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

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72 CHAPTER 6. INDIVIDUAL SOURCES6.3 Other T Tauri Stars6.3.1 A-20 – GY12A class III source GY12 (GSS30-IRS2) shows three flares in obs-A (Figure A.3). GY12 was alsodetected at the ACIS-S2 chip in obs-BF, hence we make light curve and time-sliced spectra asshown in Figure 6.10. Since N H of 3.6 +0.1−0.2 ×1022 cm −2 is the same as A-20, the X-ray emittingsource in obs-BF is surely GY12 regardless of the large positional uncertainty. In Figure 6.10, wedetect four flares with our criterion (§5.5). We therefore conclude that GY12 is an X-ray activesource showing frequent flare activity, 3–4 flares per 100 ks.Near GY12, two class I sources GSS30-IRS1 and LFAM1 = GSS30-IRS3 are located with therespective separation angles of ∼17 ′′ and ∼10 ′′ from GY12. Also, CO observations revealed theexpanding shell around them with the radius and expanding velocity of ∼15 ′′ ( ∼ = 2000 AU) and∼0.7 km s −1 (Zhang et al., 1997), which is probably due to cloud disruption as a result of youngstar formation. Although we see no significant X-rays from the two class I sources and from theshell for both observations, it may be conceivable for future works whether or not such complexsystems affect the high flare frequency of GY12.Fig. 6.10.— (top) Light curve in 0.5–9.0 keVand (middle and bottom) time evolution ofkT and EM of GY12 in obs-BF. Flare timebins (§5.5) are represented by arrows.
6.3. OTHER T TAURI STARS 736.3.2 A-23 – GY21A class II A-23 = GY21 shows two flares in obs-A (FigureA.1). The spectra show strong He-like Fe emission at∼6.7 keV both in the flare and quiescent phases (Figure6.11). We hence fit them by the MEKAL model with theabundance to be free and obtain significantly higher valuesthan the other sources; 1.0 (0.5–1.6), 3.5 (>0.6), and(2.9 +0.4−0.3 keV) and < L X > (9.1×10 30 ergs s −1 ) are significantlylarger than those in the quiescent phase of obs-A,while the abundance is lower (0.2±0.1 solar). Since theabsorption is nearly the same (4.2 +0.2−0.3 ×1022 cm −2 ), it isless possible that another source emits X-rays in obs-BFFig. 6.12.— Time-averaged spectrum ofA-24 = S2. Prominent line emission isseen at ∼ 6.7 keV.
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Contents1 Introduction 12 Review of
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List of Figures2.1 The H-R diagram
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LIST OF FIGURESix6.17 Light curves
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List of Tables3.1 Multiwavelength s
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Chapter 1IntroductionStar formation
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Chapter 2Review of Low-mass Young S
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2.1. EVOLUTION OF LOW-MASS STARS 5w
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2.2. MOLECULAR CLOUDS 72.2 Molecula
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2.3. X-RAY OBSERVATIONS OF LOW-MASS
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16 CHAPTER 3. REVIEW OF THE ρ OPHI
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Page 36 and 37: 22 CHAPTER 4. INSTRUMENTATIONrespec
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Page 46 and 47: 32 CHAPTER 5. CHANDRA OBSERVATIONS
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Page 121 and 122: Chapter 8Systematic Study of YSO Fl
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Page 129 and 130: 8.6. EVOLUTION OF YSOS AND THEIR FL
Page 131 and 132: Chapter 9ConclusionWe summarize the
Page 133 and 134: Appendix AFlare Light CurvesFig. A.
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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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