Optical Spectroscopic Studies of Two Star Forming Regions
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Scholars' Mine Doctoral Dissertations Student Theses and Dissertations Fall 2013 Optical spectroscopic studies of two star forming regions Kristen Leilani Erickson Follow this and additional works at: https://scholarsmine.mst.edu/doctoral_dissertations Part of the Physics Commons Department: Physics Recommended Citation Erickson, Kristen Leilani, "Optical spectroscopic studies of two star forming regions" (2013). Doctoral Dissertations. 2231. https://scholarsmine.mst.edu/doctoral_dissertations/2231 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. OPTICAL SPECTROSCOPIC STUDIES OF TWO STAR FORMING REGIONS by KRISTEN LEILANI ERICKSON A DISSERTATION Presented to the Faculty of the Graduate Schools of the MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY and UNIVERSITY OF MISSOURI – ST. LOUIS In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY in PHYSICS 2013 Approved by Dr. Bruce Wilking, Advisor Dr. John Schmitt, Co-Advisor Dr. Erika Gibb Dr. Michael Meyer Dr. Alexey Yamilov iii PUBLICATION DISSERTATION OPTION This dissertation has been prepared in the style utilized by the Astronomical Journal. Pages 21-71 have been published in that journal. Reproduced by permission of the AAS. Pages 72-126 will be submitted for publication in that journal. An Appendix has been added for purposes normal to dissertation writing. iv ABSTRACT The ρ Ophiuchi and Serpens molecular clouds are sites of low mass star formation. The goals of this study were to identify young stellar objects (YSOs) and estimate ages and masses in order to infer an initial mass function (IMF), investigate disk evolution, and determine the star-forming history. Optical spectroscopic surveys of an unbiased sample of candidate young stars have been completed. Optical images taken in different photometric bands were used to create color-magnitude diagrams from which sources were selected for spectroscopic observation. In combination with published data, 135 association members in ρ Ophiuchi and 63 association members plus 16 possible members in Serpens have been identified based on the presence of Hα in emission, lithium absorption, X-ray emission, a mid-infrared excess, and/or reflection nebulosity. Effective temperatures and bolometric luminosities were compared with theoretical tracks and isochrones for pre-main-sequence stars to estimate ages and masses. Both regions have similar median ages, supporting the idea that star formation is a relatively fast process. In ρ Ophiuchi, no age spread was found. In Serpens, an age spread of 1-5 Myrs was found; it could not be determined if this age spread was intrinsic or a result of contamination from foreground young stars. Consistent with these ages similar circumstellar disk frequencies were found. In ρ Ophiuchi, an IMF consistent with the field star IMF for YSOs with masses >0.2 M⊙ was inferred. In Serpens, the IMF was in agreement with the field star IMF for M>1 M⊙. Previous studies of these regions have been biased towards particular stages in the star formation process. This study has provided an unbiased sample of pre-main sequence objects, necessary to obtain a complete picture of star formation. v ACKNOWLEDGMENTS There are many people who have made this dissertation and the research contained within it possible. First and foremost I want to thank my advisor Bruce Wilking. He has been a voice of wisdom throughout the long, difficult and often frustrating process of researching and publishing two papers and turning them into a dissertation. He has shared his data, expertise and ideas with me and kept a sense of humor about the process. I appreciate all his contributions of time, ideas, energy and funding to make my Ph.D. experience productive and interesting. I would additionally like to thank Michael Meyer for his support in the research and especially in the revision process for my work to date. He has made sure that my data is fully explored, my research is properly conducted and my papers are well written truly representing the research, which was done. I would like to thank all my collaborators (Bruce and Michael included); they have shared their data, telescope time, funding and expertise with me. They have also stayed up late with me getting proposals done, worked through the night with me at the telescopes, and guided me when I was stuck in the research process. Thank you also to my dissertation committee for the time and effort you have put into my dissertation, my defense, and me. I would like to thank all the organizations that funded me making my research possible; Sigma Xi Grants in Aid of Research, NASA/ Missouri Space Grant Consortium Fellowship, Chancellor's Graduate Scholars Dissertation Fellowship, NOAO Thesis- student travel fund, and the Missouri Research Board Grant. I would like to thank my entire family for all the help, and guidance through the years. Particularly I would like to thank my father, Richard Kartchner and my grandfather, Frank Nelson for setting up telescopes for me every summer that I was growing up. Thank you to my mother Jean Kartchner for all her imaginative ideas and for always believing in me. Also special thanks to my husband, Todd Erickson for being extremely patient as well as for transforming my computer from a magical black box to a useful tool. Thank you also to my mother in law Susan Erickson for all the many hours of babysitting, with out which I would have never completed this dissertation. vi TABLE OF CONTENTS Page PUBLICATION DISSERTATION OPTION ................................................................... iii ABSTRACT....................................................................................................................... iv ACKNOWLEDGMENTS .................................................................................................. v LIST OF ILLUSTRATIONS............................................................................................. ix LIST OF TABLES............................................................................................................. xi SECTION 1. INTRODUCTION...................................................................................................... 1 1.1. STAR FORMATION ......................................................................................... 1 1.2. STAR FORMATION MECHANISMS.............................................................. 1 1.3. STAR FORMATION AND THE INITIAL MASS FUNCTION ...................... 4 1.4. EVOLUTION OF YOUNG STELLAR OBJECTS ........................................... 8 1.5. THE ρ OPHIUCHI AND SERPENS MOLECULAR CLOUDS ................... 10 1.6. OBJECTIVES AND METHOD ...................................................................... 13 REFERENCES ........................................................................................................ 17 PAPER I. The Initial Mass Function and Disk Frequency of the ρ Ophiuchi Cloud: An Extinction-Limited Sample .......................................................................................... 21 ABSTRACT............................................................................................................. 22 1. Introduction......................................................................................................... 22 2. Observations and Data Reduction........................................................................ 24 2.1. Sample Selection ....................................................................................... 24 2.2. Hydra Observations................................................................................... 26 3. Analysis of the Spectra ........................................................................................ 27 4. Results.................................................................................................................. 28 4.1. Emission-line Spectra................................................................................ 29 4.2. Identification of Pre-main-sequence Association Members ..................... 30 4.3. Distribution of Association Members ....................................................... 31 4.4. Hertzsprung-Russell Diagram ................................................................... 32 4.5. Age Distribution........................................................................................ 34 vii 4.6. An Extinction-limited Sample................................................................... 35 4.6.1. Disk Frequency .............................................................................35 4.6.2. Initial Mass Function ....................................................................37 5. Temporal Relationship with Upper Sco............................................................... 40 6. Summary.............................................................................................................. 42 7. APPENDIX.......................................................................................................... 44 REFERENCES ........................................................................................................ 45 II. A Spectroscopic Survey of the Serpens Main Cluster............................................. 72 ABSTRACT............................................................................................................