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UCLA Electronic Theses and Dissertations UCLA UCLA Electronic Theses and Dissertations Title Young Stars and Planet Formation Permalink https://escholarship.org/uc/item/4304p827 Author Haney, Laura Publication Date 2016 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California University of California Los Angeles Young Stars and Planet Formation A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Astronomy by Laura Vican Haney 2016 c Copyright by Laura Vican Haney 2016 Abstract of the Dissertation Young Stars and Planet Formation by Laura Vican Haney Doctor of Philosophy in Astronomy University of California, Los Angeles, 2016 Professor Benjamin M. Zuckerman, Chair Young stars represent important laboratories for studying stellar and planet formation. Fur- thermore, low-mass stars are not only the most common product of star formation, but also provide appealing conditions for the direct imaging of exoplanets. Determining youth in solar-type stars and low-mass stars can be challenging. I have examined young stars and the planet formation processes that occur around them from several different perspectives. First, I examined one of the most commonly-used age determination methods for solar-type stars - chromospheric activity. I compiled a large (∼2,800 star) sample of stars with known chromospheric activity levels, calculated their ages, and searched for evidence of an infrared excess (indicative of a circumstellar debris disk) using data from the Wide Field Infrared Survey Explorer (WISE). I found that, while the distribution of stars with a strong infrared excess peaks at young ages, there are a significant number of debris disks occurring at much later ages. I present 74 newly discovered debris disks. Following this work, I examined dust production mechanisms in debris disks by performing an in-depth analysis of 24 stars observed with the Herschel Space Observatory. I present 7 newly resolved stars, and char- acterize the dust formation mechanisms in 15 stars with confirmed infrared excesses. In addition, I identify four stars as potential targets for follow-up observations to search for previously unseen planets. Finally, I analyzed over 450 optical spectra of low-mass stars to identify young, nearby stars as targets for direct imaging observations. As a part of this project, I also identify 60 stars as bonafide members of nearby moving groups, 39 of which are presented for the first time. I also identify 41 stars with signatures of youth, but that ii do not appear to belong to any one particular moving group. I discovered 36 spectroscopic binaries, 30 of which are newly presented here. I used the UCAC4 catalog to search for wide binary companions to stars in my sample, and discovered 35 stars in common proper motion pairs, 32 of which are presented here for the first time. I also used my measurements of Li to re-calculate lithium depletion boundary ages for three nearby moving groups (β Pic, Tuc Hor, and AB Dor). In an effort to characterize youth indicators in low-mass stars, I investigated the magnetic activity of stars in my sample using NUV, X-Ray, and Hα emis- sion. I identify a new late-type (M4.9) debris disk host that shows some signatures of active accretion. This newly discovered debris disk host joins a very small population of late-type stars with dusty debris disks. iii The dissertation of Laura Vican Haney is approved. Kevin D. McKeegan Michael P. Fitzgerald Ian S. McLean Benjamin M. Zuckerman, Committee Chair University of California, Los Angeles 2016 iv To my students... ...who taught me to never stop learning. v Table of Contents 1 Introduction :::::::::::::::::::::::::::::::::::::: 1 1.1 Planetary Formation Processes Around Stars Near the Sun . .1 1.1.1 The Evolution of Debris Disks . .1 1.1.2 Debris Disks . .2 1.2 Young, Low-Mass Stars . .3 2 The Evolution of Dusty Debris Disks Around Solar Type Stars ::::: 4 2.1 Introduction . .4 2.2 IR Excesses . .5 2.3 Stellar Sample . .9 2.3.1 Chromospheric Activity as an Age Indicator . .9 2.3.2 Pace 2013 . 10 2.3.3 Jenkins et al. 2011 . 11 2.3.4 Isaacson & Fischer 2010 . 11 2.3.5 Wright et al. 2004 . 11 2.4 Discussion . 12 2.4.1 Comparison to Protoplanetary Disks . 12 2.4.2 Models of Dust Production . 12 2.4.3 Models of Dust Removal . 13 2.4.4 Observations . 13 2.5 Stellar Characteristics . 37 2.5.1 Spectral Type . 37 2.5.2 Distance from Earth . 38 vi 2.5.3 Metallicity . 38 2.5.4 Planet Hosts . 38 2.5.5 Lithium Abundances . 42 2.6 Issues and Warnings . 45 2.6.1 Chromospheric Activity Variations . 45 2.6.2 Issues with SED Fitting . 47 2.7 Conclusions . 49 3 Herschel Observations of Dusty Debris Disks ::::::::::::::::: 50 3.1 Introduction . 50 3.2 Stellar Sample . 50 3.3 Observations . 51 3.3.1 Herschel Non-Detections . 53 3.3.2 Systems with No Detectable Dust . 55 3.4 Sources of Possible Contamination . 56 3.4.1 Extragalactic Background . 56 3.4.2 IR Cirrus . 58 3.5 Spectral Energy Distributions . 58 3.5.1 Stellar Parameters . 62 3.5.2 Dust Parameters . 62 3.6 Resolved Disks . 63 3.6.1 Disk Radii . 64 3.7 Dust Production and Planet Formation . 67 3.7.1 Distinguishing Transient from Steady-State Events . 69 3.7.2 Steady-State Collisions - Stirring Mechanisms . 73 vii 3.7.3 Star-Grazing Comets . 76 3.7.4 Giant Impacts and Catastrophic Collisions . 77 3.8 Two-Temperature Systems . 78 3.9 Comparison with Previous Studies . 79 3.9.1 HD 15407 . 79 3.9.2 HD 23514 . 81 3.9.3 HD 35650 . 81 3.9.4 HD 43989 . 82 3.9.5 HD 54341 . 82 3.9.6 HD 76543 . 83 3.9.7 HD 76582 . 83 3.9.8 HD 84870 . 84 3.9.9 HD 85672 . 84 3.9.10 HD 99945 . 84 3.9.11 HD 113766 . 85 3.9.12 HD 121191 and HD 131488 . 85 3.9.13 HD 124718 . 86 3.9.14 BD+20 307 . 86 3.10 Conclusions . 87 3.11 Acknowledgements . 88 4 Spectroscopic Observations of Nearby Low Mass Stars in the GALNYSS Survey ::::::::::::::::::::::::::::::::::::::::::: 89 4.1 Introduction . 89 4.2 Stellar Sample . 91 viii 4.3 Observations . 92 4.4 Results . 93 4.4.1 Signatures of Youth . 93 4.4.2 Space Motions . 103 4.4.3 Spectral Indices . 104 4.5 Discussion . 107 4.5.1 Moving Group Membership . 107 4.5.2 Lithium Depletion Boundary Ages . 116 4.5.3 Binary Systems . 120 4.5.4 Signatures of Magnetic Activity . 122 4.6 Conclusions . 126 ix List of Figures 2.1 SED of HIP 14809 . .7 0 2.2 Distribution of logR HK ............................. 29 2.3 Distribution of Debris Disk Hosts in Stellar Sample . 30 2.4 Evolution of Debris Disks . 31 2.5 Distribution of Disk Semi-major Axes . 32 2.6 Debris Disk Visualization . 33 2.7 Cont'd . 34 2.8 Cont'd . 35 2.9 Distribution of Distances . 39 2.10 Distribution of [Fe/H . 40 2.11 Planet Hosts . 43 2.12 Li Evolution . 46 2.13 Blackbody Degeneracy - HIP 90593 . 48 3.1 Spectral energy distributions (SEDs) of OT1 and OT2 stars . ..
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