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

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96 CHAPTER 7. OVERALL FEATURE OF X-RAY EMISSION FROM YSOSTable 7.1: The number of X-ray sources and detection rate for each classClass Source * X-ray † Ratio ‡I . . . . . . . . . . . . . . . 15 8 53 %II . . . . . . . . . . . . . . 70 58 83 %III . . . . . . . . . . . . . . 17 17 100 %III c . . . . . . . . . . . . . 27 9 33 %Unclassified NIR · · · 12 · · ·BD&BD c . . . . . . . 15 5 33 %F . . . . . . . . . . . . . . . 3 1 33 %unidentified . . . . · · · 85 · · ·* The number of sources within the ACIS field of view.† The number of X-ray detected sources.‡ The X-ray detection rate.Fig. 7.1.— Relation between the bolometric luminosity (L bol ) and visual extinction (A V : Bontempset al., 2001, see also TableB.1). Circles, triangles, squares, and stars represent class I, class II, classIII+III c , and BD/BD c sources, respectively. Gray symbols are sources with no X-ray detection.Three X-ray non-detected class I sources with relatively high L bol are also indicated (GSS30, GY304,and GY378).
7.2. LUMINOSITY FUNCTION 977.2 Luminosity FunctionFig. 7.2.— Normalized X-ray luminosity functions of class I (dashed), class II (dash-dotted), andclass III (solid) sources in the (a) quiescent and (b) flare phases. The mean value (Mean) andstandard deviation (σ) of log[< L X >] in the unit of ergs s −1 for each class are shown in the figures.Parentheses indicate errors of the mean values.We calculate the X-ray luminosity function for the detected X-ray sources of class I, II, andIII+III c (Figure 7.2), using the ASURV statistical software package (rev.1.2) 1 based on the maximumlikelihood Kaplan-Meier estimator in order to examine the differences along the evolutionalstages. The luminosity function of class I seems to be shifted toward the higher values than thoseof class II and III+III c both in the quiescent and flare phases.To be more quantitative, we estimate the significance level using two nonparametric two-sampletests in ASURV; the Gehan’s generalized Wilcoxon test (GW) and the logrank test (Feigelson &Nelson, 1985). The results are given in Table 7.2, where blank (...) indicates that the significancelevel is less than 90 %. From Table 7.2, we see that both the GW and logrank tests for the < L X >difference between class I and the others in the flares show the marginal significance level of ∼94 %.We further should note that the effect of “undetected” faint flares of class I can not be ignored; ifwe assume an undetected class I has < L X > smaller than 10 30 ergs s −1 which is near the detectionthreshold of a class I flare, and add this source to the GW and logrank test sample, then therelevant significance level is largely reduced to < 90 %. We hence conclude that the higher < L X >of class I than class II+III during flares is marginal.On the other hand, from Table 7.2, we see no significant difference between class II andIII+III c source in the flare phase. This is contrary to the results of the Taurus-Auriga-Perseus1 see http://www.astro.psu.edu/statcodes.
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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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22 CHAPTER 4. INSTRUMENTATIONrespec
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24 CHAPTER 4. INSTRUMENTATIONangle
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26 CHAPTER 4. INSTRUMENTATIONThe AC
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30 CHAPTER 4. INSTRUMENTATIONTable
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32 CHAPTER 5. CHANDRA OBSERVATIONS
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Page 121 and 122: Chapter 8Systematic Study of YSO Fl
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Page 131 and 132: Chapter 9ConclusionWe summarize the
Page 133 and 134: Appendix AFlare Light CurvesFig. A.
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Page 145 and 146: Appendix CModeling of the FlareIn t
Page 147 and 148: C.2. PREDICTED CORRELATIONS BETWEEN
Page 149 and 150: BibliographyAgeorges, N., Eckart, A
Page 151 and 152: BIBLIOGRAPHY 137Feigelson, E. D., &
Page 153 and 154: BIBLIOGRAPHY 139Johnstone, D., Wils
Page 155 and 156: BIBLIOGRAPHY 141Rutledge, R. E., Ba
Page 157: BIBLIOGRAPHY 143Yokoyama, T. & Shib
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