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Sizing up Red Dwarfs in the Solar Neighborhood Michele Louise Silverstein

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Sizing up Red Dwarfs in the Solar Neighborhood Michele Louise Silverstein Georgia State University ScholarWorks @ Georgia State University Physics and Astronomy Dissertations Department of Physics and Astronomy 8-13-2019 Sizing Up Red Dwarfs in the Solar Neighborhood Michele Louise Silverstein Follow this and additional works at: https://scholarworks.gsu.edu/phy_astr_diss Recommended Citation Silverstein, Michele Louise, "Sizing Up Red Dwarfs in the Solar Neighborhood." Dissertation, Georgia State University, 2019. https://scholarworks.gsu.edu/phy_astr_diss/116 This Dissertation is brought to you for free and open access by the Department of Physics and Astronomy at ScholarWorks @ Georgia State University. It has been accepted for inclusion in Physics and Astronomy Dissertations by an authorized administrator of ScholarWorks @ Georgia State University. For more information, please contact [email protected]. SIZING UP RED DWARFS IN THE SOLAR NEIGHBORHOOD by MICHELE LOUISE SILVERSTEIN Under the Direction of Todd J. Henry, PhD ABSTRACT We present the Systematic Investigation of Radii and Environments of Nearby Stars (SIRENS) Project: the characterization of 1593 stars including 1504 nearby red dwarfs within 25 par- secs. The primary goal is to provide radii for the all-sky sample of red dwarf single stars and spatially resolved primaries with accurate, pre-Gaia, trigonometric parallaxes placing them within 25 parsecs, with a special focus on the understudied late-type M dwarfs that have rarely been resolved with optical or infrared long-baseline interferometers. We provide Johnson-Kron-Cousins V RI, 2MASS JHK, and WISE W 1W 2W 3 photom- etry for a total of 1593 stars, including new/updated V RI photometry for 637 stars observed at the CTIO/SMARTS 0.9m, ARCSAT 0.5m, and KPNO/WIYN 0.9m. We combine the distances and photometry and apply spectral energy distribution model fitting similar to the methodology outlined by Dieterich et al. (2014) to determine fundamental parameters — temperature, luminosity, and radius — for the sample. Comparison of our results for 26 stars to their radii determined using interferometry indicates a median absolute difference of only 6%. The result is a set of fundamental parameters for a comprehensive all-sky sample of red dwarfs spanning an unprecedented range of red dwarf spectral types, from approximately M0 to the end of the stellar main sequence. We reveal trends in the dispersion and slope of the radius-effective temperature relationship of red dwarfs and link these trends to star spot coverage. We demonstrate that the radius of a star at effective temperatures greater than 2850 K can span a ∼ 0:35 R⊙ range; an effective temperature-radius relation cannot be used to accurately or precisely calculate either of these parameters without additional information. We compare the core main sequence sample of 1503 primary stars and Proxima Centauri to control samples of 53 pre-main sequence stars and 36 cool subdwarfs to map the wide 0.06–1.08 R⊙ range in radii for red dwarfs and their young and old counterparts, with the tiniest subdwarf found to be 3/4 the size of Saturn, and the smallest dwarf just smaller than Saturn. We use large radii to identify 56 new young star candidates and small radii to identify 31 cool subdwarf candidates within 25 parsecs. We emphasize that the data required for our technique are photometry and parallaxes only, and form the basis for a much larger future effort using Gaia data combined with infrared data for low-mass stars over the entire sky. INDEX WORDS: catalogs, stars: fundamental parameters, stars: low-mass, stars: pre- main sequence, starspots, stars: late-type, subdwarfs, Galaxy: solar neighborhood SIZING UP RED DWARFS IN THE SOLAR NEIGHBORHOOD by MICHELE LOUISE SILVERSTEIN A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the College of Arts and Sciences Georgia State University 2019 Copyright by Michele Louise Silverstein 2019 SIZING UP RED DWARFS IN THE SOLAR NEIGHBORHOOD by MICHELE LOUISE SILVERSTEIN Committee Chair: Todd J. Henry Committee: Sébastien Lépine Andrew W. Mann Brian D. Thoms Russel J. White Electronic Version Approved: Office of Graduate Studies College of Arts and Sciences Georgia State University August 2019 iv CHAPTER 0 DEDICATION I’d like to dedicate this dissertation to my colleagues at GSU. I turned to many of you in times of doubt, and it is because of your combined empathy and wisdom that this dissertation has ultimately been written. I’d also like to extend this dedication to anyone who has ever talked me down from overwhelming doubt regarding school and my future, during or before graduate school. Thank you. One’s worst enemy is often oneself. “Community is a safety net from an unfair world. Let it catch you when you need it. Catch others when you can.” -Unknown v CHAPTER 0 ACKNOWLEDGMENTS There are so many people I would like to thank for a variety of support in both my academic and personal life. Thank you all for being great friends, family, and mentors. My Two Advisers • Todd Henry — more than I could possibly include in an acknowledgments section. PhD and life advisor extraordinaire. Over the course of my time on the RECONS Team, I have learned to be a first-class observer, manage an observatory (as the SMARTS Grad- uate Fellow), develop large research projects and observing programs, mentor others (undergraduate and graduate students), and make my case for starting and continuing research programs. I have learned to remain aware of who has what expertise and that networking is invaluable. Todd has shown me the importance of being extremely organized, looking to the future, and dreaming big — I intend to keep these in the forefront of my mind as I move on to my next research position. We developed this project, worked hard to achieve it, and have created a tool usable beyond this disser- tation project for a variety of low-mass star and exoplanet studies. I am proud of our work and grateful to have had Todd as a PhD adviser. • Wei-Chun Jao — effectively my second advisor. Wei-Chun helped me through research questions countless times, provided the absolute photometry and astrometry pipelines for CTIO, maintained and improved the RECONS 25 Parsec Database, and created the list of subdwarfs used in this study. Wei-Chun’s insights, deep understanding of vi nearby and low-mass stars, and sharpness in troubleshooting and have helped guide me through many of the details of day-to-day research life. His sense of humor and approachability have kept things light even when I’ve been overwhelmed with stress. I will be missing him as I move on to my next research position, and am grateful for the time I’ve had to pick his brain over research and hear his different perspectives. Although I am sure we will remain collaborators for some time, it will not be the same as being able to walk over to his door. For This Project • Jen Winters — my SMARTS fellow predecessor, who taught me photometry reduction and disentangled the multiplicity chaos of the M dwarfs • Serge Dieterich — introduced me to and showed me how to use the initial CALSED code. Fount of low-mass star knowledge and supportive friend. • Tiffany Clements — acquired photometry data for me, helped me getting LaTeX tables to cooperate. ARCSAT observing buddy and excellent friend. • Adric Riedel — provided a list of young stars and worked with me to produce a publication describing nearby young stars, which I’ve always been interested in. • CTIO Staff — made sure every observing run went smoothly from travel to telescope operation, especially Manuel Hernandez, Hernan Tirado, Roderigo Hernandez, and Ximena Herreros. vii • APO Staff — patiently helped me use the newly automated and somewhat tempera- mental ARCSAT telescope. • Fahim Zaman — summer undergraduate researcher who helped me investigate WISE data quality. The summer we spent together served as my first ever experience as a research supervisor. I hope you go far in whatever you decide to do. • Garrett Somers — creator of the evolutionary models I compare my fundamental pa- rameters to. Thank you for giving me a sneak peak of your evolutionary models! I have much to learn about stellar activity, and this was a really cool and enlightening way to start integrating it into my research. Best wishes moving forward. Friends and Family, Independent of the Project • Merida Batiste — bestower of sanity, wisdom, and friendship in times of struggle and when I need it most. Effectively my “AstroPAL” and one of my closest friends. • Crystal Gnilka — Grad school sibling and close friend, with whom I shared an office space for nearly 7 years. You’ve challenged my view of the world and kept it real, being critical at times, but in the ways I needed. When I messed up and said something I didn’t realize wasn’t so great, you forgave me and understood. You’ve been there for lots of rants and I’ve heard a lot of yours. There’s also been plenty of kindness, especially in the toughest times I’ve had. Here’s to a great friendship and the lessons learned in grad school that have nothing to do with astronomy. viii • Ryan Norris — a giver of kind advice, grad school sibling of nearly 7 years, and friend, with an interesting perspective and a listening ear. Our time together has been often quiet, but also fun and kind. We’ve gotten to know each other and our odd habits well over the years. I’ll miss having you as an officemate. • Eliot Vrijmoet — research sibling and friend. When Eliot joined the team, I felt like we had a lot in common, and we quickly became friends. Eliot has been someone to whome I’ve been able to tell my “breaking news.” I helped him learn to become the SMARTS Fellow, which I think was a beneficial experience to us both.
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