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Rochester Institute of Technology

1. Punzi, Kristina Marie. Young, Low-Mass Stars: X-rays and Circumstellar Environments.

Degree: PhD, School of Physics and Astronomy (COS), 2018, Rochester Institute of Technology

Nearby, young stars are the ideal targets for investigations of stellar and protoplanetary disk evolution, so as to understand the processes involved in planet formation and evolution, as well as the origins of our Solar System. High energy radiation (X-ray and FUV) from the central star significantly alters the structure, chemistry, and ionization of planet-forming circumstellar disks. In this dissertation, I present observations of young stars and star-disk systems to better understand the connection between stellar high energy radiation and the evolution of circumstellar environments, and to further develop methods to exploit the signatures of youth, as well as methods to identify nearby, young stars. Our unbiased radio spectroscopic survey with the Institute de Radioastronomie Millimétrique (IRAM) 30 meter telescope reveals the chemical richness of the circumstellar disk orbiting the ~2-5 Myr-old, actively accreting solar analog LkCa 15. We find that high-energy (FUV and/or X-ray) radiation from the central star, a known X-ray-luminous source, may be enhancing the abundances of CN and C 2 H within the disk. To ascertain the evolutionary status of the erratically variable star RZ Piscium (RZ Psc), we obtained observations of RZ Psc with the European Space Agency’s X-ray Multi-Mirror Mission (XMM-Newton), as well as high-resolution optical spectroscopy with the Hamilton Echelle on the Lick Shane 3 m telescope and with HIRES on the Keck I 10 m telescope. These data provide strong support for the young-star status of RZ Psc, as well as evidence for the presence of a significant mass of circumstellar gas, suggesting the recent destruction of one or more young exoplanets within 1 au of the star. It is evident from our Chandra X-ray Observatory survey of very cool members of the ~8 Myr-old TW Hydra Association (TWA) that X-ray luminosity relative to bolometric luminosity (L X /L bol ) decreases with decreasing effective temperature (T ef f ). The fraction of TWA stars that display evidence for residual primordial disk material sharply increases in this same (mid-M) spectral type regime, suggesting that disk survival times may be longer for ultra-low mass stars and brown dwarfs than for higher-mass M stars. Finally, we use parallax data available in Gaia Data Release 1 (DR1) to estimate the distances and ages of a sample of candidate young stars identified by the Galex Nearby Young Star Survey (GALNYSS). The youth of these stars is confirmed by their relative positions, compared to main sequence stars and giant stars, in Gaia-based color-magnitude and color-color diagrams produced for all Galex and WISE-detected stars with parallax measurements available in Gaia DR1. Advisors/Committee Members: Joel H. Kastner, Jeyhan Kartaltepe, Jeffrey Bary.

Subjects/Keywords: None provided

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

APA (6th Edition):

Punzi, K. M. (2018). Young, Low-Mass Stars: X-rays and Circumstellar Environments. (Doctoral Dissertation). Rochester Institute of Technology. Retrieved from http://scholarworks.rit.edu/theses/9824

Chicago Manual of Style (16th Edition):

Punzi, Kristina Marie. “Young, Low-Mass Stars: X-rays and Circumstellar Environments.” 2018. Doctoral Dissertation, Rochester Institute of Technology. Accessed October 21, 2018. http://scholarworks.rit.edu/theses/9824.

MLA Handbook (7th Edition):

Punzi, Kristina Marie. “Young, Low-Mass Stars: X-rays and Circumstellar Environments.” 2018. Web. 21 Oct 2018.

Vancouver:

Punzi KM. Young, Low-Mass Stars: X-rays and Circumstellar Environments. [Internet] [Doctoral dissertation]. Rochester Institute of Technology; 2018. [cited 2018 Oct 21]. Available from: http://scholarworks.rit.edu/theses/9824.

Council of Science Editors:

Punzi KM. Young, Low-Mass Stars: X-rays and Circumstellar Environments. [Doctoral Dissertation]. Rochester Institute of Technology; 2018. Available from: http://scholarworks.rit.edu/theses/9824

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