X-ray Study of Low-mass Young Stellar Objects in the ρ Ophiuchi ...

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2 CHAPTER 1. INTRODUCTIONIn this thesis, we report results of two deep exposure Chandra observations of ρ Oph. We firstgive brief reviews of low-mass YSOs and ρ Oph in chapters 2 and 3. Details of the Chandra satelliteand its instruments are shown in chapter 4. Chapter 5 describes the method of data analysis andgives source catalogues. Comments on some interesting sources are shown in chapter 6. Then wediscuss overall X-ray properties of YSOs in chapter 7. We further put particular emphasis on theirflare activity and predict the evolution of X-ray activity on YSOs as shown in chapter 8. Finally,chapter 9 gives a brief summary.
Chapter 2Review of Low-mass Young StellarObjects2.1 Evolution of Low-mass StarsThe evolution of low-mass stars (mass = 0.1–1.5 M 1 ⊙ ) is well traced by the locus on the Hertzsprung-Russell (H-R) diagram (Figure 2.1: Hayashi, 1966). Through a dynamical collapse, interstellarmedium starts condensing. The density soon becomes so large that the shock wave emerging atits center propagates towards the outer region, which is followed by a dynamical equilibrium statewith the timescale of ∼10 4 yr. This phase is called “protostars”, the first stage of stars. Protostarsare born at the top-right side in the H-R diagram (higher bolometric luminosity and lowersurface temperature), although we can not see the central sources because of large extinction atdense circumstellar envelope. The main mechanism of energy transportation in the stellar interioris convection (fully convective structure). They evolve along the track of reducing the luminositywith nearly constant temperature (Hayashi track). While moving down on this track, the envelopegradually disappears and the central sources become optically visible (∼10 6 yr), which is called“T Tauri stars (TTSs)”. After 10 7 yr later, the radiative energy transportation becomes dominantand the temperature gradually increases with a constant luminosity (Henyey track: Henyey, Lelevier,& Levée, 1955). During the hydrogen burning (∼10 8 yr), the stars stay at a certain point inthe H-R diagram, which is called “main-sequence stars (MSs)”. Protostars and TTSs are called“pre-main-sequence stars (PMSs)”, or “young stellar objects (YSOs)”.1 The stellar mass normalized by the solar value. 1 M ⊙ = 2.0×10 33 g.3
Page 3: Contents1 Introduction 12 Review of
Page 9 and 10: List of Figures2.1 The H-R diagram
Page 11 and 12: LIST OF FIGURESix6.17 Light curves
Page 13 and 14: List of Tables3.1 Multiwavelength s
Page 15: Chapter 1IntroductionStar formation
Page 19 and 20: 2.1. EVOLUTION OF LOW-MASS STARS 5w
Page 21 and 22: 2.2. MOLECULAR CLOUDS 72.2 Molecula
Page 23 and 24: 2.3. X-RAY OBSERVATIONS OF LOW-MASS
Page 25 and 26: 2.3. X-RAY OBSERVATIONS OF LOW-MASS
Page 27: 2.3. X-RAY OBSERVATIONS OF LOW-MASS
Page 30 and 31: 16 CHAPTER 3. REVIEW OF THE ρ OPHI
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52 CHAPTER 5. CHANDRA OBSERVATIONS
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62 CHAPTER 6. INDIVIDUAL SOURCES6.2
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96 CHAPTER 7. OVERALL FEATURE OF X-
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100 CHAPTER 7. OVERALL FEATURE OF X
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Chapter 8Systematic Study of YSO Fl
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8.2. CORRELATION BETWEEN THE FLARE
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8.3. MAGNETIC RECONNECTION MODEL 11
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8.5. EFFECT OF THE QUIESCENT X-RAYS
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8.6. EVOLUTION OF YSOS AND THEIR FL
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Chapter 9ConclusionWe summarize the
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Appendix AFlare Light CurvesFig. A.
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Fig.A.2 (Continued)121
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Fig. A.4.— Same as Figure A.1, bu
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126 APPENDIX B. PHYSICAL PARAMETERS
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128 APPENDIX B. PHYSICAL PARAMETERS
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Appendix CModeling of the FlareIn t
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C.2. PREDICTED CORRELATIONS BETWEEN
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BibliographyAgeorges, N., Eckart, A
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BIBLIOGRAPHY 137Feigelson, E. D., &
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BIBLIOGRAPHY 139Johnstone, D., Wils
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BIBLIOGRAPHY 141Rutledge, R. E., Ba
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BIBLIOGRAPHY 143Yokoyama, T. & Shib
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