subject:(Main sequence stars)

Vanderbilt University

1. Le Blanc, Thompson S. The Role of Disks in the Angular Momentum Evolution of Young, Low-Mass Stars.

Degree: PhD, Physics, 2012, Vanderbilt University

► Detailed studies of the spectral energy distributions (SEDs) of young stars can reveal much about their basic properties and their circumstellar material. Previous work suggests… (more)

▼ Detailed studies of the spectral energy distributions (SEDs) of young stars can reveal much about their basic properties and their circumstellar material. Previous work suggests that the magnetic interactions of its circumstellar disk may be the result of the influence of a young stars angular momentum content and rotation rate. The generic prediction of these “disk-locking” theories is that a disk-locked star will be forced to rotate at the same Keplerian angular velocity of the inner edge of the disk; that is, the disks radius at which it is truncated or evacuated, should be equal to its co-rotation radius. Additional interpretations of these theories also suggest a correlation between the rotation period of a star and the structure of its circumstellar disk; slow rotators possess closely truncated disks that enforce the stars slow rotation, whereas rapid rotators possess disks that are largely evacuated or anemic, interpreted as being outside of the magnetic influence of the star, whereby the star is free to speed up as it continues its pre-main sequence contraction. As a test of the expectations of these theories, we model the spectral energy distributions of 33 young stars in the IC348 region with known rotation periods, as well as infrared excesses indicative of circumstellar disks. We match the observed SED for each star, sampling a range of 0.6-8.0m, to a grid of 200,000 pre-computed star+disk radiative transfer models, from which we then infer the circumstellar disks inner truncation radius. We then compare the inferred truncation radius to the disks co-rotation radius, calculated from the stars measured rotation period. We do not find any obvious differences in the disk truncation radii of slow versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, as well as analyzing the precise location of the inner edge of the disk relative to the co-rotation radius among the subset of stars with close-in disk material. One interpretation of these results is that the disk locking is unimportant for the IC 348 stars in our sample. Alternatively, if disk locking does operate, then it must operate on both slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the disk-locked state to the disk-released state must occur more rapidly than the stellar contraction timescale. Advisors/Committee Members: Dr. David A. Weintraub (committee member), Dr. Andreas Berlind (committee member), Dr. David Ersnt (committee member), Dr. Antonella Nota (committee member), Dr. Keivan G. Stassun (Committee Chair).

Subjects/Keywords: circumstellar material; pre-main sequence; stars; rotation

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APA (6^th Edition):

Le Blanc, T. S. (2012). The Role of Disks in the Angular Momentum Evolution of Young, Low-Mass Stars. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/13325

Chicago Manual of Style (16^th Edition):

Le Blanc, Thompson S. “The Role of Disks in the Angular Momentum Evolution of Young, Low-Mass Stars.” 2012. Doctoral Dissertation, Vanderbilt University. Accessed March 05, 2021. http://hdl.handle.net/1803/13325.

MLA Handbook (7^th Edition):

Le Blanc, Thompson S. “The Role of Disks in the Angular Momentum Evolution of Young, Low-Mass Stars.” 2012. Web. 05 Mar 2021.

Vancouver:

Le Blanc TS. The Role of Disks in the Angular Momentum Evolution of Young, Low-Mass Stars. [Internet] [Doctoral dissertation]. Vanderbilt University; 2012. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1803/13325.

Council of Science Editors:

Le Blanc TS. The Role of Disks in the Angular Momentum Evolution of Young, Low-Mass Stars. [Doctoral Dissertation]. Vanderbilt University; 2012. Available from: http://hdl.handle.net/1803/13325

Rice University

2. Cauley, Paul Wilson. Diagnosing Mass Flows Around Herbig Ae/Be Stars.

Degree: PhD, Natural Sciences, 2014, Rice University

URL: http://hdl.handle.net/1911/87727

► Most stars form surrounded by a massive disk of dust and gas. As the star evolves, its interaction with the surrounding disk material has a… (more)

▼ Most stars form surrounded by a massive disk of dust and gas. As the star evolves, its interaction with the surrounding disk material has a significant impact on both the final evolutionary state of the star and the amount of material that is available in the disk to form planets, organic compounds, and, ultimately, life. Herbig Ae/Be stars (HAEBES) are recently formed intermediate mass (2-10 solar masses) pre – main sequence stars. Over 150 candidate HAEBES have been identified by various surveys. Although this number is large, it is relatively small compared to the number of identified classical T Tauri stars (CTTSs), the low mass (~1 solar mass) cousins of HAEBES. Although it is well established that both CTTSs and HAEBES are still evolving towards the main sequence, our understanding of how accretion and outflows operate around HAEBES compared to CTTSs is incomplete and there remains debate over the key launching mechanisms for the outflows in CTTSs. This is in large part due to the lack of comparisons of multi-wavelength mass flow diagnostics in large samples of HAEBES and CTTSs. In this thesis we attempt to address the gap in our knowledge of the driving mechanisms of accretion and outflows around HAEBES, and how they compare to those of CTTSs, by examining a wide variety of accretion and outflow diagnostics in the ultraviolet, optical, and near infrared with the goal of constraining the incidence of accretion and wind flows around these objects. A different incidence of accretion and outflow detections in HAEBES compared to CTTSs would indicate that the mechanisms governing the production of these flows in HAEBES differ from those in CTTSs and we can look to other key differences between these classes of stars to try to identify the mechanisms that control the flows. To accomplish this we analyze high resolution line profiles of a large number of spectral lines that are known to be good tracers of accretion and outflows around CTTSs. Our analysis reveals a significant difference between the occurrence of blue and red-shifted absorption features in HAEBES compared to CTTSs. This difference is largest for outflow signatures in the optical and is less significant in He I 10830, the near-IR diagnostic. We find that the incidence of red and blue-shifted absorption in HAEBES increases from the optical to the UV with intermediate rates being found in He I 10830. This suggests that hot (~100,000 K) mass flows are more common around HAEBES than cooler (~10,000 K) flows. We also find significant differences between the occurrence of red and blue – shifted absorption in HAe stars compared to HBe stars. In particular, our results support the idea of mangetospheric accretion occurring in HAe stars but provide more evidence for boundary layer accretion in HBe objects. In addition, we observe that the maximum red – shifted absorption velocities tracing infalling material in our sample are smaller fractions of the stellar escape velocity than is found for CTTSs. This is confirmed in both the optical diagnostics and at He I… Advisors/Committee Members: Johns-Krull, Christopher M (advisor), Hartigan, Patrick M (committee member), Gustin, Michael (committee member).

Subjects/Keywords: Pre-main sequence stars; Herbig Ae/Be stars/ Classical T Tauri stars; accretion; stellar winds

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

APA (6^th Edition):

Cauley, P. W. (2014). Diagnosing Mass Flows Around Herbig Ae/Be Stars. (Doctoral Dissertation). Rice University. Retrieved from http://hdl.handle.net/1911/87727

Chicago Manual of Style (16^th Edition):

Cauley, Paul Wilson. “Diagnosing Mass Flows Around Herbig Ae/Be Stars.” 2014. Doctoral Dissertation, Rice University. Accessed March 05, 2021. http://hdl.handle.net/1911/87727.

MLA Handbook (7^th Edition):

Cauley, Paul Wilson. “Diagnosing Mass Flows Around Herbig Ae/Be Stars.” 2014. Web. 05 Mar 2021.

Vancouver:

Cauley PW. Diagnosing Mass Flows Around Herbig Ae/Be Stars. [Internet] [Doctoral dissertation]. Rice University; 2014. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1911/87727.

Council of Science Editors:

Cauley PW. Diagnosing Mass Flows Around Herbig Ae/Be Stars. [Doctoral Dissertation]. Rice University; 2014. Available from: http://hdl.handle.net/1911/87727

University of Western Ontario

3. Patel, Parshati. The Inner Gaseous Disks Of Herbig Be Stars.

Degree: 2016, University of Western Ontario

URL: https://ir.lib.uwo.ca/etd/3692

► Herbig Ae/Be stars are intermediate mass (~2 to 20Msun) pre-main sequence stars that inherit a circumstellar disk of dust and gas from their formation phase.… (more)

▼ Herbig Ae/Be stars are intermediate mass (~2 to 20Msun) pre-main sequence stars that inherit a circumstellar disk of dust and gas from their formation phase. The region of this disk closest to the star is entirely gaseous because dust evaporates at the high temperatures there, and this gaseous region is currently poorly understood. Using non-LTE circumstellar disk codes to model the optical and near-infrared spectra of five, early-type (B0Ve to B2Ve) Herbig Be stars obtained with the Canada-France-Hawaii telescope ESPaDOnS instrument, the density structure of each inner gaseous disks was determined and estimates of the disk masses and sizes were obtained. In the modeling, the photoionizing radiation of the central B star was assumed to be disk's sole source of energy input. For the four Herbig B2e stars, BD+65 1637, HD 76534, HD 114981 and HD 21669, reasonable matches were found for all emission line profiles considered individually; however, for each star, no disk density model based on a single power law for the equatorial density was able to simultaneously fit all of the observed emission lines in the spectrum. For BD+65 1637, the equatorial disk density law was estimated to fall as 10-10(R*/R)3 g cm-3 in a 50 R* disk, and this model provided a reasonable match to the overall line shapes and strengths. The stars HD 76534, HD 114981 and HD 216629 required a similar density model to that of BD+65 1637, but in a smaller, 25 R* disk. The overall implied masses of these inner gaseous disks are in the range of ~5.7 x 10-8 to 1.2 x 10-9 M*. For BD+65 1637, the metal lines, Fe II and especially the Ca II IR triplet lines, required higher disk densities than implied by the hydrogen Balmer lines, with the disk density falling more slowly as 10-10(R*/R)2 g cm-3. In general for all stars, the metal lines of Ca II and Fe II required higher disk densities than the Balmer lines to match the observed line profiles. A more complex disk density distribution is likely required to reconcile this difference and refine the match to the spectra of these stars. The spectrum of the Herbig B0e star MWC 137 is dominated by very strong emission lines in comparison to the Herbig B2e stars. Preliminary results show that the models require extended disks to reproduce the observed Ca II and Fe II metal emission line profiles. For hydrogen Balmer lines, no disk models extending up to 200 R* were capable of reproducing the observed line strengths, indicating that even larger disks are required and/or the observed hydrogen lines are contaminated by hydrogen recombination emission from the surrounding H II region. Taken as a whole, the analysis of these five, early-type HBe stars suggest that the optical and near-IR emission lines in their spectra can be adequately accounted for by an inner, entirely gaseous, disk in Keplerian rotation, heated solely by the photoionizing energy input of the central star, and requiring only a tiny fraction ~10-7 of the central star's mass.

Subjects/Keywords: Herbig Ae/Be stars; Circumstellar Disks; Pre-main sequence stars; Emission Line stars; Physical Processes; Stars, Interstellar Medium and the Galaxy

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APA (6^th Edition):

Patel, P. (2016). The Inner Gaseous Disks Of Herbig Be Stars. (Thesis). University of Western Ontario. Retrieved from https://ir.lib.uwo.ca/etd/3692

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):

Patel, Parshati. “The Inner Gaseous Disks Of Herbig Be Stars.” 2016. Thesis, University of Western Ontario. Accessed March 05, 2021. https://ir.lib.uwo.ca/etd/3692.

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

MLA Handbook (7^th Edition):

Patel, Parshati. “The Inner Gaseous Disks Of Herbig Be Stars.” 2016. Web. 05 Mar 2021.

Vancouver:

Patel P. The Inner Gaseous Disks Of Herbig Be Stars. [Internet] [Thesis]. University of Western Ontario; 2016. [cited 2021 Mar 05]. Available from: https://ir.lib.uwo.ca/etd/3692.

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

Council of Science Editors:

Patel P. The Inner Gaseous Disks Of Herbig Be Stars. [Thesis]. University of Western Ontario; 2016. Available from: https://ir.lib.uwo.ca/etd/3692

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

4. Elliott, Paul Michael. Is multiplicity universal? : a study of multiplicity in the young moving groups.

Degree: PhD, 2016, University of Exeter

URL: http://hdl.handle.net/10871/21876

► The young moving groups are collections of nearby (<200 pc), young (5-150 Myr) pre-main sequence stars; these stars offer us one of the best opportunities… (more)

Subjects/Keywords: 523.8; binaries; star formation; pre-main-sequence stars; multiplicity

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

APA (6^th Edition):

Elliott, P. M. (2016). Is multiplicity universal? : a study of multiplicity in the young moving groups. (Doctoral Dissertation). University of Exeter. Retrieved from http://hdl.handle.net/10871/21876

Chicago Manual of Style (16^th Edition):

Elliott, Paul Michael. “Is multiplicity universal? : a study of multiplicity in the young moving groups.” 2016. Doctoral Dissertation, University of Exeter. Accessed March 05, 2021. http://hdl.handle.net/10871/21876.

MLA Handbook (7^th Edition):

Elliott, Paul Michael. “Is multiplicity universal? : a study of multiplicity in the young moving groups.” 2016. Web. 05 Mar 2021.

Vancouver:

Elliott PM. Is multiplicity universal? : a study of multiplicity in the young moving groups. [Internet] [Doctoral dissertation]. University of Exeter; 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10871/21876.

Council of Science Editors:

Elliott PM. Is multiplicity universal? : a study of multiplicity in the young moving groups. [Doctoral Dissertation]. University of Exeter; 2016. Available from: http://hdl.handle.net/10871/21876

University of Exeter

5. Sergison, Darryl James. Untangling the signals : investigating accretion and photometric variability in young stars.

Degree: PhD, 2015, University of Exeter

URL: http://hdl.handle.net/10871/18720

► In this thesis, an assessment is made of the value of optical CMDs as a useful diagnostic of the accretion properties of young stars. An… (more)

▼ In this thesis, an assessment is made of the value of optical CMDs as a useful diagnostic of the accretion properties of young stars. An analysis has been made of the phenomena that we observe and their effect on the position of stars in the CMD. Limitations and potential biases have been identified and evaluated. Variability causes some luminosity spread at a given colour in optical CMDs. A detailed characterisation of variability has been performed which places strong constraints on the magnitudes and the timescales on which the variability is seen. On timescales 15 minutes, almost no variability is detected (at levels greater than ≈ 0.2%) in the i band for a sample of ≈ 700 disc-bearing young stellar objects (YSOs). This suggests that the variability predicted by some accretion shock models is either very weak or not present. On hours to days timescales the optical variability in most stars is well described by a simple power law. The amplitude of the variability, a ∝ f−k, where f is the frequency of the variability in days. Disc-bearing and discless YSOs exhibit median values of k of 0.85 ± 0.02 and 0.95 ± 0.03 respectively, the uncertainity being the error on the median. The power law is valid up to a certain timescale (tmax) at which point the variability amplitude does not increase any further. tmax is found to be 1.50 ± 0.07 days and 1.41 ± 0.10 days for disc-bearing and discless stars respectively. Disc-bearing stars show greater variability amplitudes than the discless stars. However, it is notable that the variability timescale and power spectrum exponent are remarkably similar. This implies that the amplitude of the variability is driven by the physics of the underlying process, but that the timescales are instead driven by geometric effects. For disc-bearing stars, the highest amplitude variables are the accreting stars, which often appear to vary in the CMD along lines that correspond to changes in accretion luminosity. Four disc-bearing stars (approximately 0.5% of the disc-bearing sample) in Cep OB3b show extreme variability on timescales of years. Three (possible EXor candidates), show long-timescale changes that have a dramatic effect on their CMD position. However their small numbers mean that the overall impact on the CMDs of young associations is small. Variability on timescales of the rotational period and shorter adds uncertainty to age estimates of individual stars that are calculated by comparison with PMS models. Having provided a detailed description of variability and its impact on the CMD, it is clear that there are further significant mechanisms that affect the positions of YSOs in the CMD. I show that the spread in luminosity seen in the Orion Nebula Cluster and NGC 2264 could not be explained by accretion at rates of M ̇ ≥ 5 × 10−4 M⊙ yr−1 occurring within the protostellar phase of YSO evolution. Thus it appears that CMDs are not a useful diagnostic for study of the accretion histories of YSOs. The wavelength dependence of the extinction by dust within the inner regions of YSO discs is…

Subjects/Keywords: 500; pre-main-sequence stars; YSOs; optical variability; accretion; discs

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

APA (6^th Edition):

Sergison, D. J. (2015). Untangling the signals : investigating accretion and photometric variability in young stars. (Doctoral Dissertation). University of Exeter. Retrieved from http://hdl.handle.net/10871/18720

Chicago Manual of Style (16^th Edition):

Sergison, Darryl James. “Untangling the signals : investigating accretion and photometric variability in young stars.” 2015. Doctoral Dissertation, University of Exeter. Accessed March 05, 2021. http://hdl.handle.net/10871/18720.

MLA Handbook (7^th Edition):

Sergison, Darryl James. “Untangling the signals : investigating accretion and photometric variability in young stars.” 2015. Web. 05 Mar 2021.

Vancouver:

Sergison DJ. Untangling the signals : investigating accretion and photometric variability in young stars. [Internet] [Doctoral dissertation]. University of Exeter; 2015. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10871/18720.

Council of Science Editors:

Sergison DJ. Untangling the signals : investigating accretion and photometric variability in young stars. [Doctoral Dissertation]. University of Exeter; 2015. Available from: http://hdl.handle.net/10871/18720

University of Toledo

6. Allen, Thomas S. A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b.

Degree: PhD, Physics, 2014, University of Toledo

URL: http://rave.ohiolink.edu/etdc/view?acc_num=toledo1404697742

► We present results from an extensive multi-wavelength survey of Cep OB3b, one of the largest young clusters within 1 kpc of the Sun. We estimate… (more)

Subjects/Keywords: Astronomy; pre-main sequence stars; interstellar extinction; stellar clusters

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

APA (6^th Edition):

Allen, T. S. (2014). A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b. (Doctoral Dissertation). University of Toledo. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=toledo1404697742

Chicago Manual of Style (16^th Edition):

Allen, Thomas S. “A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b.” 2014. Doctoral Dissertation, University of Toledo. Accessed March 05, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1404697742.

MLA Handbook (7^th Edition):

Allen, Thomas S. “A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b.” 2014. Web. 05 Mar 2021.

Vancouver:

Allen TS. A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b. [Internet] [Doctoral dissertation]. University of Toledo; 2014. [cited 2021 Mar 05]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=toledo1404697742.

Council of Science Editors:

Allen TS. A Multi-wavelength survey of the Young Stellar Cluster Cep OB3b. [Doctoral Dissertation]. University of Toledo; 2014. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=toledo1404697742

7. Contreras Peña, Carlos Eduardo. Exteme variables in star forming regions.

Degree: PhD, 2015, University of Hertfordshire

URL: http://hdl.handle.net/2299/15590

► The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a constant rate during the early stages of their evolution appears to… (more)

▼ The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a constant rate during the early stages of their evolution appears to be challenged by observations of YSOs suffering sudden increases of the rate at which they gain mass from their circumstellar discs. Also, this idea that stars spend most of their lifetime with a low accretion rate and gain most of their final mass during short-lived episodes of high accretion bursts, helps to solve some long-standing problems in stellar evolution. The original classification of eruptive variables divides them in two separate subclasses known as FU Orionis stars (FUors) and EX Lupi stars (EXors). In this classical view FUors are at an early evolutionary stage and are still gaining mass from their parent envelopes, whilst EXors are thought to be older objects only surrounded by an accretion disc. The problem with this classical view is that it excludes younger protostars which have higher accretion rates but are too deeply embedded in circumstellar matter to be observed at optical wavelengths. Optically invisible protostars have been observed to display large variability in the near-infrared. These and some recent discoveries of new eruptive variables, show characteristics that can be attributed to both of the optically-defined subclasses of eruptive variables. The new objects have been proposed to be part of a new class of eruptive variables. However, a more accepted scenario is that in fact the original classes only represent two extremes of the same phenomena. In this sense eruptive variability could be explained as arising from one physical mechanism, i.e. unsteady accretion, where a variation in the parameters of such mechanism can cause the different characteristics observed in the members of this class. With the aim of studying the incidence of episodic accretion among young stellar objects, and to characterize the nature of these eruptive variables we searched for high amplitude variability in two multi-epoch infrared surveys: the UKIDSS Galactic Plane Survey (GPS) and the Vista Variables in the Via Lactea (VVV). In order to further investigate the nature of the selected variable stars, we use photometric information arising from public surveys at near- to farinfrared wavelengths. In addition we have performed spectroscopic and photometric follow-up for a large subset of the samples arising from GPS and VVV. We analyse the widely separated two-epoch K-band photometry in the 5th, 7th and 8th data releases of the UKIDSS Galactic Plane Survey. We find 71 stars with _K > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is mostly excluded from the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (27 stars). The analysis of the multi-epoch K-band photometry of 2010-2012 data from VVV covering the Galactic disc at |b| < 1◦ yields 816 high amplitude variables, which…

Subjects/Keywords: 523.8; stars: AGB and post-AGB; stars: low-mass; stars: pre-main-sequence; stars: protostars; stars: variables: T Tauri, Herbig Ae/Be; infrared: stars

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APA (6^th Edition):

Contreras Peña, C. E. (2015). Exteme variables in star forming regions. (Doctoral Dissertation). University of Hertfordshire. Retrieved from http://hdl.handle.net/2299/15590

Chicago Manual of Style (16^th Edition):

Contreras Peña, Carlos Eduardo. “Exteme variables in star forming regions.” 2015. Doctoral Dissertation, University of Hertfordshire. Accessed March 05, 2021. http://hdl.handle.net/2299/15590.

MLA Handbook (7^th Edition):

Contreras Peña, Carlos Eduardo. “Exteme variables in star forming regions.” 2015. Web. 05 Mar 2021.

Vancouver:

Contreras Peña CE. Exteme variables in star forming regions. [Internet] [Doctoral dissertation]. University of Hertfordshire; 2015. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2299/15590.

Council of Science Editors:

Contreras Peña CE. Exteme variables in star forming regions. [Doctoral Dissertation]. University of Hertfordshire; 2015. Available from: http://hdl.handle.net/2299/15590

University of Rochester

8. Pecaut, Mark (1975 - ). The star-formation history and accretion disk fraction of the Scorpius-Centaurus OB Association.

Degree: PhD, 2013, University of Rochester

URL: http://hdl.handle.net/1802/27871

► We present a study of the star-formation history and accretion disk fraction of ∼0.6- 1.8 M⊙ stars in the nearest OB Association, Scorpius-Centaurus (Sco-Cen; 10-20… (more)

▼ We present a study of the star-formation history and accretion disk fraction of ∼0.6- 1.8 M⊙ stars in the nearest OB Association, Scorpius-Centaurus (Sco-Cen; 10-20 Myr; 100-200 pc). We have performed a low-resolution spectroscopic survey for new, low-mass K- and M-type members of all three subgroups – Upper Scorpius (US), Upper Centaurus-Lupus (UCL) and Lower Centaurus-Crux (LCC). We find that young, pre-main sequence stars have different intrinsic colors for a given spectral type than their main-sequence (MS) counterparts and therefore MS colors and temperatures are unsuitable for de-reddening the low-mass members of Sco-Cen and placing them on an H-R diagram. Using nearby, pre-MS, unreddened moving groups, we derive a spectral type–intrinsic color sequence appropriate for 5-30 Myr old pre-MS stars, and use synthetic spectral energy distribution fits to infer the proper temperature and bolometric correction scale for these young stars. We use this new pre-MS intrinsic color and temperature calibration to place our ∼150 newly identified members of Sco- Cen on an H-R diagram. We derive isochronal ages for the B-type MS turn-off and the pre-MS F-type, G-Type members and the K- and M-type members of Sco-Cen. We find a Teff -dependent age trend in the K/M-type stars, similar to previous studies of other nearby star-forming regions. Our F- and G-type isochronal ages for Upper Centaurus-Lupus (UCL; 16±2 Myr; < d >=142 pc) and Lower Centaurus-Crux (LCC; 16±3 Myr; < d >=118 pc) are consistent with previous results. However, our results for Upper Scorpius (US; 10±3 Myr; < d >=145 pc) indicate it is a factor of two older than previously thought. Using ∼650 of the pre-MS members of Sco-Cen, we construct an age map, which reveals regions which are systematically younger or older than the mean Sco-Cen age, suggesting that the star-formation history of the three subgroups is more complex than the simple division into three subgroups would imply. Finally, we find a primordial disk fraction for US, UCL and LCC of 9+4 −2%, 5+2 −1% and 3+3 −1%, respectively, for K-type stars decreasing to <19% (95% CL), 2+5 −1%, and 2+4 −1%, respectively, for F-type stars at ∼10 Myr, ∼16 Myr, and ∼16 Myr, respectively.

Subjects/Keywords: Accretion disk fraction; Intrinsic colors; Pre-main sequence stars; Scorpius-Centaurus; Stellar ages; Stellar temperatures

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APA (6^th Edition):

Pecaut, M. (. -. ). (2013). The star-formation history and accretion disk fraction of the Scorpius-Centaurus OB Association. (Doctoral Dissertation). University of Rochester. Retrieved from http://hdl.handle.net/1802/27871

Chicago Manual of Style (16^th Edition):

Pecaut, Mark (1975 - ). “The star-formation history and accretion disk fraction of the Scorpius-Centaurus OB Association.” 2013. Doctoral Dissertation, University of Rochester. Accessed March 05, 2021. http://hdl.handle.net/1802/27871.

MLA Handbook (7^th Edition):

Pecaut, Mark (1975 - ). “The star-formation history and accretion disk fraction of the Scorpius-Centaurus OB Association.” 2013. Web. 05 Mar 2021.

Vancouver:

Pecaut M(-). The star-formation history and accretion disk fraction of the Scorpius-Centaurus OB Association. [Internet] [Doctoral dissertation]. University of Rochester; 2013. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1802/27871.

Council of Science Editors:

Pecaut M(-). The star-formation history and accretion disk fraction of the Scorpius-Centaurus OB Association. [Doctoral Dissertation]. University of Rochester; 2013. Available from: http://hdl.handle.net/1802/27871

9. Vieira, Rodrigo Georgetti. Envoltórios circunstelares de estrelas jovens de massa intermediária .

Degree: PhD, Astronomia, 2012, University of São Paulo

URL: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-08112012-160406/ ;

►

As estrelas Herbig Ae/Be (HAeBe) representam os objetos de massa intermediária (2-10 Msol) na pré-sequência principal. Algumas de suas propriedades físicas são pouco compreendidas até… (more)

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As estrelas Herbig Ae/Be (HAeBe) representam os objetos de massa intermediária (2-10 Msol) na pré-sequência principal. Algumas de suas propriedades físicas são pouco compreendidas até o momento. Somente o estudo conjunto das informações fornecidas em diversos comprimentos de onda pode revelar as características do material circunstelar destes objetos. O objetivo deste trabalho de doutorado é analisar sob vários aspectos a estrutura, a composição e a evolução destes ambientes circunstelares. Para realização deste estudo, adotamos a amostra de candidatas a estrelas HAeBe detectadas pelo Pico dos Dias Survey (Vieira et al. 2003). Evitamos as possíveis contaminações desta amostra por estrelas em estágios mais avançados utilizando diagramas de cores, estimativas de extinção e características espectrais. A química da poeira circunstelar foi analisada a partir das propriedades dos espectros ISO disponíveis para nossos objetos. O perfil espectral do silicato em torno de 10 microns revelou características evolutivas do material circunstelar. O status evolutivo dos objetos mais embebidos foi determinado por meio de estimativas da massa de seus envoltórios circunstelares. Este estudo indicou que a maior parte desta sub-amostra se encontra no estágio intermediário entre a Classe 0 (Menv>>M*) e a Classe I (Menv<M*) de estrelas jovens. Detalhes da morfologia do disco de PDS340 foram analisados por imagens no infravermelho-médio, obtidas em bancos de dados. Estas observações impuseram vínculos à extensão e orientação espacial do disco nesta faixa espectral. As observações disponíveis em vários comprimentos de onda revelaram características da estrutura e evolução do material circunstelar associado a estrelas HAeBe. A perspectiva do desenvolvimento de um modelo completo que abranja todas estas informações é descrita na conclusão do trabalho.

Herbig Ae/Be (HAeBe) objects are intermediate mass (2 -10 Msun) stars in the pre-main sequence. Some of their properties remain not well understood to date. Only a full multi-wavelength study is able to reveal a reasonable scenario for their circumstellar material. The purpose of the present work is to study the structure, composition and evolution of these circumstellar environments. To address this issues, the sample of HAeBe candidates detected by the Pico dos Dias Survey (Vieira et al., 2003) was adopted. To avoid the contamination by more evolved stars, we developed an analysis based on two-color diagrams, extinction values and spectral features. The chemistry of the circumstellar dust was studied based on Infrared Space Observatory spectra available to our sample. The silicate feature around 10 micron revealed evolutionary information of the circumstellar material. The evolutionary stage of the more embedded sources was determined by estimates of their envelope masses. This study indicates almost all of this sub-sample to be in the intermediate phase between Class 0 (Menv>>Msun) and Class I (Menv<Msun). Mid-infrared images, retrieved from archive data, introduced morphological…

Advisors/Committee Members: Hetem, Jane Cristina Gregorio.

Subjects/Keywords: circumstellar material; estrelas; material circunstelar; pre-main sequence; pré-sequência principal; stars

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APA (6^th Edition):

Vieira, R. G. (2012). Envoltórios circunstelares de estrelas jovens de massa intermediária . (Doctoral Dissertation). University of São Paulo. Retrieved from http://www.teses.usp.br/teses/disponiveis/14/14131/tde-08112012-160406/ ;

Chicago Manual of Style (16^th Edition):

Vieira, Rodrigo Georgetti. “Envoltórios circunstelares de estrelas jovens de massa intermediária .” 2012. Doctoral Dissertation, University of São Paulo. Accessed March 05, 2021. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-08112012-160406/ ;.

MLA Handbook (7^th Edition):

Vieira, Rodrigo Georgetti. “Envoltórios circunstelares de estrelas jovens de massa intermediária .” 2012. Web. 05 Mar 2021.

Vancouver:

Vieira RG. Envoltórios circunstelares de estrelas jovens de massa intermediária . [Internet] [Doctoral dissertation]. University of São Paulo; 2012. [cited 2021 Mar 05]. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-08112012-160406/ ;.

Council of Science Editors:

Vieira RG. Envoltórios circunstelares de estrelas jovens de massa intermediária . [Doctoral Dissertation]. University of São Paulo; 2012. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-08112012-160406/ ;

10. Pelisoli, Ingrid Domingos. White dwarf and subdwarf stars in the sloan digital sky survey.

Degree: 2018, Universidade do Rio Grande do Sul

URL: http://hdl.handle.net/10183/180510

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White dwarf stars are the final observable evolutionary state of over 95% of stars and also a common outcome in binary evolution. Therefore, studying white… (more)

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White dwarf stars are the final observable evolutionary state of over 95% of stars and also a common outcome in binary evolution. Therefore, studying white dwarfs is a powerful tool to understand both single and binary stellar evolution, local initial mass function, and post-main sequence mass loss, leading us to a better comprehension of the history of stellar formation and evolution of different stellar populations. In order to make this type of studies possible, a large and preferably complete sample of white dwarf stars, covering the whole range of physical parameters, is required. The simplest way to achieve that is to take advantage of data provided by large surveys. The Sloan Digital Sky Survey has already allowed the increase of the number of known white dwarf stars fivefold up to its data release 10. In this work, we extended the search for white dwarfs to the new objects in the data release 12, discovering 3 157 new white dwarfs and 1 349 new subdwarfs. For the first time, we have extended this search to log g < 6.5, corresponding to M < 0.3 M⊙. White dwarfs below this mass limit cannot be formed through single evolution within a Hubble time; however, if the star is part of a close binary system, the mass loss of the system may be so intense that the resulting white dwarf has mass below the single evolution limit. These objects are known as extremely-low mass white dwarfs (ELMs) They show Teff < 20 000 K and 5.0 . log g . 6.5 and spectra very similar to main sequence A stars. Less than a hundred of them are known, and most objects were discovered relying on biased selection criteria, that excluded cool (Teff < 9 000 K), lowermass (M . 0.15 M⊙) ELMs, making it difficult to validate the models and comprehend the properties of the ELMs as a class. We have identified thousands of objects whose physical properties, effective temperature and surface gravity, place them in the range of by-products of binary interaction such as the ELMs. We have called them sdAs, referring to their sub-main sequence log g and hydrogen dominated spectra. They seem to be composed of overlapping stellar populations, and we found that at least 7% are more likely ELMs or their precursors, the pre-ELMs, than main sequence stars. Obtaining time-resolved spectroscopy for 26 objects, we could confirm 15 to be in close binaries. One of them is also an eclipsing system, while another is a pulsator — the eighth member of the pulsating ELM class. Other six new pulsators were found as part of our follow-up, five of them in the vicinity of the ELM instability strip. With these results, we increase the population of ELMs by 20%, raising the fraction of cool ELMs from 4 to 20%, which is consistent with the predictions from the evolutionary models.

Estrelas anãs brancas são o último estágio evolutivo observável de mais de 95% das estrelas e também um resultado comum na evolução de estrelas binárias. O estudo de anãs brancas é, portanto, uma ferramenta poderosa na compreensão da evolução de estrelas simples e binárias, da função de massa inicial…

Advisors/Committee Members: Kepler, Souza Oliveira.

Subjects/Keywords: Anãs brancas; Stars; Stellar evolution; Estrelas; Evolucao estelar; White dwarfs; Estrelas binarias; Subdwarfs; Main sequence

11 more images…

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APA (6^th Edition):

Pelisoli, I. D. (2018). White dwarf and subdwarf stars in the sloan digital sky survey. (Thesis). Universidade do Rio Grande do Sul. Retrieved from http://hdl.handle.net/10183/180510

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):

Pelisoli, Ingrid Domingos. “White dwarf and subdwarf stars in the sloan digital sky survey.” 2018. Thesis, Universidade do Rio Grande do Sul. Accessed March 05, 2021. http://hdl.handle.net/10183/180510.

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

MLA Handbook (7^th Edition):

Pelisoli, Ingrid Domingos. “White dwarf and subdwarf stars in the sloan digital sky survey.” 2018. Web. 05 Mar 2021.

Vancouver:

Pelisoli ID. White dwarf and subdwarf stars in the sloan digital sky survey. [Internet] [Thesis]. Universidade do Rio Grande do Sul; 2018. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10183/180510.

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

Council of Science Editors:

Pelisoli ID. White dwarf and subdwarf stars in the sloan digital sky survey. [Thesis]. Universidade do Rio Grande do Sul; 2018. Available from: http://hdl.handle.net/10183/180510

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

11. Koutoulaki, Maria-Kalliopi. A closer look at protoplanetary discs : the inner few au probed with spectroscopy and optical interferometry.

Degree: 2020, University College Dublin. School of Physics

URL: http://hdl.handle.net/10197/11663

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A first step towards understanding planetary formation is the characterisation of the structure and evolution of protoplanetary discs. Although the large scale disc is understood… (more)

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A first step towards understanding planetary formation is the characterisation of the structure and evolution of protoplanetary discs. Although the large scale disc is understood in some detail, much less is known about the inner 5 au in which the main physical processes take place: accretion, ejection, and planetary formation. Even in the nearest sites of star formation, this region cannot be spatially resolved by stand-alone telescopes; only in recent years have optical and infrared interferometers been able to achieve this, and only in the case of the brightest sources. Hydrogen recombination lines are present in the spectra of young stars. In particular, the Bracket gamma line is the brightest line in the K-band. HD50138 is a target that exhibits bright Bracket gamma and faint high-n Pfund (from level n=24 to n=19) emission. Our results show that the circumstellar environment of the target is complex and shows asymmetries in both the Bracket gamma and the continuum emitting regions. The Bracket gamma is more compact than the continuum emitting region and originates from a wind with a wide opening angle. The origin of the Bracket gamma line is still controversial and it has been found to be associated with both accretion and ejection processes. Thus, more tracers are needed to better constrain the inner gaseous disc properties. Molecules are also present in this part of the disc. In particular, the CO overtone emission at 2.3,mic is a good tracer of the inner disc properties. This emission is not common and in the case of T Tauri stars it has been observed in only three sources. RW Aur A is a CTTS that exhibits irregular dimming events. It shows CO overtone emission in both the bright and dim states. Modelling this emission with an LTE CO ring in Keplerian rotation, we find that the CO conditions do not change during the dimming events. Moreover, no significant accretion variation is detected between the two states, leading to the conclusion that the dimmings are caused by occulting material very close to the star (within 1 au). The CO ro-vibrational emission at 2.3,mic observed with the second generation interferometer VLTI/GRAVITY opens a new window on constraining the physical properties of the inner gaseous disc, by spatially resolving the CO emission. 51Oph is a target which shows bright CO overtone emission. By modelling the CO emission, the CO is found to emitt very close to the star from a warm and dense gas. This is the first observational evidence of the physical properties so close to the star (~0.1 au) where there is no dust. This is consistent with previous LTE models of the physical conditions in the dust-free disc.

Irish Research Council

Science Foundation Ireland

Subjects/Keywords: Protoplanetary discs; Bracket gamma line; CO overtone emission; Pre-main sequence stars

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APA (6^th Edition):

Koutoulaki, M. (2020). A closer look at protoplanetary discs : the inner few au probed with spectroscopy and optical interferometry. (Thesis). University College Dublin. School of Physics. Retrieved from http://hdl.handle.net/10197/11663

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):

Koutoulaki, Maria-Kalliopi. “A closer look at protoplanetary discs : the inner few au probed with spectroscopy and optical interferometry.” 2020. Thesis, University College Dublin. School of Physics. Accessed March 05, 2021. http://hdl.handle.net/10197/11663.

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

MLA Handbook (7^th Edition):

Koutoulaki, Maria-Kalliopi. “A closer look at protoplanetary discs : the inner few au probed with spectroscopy and optical interferometry.” 2020. Web. 05 Mar 2021.

Vancouver:

Koutoulaki M. A closer look at protoplanetary discs : the inner few au probed with spectroscopy and optical interferometry. [Internet] [Thesis]. University College Dublin. School of Physics; 2020. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10197/11663.

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

Council of Science Editors:

Koutoulaki M. A closer look at protoplanetary discs : the inner few au probed with spectroscopy and optical interferometry. [Thesis]. University College Dublin. School of Physics; 2020. Available from: http://hdl.handle.net/10197/11663

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

12. Giarrusso, Marina. Lithium and age of pre-main sequence stars.

Degree: 2016, Università degli Studi di Catania

URL: http://hdl.handle.net/10761/3892

► The expectation to date the age of low mass pre-main sequence stars from lithium has been tested by comparing the observed lithium and the predicted… (more)

Subjects/Keywords: Area 02 - Scienze fisiche; Astrophysics, nuclear, stars, pre-main sequence, binary, lithium

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APA (6^th Edition):

Giarrusso, M. (2016). Lithium and age of pre-main sequence stars. (Thesis). Università degli Studi di Catania. Retrieved from http://hdl.handle.net/10761/3892

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):

Giarrusso, Marina. “Lithium and age of pre-main sequence stars.” 2016. Thesis, Università degli Studi di Catania. Accessed March 05, 2021. http://hdl.handle.net/10761/3892.

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

MLA Handbook (7^th Edition):

Giarrusso, Marina. “Lithium and age of pre-main sequence stars.” 2016. Web. 05 Mar 2021.

Vancouver:

Giarrusso M. Lithium and age of pre-main sequence stars. [Internet] [Thesis]. Università degli Studi di Catania; 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10761/3892.

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

Council of Science Editors:

Giarrusso M. Lithium and age of pre-main sequence stars. [Thesis]. Università degli Studi di Catania; 2016. Available from: http://hdl.handle.net/10761/3892

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

13. Canty, James Ignatius. Investigating the properties of brown dwarfs using intermediate-resolution spectroscopy.

Degree: PhD, 2015, University of Hertfordshire

URL: http://hdl.handle.net/2299/15194

► This thesis is an investigation into some properties of brown dwarfs using medium-resolution spectroscopy. In the first part of the thesis, I address the issue… (more)

Subjects/Keywords: 523.8; stars: formation; pre-main sequence; low-mass; brown dwarfs; atmospheres; luminosity function; mass function

10 more images…

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APA (6^th Edition):

Canty, J. I. (2015). Investigating the properties of brown dwarfs using intermediate-resolution spectroscopy. (Doctoral Dissertation). University of Hertfordshire. Retrieved from http://hdl.handle.net/2299/15194

Chicago Manual of Style (16^th Edition):

Canty, James Ignatius. “Investigating the properties of brown dwarfs using intermediate-resolution spectroscopy.” 2015. Doctoral Dissertation, University of Hertfordshire. Accessed March 05, 2021. http://hdl.handle.net/2299/15194.

MLA Handbook (7^th Edition):

Canty, James Ignatius. “Investigating the properties of brown dwarfs using intermediate-resolution spectroscopy.” 2015. Web. 05 Mar 2021.

Vancouver:

Canty JI. Investigating the properties of brown dwarfs using intermediate-resolution spectroscopy. [Internet] [Doctoral dissertation]. University of Hertfordshire; 2015. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2299/15194.

Council of Science Editors:

Canty JI. Investigating the properties of brown dwarfs using intermediate-resolution spectroscopy. [Doctoral Dissertation]. University of Hertfordshire; 2015. Available from: http://hdl.handle.net/2299/15194

McMaster University

14. Klassen, Mikhail. Simulating Protostellar Evolution and Radiative Feedback in the Cluster Environment.

Degree: MSc, 2011, McMaster University

URL: http://hdl.handle.net/11375/11313

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Stars form in clusters amidst complex and coupled physical phenomena. Among the most important of these is radiative feedback, which heats the surrounding gas… (more)

Subjects/Keywords: star formation; molecular clouds; HII regions; protostellar evolution; pre-main-sequence stars; numerical simulation; Stars, Interstellar Medium and the Galaxy; Stars, Interstellar Medium and the Galaxy

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APA (6^th Edition):

Klassen, M. (2011). Simulating Protostellar Evolution and Radiative Feedback in the Cluster Environment. (Masters Thesis). McMaster University. Retrieved from http://hdl.handle.net/11375/11313

Chicago Manual of Style (16^th Edition):

Klassen, Mikhail. “Simulating Protostellar Evolution and Radiative Feedback in the Cluster Environment.” 2011. Masters Thesis, McMaster University. Accessed March 05, 2021. http://hdl.handle.net/11375/11313.

MLA Handbook (7^th Edition):

Klassen, Mikhail. “Simulating Protostellar Evolution and Radiative Feedback in the Cluster Environment.” 2011. Web. 05 Mar 2021.

Vancouver:

Klassen M. Simulating Protostellar Evolution and Radiative Feedback in the Cluster Environment. [Internet] [Masters thesis]. McMaster University; 2011. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/11375/11313.

Council of Science Editors:

Klassen M. Simulating Protostellar Evolution and Radiative Feedback in the Cluster Environment. [Masters Thesis]. McMaster University; 2011. Available from: http://hdl.handle.net/11375/11313

University of Exeter

15. Bell, Cameron Pearce MacDonald. A critical assessment of ages derived using pre-main-sequence isochrones in colour-magnitude diagrams.

Degree: PhD, 2012, University of Exeter

URL: https://ore.exeter.ac.uk/repository/handle/10036/4017 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571885

► In this thesis a critical assessment of the ages derived using theoretical pre-main-sequence (pre-MS) stellar evolutionary models is presented by comparing the predictions to the… (more)

▼ In this thesis a critical assessment of the ages derived using theoretical pre-main-sequence (pre-MS) stellar evolutionary models is presented by comparing the predictions to the low-mass pre-MS population of 14 young star-forming regions (SFRs) in colour-magnitude diagrams (CMDs). Deriving pre-MS ages requires precise distances and estimates of the reddening. Therefore, the main-sequence (MS) members of the SFRs have been used to derive a self-consistent set of statistically robust ages, distances and reddenings with associated uncertainties using a maximum-likelihood fitting statistic and MS evolutionary models. A photometric method (known as the Q-method) for de-reddening individual stars in regions where the extinction is spatially variable has been updated and is presented. The effects of both the model dependency and the SFR composition on these derived parameters are also discussed. The problem of calibrating photometric observations of red pre-MS stars is examined and it is shown that using observations of MS stars to transform the data into a standard photometric system can introduce significant errors in the position of the pre-MS locus in CMD space. Hence, it is crucial that precise photometric studies (especially of pre- MS objects) be carried out in the natural photometric system of the observations. This therefore requires a robust model of the system responses for the instrument used, and thus the calculated responses for the Wide-Field Camera on the Isaac Newton Telescope are presented. These system responses have been tested using standard star observations and have been shown to be a good representation of the photometric system. A benchmark test for the pre-MS evolutionary models is performed by comparing them to a set of well-calibrated CMDs of the Pleiades in the wavelength regime 0.4−2.5 μm. The masses predicted by these models are also tested against dynamical masses using a sample of MS binaries by calculating the system magnitude in a given photometric band- pass. This analysis shows that for Teff ≤ 4000 K the models systematically overestimate the flux by a factor of 2 at 0.5 μm, though this decreases with wavelength, becoming negligible at 2.2 μm. Thus before the pre-MS models are used to derive ages, a recalibration of the models is performed by incorporating an empirical colour-Teff relation and bolometric corrections based on the Ks-band luminosity of Pleiades members, with theoretical corrections for the dependence on the surface gravity (log g). The recalibrated pre-MS model isochrones are used to derive ages from the pre-MS populations of the SFRs. These ages are then compared with the MS derivations, thus providing a powerful diagnostic tool with which to discriminate between the different pre- MS age scales that arise from a much stronger model dependency in the pre-MS regime. The revised ages assigned to each of the 14 SFRs are up to a factor two older than previous derivations, a result with wide-ranging implications, including that circumstellar discs survive longer and that the…

Subjects/Keywords: 523.88; stars: evolution; stars: formation; stars: pre-main-sequence; techniques: photometric; open clusters and associations: general; Hertzsprung-Russell and colour-magnitude diagrams

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APA (6^th Edition):

Bell, C. P. M. (2012). A critical assessment of ages derived using pre-main-sequence isochrones in colour-magnitude diagrams. (Doctoral Dissertation). University of Exeter. Retrieved from https://ore.exeter.ac.uk/repository/handle/10036/4017 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571885

Chicago Manual of Style (16^th Edition):

Bell, Cameron Pearce MacDonald. “A critical assessment of ages derived using pre-main-sequence isochrones in colour-magnitude diagrams.” 2012. Doctoral Dissertation, University of Exeter. Accessed March 05, 2021. https://ore.exeter.ac.uk/repository/handle/10036/4017 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571885.

MLA Handbook (7^th Edition):

Bell, Cameron Pearce MacDonald. “A critical assessment of ages derived using pre-main-sequence isochrones in colour-magnitude diagrams.” 2012. Web. 05 Mar 2021.

Vancouver:

Bell CPM. A critical assessment of ages derived using pre-main-sequence isochrones in colour-magnitude diagrams. [Internet] [Doctoral dissertation]. University of Exeter; 2012. [cited 2021 Mar 05]. Available from: https://ore.exeter.ac.uk/repository/handle/10036/4017 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571885.

Council of Science Editors:

Bell CPM. A critical assessment of ages derived using pre-main-sequence isochrones in colour-magnitude diagrams. [Doctoral Dissertation]. University of Exeter; 2012. Available from: https://ore.exeter.ac.uk/repository/handle/10036/4017 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571885

North-West University

16. Czanik, Robert Johann. An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik .

Degree: 2013, North-West University

URL: http://hdl.handle.net/10394/9102

► This study consisted of an optical photometric and spectroscopic analysis on a 7′ 7′ field around the Southern high mass star forming region RCW 34.… (more)

Subjects/Keywords: RCW 34; T Tauri; GUM 19; HII region; Pre-main sequence stars; Star formation; Photometry; Spectroscopy; SAAO; IRAF; DANDICAM

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APA (6^th Edition):

Czanik, R. J. (2013). An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik . (Thesis). North-West University. Retrieved from http://hdl.handle.net/10394/9102

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):

Czanik, Robert Johann. “An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik .” 2013. Thesis, North-West University. Accessed March 05, 2021. http://hdl.handle.net/10394/9102.

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

MLA Handbook (7^th Edition):

Czanik, Robert Johann. “An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik .” 2013. Web. 05 Mar 2021.

Vancouver:

Czanik RJ. An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik . [Internet] [Thesis]. North-West University; 2013. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10394/9102.

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

Council of Science Editors:

Czanik RJ. An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik . [Thesis]. North-West University; 2013. Available from: http://hdl.handle.net/10394/9102

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

17. Blevins, Sandra Melissa. The Distribution of Volatiles in Protoplanetary Disks.

Degree: 2016, The Catholic University of America

URL: http://hdl.handle.net/1961/cuislandora:30403

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Degree Awarded: Ph.D. Physics. The Catholic University of America

This dissertation addresses several distinct goals, all relating to the distribution of molecular gas in planet-forming… (more)

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Degree Awarded: Ph.D. Physics. The Catholic University of America

This dissertation addresses several distinct goals, all relating to the distribution of molecular gas in planet-forming regions of protoplanetary disks surrounding young, Sun-like stars. First, water surface snow line radii are measured for four classical protoplanetary disks. These measurements have been theoretically predicted using hydrodynamic and radiative transfer models but with contrasting results (Kennedy and Kenyon, 2008; Martin and Livio, 2013), and until now have not yet been measured using observations. Next a detailed analysis of the inner disk chemistry of one classical disk from the sample is presented and the long-standing question is addressed: to what degree is interstellar chemistry inherited by planet-forming material, or are protoplanetary disks themselves intrinsic "chemical factories" (Pontoppidan et al., 2014; van Dishoeck et al., 2014).Finally, rare CO isotopologue emission in the inner disk region of one transitional disk is presented. Transitional disks have inner regions heavily depleted in small dust grains, with known gaps in their dust structures. Estimates of the inner and outer disk gas-to- dust mass ratios may support evidence for dust clearing due to grain growth, and/or developing planetesimals.Two-dimensional radiative transfer modeling is used to retrieve dust density and temperature structures and render infrared line spectra. These models constitute modeling grids used to fit a parameterized gas distribution to the data. Best-fit model parameters determine the radial location where water vapor is observed to decrease by orders of magnitude, thus allowing the retrieval of surface snow line locations in the classical disk sample. This modeling framework is also applied to retrieve the molecular concentrations of H2O, CO, HCN, C2H2, and CO2 for one classical disk in the same sample, so that its inner disk chemistry can be compared to that of cold molecular clouds and solar system comets (Pontoppidan and Blevins, 2014). Lastly, the dust modeling framework is applied to observations of the transitional disk, SR 21, to estimate gas-to-dust mass ratios in the inner planet-forming region and beyond.Results are obtained addressing each research goal. First, water surface snow lines are measured at ~ 3 - 11 AU for the classical disk sample. Assuming a canonical gas-to-dust ratio of 100, as well as coupled gas and dust temperatures, the best-fit inner water abundances become implausibly high (0.01-1.0 per H2). Conversely, models in which the gas and dust temperatures are decoupled leads to canonical inner disk water abundances of ~ 10-4 per H2, while retaining gas-to-dust ratios of 100. That is, the evidence for gas-dust decoupling in disk surfaces is stronger than for enhanced gas-to-dust ratios.Next concentrations of dominant molecular carriers of carbon, oxygen, and nitrogen in the terrestrial region around 1 AU for classical disk RNO 90 were retrieved and compared to the chemical inventory of dense clouds and…

Advisors/Committee Members: Duilia F de Mello (Advisor), Klaus M Pontoppidan (Advisor), Steven Kraemer (Other), Tommy Wiklind (Other).

Subjects/Keywords: Astrophysics; Chemistry; Astronomy; astrochemistry; infrared spectroscopy; molecular spectroscopy; planet formation; pre-main sequence stars; protoplanetary disks

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

APA (6^th Edition):

Blevins, S. M. (2016). The Distribution of Volatiles in Protoplanetary Disks. (Thesis). The Catholic University of America. Retrieved from http://hdl.handle.net/1961/cuislandora:30403

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):

Blevins, Sandra Melissa. “The Distribution of Volatiles in Protoplanetary Disks.” 2016. Thesis, The Catholic University of America. Accessed March 05, 2021. http://hdl.handle.net/1961/cuislandora:30403.

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

MLA Handbook (7^th Edition):

Blevins, Sandra Melissa. “The Distribution of Volatiles in Protoplanetary Disks.” 2016. Web. 05 Mar 2021.

Vancouver:

Blevins SM. The Distribution of Volatiles in Protoplanetary Disks. [Internet] [Thesis]. The Catholic University of America; 2016. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1961/cuislandora:30403.

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

Council of Science Editors:

Blevins SM. The Distribution of Volatiles in Protoplanetary Disks. [Thesis]. The Catholic University of America; 2016. Available from: http://hdl.handle.net/1961/cuislandora:30403

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

18. Horenstein, Daniel. A New All-sky Catalogue of Candidate Protoplanetary Disks from Aggregated Optical and Infrared Surveys.

Degree: MS, Physics and Astronomy, 2017, Georgia State University

URL: https://scholarworks.gsu.edu/phy_astr_theses/21

► To guide research into formation scenarios for giant planets, I present a catalogue of 199,391 sources with candidate protoplanetary disks. These candidates are identified… (more)

Subjects/Keywords: protoplanetary disks; stars: pre-main sequence; surveys

…capture both main sequence stars that emit primarily at optical wavelengths and stars with… …gaseous envelopes from the pre-main sequence circumstellar material (Pollack et al. 1996… …collapsed into a disk but before the protostar has reached the zero-age main sequence. While the… …main sequence in a few color-color plots for these intermediate fields, reddening was… …v CHAPTER 0 LIST OF TABLES Table 2.1 Literature Sources of Stars with Known…

1 more image…

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APA (6^th Edition):

Horenstein, D. (2017). A New All-sky Catalogue of Candidate Protoplanetary Disks from Aggregated Optical and Infrared Surveys. (Thesis). Georgia State University. Retrieved from https://scholarworks.gsu.edu/phy_astr_theses/21

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):

Horenstein, Daniel. “A New All-sky Catalogue of Candidate Protoplanetary Disks from Aggregated Optical and Infrared Surveys.” 2017. Thesis, Georgia State University. Accessed March 05, 2021. https://scholarworks.gsu.edu/phy_astr_theses/21.

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

MLA Handbook (7^th Edition):

Horenstein, Daniel. “A New All-sky Catalogue of Candidate Protoplanetary Disks from Aggregated Optical and Infrared Surveys.” 2017. Web. 05 Mar 2021.

Vancouver:

Horenstein D. A New All-sky Catalogue of Candidate Protoplanetary Disks from Aggregated Optical and Infrared Surveys. [Internet] [Thesis]. Georgia State University; 2017. [cited 2021 Mar 05]. Available from: https://scholarworks.gsu.edu/phy_astr_theses/21.

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

Council of Science Editors:

Horenstein D. A New All-sky Catalogue of Candidate Protoplanetary Disks from Aggregated Optical and Infrared Surveys. [Thesis]. Georgia State University; 2017. Available from: https://scholarworks.gsu.edu/phy_astr_theses/21

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

19. Khorrami, Zeinab. Imagerie à haute résolution des amas R136 et NGC3603 dévoilent la nature de leurs populations stellaires : A sharpened close-up of R136 and NGC3603 : unshrouding the nature of their stellar population.

Degree: Docteur es, Astrophysique relativiste, 2016, Nice

URL: http://www.theses.fr/2016NICE4030

►

Cette thèse a pour objectif de comprendre les différents aspects de l'évolution des amas d’étoiles massives NGC3603 et R136 qui possèdent les étoiles les plus… (more)

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Cette thèse a pour objectif de comprendre les différents aspects de l'évolution des amas d’étoiles massives NGC3603 et R136 qui possèdent les étoiles les plus massives connues de l'univers local. L'analyse photométrique des noyaux de R136 et NGC3603 utilisant l’imagerie infrarouge de l’instrument SPHERE sur VLT et son système d’optique adaptative extrême de SPHERE, m’a permis de détecter pour la 1ière fois un grand nombre d’étoiles de faibles masse et luminosité au coeur de ces amas et pour la plupart au voisinage des étoiles les plus lumineuses et massives. La comparaison des données de SPHERE de NGC3603 à celles du HST montre l’absence de ségrégation de masse dans le noyau de cet amas. De plus la pente de la fonction de masse de cette région est la même que celle de la région suivante et similaire aux valeurs de la MF correspondant aux régions extérieures de l’amas connues jusqu’ici. L’amas R136 est partiellement résolu par SPHERE/IRDIS dans l’IR. La majorité de ses étoiles massives ont des compagnons visuels. En prenant compte des mesures spectroscopiques et photométriques et leurs erreurs sur l'extinction et l'âge des membres de l’amas, j’ai estimé une gamme de masse pour chaque étoile identifiée. La MF a été calculée pour différents âges ainsi que les erreurs sur les masses stellaires. J’ai simulé des séries d'images de R136 grâce au code Nbody6, et les ai comparées aux observations du HST/WFPC2. Ces simulations permettent de vérifier l'effet de la binarité initiale des étoiles de l’amas, la ségrégation de masse et l'évolution des étoiles sur l'évolution dynamique propre à R136.

This thesis aims at studying 2 massive clusters NGC3603 and R136, and the mechanisms that govern their physics, These clusters host the most massive stars known in the local universe so far and are important clues to understand the formation and fate of very massive star clusters. The manuscript outlines the photometric analysis of the core of R136 and NGC3603 on the basis of HST data in the visible and the VLT high dynamic imaging that I obtained in the infrared thanks to the SPHERE focal instrument operated since 2015 and its extreme Adaptive Optics, In an extensive photometric study of these data I discovered a significantly larger number of faint low-mass stars in the core of both these clusters compared to previous works. These stars are often detected in the vicinity of known massive bright objects. By comparing HST and SPHERE measures, NGC3603 does not show any signature of mass segregation in its core since the MF slope of the very core and the next radial bin are similarly flat and agree well with the MF found in previous works of the outer regions. On the other hand R136 is partially resolved using the SPHERE/IRDIS mode with most of the massive stars having visual companions. Considering the spectroscopic and photometric errors on the extinction and the age of cluster members, I estimate a mass range for each detected star. The MF is plotted at different ages with given errors on stellar masses. Finally I demonstrate that we…

Advisors/Committee Members: Vakili, Farrokh (thesis director), Lanz, Thierry (thesis director).

Subjects/Keywords: Amas stellaires : individuel (R136, NGC3603); Étoiles : étoiles massives; Étoiles : imagerie; Étoiles : fonction de masse luminosité; Étoiles : pré-séquence principale; Étoiles : séquence principale; Instrumentation : haute résolution angulaire; Méthodes : numérique; Méthodes : observationnelle; Star clusters: individual (R136, NGC3603); Stars: imaging; Stars: luminosity function, mass function; Stars: massive; Stars: pre-main sequence; Stars: main sequence; Instrumentation: high angular resolution; Methods: numerical; Methods: observational

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

APA (6^th Edition):

Khorrami, Z. (2016). Imagerie à haute résolution des amas R136 et NGC3603 dévoilent la nature de leurs populations stellaires : A sharpened close-up of R136 and NGC3603 : unshrouding the nature of their stellar population. (Doctoral Dissertation). Nice. Retrieved from http://www.theses.fr/2016NICE4030

Chicago Manual of Style (16^th Edition):

Khorrami, Zeinab. “Imagerie à haute résolution des amas R136 et NGC3603 dévoilent la nature de leurs populations stellaires : A sharpened close-up of R136 and NGC3603 : unshrouding the nature of their stellar population.” 2016. Doctoral Dissertation, Nice. Accessed March 05, 2021. http://www.theses.fr/2016NICE4030.

MLA Handbook (7^th Edition):

Khorrami, Zeinab. “Imagerie à haute résolution des amas R136 et NGC3603 dévoilent la nature de leurs populations stellaires : A sharpened close-up of R136 and NGC3603 : unshrouding the nature of their stellar population.” 2016. Web. 05 Mar 2021.

Vancouver:

Khorrami Z. Imagerie à haute résolution des amas R136 et NGC3603 dévoilent la nature de leurs populations stellaires : A sharpened close-up of R136 and NGC3603 : unshrouding the nature of their stellar population. [Internet] [Doctoral dissertation]. Nice; 2016. [cited 2021 Mar 05]. Available from: http://www.theses.fr/2016NICE4030.

Council of Science Editors:

Khorrami Z. Imagerie à haute résolution des amas R136 et NGC3603 dévoilent la nature de leurs populations stellaires : A sharpened close-up of R136 and NGC3603 : unshrouding the nature of their stellar population. [Doctoral Dissertation]. Nice; 2016. Available from: http://www.theses.fr/2016NICE4030

University of Michigan

20. Espaillat, Catherine C. The Evolution of Dusty Disks Around Low-Mass Pre-Main Sequence Stars.

Degree: PhD, Astronomy and Astrophysics, 2009, University of Michigan

URL: http://hdl.handle.net/2027.42/63766

► The evolution of protoplanetary disks is intricately tied to the origin of planets. The details of how these disks evolve from initially well-mixed distributions of… (more)

▼ The evolution of protoplanetary disks is intricately tied to the origin of planets. The details of how these disks evolve from initially well-mixed distributions of gas and dust into systems composed mostly of rocky planets and gas giants like our own solar system is not well understood and is a fundamental question in astronomy. It is widely accepted that dust grain growth and settling to the disk midplane play an integral part in creating the planetesimals that amalgamate into planets. Newly formed planets will then interact with the disk, clearing the material around themselves and creating gaps and holes. Several disks which have nearly photospheric near-infrared emission but substantial excesses above the stellar photosphere at wavelengths beyond ~20 μm have been observed and are referred to as “transitional disks.” This deficit of flux can be explained by the presence of an inner disk hole that is mostly devoid of small dust. Here we model the transitional disks of CS Cha and CVSO 224. We also present evidence for a new class of “pre-transitional disks” around UX Tau A and LkCa 15. These objects have a deficit of flux in the mid-infrared (5–20 μm) and significant emission at longer wavelengths, as is seen in transitional disks. However, pre-transitional disks have significant near-infrared excesses (2–5 μm) relative to their stellar photospheres, indicative of an optically thick inner disk. This points to a gap within the disk rather than an inner disk hole. We also present simulated spectral energy distributions of ~240 disks around low-mass classical T Tauri stars and find that the majority of observed disks within Taurus, Chamaeleon, and Ophiuchus lie within the parameter space probed by the models and are therefore “full disks.” However, we find that some disks cannot be explained by full disk models and are not known to be transitional or pre-transitional disks. We propose that these objects are pre-transitional disks with smaller gaps than previously observed, emphasizing that much still remains to be understood regarding the dust component of disks. Advisors/Committee Members: Calvet, Nuria P. (committee member), Adams, Fred C. (committee member), Bergin, Edwin A. (committee member), Hartmann, Lee Williams (committee member), Miller, Jon Matthew (committee member).

Subjects/Keywords: Low-mass Pre-main Sequence Stars; Accretion Disks; T Tauri Stars; Astronomy; Science

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

APA (6^th Edition):

Espaillat, C. C. (2009). The Evolution of Dusty Disks Around Low-Mass Pre-Main Sequence Stars. (Doctoral Dissertation). University of Michigan. Retrieved from http://hdl.handle.net/2027.42/63766

Chicago Manual of Style (16^th Edition):

Espaillat, Catherine C. “The Evolution of Dusty Disks Around Low-Mass Pre-Main Sequence Stars.” 2009. Doctoral Dissertation, University of Michigan. Accessed March 05, 2021. http://hdl.handle.net/2027.42/63766.

MLA Handbook (7^th Edition):

Espaillat, Catherine C. “The Evolution of Dusty Disks Around Low-Mass Pre-Main Sequence Stars.” 2009. Web. 05 Mar 2021.

Vancouver:

Espaillat CC. The Evolution of Dusty Disks Around Low-Mass Pre-Main Sequence Stars. [Internet] [Doctoral dissertation]. University of Michigan; 2009. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/2027.42/63766.

Council of Science Editors:

Espaillat CC. The Evolution of Dusty Disks Around Low-Mass Pre-Main Sequence Stars. [Doctoral Dissertation]. University of Michigan; 2009. Available from: http://hdl.handle.net/2027.42/63766

Penn State University

21. Esplin, Taran LeRoy. Observations of Brown Dwarfs at Low Temperatures and Low Masses.

Degree: 2017, Penn State University

URL: https://submit-etda.libraries.psu.edu/catalog/14171tle918

► We have contributed to the characterization and discovery of brown dwarfs at low temperatures and low masses. Because the coolest brown dwarfs overlap with giant… (more)

▼ We have contributed to the characterization and discovery of brown dwarfs at low temperatures and low masses. Because the coolest brown dwarfs overlap with giant planets in temperature, they can be used as proxies for studying planetary atmospheres. In multiple temperature regimes for brown dwarfs, condensates are predicted to form clouds. Based on observations of both terrestrial planets and gas giants in our solar system, clouds of water ice are likely to be a prominent constituent in the atmospheres of some brown dwarfs. If these clouds are present, they should be patchy, which should produce a variable light curve. In the last few years, a few brown dwarfs have been discovered that should be cool enough to harbor water ice clouds (< 375 K). We have searched for evidence of such clouds in the coldest known brown dwarf (~250 K) in light curves obtained at 3.6 and 4.5 microns with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We did detect variability, but its low amplitude is difficult to explain using the theoretical models of water ice clouds unless there is only a very small deviation in cloud coverage between hemispheres. Alternatively, the similarity in mid-infrared variability amplitudes between this object and warmer T and Y dwarfs may suggest that they share a common origin for their variability (i.e., not water clouds). Because brown dwarfs are the product of the process of star formation, detecting the minimum mass at which they form is a fundamental test of star formation theories. The most thorough surveys to detect this minimum mass are complete down to ~10 MJup, but have found objects with masses as low as ~5 MJup. Thus, the minimum mass has not been detected. Nearby star-forming regions are the most promising sites where large numbers of young (and hence bright) brown dwarfs <10 MJup can be found. Proper motion measurements can be used to identify new brown dwarfs in these regions. Because IRAC images are available at multiple epochs spanning a decade for most nearby sites of star formation, proper motions can be measured with these data. However, the expected motions of these regions over this time frame range from 50–200 mas and the error in a typical IRAC astrometric measurement is ∼100 mas. To more fully realize IRAC’s astrometric capabilities, we have measured new distortion corrections for the 3.6 and 4.5 micron arrays. Using these corrections, we have identified a method for measuring astrometry of point sources in IRAC images that can achieve a total astrometric error of 20 mas, which is sufficiently accurate for identifying candidate brown dwarfs in nearby star-forming regions. We have performed a search for planetary-mass brown dwarfs in the Chamaeleon I and Taurus star-forming regions using proper motions measured with IRAC and other wide-field surveys and using optical and near-infrared photometry. Through near-infrared spectroscopy, we have confirmed 6 and 18 candidates as new late-type members of Chamaeleon I and Taurus, respectively. These objects include the… Advisors/Committee Members: Kevin Luhman, Dissertation Advisor/Co-Advisor, Kevin Luhman, Committee Chair/Co-Chair, Lawrence William Ramsey, Committee Member, Eric D Feigelson, Committee Member, Sarah Elizabeth Shandera, Outside Member, Jason Thomas Wright, Committee Member.

Subjects/Keywords: open clusters and associations: general; astrometry; brown dwarfs; infrared: stars; planets and satellites: atmospheres; solar neighborhood; stars: low-mass; planetary systems; protoplanetary disks; stars: formation; stars: luminosity function; stars: pre-main sequence

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

APA (6^th Edition):

Esplin, T. L. (2017). Observations of Brown Dwarfs at Low Temperatures and Low Masses. (Thesis). Penn State University. Retrieved from https://submit-etda.libraries.psu.edu/catalog/14171tle918

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):

Esplin, Taran LeRoy. “Observations of Brown Dwarfs at Low Temperatures and Low Masses.” 2017. Thesis, Penn State University. Accessed March 05, 2021. https://submit-etda.libraries.psu.edu/catalog/14171tle918.

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

MLA Handbook (7^th Edition):

Esplin, Taran LeRoy. “Observations of Brown Dwarfs at Low Temperatures and Low Masses.” 2017. Web. 05 Mar 2021.

Vancouver:

Esplin TL. Observations of Brown Dwarfs at Low Temperatures and Low Masses. [Internet] [Thesis]. Penn State University; 2017. [cited 2021 Mar 05]. Available from: https://submit-etda.libraries.psu.edu/catalog/14171tle918.

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

Council of Science Editors:

Esplin TL. Observations of Brown Dwarfs at Low Temperatures and Low Masses. [Thesis]. Penn State University; 2017. Available from: https://submit-etda.libraries.psu.edu/catalog/14171tle918

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

Queens University

22. Grunhut, Jason. Using High-Resolution Spectroscopy To Improve The Determination Of Effective Temperatures OF Pre-Main Sequence Stars .

Degree: Physics, Engineering Physics and Astronomy, 2009, Queens University

URL: http://hdl.handle.net/1974/1707

► Herbig Ae/Be (HAeBe) stars are the pre-main sequence progenitors of main sequence A and B stars, and are characterized observationally by strong emission in spectral… (more)

▼ Herbig Ae/Be (HAeBe) stars are the pre-main sequence progenitors of main sequence A and B stars, and are characterized observationally by strong emission in spectral lines and significant infra-red excess that results from their presence in dust-obscured regions. These stars are usually surrounded by a complex environment composed of gas and dust and often a significant stellar wind and a circumstellar disc. This complex circumstellar environment can have a significant affect on their spectral energy distributions, leading to large systematic uncertainties in determinations of their effective temperatures from photometric methods. In an attempt to improve temperature determinations for HAeBe stars, we have conducted an experiment to evaluate the potential of high-resolution spectra to constrain their atmospheric parameters. To this end, high-resolution (R~68 000) and low-resolution (R~1500) spectra obtained using the ESPaDOnS spectropolarimeter (at the Canada-France-Hawaii telescope) and the FORS1 spectropolarimeter (at the Very Large Telescope) have been used with an automatic spectrum fitting procedure. This procedure compares spectroscopic data to a grid of synthetic LTE, solar abundance spectra, spanning a range in effective temperature, surface gravity, and micro-turbulence. This analysis was applied to the spectra of a sample of twelve previously well-studied HAeBe stars. Our temperatures were found to be consistent with previously published values, while providing much lower uncertainties - in some cases about 5 times smaller. Numerous methods were investigated to obtain these quantitative uncertainties (chi-squared statistics, Bayesian analysis, Monte Carlo bootstrap method, individual temperature sensitive line region analysis). We conclude that our method can be used to efficiently and effectively obtain temperatures of HAeBe stars in addition to providing us with a characterization of the degree of departure of the spectrum from solar abundance, LTE photospheric models.

Subjects/Keywords: stars ; high-resolution spectroscopy ; pre-main sequence stars ; Herbig stars ; HAeBe stars ; effective temperature

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

APA (6^th Edition):

Grunhut, J. (2009). Using High-Resolution Spectroscopy To Improve The Determination Of Effective Temperatures OF Pre-Main Sequence Stars . (Thesis). Queens University. Retrieved from http://hdl.handle.net/1974/1707

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. “Using High-Resolution Spectroscopy To Improve The Determination Of Effective Temperatures OF Pre-Main Sequence Stars .” 2009. Thesis, Queens University. Accessed March 05, 2021. http://hdl.handle.net/1974/1707.

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. “Using High-Resolution Spectroscopy To Improve The Determination Of Effective Temperatures OF Pre-Main Sequence Stars .” 2009. Web. 05 Mar 2021.

Vancouver:

Grunhut J. Using High-Resolution Spectroscopy To Improve The Determination Of Effective Temperatures OF Pre-Main Sequence Stars . [Internet] [Thesis]. Queens University; 2009. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1974/1707.

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. Using High-Resolution Spectroscopy To Improve The Determination Of Effective Temperatures OF Pre-Main Sequence Stars . [Thesis]. Queens University; 2009. Available from: http://hdl.handle.net/1974/1707

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

23. Galli, Phillip Andreas Brenner. Determinação de distâncias cinemáticas de estrelas pré-sequência principal em regiões de formação estelar .

Degree: PhD, Astronomia, 2012, University of São Paulo

URL: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-01042013-194055/ ;

►

Este trabalho tem como objetivo principal a determinação da distância de estrelas pré-sequência principal em regiões de formação estelar próximas. A determinação precisa da distância… (more)

▼

Este trabalho tem como objetivo principal a determinação da distância de estrelas pré-sequência principal em regiões de formação estelar próximas. A determinação precisa da distância individual das estrelas é necessária para obter os principais parâmetros físicos de cada estrela e para investigar a estrutura da Galáxia. Em particular, investigamos as regiões de formação estelar de Lupus e Ophiuchus que contém uma das associações mais ricas em estrelas T Tauri. A grande maioria das estrelas pré-sequência principal nessas regiões não foi observada pelo satélite Hipparcos devido à sua magnitude e também não têm paralaxe trigonométrica medida a partir do solo devido à distância em que se encontram. O procedimento aqui empregado para a obter a distância individual das estrelas baseia-se na estratégia de ponto de convergência e utiliza dados de movimento próprio e velocidade radial. Desenvolvemos uma nova versão do método de ponto de convergência que permite simultaneamente determinar a posição do ponto de convergência e selecionar os membros de um moving group. Partindo dos dados de movimento próprio e o novo método aqui desenvolvido investigamos as propriedades cinemáticas e realizamos uma análise de pertinência das estrelas em cada região estudada o que nos permitiu identificar um moving group com 114 estrelas em Lupus e 55 estrelas em Ophiuchus. Calculamos a distância para cada membro do grupo usando velocidades radiais publicadas, que foram complementadas com novas observações, e a velocidade espacial do moving grup para as estrelas com velocidade radial não conhecida. Calculamos as paralaxes com precisão de 1-2~mas o que implica em um erro relativo médio de 25% nas distâncias obtidas. Finalmente, investigamos as propriedades dos diversos subgrupos e a estrutura tridimensional dos complexos de nuvens em Lupus e Ophiuchus, concluindo que existem efeitos de profundidade importantes. Utilizamos os novos resultados de distância para obter os parâmetros físicos (luminosidade, massa e idade) das estrelas e o diagrama-HR de cada região de formação estelar considerada, confirmando a distribuição de idade diferente das duas subclasses de estrelas T Tauri. Os resultados aqui obtidos representam um primeiro passo no sentido de melhor entender a estrutura das regiões de formação estelar e os estágios iniciais da formação de estrelas e planetas.

The main objective of this work is to determine the distance of pre-main sequence stars in nearby star-forming regions. A precise determination of the distance to individual stars is required to accurately determine the main physical parameters of each star and the structure of the Galaxy. Here we investigate the Lupus and Ophiuchus star-forming regions that contain one of the richest associations of T Tauri stars. Most pre-main sequence stars in these regions were neither observed by the Hipparcos satellite due to their magnitude nor have any trigonometric parallax measured from the ground due to their distance. The procedure that we use here to derive the distance to individual…

Advisors/Committee Members: Teixeira, Ramachrisna.

Subjects/Keywords: convergent point; distance; distância; estrelas pré-sequência principal; movimento próprio; moving group; moving group; ponto de convergência; pre-main sequence stars; proper motion

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

APA (6^th Edition):

Galli, P. A. B. (2012). Determinação de distâncias cinemáticas de estrelas pré-sequência principal em regiões de formação estelar . (Doctoral Dissertation). University of São Paulo. Retrieved from http://www.teses.usp.br/teses/disponiveis/14/14131/tde-01042013-194055/ ;

Chicago Manual of Style (16^th Edition):

Galli, Phillip Andreas Brenner. “Determinação de distâncias cinemáticas de estrelas pré-sequência principal em regiões de formação estelar .” 2012. Doctoral Dissertation, University of São Paulo. Accessed March 05, 2021. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-01042013-194055/ ;.

MLA Handbook (7^th Edition):

Galli, Phillip Andreas Brenner. “Determinação de distâncias cinemáticas de estrelas pré-sequência principal em regiões de formação estelar .” 2012. Web. 05 Mar 2021.

Vancouver:

Galli PAB. Determinação de distâncias cinemáticas de estrelas pré-sequência principal em regiões de formação estelar . [Internet] [Doctoral dissertation]. University of São Paulo; 2012. [cited 2021 Mar 05]. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-01042013-194055/ ;.

Council of Science Editors:

Galli PAB. Determinação de distâncias cinemáticas de estrelas pré-sequência principal em regiões de formação estelar . [Doctoral Dissertation]. University of São Paulo; 2012. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-01042013-194055/ ;

Vanderbilt University

24. Aarnio, Alicia N. The Role of Magnetic Fields in the Pre-Main Sequence Evolution of Solar Type Stars.

Degree: PhD, Physics, 2010, Vanderbilt University

URL: http://hdl.handle.net/1803/11846

► T Tauri stars, being pre-main sequence and solar mass, tell us what our Sun was like when it was very young. T Tauri stars and… (more)

▼ T Tauri stars, being pre-main sequence and solar mass, tell us what our Sun was like when it was very young. T Tauri stars and their protoplanetary disks are ideal astrophysical laboratories for studying the solar system when planets were forming. At the same time, there is no astrophysical laboratory like the present-day Sun for studying in detail the microphysics needed to understand processes involved in early stellar evolution. Specifically, a goal of this work is to understand the role of large-scale structures in stellar magnetic fields. We begin with a general overview of star formation and stellar evolution, focusing on the role of magnetic fields in these processes. Under the broad aegis of star formation and evolution, the remainder of this work aims to methodically explore methods of identifying groups of young stars, star-disk interaction, and a new solar-calibrated pre-main sequence angular momentum loss model. In summary, we begin with a broad focus on a group of young stars, then examine more closely the interaction of young stars with their disks via the stellar magnetic field, and finally we assess other ways in which the field can affect stellar evolution. In searching for a coeval group of young stars, we find the quite surprising result that the particular young trio of stars in question apparently formed separately from any known association or star forming region in the vicinity. Turning then to a well-studied group of million year old stars, the Orion Nebula Cluster, we seek to determine whether a group of young stars' magnetospheres are linked to circumstellar disks. In the majority of cases, we found that large-scale loops do not intersect disk material. This leads naturally into the question of how such large structures then could affect stellar evolution if not via star-disk interaction. We invoke solar physics to relate solar flare flux to corresponding CME mass in order to begin calibration of a stellar CME mass loss rate, the first effort in this field to-date. Advisors/Committee Members: Kelly Holley-Bockelmann (committee member), David Weintraub (committee member), Andreas Berlind (committee member), David Ernst (committee member), Keivan Stassun (Committee Chair).

Subjects/Keywords: stellar flares; solar flares; stellar angular momentum; pre-main sequence stars

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

APA (6^th Edition):

Aarnio, A. N. (2010). The Role of Magnetic Fields in the Pre-Main Sequence Evolution of Solar Type Stars. (Doctoral Dissertation). Vanderbilt University. Retrieved from http://hdl.handle.net/1803/11846

Chicago Manual of Style (16^th Edition):

Aarnio, Alicia N. “The Role of Magnetic Fields in the Pre-Main Sequence Evolution of Solar Type Stars.” 2010. Doctoral Dissertation, Vanderbilt University. Accessed March 05, 2021. http://hdl.handle.net/1803/11846.

MLA Handbook (7^th Edition):

Aarnio, Alicia N. “The Role of Magnetic Fields in the Pre-Main Sequence Evolution of Solar Type Stars.” 2010. Web. 05 Mar 2021.

Vancouver:

Aarnio AN. The Role of Magnetic Fields in the Pre-Main Sequence Evolution of Solar Type Stars. [Internet] [Doctoral dissertation]. Vanderbilt University; 2010. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1803/11846.

Council of Science Editors:

Aarnio AN. The Role of Magnetic Fields in the Pre-Main Sequence Evolution of Solar Type Stars. [Doctoral Dissertation]. Vanderbilt University; 2010. Available from: http://hdl.handle.net/1803/11846

University of St. Andrews

25. Gregory, Scott. T Tauri stars : mass accretion and X-ray emission .

Degree: 2007, University of St. Andrews

URL: http://hdl.handle.net/10023/336

► I develop the first magnetospheric accretion model to take account of the observed complexity of T Tauri magnetic fields, and the influence of stellar coronae.… (more)

▼ I develop the first magnetospheric accretion model to take account of the observed complexity of T Tauri magnetic fields, and the influence of stellar coronae. It is now accepted that accretion onto classical T Tauri stars is controlled by the stellar magnetosphere, yet to date the majority of accretion models have assumed that the stellar magnetic field is dipolar. By considering a simple steady state accretion model with both dipolar and complex magnetic fields I find a correlation between mass accretion rate and stellar mass of the form M[dot above] proportional to M[asterisk subscript, alpha superscript], with my results consistent within observed scatter. For any particular stellar mass there can be several orders of magnitude difference in the mass accretion rate, with accretion filling factors of a few percent. I demonstrate that the field geometry has a significant effect in controlling the location and distribution of hot spots, formed on the stellar surface from the high velocity impact of accreting material. I find that hot spots are often at mid to low latitudes, in contrast to what is expected for accretion to dipolar fields, and that particularly for higher mass stars, accreting material is predominantly carried by open field lines. Material accreting onto stars with fields that have a realistic degree of complexity does so with a distribution of in-fall speeds. I have also modelled the rotational modulation of X-ray emission from T Tauri stars assuming that they have isothermal, magnetically confined coronae. By extrapolating from surface magnetograms I find that T Tauri coronae are compact and clumpy, such that rotational modulation arises from X-ray emitting regions being eclipsed as the star rotates. Emitting regions are close to the stellar surface and inhomogeneously distributed about the star. However some regions of the stellar surface, which contain wind bearing open field lines, are dark in X-rays. From simulated X-ray light curves, obtained using stellar parameters from the Chandra Orion Ultradeep Project, I calculate X-ray periods and make comparisons with optically determined rotation periods. I find that X-ray periods are typically equal to, or are half of, the optical periods. Further, I find that X-ray periods are dependent upon the stellar inclination, but that the ratio of X-ray to optical period is independent of stellar mass and radius. I also present some results that show that the largest flares detected on T Tauri stars may occur inside extended magnetic structures arising from the reconnection of open field lines within the disc. I am currently working to establish whether such large field line loops can remain closed for a long enough time to fill with plasma before being torn open by the differential rotation between the star and the disc. Finally I discuss the current limitations of the model and suggest future developments and new avenues of research. Advisors/Committee Members: Jardine, Moira (advisor).

Subjects/Keywords: Star formation; Pre-main sequence stars; Stellar magnetic fields; Stellar coronae

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APA (6^th Edition):

Gregory, S. (2007). T Tauri stars : mass accretion and X-ray emission . (Thesis). University of St. Andrews. Retrieved from http://hdl.handle.net/10023/336

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):

Gregory, Scott. “T Tauri stars : mass accretion and X-ray emission .” 2007. Thesis, University of St. Andrews. Accessed March 05, 2021. http://hdl.handle.net/10023/336.

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

MLA Handbook (7^th Edition):

Gregory, Scott. “T Tauri stars : mass accretion and X-ray emission .” 2007. Web. 05 Mar 2021.

Vancouver:

Gregory S. T Tauri stars : mass accretion and X-ray emission . [Internet] [Thesis]. University of St. Andrews; 2007. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/10023/336.

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

Council of Science Editors:

Gregory S. T Tauri stars : mass accretion and X-ray emission . [Thesis]. University of St. Andrews; 2007. Available from: http://hdl.handle.net/10023/336

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

26. Vidotto, Aline de Almeida. Simulações Numéricas Tri-dimensionais de Ventos Magnetizados de Estrelas de Baixa Massa.

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

URL: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-05082010-071118/ ;

► O tópico abordado nesta tese é a perda de massa através de ventos coronais magnetizados em estrelas de baixa massa. Ventos estelares têm sido estudados… (more)

▼ O tópico abordado nesta tese é a perda de massa através de ventos coronais magnetizados em estrelas de baixa massa. Ventos estelares têm sido estudados extensivamente há vários anos, tendo inicialmente como foco o vento solar. Atualmente, sabe-se que o campo magnético é essencial na aceleração e aquecimento dos ventos coronais. Apesar do conhecimento detalhado que temos da estrutura magnética do Sol, pouco se sabe sobre a configuração do campo magnético em outras estrelas. Nesta tese, é investigada a estrutura do campo magnético nas coroas de estrelas do tipo solar na Seqüência Principal e de suas predecessoras na pré Seqüência Principal através de simulações numéricas magneto-hidrodinâmicas tri-dimensionais. Aqui, consideramos de forma auto-consistente a interação entre o vento e o campo magnético e vice-versa. Dessa forma, pela interação entre forças magnéticas e forças do vento, consegue-se determinar a configuração do campo magnético e a estrutura dos ventos coronais. Realizamos um estudo de ventos de estrelas do tipo solar e a dependência dos mesmos com o parâmetro beta do plasma (a razão entre as densidades de energia térmica e magnética). Este é o primeiro estudo a realizar tal análise resolvendo as equações tri-dimensionais da magneto-hidrodinâmica ideal. Em nossas simulações, adotamos um parâmetro de aquecimento descrito por gamma, que é responsável pela aceleração térmica do vento. Então, nós analisamos ventos com intensidades de campo magnético nos pólos no intervalo de B0 = 1 a 20 G e mostramos que a estrutura do vento apresenta características que são similares à do vento coronal do Sol. No estado estacionário, a topologia do campo magnético obtida é similar para todos os casos estudados, apresentando uma configuração do tipo helmet streamer, com zonas de linhas fechadas e abertas de campo magnético co-existindo. Intensidades mais altas de campo levam a ventos mais acelerados e mais quentes. O aumento na intensidade do campo gera também uma zona morta maior no vento, i.e., os loops fechados que previnem que a matéria escape da coroa em latitudes menores que ~45 graus se estendem a maiores distâncias da estrela. Além disso, mostramos também que a força de Lorentz gera naturalmente um vento que é dependente da latitude. Ao aumentar a densidade da coroa mantendo B0 = 20 G, mostramos que o sistema volta a apresentar ventos menos acelerados e mais frios. Para um valor fixo de gamma, mostramos que o parâmetro essencial na determinação do perfil de velocidade do vento é o parâmetro beta calculado na base da coroa. Dessa forma, acredita-se que haja um grupo de ventos magnetizados que apresenta a mesma velocidade terminal independentemente das densidades de energia térmica ou magnética, desde que o parâmetro beta seja o mesmo. No entanto, essa degenerescência pode ser removida ao se comparar outros parâmetros físicos do vento, tal como a taxa de perda de massa. Nós também analisamos a influência do gamma nos nossos resultados e mostramos que ele é importante na determinação da estrutura do vento. Além disso,… Advisors/Committee Members: Pereira, Vera Jatenco Silva.

Subjects/Keywords: campos magnéticos; estrelas: late-type; estrelas: pre Seqüência Principal; estrelas: ventos; magnetic fields; methods: numerical; métodos: numérico; MHD; outflows; planetas e satélites: geral; planets and satellites: general; stars: late-type; stars: pre-main sequence; stars: winds

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

APA (6^th Edition):

Vidotto, A. d. A. (2009). Simulações Numéricas Tri-dimensionais de Ventos Magnetizados de Estrelas de Baixa Massa. (Doctoral Dissertation). University of São Paulo. Retrieved from http://www.teses.usp.br/teses/disponiveis/14/14131/tde-05082010-071118/ ;

Chicago Manual of Style (16^th Edition):

Vidotto, Aline de Almeida. “Simulações Numéricas Tri-dimensionais de Ventos Magnetizados de Estrelas de Baixa Massa.” 2009. Doctoral Dissertation, University of São Paulo. Accessed March 05, 2021. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-05082010-071118/ ;.

MLA Handbook (7^th Edition):

Vidotto, Aline de Almeida. “Simulações Numéricas Tri-dimensionais de Ventos Magnetizados de Estrelas de Baixa Massa.” 2009. Web. 05 Mar 2021.

Vancouver:

Vidotto AdA. Simulações Numéricas Tri-dimensionais de Ventos Magnetizados de Estrelas de Baixa Massa. [Internet] [Doctoral dissertation]. University of São Paulo; 2009. [cited 2021 Mar 05]. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-05082010-071118/ ;.

Council of Science Editors:

Vidotto AdA. Simulações Numéricas Tri-dimensionais de Ventos Magnetizados de Estrelas de Baixa Massa. [Doctoral Dissertation]. University of São Paulo; 2009. Available from: http://www.teses.usp.br/teses/disponiveis/14/14131/tde-05082010-071118/ ;

Leiden University

27. Lommen, D.J.P. The first steps of planet formation : studying grain growth with millimetre interferometers.

Degree: 2009, Leiden University

URL: http://hdl.handle.net/1887/13752

► We present Submillimeter-Array (SMA) observations of two embedded young stellar objects, Elias 29 and IRS 63. The masses of the central stars, the discs, and… (more)

Subjects/Keywords: Circumstellar matter; Stars: formation; Stars: planetary systems: protoplanetary discs; Stars: pre-main-sequence; Stars: individual: IRS 63; Stars: individual: Elias 29; Stars: individual: WW Cha; Stars: individual: RU Lup; Stars: individual: CS Cha

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

APA (6^th Edition):

Lommen, D. J. P. (2009). The first steps of planet formation : studying grain growth with millimetre interferometers. (Doctoral Dissertation). Leiden University. Retrieved from http://hdl.handle.net/1887/13752

Chicago Manual of Style (16^th Edition):

Lommen, D J P. “The first steps of planet formation : studying grain growth with millimetre interferometers.” 2009. Doctoral Dissertation, Leiden University. Accessed March 05, 2021. http://hdl.handle.net/1887/13752.

MLA Handbook (7^th Edition):

Lommen, D J P. “The first steps of planet formation : studying grain growth with millimetre interferometers.” 2009. Web. 05 Mar 2021.

Vancouver:

Lommen DJP. The first steps of planet formation : studying grain growth with millimetre interferometers. [Internet] [Doctoral dissertation]. Leiden University; 2009. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1887/13752.

Council of Science Editors:

Lommen DJP. The first steps of planet formation : studying grain growth with millimetre interferometers. [Doctoral Dissertation]. Leiden University; 2009. Available from: http://hdl.handle.net/1887/13752

28. Geers, Vincent Carlo. Polycyclic aromatic hydrocarbons in disks around young solar-type stars.

Degree: 2007, Leiden Observatory, Faculty of Science, Leiden University

URL: http://hdl.handle.net/1887/12414

► In this thesis we study the dust around solar-type young stars. In particular, we focus on one specific species of dust, namely the Polycyclic Aromatic… (more)

Subjects/Keywords: Stars: Pre-main sequence; Stars: planetary systems: protoplanetary disks; Circumstellar matter; Astrochemistry; ISM: molecules; Stars: Pre-main sequence; Stars: planetary systems: protoplanetary disks; Circumstellar matter; Astrochemistry; ISM: molecules

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

APA (6^th Edition):

Geers, V. C. (2007). Polycyclic aromatic hydrocarbons in disks around young solar-type stars. (Doctoral Dissertation). Leiden Observatory, Faculty of Science, Leiden University. Retrieved from http://hdl.handle.net/1887/12414

Chicago Manual of Style (16^th Edition):

Geers, Vincent Carlo. “Polycyclic aromatic hydrocarbons in disks around young solar-type stars.” 2007. Doctoral Dissertation, Leiden Observatory, Faculty of Science, Leiden University. Accessed March 05, 2021. http://hdl.handle.net/1887/12414.

MLA Handbook (7^th Edition):

Geers, Vincent Carlo. “Polycyclic aromatic hydrocarbons in disks around young solar-type stars.” 2007. Web. 05 Mar 2021.

Vancouver:

Geers VC. Polycyclic aromatic hydrocarbons in disks around young solar-type stars. [Internet] [Doctoral dissertation]. Leiden Observatory, Faculty of Science, Leiden University; 2007. [cited 2021 Mar 05]. Available from: http://hdl.handle.net/1887/12414.

Council of Science Editors:

Geers VC. Polycyclic aromatic hydrocarbons in disks around young solar-type stars. [Doctoral Dissertation]. Leiden Observatory, Faculty of Science, Leiden University; 2007. Available from: http://hdl.handle.net/1887/12414

University of Florida

29. Fleck, Robert Charles, 1949-. Magnetic braking during star formation.

Degree: 1977, University of Florida

URL: https://ufdc.ufl.edu/UF00097484

Subjects/Keywords: Angular momentum; Braking; Cooling; Cosmic rays; Ionization; Magnetic fields; Magnetism; Magnets; Main sequence stars; Stellar rotation; Astronomy thesis Ph. D; Stars – Evolution; Stars – Rotation; Stars, New

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

APA (6^th Edition):

Fleck, Robert Charles, 1. (1977). Magnetic braking during star formation. (Thesis). University of Florida. Retrieved from https://ufdc.ufl.edu/UF00097484

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):

Fleck, Robert Charles, 1949-. “Magnetic braking during star formation.” 1977. Thesis, University of Florida. Accessed March 05, 2021. https://ufdc.ufl.edu/UF00097484.

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

MLA Handbook (7^th Edition):

Fleck, Robert Charles, 1949-. “Magnetic braking during star formation.” 1977. Web. 05 Mar 2021.

Vancouver:

Fleck, Robert Charles 1. Magnetic braking during star formation. [Internet] [Thesis]. University of Florida; 1977. [cited 2021 Mar 05]. Available from: https://ufdc.ufl.edu/UF00097484.

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

Council of Science Editors:

Fleck, Robert Charles 1. Magnetic braking during star formation. [Thesis]. University of Florida; 1977. Available from: https://ufdc.ufl.edu/UF00097484

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

Universidade Federal de Santa Maria

30. Márcio do Carmo Pinheiro. ESTUDO MULTIBANDA DO CONTEÚDO ESTELAR DE REGIÕES Hii DO HEMISFÉRIO SUL.

Degree: 2012, Universidade Federal de Santa Maria

URL: http://coralx.ufsm.br/tede/tde_busca/arquivo.php?codArquivo=5089

► We present a multi-wavelength study of the stellar content of 11 optical/infrared Southern Galactic Hii regions with 10 h <(J2000) <−17 h and −65 <(J2000)… (more)

▼ We present a multi-wavelength study of the stellar content of 11 optical/infrared Southern Galactic Hii regions with 10 h <(J2000) <−17 h and −65 <(J2000) <−35. Nine optical objects with no published or uncertain distances were examined in order to identify their ionising sources and to determine their distances, whereas young stellar objects (YSOs) and main sequence ionising stars were photometrically classified in the two infrared clusters. We carried out optical spectroscopy and UBV photometry of the stellar content of these Hii regions and obtained the distance of individual stars by spectroscopic parallax. To avoid using a fixed value for the total-to-selective extinction ratio RV , the reddening AV was determined directly by the colour-difference method. We classified as types O or B 24 out of the 31 stars for which optical spectra were obtained. In particular, we identified two new O stars in RCW98 and RCW99. The values for reddening obtained correspond to a mean hRV i = 3.44, which is about 10% higher of the mean value found for field stars over all directions of the Galaxy. For the Hii regions NGC3503, NGC6334, RCW55, RCW87, RCW98 e RCW99, we obtained more precise distances calculated as the median of the spectroscopic parallaxes obtained for two to six different stars in each nebulae, with an internal dispersion of less than 5%. Among the objects more obscured in the Norma region, we analysed the stellar content of the East part of the large complex of Hii regions GAL331.5-00.1, which contains eight bright extended radio sources. This study comprises the infrared clusters [DBS2003] 156 and [DBS2003] 157, respectively associated to Hii regions GAL331.11-00.51 and GAL331.31-00.34. In order to isolate the brightest 2MASS sources of their unresolved companions, we carried out JHK photometry with resolution better than 2MASS data. 47 Near-infrared (NIR) sources with Ks-band excess were identified following usual methods. Other 70 YSOs were also identified by using Mid-IR on-line data of the GLIMPSE survey. The search for radial-velocity measurements in the literature and the similarity between the stellar population explored have indicated the two regions as physically associated. With the determination of the spectroscopic parallaxes of four O-type and two B-type stars spread over the both clusters, this hypothesis was verified. The parallaxes of these 6 stars returned very compatible distances (hdhelioci = 3.30 0.29 kpc). The Near- and Mid-IR counterparts of the IRAS source 16085-5138 was found close to the field of [DBS2003] 157. This source has showed typical colours of a Ultra-compact ii region (UCHii) and spectral index = 3.6 between 2 and 25 μm, which is typical of YSOs immersed in protostellar envelopes. A lower limit to the bolometric luminosity of the protostar embedded was computed as L = 7.7×103L (M = 10M), which corresponds to a BO-B1 zero-age star. The cluster [DBS2003] 157 was found to be spread over all 40 × 40 region demarcated by a intense shell-like dust emission, where… Advisors/Committee Members: Zulema Abraham, Elysandra Figueredo, Alex Andre Schmidt, Rogemar André Riffel, Marcus Vinicius Fontana Copetti.

Subjects/Keywords: extinção infravermelho: estrelas; pré-sequência: principal matéria circum-estelar poeira; formação; distâncias; regiões Hii estrelas: estrelas massivas; FISICA; formation; pre-main-sequence circumstellar matter dust; distances; Hii regions stars: early-type; extinction infrared: stars

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

APA (6^th Edition):

Pinheiro, M. d. C. (2012). ESTUDO MULTIBANDA DO CONTEÚDO ESTELAR DE REGIÕES Hii DO HEMISFÉRIO SUL. (Thesis). Universidade Federal de Santa Maria. Retrieved from http://coralx.ufsm.br/tede/tde_busca/arquivo.php?codArquivo=5089

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):

Pinheiro, Márcio do Carmo. “ESTUDO MULTIBANDA DO CONTEÚDO ESTELAR DE REGIÕES Hii DO HEMISFÉRIO SUL.” 2012. Thesis, Universidade Federal de Santa Maria. Accessed March 05, 2021. http://coralx.ufsm.br/tede/tde_busca/arquivo.php?codArquivo=5089.

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

MLA Handbook (7^th Edition):

Pinheiro, Márcio do Carmo. “ESTUDO MULTIBANDA DO CONTEÚDO ESTELAR DE REGIÕES Hii DO HEMISFÉRIO SUL.” 2012. Web. 05 Mar 2021.

Vancouver:

Pinheiro MdC. ESTUDO MULTIBANDA DO CONTEÚDO ESTELAR DE REGIÕES Hii DO HEMISFÉRIO SUL. [Internet] [Thesis]. Universidade Federal de Santa Maria; 2012. [cited 2021 Mar 05]. Available from: http://coralx.ufsm.br/tede/tde_busca/arquivo.php?codArquivo=5089.

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

Council of Science Editors:

Pinheiro MdC. ESTUDO MULTIBANDA DO CONTEÚDO ESTELAR DE REGIÕES Hii DO HEMISFÉRIO SUL. [Thesis]. Universidade Federal de Santa Maria; 2012. Available from: http://coralx.ufsm.br/tede/tde_busca/arquivo.php?codArquivo=5089

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

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