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

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114 CHAPTER 8. SYSTEMATIC STUDY OF YSO FLARESAlthough there are slight differences between these values and the previous results, the relativetendency is the same; higher B for younger sources and almost comparable L to the stellar size.We hence conclude that, even if we use the quiescent spectra as the background level for theflare spectra, the main results in the previous section are not affected so seriously.Fig. 8.4.— Same as Figure 7.4(b), but for the fitting results when the quiescent X-rays are used asbackground spectra.Fig. 8.5.— Same as Figure 8.2, but for the resultswhen the quiescent X-rays are used as backgroundspectra. Symbols are the same as Figure 7.6. Thedashed and solid lines are the constant L and Blines derived by Eqs.(C.15) and (C.14).
8.6. EVOLUTION OF YSOS AND THEIR FLARE ACTIVITY 1158.6 Evolution of YSOs and Their Flare ActivityCombining all the results discussed in the previous sections, we propose a simple view of theevolution of flare activity on low-mass objects as follows. In their earlier stage (class I), sources haverelatively strong magnetic field (≈500 G) and show frequent X-ray flares with higher temperature(≈5 keV). As stars evolve (class II and IIIs), the magnetic field gradually decreases (200–300 G)and makes moderate temperature plasma (2–4 keV) via X-ray flares. During these phases (classI–III), the length of the flare loop does not change significantly (10 10 –10 11 cm). As approachingto the main-sequence stage, the magnetic field and length of the flare loop are becoming weak(50–150 G for the sun) and short (10 8 –10 9 cm), which causes lower plasma temperature (0.1–1keV) and shorter flare timescales (10–100 s) as seen in the sun.B(G)PMSMSlog[L(cm)]1000binary?RS CVn1110single9100sun84 5 6 7 8log[Age(yr)]Fig. 8.6.— Schematic view of the evolution of X-ray flares of low-mass objects. Thick solid anddashed lines represent the predicted evolution of the magnetic field strength (B) and loop length(L), respectively.We should note that the flare from the class 0 candidate A-29 (§6.5) has relatively short rise anddecay timescales (1–2 ks). Although we could not plot the data of the A-29 flare in the < kT >–τ rplane because < kT > is not determined due to the limited statistics, the small τ r value predictsthat A-29 has a large magnetic field; if < kT > is larger than 10 keV, the expected B value is1000 G, which may be the initial value of magnetic field in the YSO evolution.Generally, RS CVn systems show smaller flare timescales than YSOs (∼100 s), while < kT >is comparable (∼5 keV). Based on the above idea, this may be due to larger B value. In fact,
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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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62 CHAPTER 6. INDIVIDUAL SOURCES6.2
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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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X-ray Study of Low-mass Young Stellar Objects in the ρ Ophiuchi ...

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