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Far-Ultraviolet Spectroscopy of the Circumstellar and Interstellar Environment of Young Stars By

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Far-Ultraviolet Spectroscopy of the Circumstellar and Interstellar Environment of Young Stars By Far-Ultraviolet Spectroscopy of the Circumstellar and Interstellar Environment of Young Stars by Matthew McJunkin B.S., Mathematics and Physics, Case Western Reserve University, 2010 M.S., Astrophysical and Planetary Sciences, University of Colorado, 2012 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Astrophysical and Planetary Sciences 2016 – ii – This thesis entitled: Far-Ultraviolet Spectroscopy of the Circumstellar and Interstellar Environment of Young Stars written by Matthew Scott McJunkin has been approved for the Department of Astrophysical and Planetary Sciences Dr. Kevin France Dr. James Green Dr. Phil Armitage Dr. Seth Hornstein Dr. Ana Maria Rey Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. – iii – McJunkin, Matthew Scott (Ph.D., Astrophysical and Planetary Sciences) Far-Ultraviolet Spectroscopy of the Circumstellar and Interstellar Environment of Young Stars Thesis directed by: Dr. Kevin France I have analyzed absorption from the CO Fourth Positive band system (A 1Π X 1Σ+) − in the ultraviolet spectra of 6 Classical T Tauri stars, tripling the measurements in the literature. CO traces the molecular gas in the inner disk, providing constraints on the material in the planet-forming environment. I fit an absorption model in order to determine the column density and temperature of the gas in the disk. My CO rotational temperatures agree well with CO fluorescence measurements in the ultraviolet, but are in between infrared CO absorption and emission measurements. I also fit absorption profiles of H I against the Lyman-α emission from a large sample of young stars (Classical T Tauri and Herbig Ae/Be) in order to determine the amount of interstellar extinction along the line of sight. Knowing the extinction value will allow us to reconstruct the intrinsic emission from the stars, which is the radiation impacting the protoplanetary disk. This radiation determines the thermal and chemical structure of the material that may form planets. I find lower visual extinction values than those in the literature using optical, infrared, and X-ray measurement techniques. In addition, I have created a new technique using H2 fluorescence to empirically estimate the full ultraviolet extinction curve of young stars. I compare predicted line fluxes from my created H2 fluorescence model to observed fluxes from 7 strong progressions in order to determine the extinction over the 1100 - 1700 A˚ range. I then fit my extinction curves with models from the literature to determine best-fit AV and RV values. I find that this technique is limited by the degeneracy between the AV and RV values, needing one or the other to be determined independently. I hope to improve the technique and mitigate the limitations in future work. – iv – Dedication “Yet what is any ocean but a multitude of drops?” -David Mitchell, Cloud Atlas For my friends, family, and collaborators who helped create this ocean of a thesis one drop at a time. –v– Acknowledgments I’d like to thank all the people who supported me and bolstered me along the long path towards this thesis. My research advisors, both in undergraduate and graduate school (Chris Mihos, Earle Luck, Jim Green, and Kevin France), inspired my research and helped with the challenges. I thank them for pushing me when I would get stuck in an unproductive rut. To my many other collaborators over my research career (Greg Herczeg, Christian Schneider, Lynne Hillenbrand, Eric Schindhelm, Suzan Edwards, Alex Brown, Eric Burgh, Joanna Brown, and Keri Hoadley), I want to thank you for your help in creating figures and writing portions of our papers, your thoughtful comments, and your many hours of proofreading. To my parents, I’m thankful for your encouragement and your belief that I could do anything if I worked hard enough. Thank you for providing me with the opportunities I needed to expand my mind and choose my own path. To my sister, Sarah, I treasure all the laughs we had growing up. Thank you for being such an amazing role model who inspires me to be my best. For me, grad school is not just about research. To succeed, I needed a support system to help take my mind off work every once in a while. So to my fellow graduate students, you have an amazing ability to cheer me up when research is not going well. I truly think we have the closest knit group of grad students in the country, and I count you all among my closest friends. Specifically to Jen, Katy, Chris, Eric, Keri, Evan, and David, you have become like family to me. I love y’all so much and I couldn’t have done it without you! And lastly, I’d like to thank Boulder itself for being a bastion of tolerance and progressive thought where I felt free to live as my true self without fear or judgment. Plus, the craft beer and mountains are a pretty good bonus! – vi – Contents 1 Introduction 1 1.1 StarFormation .................................. 2 1.2 ScienceGoals ................................... 3 1.2.1 Understanding planet formation and migration . 3 1.2.2 Determining the composition of protoplanetary disks . 8 1.2.3 How stellar SEDs affect disk mass, temperature and chemistry . ... 10 1.2.4 Estimating extinction curves toward young stars . .. 14 1.3 PreviousWork .................................. 16 1.3.1 Observational work on molecules in protoplanetary disks . .. 16 1.3.2 Protoplanetarydiskmodels . 18 1.3.3 Previous extinction measurement work in many wavelength regions . 21 1.4 MolecularPhysics................................. 23 1.4.1 Rovibrational transitions . 23 1.4.2 Selectionrules............................... 27 1.4.3 Molecular Band and Progression Structure . 29 2 CO Absorption Line Spectroscopy 31 2.1 Introduction.................................... 32 2.2 TargetsandObservations . .. .. 34 2.3 Analysis ...................................... 39 – vii – 2.3.1 DataAnalysis............................... 39 2.3.2 Model Description and Fitting Procedure . 42 2.3.3 ModelFitsandErrors .......................... 46 2.4 ResultsandDiscussion .............................. 55 2.4.1 CO Velocity and Isotopic Fraction . 55 2.4.2 COTemperatureandDensity . 57 2.4.3 ComparisonofCOwithSystemParameters . 61 2.5 Conclusions .................................... 62 3 H I Lyα Absorption 67 3.1 Introduction.................................... 67 3.2 TargetsandObservations . .. .. 71 3.2.1 COSObservations ............................ 72 3.2.2 STISObservations ............................ 72 3.3 N(H I)Analysis.................................. 75 3.3.1 Overview of Lyα Profiles ........................ 75 3.3.2 Lyα ProfileFitting ............................ 76 3.3.3 Extinction from Optical/Infrared Colors and Spectrophotometry... 88 3.3.4 X-raySpectralFitting .......................... 91 3.4 Results....................................... 94 3.5 Discussion..................................... 99 – viii – 3.5.1 Sources of Hydrogen Along the Line of Sight . 99 3.5.2 Discrepancy Among Lyα, Optical, and IR-based extinction determi- nations................................... 102 3.5.3 OriginofX-rayAbsorbingGas . 106 3.6 Conclusions .................................... 107 4 H2 Fluorescence Modeling 109 4.1 Introduction.................................... 109 4.2 TargetsandObservations . .. .. 113 4.3 H2 Fluorescence.................................. 113 4.4 Models....................................... 117 4.4.1 λ> 1450 AFits˚ ............................. 117 4.4.2 Self-Absorption Calculation . 124 4.4.3 ExtinctionCurveFits .......................... 125 4.5 Results....................................... 128 4.5.1 Best-FitModelsandParameters. 128 4.5.2 ModelandParameterAnalysis . 129 4.5.3 Predicted 2175 ANUVBump˚ ...................... 133 4.6 Discussion..................................... 134 4.7 Conclusions .................................... 140 5 Conclusions 141 – ix – 5.1 The limits of HST COabsorptionmeasurements . 141 5.2 The difficulties of extinction measurements . 141 5.3 Evidence of grain processing/non-thermal H2 populations in CTTS disks . 142 6 Future Work 144 6.1 Updating the H2 fluorescencecode ....................... 144 6.2 The 2175 Abump.................................˚ 145 6.3 Extinction Towards Early-Type Stars In Local Star-Forming Regions . 147 6.4 ExploringtheOutflowComponent . 150 6.5 Gasanddustdiskevolution ........................... 152 7 Bibliography 154 A Appendix: Inclination Measurements 179 A.1 Most accurate Inclination Measurements . 179 A.2 Less accurate Inclination Measurements . .... 181 A.3 OtherInclinationMeasurements . 181 –x– List of Tables 2.1 TargetParameters ................................ 36 2.2 HST -COSG130M/G160MObservationsofTargets . 36 2.3 COFitParameters ................................ 38 2.4 ProtoplanetaryDiskWarmGasParameters . .. 60 3.1 TargetParameters ................................ 73 3.2 ExtinctionValues ................................ 86 3.3 AdditionalModelParameters . 87 3.4 Additional AV Values .............................. 89 3.4 Additional AV Values .............................. 90 3.5 X-ray Measurements for Pre-Main Sequence Stars in the Sample ....... 93 4.1 H2 ModelBest-FitParameters . 123 4.2 ExtinctionModelBest-FitParameters . 130 4.3 AV ComparisonForBest-FitTargets . 131 6.1 TargetParameters ...............................
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