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

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90 CHAPTER 6. INDIVIDUAL SOURCESThe average temperature of the soft-band unidentified sources is ∼0.2 keV, which is significantlylower than those of YSOs, although the data excess around 1–2 keV (Figure 6.23a) indicatesthe existence of higher temperature component of < kT > = 1–2 keV. Considering the low temperatureplasma and small absorption column (∼ 2×10 21 cm −2 ), one plausible idea is coronal emissionof MS stars in front of the ρ Oph cloud. However, it would be less possible because there is nooptical counterpart (Chini, 1981). Another idea is that an outflow from YSOs in ρ Oph collides ata dense interstellar matter and makes a low temperature (0.1–0.5 keV) plasma, like X-ray emissionfrom Herbig-Haro objects (HHs: Pravdo et al., 2001; Favata et al., 2002). In particular, A-S1 islocated in the direction of CO outflow from the class 0 source VLA1623 (Figure 6.25), hence is astrong candidate of jet-induced X-rays. The average flux (absorption-corrected) per one source of1.4×10 −15 ergs s −1 cm −2 is converted to < L X > of 3.5×10 27 ergs s −1 assuming the distance of145 pc, which is about 100 times lower than those of HHs (∼ 10 29 ergs s −1 ). This indicates thatthe emitting region of soft-band unidentified sources has smaller volume and/or density than thatof HHs.The hard-band unidentified sources show nearly the same spectral parameters as the totalbandsources, although the average flux is about four times lower, hence are also thought to bebackground AGNs.Fig. 6.24.— Spatial distribution of unidentified sources overlaid on the 1.3 mm continuum map(Motte et al., 1998). Crosses, squares, and diamonds represent total-band, soft-band, and hardbandunidentified sources, respectively.
6.6. UNIDENTIFIED SOURCES 91Fig. 6.25.— ACIS image around the ρ Ophcore A region in 0.5–2.0 keV. Solid, dotted,and dashed contours show 1.3 mm radio continuum,blueshifted and redshifted CO (2–1)intensities, respectively (André et al., 1993).Arrows indicate the positions of the class 0source VLA1623 and mm cores (SM1, SM1N,and SM2). The position of A-S1 is shown bythe circle.Table 6.7: Best-fit parameters of the composite spectra of unidentified sourcesClass * N † < kT >/Γ ‡§ N H§Flux ‖ Flux c#(keV/–) (10 22 cm −2 ) (10 −15 ergs s −1 cm −2 )Total 60 1.5(1.1–1.7) 5.3(4.2–6.6) 441.7(7.4) 905.3(15.1)Soft 10 0.16(0.042–0.26) 0.20(
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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 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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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
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BIBLIOGRAPHY 141Rutledge, R. E., Ba
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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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