, Mubela. HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey.

Degree: 2018, University of Hertfordshire

URL: http://hdl.handle.net/2299/21070

► This thesis presents data from the Ku-band Galactic Reconnaissance Survey (KuGARS), a large area survey observed on the Jansky Very Large Array (JVLA). KuGARS is… (more)

▼ This thesis presents data from the Ku-band Galactic Reconnaissance Survey (KuGARS), a large area survey observed on the Jansky Very Large Array (JVLA). KuGARS is the first galactic plane survey to explore the sub-arcsecond and sub-mJy regime at 14 GHz. We have described the development of the data reduction procedures in CASA for the On the Fly (OTF) mapping method used for KuGARS. Included in our discussion are the calibration and imaging processes: as the OTF mapping method has not been extensively explored we have gone through several steps to present quality assurance of the calibration. Due to the large volume of data, we focused on a pilot study of the area surrounding the W49A massive star forming region and a subset of the final frequency range. Using an automated source finding algorithm, AEGEAN (Hancock et al., 2012), we have detected 35 islands with 57 components. We compared the brightest of these sources to the literature to determine their nature. In order to carry out a robust analysis, we compared our detections to observations over multiple frequencies. Comparing to GLIMPSE and Herschel showed our sources deeply embedded in 8μm and 70μm emission, respectively, which indicate heated dust and therefore infer star formation. We further, through the SIMBAD database, found several star formation tracers, including: Masers, YSOs, and HII regions, associated with our KuGARS detections. Our comparison with CORNISH and De Pree et al. (1997) revealed previous detections of these sources as HII regions with similar morphologies to KuGARS. We have detected and identified 2 spherical or unresolved HII regions, and 2 irregular HII regions in the ring of HII regions (W49 North), 1 isolated spherical/unresolved HII region, and 1 cometary HII region in W49 South. We find that one of the objects (source B) is recovered by KuGARS and De Pree et al. (1997) but not in CORNISH. This source, which is undetected at 5GHz and below has a steep positive spectrum (α = 1:1) and has broad radio recombination lines with line widths (> 45kms􀀀1) (De Pree et al., 1997). It, therefore, must be a Hypercompact HII region and thus demonstrates KuGARS capability to detect Hypercompact HII regions.

Subjects/Keywords: Star formation; Massive Stars; Radio continuum; Spectral line; HII regions; ISM

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APA (6^th Edition):

Mutale, M. (2018). HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey. (Masters Thesis). University of Hertfordshire. Retrieved from http://hdl.handle.net/2299/21070

Chicago Manual of Style (16^th Edition):

Mutale, Mubela. “HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey.” 2018. Masters Thesis, University of Hertfordshire. Accessed March 05, 2021. http://hdl.handle.net/2299/21070.

MLA Handbook (7^th Edition):

Mutale, Mubela. “HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey.” 2018. Web. 05 Mar 2021.

Vancouver:

Mutale M. HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey. [Internet] [Masters thesis]. University of Hertfordshire; 2018. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2299/21070.

Council of Science Editors:

Mutale M. HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey. [Masters Thesis]. University of Hertfordshire; 2018. Available from: http://hdl.handle.net/2299/21070

20. André, Quentin. Ondes gravito-inertielles dans les étoiles et les planètes géantes : propagation, dissipation et échanges de moment cinétique : Gravito-inertial waves in stars and giant planets : propagation, dissipation and angular momentum transport.

Degree: Docteur es, Physique. Astronomie et astrophysique, 2019, Université de Paris (2019-....)

URL: http://www.theses.fr/2019UNIP7073

► Les ondes internes gravito-inertielles sont des ondes se propageant dans les milieux fluides stablement stratifiés en rotation. Leurs forces de rappel sont la poussée d'Archimède… (more)

▼ Les ondes internes gravito-inertielles sont des ondes se propageant dans les milieux fluides stablement stratifiés en rotation. Leurs forces de rappel sont la poussée d'Archimède et l'accélération de Coriolis. Elles sont capables de redistribuer de l'énergie et du moment cinétique du fait de leur dissipation et de leur possible déferlement non-linéaire, jouant ainsi un rôle crucial dans l’évolution dynamique des corps dans lesquels elles se propagent. Dans cette thèse, nous nous attachons à caractériser leur propagation, leur amortissement et les échanges de moment cinétique qu’elles induisent, dans les environnements complexes que sont les intérieurs stellaires et de planètes géantes.Au sein des planètes géantes, nous étudions la propagation et la dissipation d’ondes gravito-inertielles de marée, dans une région de convection stratifiée susceptible de se développer proche du cœur. Nous nous intéressons tout d’abord à leur propagation libre et nous montrons qu’une onde incidente sur une telle région est efficacement transmise à condition qu’elle soit résonante avec un de ses modes propres. Sinon, l’onde est réfléchie et ne pénètre pas dans les régions plus profondes de la planète. Ensuite, nous étudions numériquement la dissipation de marée induite lorsque ces ondes sont excitées par un forçage gravitationnel dû à la présence d’un satellite. Nous montrons que le taux de dissipation de marée est en moyenne augmenté par rapport à un milieu purement convectif. Les contributions les plus importantes à cette augmentation proviennent de la dissipation des ondes gravito-inertielles résonantes avec les modes propres de la région de convection stratifiée, qui sont aussi celles qui sont efficacement transmises. Ces résultats sont compatibles avec les hauts taux de dissipation de marée récemment observés dans Jupiter et Saturne.Dans les zones radiatives des étoiles, nous présentons en premier lieu une étude semi-analytique linéaire de l’influence de la rotation globale et différentielle, sur le transport de moment cinétique induit par la dissipation des ondes gravito-inertielles. Dans un modèle équatorial, nous montrons que la rotation a pour effet l’augmentation de la dissipation thermique des ondes. Celle-ci est particulièrement significative dans leur région d’excitation, modifiant ainsi le dépôt de moment cinétique. Nous montrons que cet effet se révèle d’autant plus efficace que l’étoile est jeune et massive. En parallèle de ce travail semi-analytique, cette thèse s’est attachée à développer un modèle 3D non-linéaire ab initio d’une étoile massive couplant le coeur convectif à une enveloppe radiative étendue, sous l’influence de la rotation. L’analyse détaillée de simulations numériques à haute performance, réalisées avec le code ASH, nous a permis de caractériser les propriétés du spectre d’excitation des ondes et des modes résonants qui s’établissent dans l’enveloppe radiative. Proche de la surface de l’étoile, nous montrons que les ondes peuvent atteindre une amplitude suffisante pour interagir de manière significative… Advisors/Committee Members: Mathis, Stéphane (thesis director), Brun, Allan Sacha (thesis director).

Subjects/Keywords: Interactions de marées; Hydrodynamics; Modelisation; Numerical simulation; Waves; Convection; Giant planets; Tides; Stars – Rotation; Stars – Evolution; Massive stars

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APA (6^th Edition):

André, Q. (2019). Ondes gravito-inertielles dans les étoiles et les planètes géantes : propagation, dissipation et échanges de moment cinétique : Gravito-inertial waves in stars and giant planets : propagation, dissipation and angular momentum transport. (Doctoral Dissertation). Université de Paris (2019-....). Retrieved from http://www.theses.fr/2019UNIP7073

Chicago Manual of Style (16^th Edition):

André, Quentin. “Ondes gravito-inertielles dans les étoiles et les planètes géantes : propagation, dissipation et échanges de moment cinétique : Gravito-inertial waves in stars and giant planets : propagation, dissipation and angular momentum transport.” 2019. Doctoral Dissertation, Université de Paris (2019-....). Accessed March 05, 2021. http://www.theses.fr/2019UNIP7073.

MLA Handbook (7^th Edition):

André, Quentin. “Ondes gravito-inertielles dans les étoiles et les planètes géantes : propagation, dissipation et échanges de moment cinétique : Gravito-inertial waves in stars and giant planets : propagation, dissipation and angular momentum transport.” 2019. Web. 05 Mar 2021.

Vancouver:

André Q. Ondes gravito-inertielles dans les étoiles et les planètes géantes : propagation, dissipation et échanges de moment cinétique : Gravito-inertial waves in stars and giant planets : propagation, dissipation and angular momentum transport. [Internet] [Doctoral dissertation]. Université de Paris (2019-....); 2019. [cited 2021 Mar 05]. Available from: http://www.theses.fr/2019UNIP7073.

Council of Science Editors:

André Q. Ondes gravito-inertielles dans les étoiles et les planètes géantes : propagation, dissipation et échanges de moment cinétique : Gravito-inertial waves in stars and giant planets : propagation, dissipation and angular momentum transport. [Doctoral Dissertation]. Université de Paris (2019-....); 2019. Available from: http://www.theses.fr/2019UNIP7073

21. Fullard, Andrew G. A Spectropolarimetric Study of Southern WR + O Binaries.

Degree: PhD, Physics and Astronomy, 2020, U of Denver

URL: https://digitalcommons.du.edu/etd/1762

► The classical Wolf-Rayet (WR) state is the evolved stage of a massive star, post main-sequence. They are characterized by their strong emission line spectra… (more)

▼ The classical Wolf-Rayet (WR) state is the evolved stage of a massive star, post main-sequence. They are characterized by their strong emission line spectra and stellar winds that are often more than 10 times denser than that of their progenitor O-type stars, which have mass loss rates of 10^-6 M_Θyr^-1. The evolution of WR stars and their connection to specific types of supernovae (SNe) is an open question. Current theory suggests that rapidly rotating massive stars may be the progenitors of SNe that produce long-duration gamma-ray bursts. The interaction between WR stars and their companion in binary systems may provide sufficient angular momentum to create such progenitors. Angular momentum (and therefore rotation) tends to create aspherical structures in astronomical objects (e.g. Be star disks, T Tauri jets caused by decretion and accretion respectively) that can be investigated using linear polarimetry, even for unresolved sources. I have investigated WR stars in detail to determine the geometric structure of their winds using spectropolarimetry. I began by using archival broadband polarimetric data to search for intrinsic polarization in a sample of more than 40 single and binary WR stars, finding that 12 of the stars exhibit intrinsic continuum polarization or line polarization effects that indicate aspherical or non-uniform winds. In the later stages of the project, I used the Southern African Large Telescope (SALT) to obtain time-dependent spectropolarimetric observations of 10 of the stars in that sample, along with 8 additional targets. These targets are all WR + O binary systems, whose complex winds are best observed over time with spectropolarimetry to determine the geometry of the wind across different emission lines and the continuum. I investigated two stars in the sample, WR 42 and WR 79, and found that they exhibit classic continuum polarization signatures of binary orbits, as well as intriguing orbital line polarization effects. I compared the line polarization behaviour with the predictions of existing spectrally-derived models of the systems to obtain new information about the structure of the colliding wind regions. Finally, I have modified an existing 3-D Monte Carlo radiative transfer code to include an additional source of photons that represents a companion star. This allows the code to treat the asymmetric structures seen in massive binary systems. I used this updated code to simulate the well-observed WR + O system V444 Cygni. I created a set of emission regions to simulate line emission from both the WR wind and wind-wind collision regions, finding that the wind-wind collision creates very strong polarimetric signals that appear similar to those in other systems in my SALT sample. The results shed new light on the relationships among WR + O binaries and yield clues to their subsequent evolution and potential roles as SN and GRB progenitors. Advisors/Committee Members: Jennifer L. Hoffman, Toshiya Ueta, Robert Stencel.

Subjects/Keywords: Binary stars; Massive stars; Polarization; Radiative transfer; Wolf-rayet; Astrophysics and Astronomy; Stars, Interstellar Medium and the Galaxy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Fullard, A. G. (2020). A Spectropolarimetric Study of Southern WR + O Binaries. (Doctoral Dissertation). U of Denver. Retrieved from https://digitalcommons.du.edu/etd/1762

Chicago Manual of Style (16^th Edition):

Fullard, Andrew G. “A Spectropolarimetric Study of Southern WR + O Binaries.” 2020. Doctoral Dissertation, U of Denver. Accessed March 05, 2021. https://digitalcommons.du.edu/etd/1762.

MLA Handbook (7^th Edition):

Fullard, Andrew G. “A Spectropolarimetric Study of Southern WR + O Binaries.” 2020. Web. 05 Mar 2021.

Vancouver:

Fullard AG. A Spectropolarimetric Study of Southern WR + O Binaries. [Internet] [Doctoral dissertation]. U of Denver; 2020. [cited 2021 Mar 05]. Available from: https://digitalcommons.du.edu/etd/1762.

Council of Science Editors:

Fullard AG. A Spectropolarimetric Study of Southern WR + O Binaries. [Doctoral Dissertation]. U of Denver; 2020. Available from: https://digitalcommons.du.edu/etd/1762

22. Harris, Amy. The kinematics of the outer Galactic disk from A and F stars.

Degree: PhD, 2019, University of Hertfordshire

URL: http://hdl.handle.net/2299/22451

► The kinematics of stars in the outer Galactic disk is poorly known. In addition to constraining the Galactic potential, knowledge of the motions of stars… (more)

▼ The kinematics of stars in the outer Galactic disk is poorly known. In addition to constraining the Galactic potential, knowledge of the motions of stars throughout the disk facilitates studies of non-axisymmetric motion, such as streaming motions due to spiral arms. Understanding the kinematics of the disk in full, including the rotation law, will help to map out its structure, and set constraints on its formation and evolution. I explore the kinematics of A/F stars in two outer-disk pencil beams. I show that A stars in particular are useful probes of outer Galactic disk kinematics. The use of these relatively early-type stars is an alternative to the ISM gas tracers and clump giants that have been commonly used in previous studies. A/F stars offer the advantage of reduced kinematic scatter and asymmetric drift as compared to the older clump giants, and can provide a much denser sampling in the outer disk than ISM gas tracers. They are bright so can be detected out to great distances, and large samples can be efficiently selected from the IPHAS r-i, r-Hα plane. The sightlines were chosen to sample the strong shear in Galactic rotation (l= 118 ̊), and as a control (l= 178 ̊). Radial velocities (RVs) and extinction-corrected spectro-photometric distances are computed for the sample of >1300 A/F stars with the aid of MCMC parameter fitting. The rotation law measured at l=118 ̊ using the RV data is sharply rising out from RG ~11 kpc, going against expectations of a flat or slowly rising law. Gaia DR2 astrometry, released in April 2018, provided proper motions for the sample. On combining these with the measured RVs and spectro-photometric distances, full space motions are obtained. The Galactocentric radial, azimuthal, and vertical velocity trends are constructed without any prior assumption about the velocity field. The measured rotation curve incorporating proper motion data is flat at l = 178 ̊, but remains sharply rising at l = 118 ̊, albeit less so than that determined using only RV data. I consider the detailed form of the observed Galactocentric trends with specific perturbers in mind, finding no clear interpretation in terms of perturbation from the central bar or spiral arms. The variation of observed trends with longitude and distance is a reflection of the complex dynamics in our Galaxy. The methods developed in this work and the use of A stars as tracers will be used in the future for fuller exploitation via spectroscopy on forthcoming massively multiplexed wide-field spectrographs. In particular, the PTMCMC method presented will be used to analyse WEAVE survey products. Future use of these young stellar tracers will help us to understand how our Galaxy is, and came to be, how it is now.

Subjects/Keywords: Astronomy; Astrophysics; Kinematics; Stars; Milky Way; Galaxy; galactic disk; rotation curve; young stars; massive stars; F stars; A stars; Dynamics; outer disk; Gaia; proper motion; radial velocity; spectroscopy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Harris, A. (2019). The kinematics of the outer Galactic disk from A and F stars. (Doctoral Dissertation). University of Hertfordshire. Retrieved from http://hdl.handle.net/2299/22451

Chicago Manual of Style (16^th Edition):

Harris, Amy. “The kinematics of the outer Galactic disk from A and F stars.” 2019. Doctoral Dissertation, University of Hertfordshire. Accessed March 05, 2021. http://hdl.handle.net/2299/22451.

MLA Handbook (7^th Edition):

Harris, Amy. “The kinematics of the outer Galactic disk from A and F stars.” 2019. Web. 05 Mar 2021.

Vancouver:

Harris A. The kinematics of the outer Galactic disk from A and F stars. [Internet] [Doctoral dissertation]. University of Hertfordshire; 2019. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2299/22451.

Council of Science Editors:

Harris A. The kinematics of the outer Galactic disk from A and F stars. [Doctoral Dissertation]. University of Hertfordshire; 2019. Available from: http://hdl.handle.net/2299/22451

23. Harris, Amy. The kinematics of the outer Galactic disk from A and F stars.

Degree: PhD, 2019, University of Hertfordshire

URL: https://doi.org/10.18745/th.22451 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.802952

► The kinematics of stars in the outer Galactic disk is poorly known. In addition to constraining the Galactic potential, knowledge of the motions of stars… (more)

▼ The kinematics of stars in the outer Galactic disk is poorly known. In addition to constraining the Galactic potential, knowledge of the motions of stars throughout the disk facilitates studies of non-axisymmetric motion, such as streaming motions due to spiral arms. Understanding the kinematics of the disk in full, including the rotation law, will help to map out its structure, and set constraints on its formation and evolution. I explore the kinematics of A/F stars in two outer-disk pencil beams. I show that A stars in particular are useful probes of outer Galactic disk kinematics. The use of these relatively early-type stars is an alternative to the ISM gas tracers and clump giants that have been commonly used in previous studies. A/F stars offer the advantage of reduced kinematic scatter and asymmetric drift as compared to the older clump giants, and can provide a much denser sampling in the outer disk than ISM gas tracers. They are bright so can be detected out to great distances, and large samples can be efficiently selected from the IPHAS r-i, r-Hα plane. The sightlines were chosen to sample the strong shear in Galactic rotation (l= 118 ̊), and as a control (l= 178 ̊). Radial velocities (RVs) and extinction-corrected spectro-photometric distances are computed for the sample of >1300 A/F stars with the aid of MCMC parameter fitting. The rotation law measured at l=118 ̊ using the RV data is sharply rising out from RG ~11 kpc, going against expectations of a flat or slowly rising law. Gaia DR2 astrometry, released in April 2018, provided proper motions for the sample. On combining these with the measured RVs and spectro-photometric distances, full space motions are obtained. The Galactocentric radial, azimuthal, and vertical velocity trends are constructed without any prior assumption about the velocity field. The measured rotation curve incorporating proper motion data is flat at l = 178 ̊, but remains sharply rising at l = 118 ̊, albeit less so than that determined using only RV data. I consider the detailed form of the observed Galactocentric trends with specific perturbers in mind, finding no clear interpretation in terms of perturbation from the central bar or spiral arms. The variation of observed trends with longitude and distance is a reflection of the complex dynamics in our Galaxy. The methods developed in this work and the use of A stars as tracers will be used in the future for fuller exploitation via spectroscopy on forthcoming massively multiplexed wide-field spectrographs. In particular, the PTMCMC method presented will be used to analyse WEAVE survey products. Future use of these young stellar tracers will help us to understand how our Galaxy is, and came to be, how it is now.

Subjects/Keywords: Astronomy; Astrophysics; Kinematics; Stars; Milky Way; Galaxy; galactic disk; rotation curve; young stars; massive stars; F stars; A stars; Dynamics; outer disk; Gaia; proper motion; radial velocity; spectroscopy

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APA (6^th Edition):

Harris, A. (2019). The kinematics of the outer Galactic disk from A and F stars. (Doctoral Dissertation). University of Hertfordshire. Retrieved from https://doi.org/10.18745/th.22451 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.802952

Chicago Manual of Style (16^th Edition):

Harris, Amy. “The kinematics of the outer Galactic disk from A and F stars.” 2019. Doctoral Dissertation, University of Hertfordshire. Accessed March 05, 2021. https://doi.org/10.18745/th.22451 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.802952.

MLA Handbook (7^th Edition):

Harris, Amy. “The kinematics of the outer Galactic disk from A and F stars.” 2019. Web. 05 Mar 2021.

Vancouver:

Harris A. The kinematics of the outer Galactic disk from A and F stars. [Internet] [Doctoral dissertation]. University of Hertfordshire; 2019. [cited 2021 Mar 05]. Available from: https://doi.org/10.18745/th.22451 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.802952.

Council of Science Editors:

Harris A. The kinematics of the outer Galactic disk from A and F stars. [Doctoral Dissertation]. University of Hertfordshire; 2019. Available from: https://doi.org/10.18745/th.22451 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.802952

University of California – Santa Cruz

24. Sukhbold, Tuguldur. The Evolution and Explosion of Massive Stars.

Degree: Astronomy & Astrophysics, 2016, University of California – Santa Cruz

URL: http://www.escholarship.org/uc/item/6gr8s8cp

► How a massive star ends its life depends upon how that life has been lived - the rotation, mass and composition it was born with,… (more)

Subjects/Keywords: Astrophysics; Light Curves; Massive Stars; Neutrino-Driven Mechanism; Nucleosynthesis; Stellar Evolution; Supernovae

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APA (6^th Edition):

Sukhbold, T. (2016). The Evolution and Explosion of Massive Stars. (Thesis). University of California – Santa Cruz. Retrieved from http://www.escholarship.org/uc/item/6gr8s8cp

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Sukhbold, Tuguldur. “The Evolution and Explosion of Massive Stars.” 2016. Thesis, University of California – Santa Cruz. Accessed March 05, 2021. http://www.escholarship.org/uc/item/6gr8s8cp.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Sukhbold, Tuguldur. “The Evolution and Explosion of Massive Stars.” 2016. Web. 05 Mar 2021.

Vancouver:

Sukhbold T. The Evolution and Explosion of Massive Stars. [Internet] [Thesis]. University of California – Santa Cruz; 2016. [cited 2021 Mar 05]. Available from: http://www.escholarship.org/uc/item/6gr8s8cp.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Sukhbold T. The Evolution and Explosion of Massive Stars. [Thesis]. University of California – Santa Cruz; 2016. Available from: http://www.escholarship.org/uc/item/6gr8s8cp

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

25. Britavskiy - ( ΜΠΡΙΤΑΒΣΚΙ), Mikola - ( ΜΙΚΟΛΑ). Dusty massive stars in the local group.

Degree: 2016, National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ)

URL: http://hdl.handle.net/10442/hedi/37130

► The role of episodic mass loss in massive star evolution is one of the most important open questions of current stellar evolution theory. Episodic mass… (more)

▼ The role of episodic mass loss in massive star evolution is one of the most important open questions of current stellar evolution theory. Episodic mass loss produces dust and therefore causes evolved massive stars to be very luminous in the mid-infrared and dim at optical wavelengths. Star forming dwarf irregular (dIrr) galaxies serve as ideal laboratories for investigating the evolution and mass loss phenomenon of red supergiants (RSGs), supergiants B[e] (sgB[e]), and luminous blue variables (LBVs) within the context of different metallicities of host galaxies. Also, RSGs may be used for abundance determinations in dIrrs. The extremely low number of spectroscopically confirmed RSGs and other types of dusty massive stars mentioned before, in external galaxies makes the identification of new stars of these types statistically significant. Increasing the statistics of spectroscopically confirmed evolved massive stars in the Local Group enables the investigation of the mass loss phenomena that occur in these stars in the late stages of their evolution.We aim to complete the census of luminous mid-IR sources in star-forming dwarf irregular galaxies of the Local Group. To achieve this we employed mid-IR photometric selection criteria to identify evolved massive stars, such as RSGs and luminous blue variables (LBVs), by using the fact that these types of stars have infrared excess due to dust. The method is based on 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies and J-band photometry from 2MASS. We applied our criteria to 7 dIrr galaxies: Pegasus, Phoenix, Sextans A, Sextans B, WLM, IC 10 and IC 1613 selecting 124 point sources, which we observed with the VLT/FORS2, GTC/OSIRIS and duPont/WFCCD spectrographs in multi-object and long-slit spectroscopy modes.We identified 28 RSGs, of which 21 are new discoveries, also 2 new emission line stars, and 8 carbon stars. Among the other observed objects we identified foreground giants, and background objects, such as a quasar and an early-type galaxy that contaminate our survey. We use the results of our spectroscopic survey to revise the mid-IR and optical selection criteria for identifying RSGs from photometric measurements. The optical selection criteria are more efficient in separating extragalactic RSGs from foreground giants than mid-IR selection criteria, however the mid-IR selection criteria are useful for identifying dusty stars in the Local Group. For some of the newly identified RSGs we measured the fundamental physical parameters by fitting their observational spectral energy distributions with MARCS stellar atmosphere models. This work serves as a basis for further investigation of the newly discovered dusty massive stars and their host galaxies.This PhD thesis is organized as follows: Chapter 1 provides the scientific context of the present study. In Chapter 2 the procedure for selecting sources is presented. Descriptions of the observations and data reduction are presented in Chapter 3. Chapter 4 is devoted to the spectral…

Subjects/Keywords: ΑΣΤΕΡΕΣ ΜΕΓΑΛΗΣ ΜΑΖΑΣ; ΕΡΥΘΡΟΙ ΥΠΕΡΓΙΓΑΝΤΕΣ; Απώλεια μάζας; Massive stars; RED SUPERGIANTS; Mass loss

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APA (6^th Edition):

Britavskiy - ( ΜΠΡΙΤΑΒΣΚΙ), M. -. (. �. (2016). Dusty massive stars in the local group. (Thesis). National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ). Retrieved from http://hdl.handle.net/10442/hedi/37130

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Britavskiy - ( ΜΠΡΙΤΑΒΣΚΙ), Mikola - ( ΜΙΚΟΛΑ). “Dusty massive stars in the local group.” 2016. Thesis, National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ). Accessed March 05, 2021. http://hdl.handle.net/10442/hedi/37130.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Britavskiy - ( ΜΠΡΙΤΑΒΣΚΙ), Mikola - ( ΜΙΚΟΛΑ). “Dusty massive stars in the local group.” 2016. Web. 05 Mar 2021.

Vancouver:

Britavskiy - ( ΜΠΡΙΤΑΒΣΚΙ) M-(�. Dusty massive stars in the local group. [Internet] [Thesis]. National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ); 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10442/hedi/37130.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Britavskiy - ( ΜΠΡΙΤΑΒΣΚΙ) M-(�. Dusty massive stars in the local group. [Thesis]. National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ); 2016. Available from: http://hdl.handle.net/10442/hedi/37130

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

McMaster University

26. Klassen, Mikhail. Simulating Radiative Feedback and the Formation of Massive Stars.

Degree: PhD, 2016, McMaster University

URL: http://hdl.handle.net/11375/19758

►

This thesis is a study of massive star formation: the environments in which they form and the effect that their radiation feedback has on their… (more)

▼

This thesis is a study of massive star formation: the environments in which they form and the effect that their radiation feedback has on their environments. We present high-performance supercomputer simulations of massive star formation inside molecular cloud clumps and cores. First, we present a novel radiative transfer code that hybridizes two previous approaches to radiative transfer (raytracing and flux-limited diffusion) and implements it in a Cartesian grid-based code with adaptive mesh refinement, representing the first of such implementations. This hybrid radiative transfer code allows for more accurate calculations of the radiation pressure and irradiated gas temperature that are the hallmark of massive star formation and which threaten to limit the mass which stars can ultimately obtain. Next, we apply this hybrid radiative transfer code in simulations of massive protostellar cores. We simulate their gravitational collapse and the formation of a massive protostar surrounded by a Keplerian accretion disk. These disks become gravitationally unstable, increasing the accretion rate onto the star, but do not fragment to form additional stars. We demonstrate that massive stars accrete material predominantly through their circumstellar disks, and via radiation pressure drive large outflow bubbles that appear stable to classic fluid instabilities. Finally, we present simulations of the larger context of star formation: turbulent, magnetised, filamentary cloud clumps. We study the magnetic field geometry and accretion flows. We find that in clouds where the turbulent and magnetic energies are approximately equal, the gravitational energy must dominate the kinetic energy for there to be a coherent magnetic field structure. Star cluster formation takes place inside the primary filament and the photoionisation feedback from a single massive star drives the creation of a bubble of hot, ionised gas that ultimately engulfs the star cluster and destroys the filament.

Thesis

Doctor of Philosophy (PhD)

Advisors/Committee Members: Pudritz, Ralph, Physics and Astronomy.

Subjects/Keywords: physics; astrophysics; star formation; radiative transfer; interstellar medium; numerical simulation; astronomy; massive stars; radiation; hydrodynamics

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APA (6^th Edition):

Klassen, M. (2016). Simulating Radiative Feedback and the Formation of Massive Stars. (Doctoral Dissertation). McMaster University. Retrieved from http://hdl.handle.net/11375/19758

Chicago Manual of Style (16^th Edition):

Klassen, Mikhail. “Simulating Radiative Feedback and the Formation of Massive Stars.” 2016. Doctoral Dissertation, McMaster University. Accessed March 05, 2021. http://hdl.handle.net/11375/19758.

MLA Handbook (7^th Edition):

Klassen, Mikhail. “Simulating Radiative Feedback and the Formation of Massive Stars.” 2016. Web. 05 Mar 2021.

Vancouver:

Klassen M. Simulating Radiative Feedback and the Formation of Massive Stars. [Internet] [Doctoral dissertation]. McMaster University; 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/11375/19758.

Council of Science Editors:

Klassen M. Simulating Radiative Feedback and the Formation of Massive Stars. [Doctoral Dissertation]. McMaster University; 2016. Available from: http://hdl.handle.net/11375/19758

University of Colorado

27. Battersby, Cara. The Structure and Evolution of Massive Star and Cluster Forming Regions.

Degree: PhD, Astrophysical & Planetary Sciences, 2013, University of Colorado

URL: https://scholar.colorado.edu/astr_gradetds/29

► The formation of massive stars and stellar clusters is important in understanding the light we receive from other galaxies, the life cycle of matter… (more)

▼ The formation of massive stars and stellar clusters is important in understanding the light we receive from other galaxies, the life cycle of matter in the Galaxy, and the global process of star formation. However, this problem has remained elusive as the relative rarity, large distances, confusion, and obscured nature of massive star forming regions has made a global and high-resolution understanding of their formation intractable for decades. The advent of large Galactic Plane Surveys and high-resolution observing facilities have allowed us to make large strides in this field by constraining the physical properties at the onset of massive star formation in clustered environments, identifying the stages of massive star formation, and estimating the lifetimes of these phases. We present a detailed analysis of two young massive star forming regions in different evolutionary stages embedded within a single Infrared Dark Cloud using NH3 on the Karl G. Jansky Very Large Array. In this analysis, we characterize the physical structure (column density, temperature, and virial parameter) just prior to the onset of massive star formation and infer evolution in this structure by measuring it at different evolutionary stages. We expand this analysis to a global scale using Herschel and Spitzer surveys of the Galactic Plane from mid-to far-IR, devising a method to identify precursors to stellar clusters throughout the Galaxy for the first time. By separating the diffuse Galactic cirrus emission from the dense molecular clumps, we derive the dust temperatures and column densities characteristic of cluster-forming clumps. We compare these physical properties with star formation tracers in a systematic way to distinguish and characterize their evolutionary phases. We compare the physical properties derived from gas with those derived using dust. We estimate lifetimes for these evolutionary phases and speculate on the large-scale dynamics in the formation of stellar clusters. We constrain the conditions at the onset of massive star formation, measure how these conditions change with evolutionary phase, and estimate the duration of each phase. This thesis places global and high-resolution constraints on the physical properties, evolution, and lifetimes of massive star and cluster forming regions. Advisors/Committee Members: John Bally, Jeremy Darling, Neal J. Evans II, James M. Jackson, J. Michael Shull.

Subjects/Keywords: Dust; Giant Molecular Clouds; Massive Stars; Milky Way; Observational; Star Formation; Astrophysics and Astronomy

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APA (6^th Edition):

Battersby, C. (2013). The Structure and Evolution of Massive Star and Cluster Forming Regions. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/astr_gradetds/29

Chicago Manual of Style (16^th Edition):

Battersby, Cara. “The Structure and Evolution of Massive Star and Cluster Forming Regions.” 2013. Doctoral Dissertation, University of Colorado. Accessed March 05, 2021. https://scholar.colorado.edu/astr_gradetds/29.

MLA Handbook (7^th Edition):

Battersby, Cara. “The Structure and Evolution of Massive Star and Cluster Forming Regions.” 2013. Web. 05 Mar 2021.

Vancouver:

Battersby C. The Structure and Evolution of Massive Star and Cluster Forming Regions. [Internet] [Doctoral dissertation]. University of Colorado; 2013. [cited 2021 Mar 05]. Available from: https://scholar.colorado.edu/astr_gradetds/29.

Council of Science Editors:

Battersby C. The Structure and Evolution of Massive Star and Cluster Forming Regions. [Doctoral Dissertation]. University of Colorado; 2013. Available from: https://scholar.colorado.edu/astr_gradetds/29

28. Hindson, Luke Paul. The G305 star forming complex : a panoramic view of the environment and star formation.

Degree: PhD, 2012, University of Hertfordshire

URL: http://hdl.handle.net/2299/9197

► This thesis presents molecular line and radio continuum observations of the giant molecular cloud (GMC) complex known as G305. The energy input from high-mass stars… (more)

▼ This thesis presents molecular line and radio continuum observations of the giant molecular cloud (GMC) complex known as G305. The energy input from high-mass stars in the form of powerful winds and ionising radiation is one of the primary feedback mechanisms in GMCs. This feedback is thought to play a dual role both dispersing and destroying the natal environment but also sweeping up and compressing molecular gas and potentially triggering new episodes of star formation. Despite their importance to the evolution of GMCs and galaxies as a whole, the physical processes behind the formation and evolution of high-mass stars remains poorly understood. We therefore set out to obtain wide-field observations of the ionised and molecular environment to study the impact of high-mass stars on the evolution of G305. Observations conducted with the Mopra telescope of the molecular gas traced by NH3 in the (1,1), (2,2) and (3,3) transition and CO (12CO, 13CO and C18O J = 1–0) reveals the reservoir for future star formation in G305 and allows the physical properties and kinematics of the region to be studied. We identify 15 large molecular clouds and 57 smaller molecular clumps towards G305. The physical properties of the molecular gas are consistent with G305 being amongst the most massive a vigorous star forming regions in the Galaxy. We find a total molecular gas mass of 2:5–6:5 105M indicating that there is a large reservoir for future star formation. By considering virial equilibrium within the molecular clumps we discover that only 14% of the molecular clumps in G305 are gravitationally unstable, however these clumps contain > 30% of the molecular mass in G305 suggesting there is scope for considerable future star formation. To study the ionised environment towards G305 we have obtained some of the largest and most detailed wide-area mosaics with the Australia Telescope Compact Array to date. These radio continuum observations were performed simultaneously at 5.5 and 8.8 GHz and by applying two imaging techniques we are able to resolve HII regions from the ultra-compact to classical evolutionary phase. This has allowed high-mass star formation within G305 to be traced over the extent and lifetime of the complex. We discover that more than half of the observable total ionising flux in G305 is associated with embedded high-mass star formation around the periphery of a central cavity that has been driven into the molecular gas by a cluster of optically visible massive stars. By considering the contribution of embedded and visible massive stars to the observed radio continuum we suggest that more than 45 massive stars exist within G305. Combination of these two studies and recent and ongoing star formation provides the most in depth view of G305 to date and allows the star formation history and impact of high-mass stars to be investigated. We find compelling morphological evidence that suggests triggering is responsible for at least some of the observed high-mass star formation and construct a star formation history for the…

Subjects/Keywords: 523.8; Star Formation; Massive Stars; Triggering; ISM; Giant Molecular Clouds; Masers; Spectral Line; Radio Continuum

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APA (6^th Edition):

Hindson, L. P. (2012). The G305 star forming complex : a panoramic view of the environment and star formation. (Doctoral Dissertation). University of Hertfordshire. Retrieved from http://hdl.handle.net/2299/9197

Chicago Manual of Style (16^th Edition):

Hindson, Luke Paul. “The G305 star forming complex : a panoramic view of the environment and star formation.” 2012. Doctoral Dissertation, University of Hertfordshire. Accessed March 05, 2021. http://hdl.handle.net/2299/9197.

MLA Handbook (7^th Edition):

Hindson, Luke Paul. “The G305 star forming complex : a panoramic view of the environment and star formation.” 2012. Web. 05 Mar 2021.

Vancouver:

Hindson LP. The G305 star forming complex : a panoramic view of the environment and star formation. [Internet] [Doctoral dissertation]. University of Hertfordshire; 2012. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2299/9197.

Council of Science Editors:

Hindson LP. The G305 star forming complex : a panoramic view of the environment and star formation. [Doctoral Dissertation]. University of Hertfordshire; 2012. Available from: http://hdl.handle.net/2299/9197

University of Arizona

29. Senchyna, Peter Edward. Low-Metallicity Stars and High-Redshift Galaxies Through the Lens of Local Metal-Poor Star-Forming Regions .

Degree: 2020, University of Arizona

URL: http://hdl.handle.net/10150/645774

► Over the last decade, unprecedented imaging campaigns and deep spectroscopy have delivered our first glimpse of galaxies in the reionization era, and the results have… (more)

▼ Over the last decade, unprecedented imaging campaigns and deep spectroscopy have delivered our first glimpse of galaxies in the reionization era, and the results have stymied interpretation. The prominent nebular emission in CIII], CIV, and other high-ionization lines detected in the first rest-UV spectra at these redshifts suggests that hard ionizing radiation fields are common at z>6, in striking contrast to typical star-forming systems at lower redshift. The difficulty in interpreting this emission is fundamentally tied to the lack of empirical constraints on massive stars at the very low metallicities we expect to encounter in the first billion years of the Universe. Nearby star-forming regions hosting stars and gas extending to metallicities below that of the SMC (<20% solar) represent a critical laboratory for study of such young stellar populations. In this dissertation, I first present HST/COS UV spectroscopy of HeII-emitters which reveal a clear transition from UV spectra dominated by stellar features above 20% solar metallicity to high-ionization nebular line emission at lower metallicities, tracked by a significant hardening in the inferred ionizing spectrum. I demonstrate that nebular HeII and CIV are ubiquitous among local extremely metal-poor galaxies (XMPs, <10% solar), and that CIV in particular may be an effective signpost of rapidly-assembling systems at these low metallicities in the distant Universe. I then present a new technique for locating XMPs dominated by very young stars in broadband photometry, and apply it to SDSS imaging to uncover 32 such systems at typical effective ages of tens of megayears. I demonstrate that the nebular HeII commonly encountered in such systems is inconsistent with an origin in high-mass X-ray binaries or the most massive short-lived stars, and suggest instead that this line may provide insight onto stripped stars and other uncertain products of binary evolution at very low metallicity. I also present evidence from stellar population synthesis modeling that an overabundance of massive stars or spun-up binary products are necessary to explain the strongest stellar wind features in very young systems at higher metallicities where these winds are prominent. Finally, I conclude by outlining a path forward from testing to direct calibration of models for massive stars below the metallicity of the SMC. Advisors/Committee Members: Stark, Daniel P (advisor), Smith, Nathan (committeemember), Sand, David (committeemember), Kennicutt, Robert C. (committeemember), Weiner, Benjamin (committeemember).

Subjects/Keywords: dwarf galaxies; galaxy evolution; massive stars; metal poor stellar populations; ultraviolet spectroscopy

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APA (6^th Edition):

Senchyna, P. E. (2020). Low-Metallicity Stars and High-Redshift Galaxies Through the Lens of Local Metal-Poor Star-Forming Regions . (Doctoral Dissertation). University of Arizona. Retrieved from http://hdl.handle.net/10150/645774

Chicago Manual of Style (16^th Edition):

Senchyna, Peter Edward. “Low-Metallicity Stars and High-Redshift Galaxies Through the Lens of Local Metal-Poor Star-Forming Regions .” 2020. Doctoral Dissertation, University of Arizona. Accessed March 05, 2021. http://hdl.handle.net/10150/645774.

MLA Handbook (7^th Edition):

Senchyna, Peter Edward. “Low-Metallicity Stars and High-Redshift Galaxies Through the Lens of Local Metal-Poor Star-Forming Regions .” 2020. Web. 05 Mar 2021.

Vancouver:

Senchyna PE. Low-Metallicity Stars and High-Redshift Galaxies Through the Lens of Local Metal-Poor Star-Forming Regions . [Internet] [Doctoral dissertation]. University of Arizona; 2020. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10150/645774.

Council of Science Editors:

Senchyna PE. Low-Metallicity Stars and High-Redshift Galaxies Through the Lens of Local Metal-Poor Star-Forming Regions . [Doctoral Dissertation]. University of Arizona; 2020. Available from: http://hdl.handle.net/10150/645774

30. Spetsieri, Zoi - TZogia. Transient variability and variability of massive stars with the Hubble space telescope.

Degree: 2019, National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ)

URL: http://hdl.handle.net/10442/hedi/46426

► Massive stars (stars with Mstar >8 M⊙) are among the most enigmatic types of stars.They lie at the upper part of the Hertzsprung-Russell diagram and… (more)

▼ Massive stars (stars with Mstar >8 M⊙) are among the most enigmatic types of stars.They lie at the upper part of the Hertzsprung-Russell diagram and despite their scantnumber they play a major role in the evolution of the Universe. They are the progenitorsof various sub-classes of supernovae, responsible for the re-ionization of the Universe andthe sources that produce the most energetic phenomenon yet found, gamma-ray bursts.Transients are astronomical objects or phenomena whose duration may be from secondsto days, weeks, or even several years. Supernovae, novae, dwarf nova outbursts, gammaraybusts and tidal disruption events are some examples of violent transients. The HubbleSpace Telescope since 1991 has created one of largest archives available for the study ofboth massive stars and transients at distances beyond the Local Group.This thesis is structured in two parts. In the first part we present the results of the analysisof the massive star population in four nearby galaxies (at distances ranging from 16-20Mpc). The galaxies are NGC 1326A, NGC 1425, NGC 4535 and NGC 4548. Usingdeep HST WFPC2 images in filters F555W and F814W, through PSF photometry weanalysed the massive star population of the four galaxies. In total we identified 11402 bluesupergiants, 3155 yellow supergiants and 4640 red supergiants. In addition, we estimatedthe ratio of blue to red supergiants as a function of galactocentric radius and estimatedphotometrically the star formation history of the four fields. We examined all the sourcesidentified through photometry in each field for variability using three variabilibity indexes:The Mean Absolute Deviation (MAD), the interquartile range (IQR) and the inverse vonNeumann ratio. The variability search yielded 363 new variable stars among which are 8blue supergiants, 29 red supergiants, 15 yellow supergiants and 1 candidate LBV whichwe propose for follow-up observations.In the second part of the thesis, we describe the transients and high-amplitude variablesfound in the Hubble Catalog of Variables (HCV; Bonanos et al. 2019). The HCVcontains all variable objects detected through a robust variability search in the light curvesof all sources included in the Hubble Source Catalog v3 (Whitmore et al. 2016). Wequeried the HCV to detect all variables with amplitude of variability ≥ 1 mag. Our query resulted in 6,500 matches; 1107 multi-filter and 5593 single-filter variables (Spetsieri etal., in prep.). The next step was to distinguish the sources that had been previously studied.We therefore cross-matched the sources with the whole CDS with a search radius of 3 ′′ .Although our query was applied to the total number of variables (multi-filter and single-filter) we initially focused on the multi-filter candidate variable stars that were flagged as“true variables” in the HCV. Our search yielded 243 multi-filter sources that have notbeen previously reported in the literature. For all 243 sources we created the CMD andtheir lightcurves. We report two candidate transients among our new high-amplitude…

Subjects/Keywords: Μεταβλητότητα; Αστέρες μεγάλης μάζας; Hubble space telescope; Massive stars; Transients; Variability; Hubble catalog of variables

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APA (6^th Edition):

Spetsieri, Z. -. T. (2019). Transient variability and variability of massive stars with the Hubble space telescope. (Thesis). National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ). Retrieved from http://hdl.handle.net/10442/hedi/46426

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Spetsieri, Zoi - TZogia. “Transient variability and variability of massive stars with the Hubble space telescope.” 2019. Thesis, National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ). Accessed March 05, 2021. http://hdl.handle.net/10442/hedi/46426.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Spetsieri, Zoi - TZogia. “Transient variability and variability of massive stars with the Hubble space telescope.” 2019. Web. 05 Mar 2021.

Vancouver:

Spetsieri Z-T. Transient variability and variability of massive stars with the Hubble space telescope. [Internet] [Thesis]. National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ); 2019. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10442/hedi/46426.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Spetsieri Z-T. Transient variability and variability of massive stars with the Hubble space telescope. [Thesis]. National and Kapodistrian University of Athens; Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (ΕΚΠΑ); 2019. Available from: http://hdl.handle.net/10442/hedi/46426

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Open Access Theses and Dissertations