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Young, Low-Mass Stars: X-Rays and Circumstellar Environments

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Young, Low-Mass Stars: X-Rays and Circumstellar Environments Rochester Institute of Technology RIT Scholar Works Theses 6-22-2018 Young, Low-Mass Stars: X-rays and Circumstellar Environments Kristina Marie Punzi [email protected] Follow this and additional works at: https://scholarworks.rit.edu/theses Recommended Citation Punzi, Kristina Marie, "Young, Low-Mass Stars: X-rays and Circumstellar Environments" (2018). Thesis. Rochester Institute of Technology. Accessed from This Dissertation is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. Rochester Institute of Technology Ph.D. Dissertation Young, Low-Mass Stars: X-rays and Circumstellar Environments Author: Advisor: Kristina Marie Punzi Joel H. Kastner A dissertation submitted in partial fulfillment of the requirements for the degree of Ph.D. in Astrophysical Sciences and Technology in the School of Physics and Astronomy June 22, 2018 Rochester Institute of Technology Ph.D. Dissertation Young, Low-Mass Stars: X-rays and Circumstellar Environments Author: Advisor: Kristina Marie Punzi Joel H. Kastner A dissertation submitted in partial fulfillment of the requirements for the degree of Ph.D. in Astrophysical Sciences and Technology in the School of Physics and Astronomy Approved by Professor Joel H. Kastner Date Director, Astrophysical Sciences and Technology Certificate of Approval Astrophysical Sciences and Technologies R·I·T College of Science Rochester, NY, USA The Ph.D. Dissertation of Kristina Marie Punzi has been approved by the undersigned members of the dissertation committee as satisfactory for the degree of Doctor of Philosophy in Astrophysical Sciences and Technology. Dr. Grover Swartzlander, Committee Chair Date Dr. Joel H. Kastner, Dissertation Advisor Date Dr. Jeyhan Kartaltepe Date Dr. Jeffrey Bary Date To everyone who believed in me, even when I did not believe in myself. ABSTRACT 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 Millim´etrique (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 C2H 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 (LX/Lbol) decreases with decreasing effective temperature (Teff ). 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. i CONTENTS Abstract i Declaration v Acknowledgements vi List of published work vii List of Tables viii List of Figures x 1 Introduction 1 1.1 Star and Planet Formation................................1 1.2 Physical and Chemical Processes in Irradiated Circumstellar Environments.....3 1.3 Nearby, Young Moving Groups..............................9 1.4 Stellar X-rays........................................ 11 1.4.1 X-rays from Accretion vs. Coronal Activity................... 13 1.5 The Lowest Mass Stars................................... 15 1.5.1 Planet Formation Around Low-Mass Stars.................... 17 1.6 Methods........................................... 21 1.6.1 Molecular Line Emission.............................. 21 1.6.2 Optical Depth................................... 22 1.6.3 Radial Velocity Cross-Correlation Technique.................. 24 1.6.4 Spectroscopic Diagnostics of Stellar Surface Gravities............. 24 1.6.5 Dust Mass Necessary for Optical Dropouts................... 25 1.7 Overview.......................................... 26 ii CONTENTS 2 An Unbiased 1.3 mm Emission Line Survey of the Protoplanetary Disk Orbiting LkCa 15 39 2.1 Abstract........................................... 40 2.2 Introduction......................................... 40 2.3 Observations and Data Reduction............................ 42 2.4 Results and Analysis.................................... 43 2.4.1 Molecular Line Inventory............................. 43 2.4.2 Line Intensity Measurements........................... 44 2.4.3 Column Density Estimates............................ 45 2.4.4 Opacities in CO Lines............................... 47 2.4.5 CN and C2H Hyperfine Component Analysis: Optical Depths, Excitation Temperatures, and Column Densities....................... 48 2.5 Discussion.......................................... 49 2.6 Summary.......................................... 52 3 Is The Young Star RZ Piscium Consuming its Own (Planetary) Offspring? 71 3.1 Abstract........................................... 72 3.2 Introduction......................................... 72 3.3 Observations........................................ 74 3.3.1 XMM-Newton European Photon Imaging Cameras (EPIC).......... 74 3.3.2 High-Resolution Optical Spectroscopy...................... 75 3.3.3 Keck II 10 m Echellette Spectrograph and Imager (ESI)............ 76 3.3.4 WIYN-0.9 m Half Degree Imager (HDI)..................... 76 3.4 Results and Analysis.................................... 76 3.4.1 Model Atmosphere Analysis............................ 76 3.4.2 Spectral Type.................................... 79 3.4.3 Stellar Activity and Rotation........................... 79 3.4.4 Radial Velocities.................................. 81 3.4.5 Modeling the X-ray Spectrum of RZ Psc..................... 82 3.4.6 XMM-Newton Optical Monitor Data....................... 83 3.4.7 Search for Comoving Low-Mass Stellar Companions.............. 84 3.5 Discussion.......................................... 85 3.5.1 Age Diagnostics: Stellar Activity and Li Line Strength............. 85 3.5.2 X-ray Absorption versus Optical Extinction................... 87 3.5.3 The Puzzling Radial Velocity Behavior of RZ Psc................ 88 3.5.4 What is the Origin of the Circumstellar Material Orbiting RZ Psc?...... 89 3.6 Summary and Conclusions................................. 90 4 M Stars in the TW Hya Association 108 4.1 Abstract........................................... 109 4.2 Introduction......................................... 110 4.2.1 Sample and Observations............................. 113 4.2.2 Presence or Absence of Circumstellar Disks................... 114 4.3 Results and Analysis.................................... 115 iii CONTENTS 4.3.1 Estimating Bolometric Luminosities and Effective Temperatures....... 115 4.3.2 Chandra X-Ray Spectral Analysis........................ 115 4.3.3 X-Ray Luminosities................................ 118 4.4 Notes on Inclusion of Sources............................... 119 4.4.1 BANYAN Method................................. 119 4.5 Discussion.......................................... 123 4.5.1 Trends in X-Ray Luminosity and Disk Fraction................. 123 4.5.2 Trends in TX ?................................... 123 4.5.3 Variability...................................... 124 4.5.4 Log(LX/Lbol): A Possible Predictor of H-burning Limit?............ 125 4.6 Summary and Conclusions................................. 127 5 Identifying Nearby, Young Stars with Gaia 165 5.1 Abstract........................................... 166 5.2 Introduction......................................... 166 5.3 Methods and Results.................................... 168 5.3.1 The Gaia DR1/TGAS GALNYSS Subsample.................. 168 5.3.2 A Comparison of the GALNYSS Subsample with NYMG Members and Pre- Main Sequence Isochrones............................
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