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Characterization of the Stellar / Substellar Boundary

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Characterization of the Stellar / Substellar Boundary Georgia State University ScholarWorks @ Georgia State University Physics and Astronomy Dissertations Department of Physics and Astronomy Fall 11-18-2013 Characterization of the Stellar / Substellar Boundary Sergio Bonucci Dieterich Follow this and additional works at: https://scholarworks.gsu.edu/phy_astr_diss Recommended Citation Dieterich, Sergio Bonucci, "Characterization of the Stellar / Substellar Boundary." Dissertation, Georgia State University, 2013. https://scholarworks.gsu.edu/phy_astr_diss/66 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]. CHARACTERIZATION OF THE STELLAR / SUBSTELLAR BOUNDARY by SERGIO BONUCCI DIETERICH Under the Direction of Todd J. Henry ABSTRACT The aim of this dissertation is to address the topic of distinguishing very low mass stars from brown dwarfs through observational means. To that end, we seek to better charac- terize both populations and establish mechanisms that facilitate establishing an individual object’s membership in either the very low mass star or the brown dwarf populations. The dissertation is composed of three separate observational studies. In the first study we report on our analysis of HST/NICMOS snapshot high resolution images of 255 stars in 201 systems within ∼10 parsecs of the Sun. We establish magnitude and separation limits for which companions can be ruled out for each star in the sample, and then perform a comprehensive sensitivity and completeness analysis for the subsample of 138 +3.5 M dwarfs in 126 systems. We calculate a multiplicity fraction of 0.0−0.0% for L companions +5.0 to M dwarfs in the separation range of 5 to 70 AU, and 2.3−0.7% for L and T companions to M dwarfs in the separation range of 10 to 70 AU. Considering these results and results from several other studies, we argue that the so-called “brown dwarf desert” extends to binary systems with low mass primaries and is largely independent of primary mass, mass ratio, and separation. In the second study we construct a Hertzsprung-Russell diagram for the stellar/substellar boundary based on a sample of 63 objects ranging in spectral type from M6V to L4. We report new VRI photometry for 63 objects and new trigonometric parallaxes for 37 objects. We employ a novel SED fitting algorithm to determine effective temperatures, bolometric luminosities, and radii. We find evidence for the local minimum in the radius−temperature and radius−luminosity trends that may indicate the end of the stellar main sequence and the start of the brown dwarf sequence at Teff ∼ 2075K, log(L/L⊙) ∼ −3.9, and (R/R⊙) ∼ 0.086. The third study is a pilot study for future work and part of a long term search for astro- metric binaries that have the potential to yield dynamical masses. We report the discovery of five new multiple systems and discuss their potential for determining dynamical masses: LHS 2071AB, GJ 1215 ABC, LTT 7434 AB, LHS 501 AC, and LHS 3738 AB. INDEX WORDS: Astronomy, Binaries: close, Brown dwarfs, Galactic structure, Hertzsprung-Russell and C-M diagrams, Infrared: stars, Parallaxes, Solar neighborhood, Stars: fundamental parameters, Stars: low-mass, Stars: statistics CHARACTERIZATION OF THE STELLAR / SUBSTELLAR BOUNDARY by SERGIO BONUCCI DIETERICH 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 2013 Copyright by Sergio B. Dieterich 2013 CHARACTERIZATION OF THE STELLAR / SUBSTELLAR BOUNDARY by SERGIO BONUCCI DIETERICH Committee Chair: Todd J. Henry Committee: Adam Burgasser Douglas R. Gies Gary Hastings Sebastien Lepine Russel J. White Electronic Version Approved: Office of Graduate Studies College of Arts and Sciences Georgia State University December 2013 iv CHAPTER 0 DEDICATION This dissertation is dedicated to the strongest person I know, my wife Bonny Dieterich, and to her physician, Dr. Stephen Szabo. Through the challenges life threw at us in the course of my graduate studies, Bonny showed unimaginable strength and positive thinking, and Dr. Szabo was there to guide and help us every step of the way. v CHAPTER 0 ACKNOWLEDGMENTS Special Thanks goes to: My advisor Dr. Todd Henry, who was there to guide me every step of the way and help make this project a reality. To my colleagues Adric Riedel, Jen Winters, Wei-Chun Jao, Mark Boyd, Altonio Hosey, and John Lurie. Through the course of our work, my problems often became their problems, and our successes were mutually celebrated. To the other members of my dissertation committee, who were there to guide me and at times rein in some crazy ideas: Adam Burgasser, Douglas Gies, Gary Hastings, Sebastien Lepine, and Russel White. To my mother, my sisters, brothers-in-law, nieces, and nephews, who shared the excite- ment of every development and discovery, no matter how small. To Alvin Das, who a long long time ago constructed a LATEX package for GSU disser- tation preparation, and to Adric Riedel for being its most recent curator. A generation of Astronomy Ph.D. students is indebted to Alvin for this work. vi CHAPTER 0 TABLE OF CONTENTS ACKNOWLEDGMENTS .............................. v LISTOFTABLES .................................. x LISTOFFIGURES ................................. xi LISTOFABBREVIATIONS . .. .. xiv 1 INTRODUCTIONANDMOTIVATION . 1 1.1 A Basic Overview of What is a star and What is a Brown Dwarf . 2 1.2 The M, L, T, and Y Spectral Classes ................... 4 1.3 Motivation .................................... 5 1.4 Three Interconnected Studies ........................ 6 2 History and Overview of the Field . 8 2.1 Postulation and Early Searches ....................... 8 2.2 Large Sky Surveys ............................... 10 2.3 Theoretical Developments .......................... 11 2.4 The Diversity of M, L, and T dwarfs ................... 14 2.5 Trigonometric Parallaxes ........................... 20 2.6 M Dwarfs in the Solar Neighborhood ................... 21 2.7 The Luminosity Function and the Mass Function ........... 22 3 Overview of the HST/NICMOS Multiplicity Study . 25 3.1 Introduction ................................... 25 3.2 General Characteristics of the Sample .................. 27 3.3 Observations and Data Reduction ..................... 29 vii 3.4 Determining the Sensitivity of the Search ................ 35 3.5 Results ...................................... 36 3.5.1 Color−Magnitude Diagrams .................... 36 3.5.2 Astrometry of Known Binaries .................. 42 3.5.3 Results from the Sensitivity Search ................ 44 4 M Dwarf Multiplicity and its Implications . 52 4.1 Establishing Search Completeness for M Dwarfs ............ 52 4.2 The M Dwarf Multiplicity Fraction .................... 56 4.2.1 M0V to M9V Companions at Separations of 5 to 70 AU . 58 4.2.2 L0 to L9 Companions at Separations of 5 to 70 AU ..... 59 4.2.3 L0 to T9 Companions at Separations of 10 to 70 AU .... 60 4.3 Sensitivity to Companion Masses ..................... 61 4.4 A Current Map of the Brown Dwarf Desert ............... 63 4.5 Is the Desert Real? .............................. 65 4.6 The CMF, the IMF, and the Big Picture ................. 67 4.6.1 Isolated Objects ............................ 68 4.6.2 Testing Formation Scenarios .................... 70 5 The HLIMIT Survey − Overview and Observations . 74 5.1 Introduction ................................... 74 5.1.1 Possible Tests for Detecting the Stellar/Substellar Boundary 76 5.2 The Observed Sample ............................. 80 5.3 Photometric Observations .......................... 81 5.4 Astrometric Observations .......................... 85 5.5 Methodology for Calculating Effective Temperature .......... 87 5.6 Methodology for Calculating Luminosity and Radius ......... 93 6 ResultsfromtheHLIMITSurvey . 104 viii 6.1 Photometric Results .............................. 104 6.2 New Trigonometric Parallaxes ....................... 107 6.3 Effective Temperatures and Luminosities ................. 112 6.3.1 χ2 Tests for Temperature Fits ................... 122 6.4 Color-Magnitude Relations ......................... 127 6.5 Optical Variability ............................... 132 6.6 DENIS J1454-6604AB − A New Astrometric Binary ......... 134 6.7 The End of the Stellar Main Sequence .................. 136 6.7.1 A Discontinuity at the End of the Main Sequence ...... 145 6.7.2 Kinematic Analysis .......................... 149 6.7.3 Comparison of the HR Diagram to Evolutionary Models . 151 6.7.4 Comparison of Radii With Other Studies ............ 161 6.8 Notes on Individual Objects ......................... 162 7 The Gemini Adaptive Optics High Resolution Imaging Survey . 169 7.1 Introduction ................................... 169 7.2 Astrometric Binaries − an Overview ................... 172 7.2.1 From Photocentric Orbits to Component Masses ....... 174 7.3 Gemini/NIRI Observations ......................... 177 7.4 Searching for Companions .......................... 178 7.5 Results ...................................... 179 7.5.1 LHS 2071AB .............................. 180 7.5.2 GJ 1215 ABC ............................. 183 7.5.3 LTT 7434AB .............................. 185 7.5.4 LHS 501AC ............................... 187 7.5.5 LHS 3738AB .............................. 187
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