Multiwavelength Observations of Young Stars and Their Circumstellar Disks
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Rochester Institute of Technology RIT Scholar Works Theses 8-2014 Multiwavelength Observations of Young Stars and Their Circumstellar Disks David A. Principe Follow this and additional works at: https://scholarworks.rit.edu/theses Recommended Citation Principe, David A., "Multiwavelength Observations of Young Stars and Their Circumstellar Disks" (2014). 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. Degree Dissertation Multiwavelength Observations of Young Stars and Their Circumstellar Disks Author: Dissertation Advisor: David A. Principe Dr. Joel H. Kastner This dissertation has been approved by the undersigned members of the dissertation committee as satisfactory for the degree of Doctor of Philosophy: Astrophysical Sciences and Technology in the Laboratory for Multiwavelength Astrophysics School of Physics and Astronomy John Kerekes: Committee Chair Joel Kastner: Dissertation Advisor Signature Date Signature Date Christopher O’Dea Eric Mamajek Signature Date Signature Date ! ! ! ! ! ! ! ! ! ! Multiwavelength Observations of Young Stars and Their Circumstellar Disks ! By! David A.! Principe A dissertation submitted in partial fulfillment of the requirements for the degree of Ph.D. in Astrophysical Sciences and Technology, in the College of Science, Rochester Institute! of Technology! ! August 2014! ! ! ! ! ! ! Approved by!!___________________________________________________________! ! Professor Andrew Robinson! Date! ! Director, Astrophysical Sciences and Technology Abstract School of Physics and Astronomy Doctor of Philosophy: Astrophysical Sciences and Technology Multiwavelength Observations of Young Stars and Their Circumstellar Disks by David A. Principe Observational studies of star and planet formation represent a fundamental means to understand the origins of exoplanetary systems and our own solar system. In this dissertation I present a multiwavelength approach to study a wide range of stages of the evolution of protostars and pre-main sequence (pre-MS) stars. I have investigated, via an infrared and multi-epoch X-ray study of the L1630 dark cloud, whether and how X-ray variability in young stellar objects is related to protostellar evolutionary state. Among a subsample of 52 X-ray-emitting young stars in L1630, I find that the earliest stages of young stellar evolution show the highest levels of X-ray variability, indicative of high levels of magnetic activity during star formation. I also find evidence of active magnetospheric accretion in three L1630 stars with circumstellar disks. I also present multiwavelength analyses of several phenomenologically interesting young stars at di↵erent stages of pre-MS stellar evolution. I investigate, via contemporaneous X-ray and optical/IR observations, the nearby, pre-main sequence star/disk systems T Chamaeleontis (T Cha) and TWA 30A and 30B. I analyze X-ray and optical emission signatures of accretion and magnetic activity in T Cha, and infer the X-ray absorbing properties of its circumstellar disk. Like T Cha, each component of the wide binary TWA 30A and 30B is viewed through a highly inclined circumstellar disk. Both TWA 30A and 30B display large near-IR variability, suggestive of (respectively) variable obscuration of the stellar photosphere and a possible disk-rim warp. In the case of T Cha and TWA 30A, I find a correlation of optical/near-IR and X-ray extinction consistent with that of photospheric obscuration from an intervening disk clump. ii Acknowledgements There are many people in my life who have helped contribute to this dissertation in their own special way. First and foremost, I would not have been able to succeed in graduate school without the continual support of my family. I am very grateful to my father for providing me with a sense of practicality towards life and to my mother for encouraging me to be creative and to pursue something with the sole requirement that it makes me happy. I am also thankful to my brother and sister who led by example and showed me that receiving good grades in college can be obtained with hard work and dedication. I am extraordinarily thankful for the continual support and guidance from my dissertation advisor Joel H. Kastner. Without our enlightening conversations and his last minute proposal corrections, I would not have become the astronomer I am today. He has provided me many opportunities to advance my career, explore the world, and meet a number of interesting and great people. I look forward to our future collaboration together and I hope I have made his experience at RIT at least a fraction as enjoyable as he made mine. I would also like to thank the continued support and dedication of all RIT faculty/sta↵ involved in the AST graduate program. I am thankful for several friends, students and post doctoral researchers for their friendship and professional support. My first two years at RIT were perhaps the most difficult and I am appreciative of the help from Rodolfo Montez Jr. installing programs, learning IDL and performing Chandra data analyses. He also seemed to know the best places in Rochester to find great beer. I am thankful for advice from Grant Tremblay about applying to postdoc positions and reminding me that there is always plenty of time to accomplish tasks. I appreciate the many conversations and support of fellow graduate students and post docs like Dmitry Vorobiev, Valerie Rapson, Prabath Peiris, Fabio Antonini, Germano Sacco, Rachel Curran, Sravani Vaddi, Billy Vazquez, and Davide Lena. I would also like to acknowledge my friends Ian Strickland, TJ Todd, Bryan Crosby, Colin Kingsley and Rosa Mitsumasu who have helped me in one way or another through my career as a graduate student. Last but certainly not least I would like to thank Kathleen McBennett for her courage and endless support of my desire to learn all I can about the Universe. iii Dedication I dedicate this work to my parents. Their sacrifice a↵orded me the opportunity to pursue excellence. Contents Abstract i Contents iv List of Figures vii 1 Star Formation: An Introduction 1 1.1 Introduction....................................... 1 1.1.1 Star Formation: The Short Story . 1 1.1.2 Context: Why is the Study of Star and Planet Formation Important? . 3 1.2 The Formation and Role of Circumstellar Disks . 4 1.2.1 Circumstellar Disks: Composition and Processes . 4 1.2.1.1 The Role of Dust . 4 1.2.1.2 The Role of Gas . 5 1.2.1.3 Heating the Soup: Photo-ionizing the circumstellar Disk . 7 1.2.1.4 Disk Dissipation . 10 1.2.2 Star-Disk Interactions via Magnetic Fields . 11 1.2.2.1 Relating X-ray Emission Variability to Protostellar Magnetic Activity................................ 15 1.2.2.2 Magnetic Activity in the Lowest Mass Stars . 16 1.2.3 Identifying and Classifying Young Stars . 18 1.2.3.1 X-ray Spectral Modeling . 22 1.2.4 Telescopes and Instruments . 24 1.2.5 CurrentQuestions ............................... 24 2 Star Formation in Orion’s L1630 Cloud: an Infrared and Multi-epoch X-ray Study 28 2.1 Abstract......................................... 28 2.2 Introduction....................................... 29 2.3 Observations and Data Analysis . 32 2.3.1 Spitzer and 2MASS IR Source Classification . 32 2.3.2 Chandra X-ray Analysis . 34 2.4 Results ......................................... 37 iv Contents v 2.4.1 X-ray Characteristics and YSO Class . 37 2.4.2 Individual Sources . 39 2.5 Discussion........................................ 41 2.5.1 L1630 YSO X-ray Detection Fraction . 41 2.5.2 L1630 YSO X-ray Variability by Class . 43 2.5.3 L1630 YSOs X-ray Spectral Characteristics . 45 2.6 Conclusions....................................... 47 3 Investigating the Extreme Variability of the Nearby, Pre-MS Binary TWA 30 84 3.1 Introduction....................................... 84 3.1.1 The Young, Wide, Low-mass Binary System TWA 30 A and B . 85 3.2 Observations ...................................... 86 3.2.1 Near Infrared and Optical . 86 3.2.2 X-rays...................................... 87 3.3 Results.......................................... 89 3.3.1 Near-IR and Optical Spectroscopy . 89 3.3.2 X-ray Properties of TWA 30 A and B . 91 3.3.3 Comparing NH and AV for TWA 30A . 95 3.4 Discussion........................................ 97 3.4.1 Near Infrared and X-ray Variability . 97 3.4.2 Relationship Between Atomic and Optical Extinction . 103 3.4.3 Magnetic Activity of TWA 30A and 30B . 103 3.4.4 Accretion at TWA 30A . 104 3.5 Summary ........................................105 4 Heating the Primordial Soup: X-raying the Circumstellar Disk of T Cha 107 4.1 Introduction.......................................107 4.1.1 T Chamaeleontis . 108 4.2 Observations . 110 4.2.1 X-ray Observations . 110 4.2.2 Optical Spectroscopy . 114 4.3 Results..........................................115 4.3.1 X-ray Properties of T Cha . 115 4.3.2 X-ray Spectral Modeling . 116 4.3.3 Emission Lines in the X-ray Spectrum of T Cha . 117 4.3.4 Optical Spectroscopy of T Cha . 118 4.4 Discussion........................................119 4.4.1 X-rays from T Cha: Coronal Activity vs. Accretion . 119 4.4.2 X-ray and Optical Variability: Signature of Accretion? . 123 4.4.3 Reconstructing the Intrinsic X-ray Spectrum of T Cha . 124 4.5 Summary ........................................128 Contents vi 5 Conclusions and Future Work 134 5.1 Conclusions . 134 5.2 FutureWork ......................................136 5.2.1 Embedded Young Stars in L1630 . 136 5.2.2 X-raying the Disk of T Cha . 136 5.2.3 Investigating Disk Variability in TWA 30A and 30B . 137 5.2.4 Magnetic Activity in Very Low-mass Stars . 137 List of Figures 1.1 Illustration of a cTTS disk from Testi et al. [150] showing the dust grain transport and collision mechanisms (left) where the lengths of the arrows correspond to the velocities of di↵erent grains.