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

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84 CHAPTER 6. INDIVIDUAL SOURCES6.5.3 X-ray spectra and luminositiesFigure 6.20 shows the X-ray spectra of A-29, A-31, and BF-36 during the flare phases and thatof BF-36 in quiescent. We fit them by the MEKAL model with the fixed abundance of 0.3 solar.However, reasonable constraint can not be obtained on < kT > and N H with the limited statisticsfor A-29 and A-31. We hence fix the temperature at three typical values (1, 5, and 10 keV) of theother X-ray sources. The 1 keV temperature is typical of class II–III sources in quiescent, whilesome flares from class I–II sources have the 5 keV temperature and extremely high temperatureof 10 keV is found in some giant flares; e.g., YLW16A = BF-64 (§6.1.5). Although all fittingsare acceptable, the assumed temperature of 1 keV gives uncomfortably high luminosity of (4–7)×10 31 ergs s −1 , hence we discard the case of the 1 keV temperature. Table 6.6 shows the best-fitparameters, while the best-fit models (5 keV models for A-29 and A-31) are shown in Figure 6.20.For the quiescent phase of A-29 and A-31, we assume the same parameters as those of the flare.Since no significant X-ray is found in the quiescent phase for A-31, we estimate the 99.9 % upperlimit of the X-ray luminosity (Table 6.6). The quiescent luminosities are 2–30 times lower thanthose in the flare phases.Table 6.6: Spectral parameters of A-29, A-31, and BF-36No. Cts * < kT > ‡ N H‡< L X >(flare) ‡§ < L X >(quiescent) §(keV) (10 52 cm −3 ) (10 23 cm −2 ) (10 29 ergs s −1 ) (10 29 ergs s −1 )A-29 † . . . . . . . . . . . 21(5) 5 7.5(3.1–16) 2.5(1.3–4.7) 11 0.37· · · 10 5.0(2.1–10) 2.2(1.1–4.4) 8.1 0.27A-31 † . . . . . . . . . . . 10(2) 5 5.0(0.53–110) 5.4(1.5–20) 6.9 in the quiescent phase for A-29 and A-31 isderived with the assumption of the same absorption as that in the flare phase.‖ Derived by the simultaneous fitting of the flare and quiescent spectra.
6.5. NEW YSO CANDIDATES – A-29, A-31, AND BF-36 85A-29 A-31 BF-36Fig. 6.20.— X-ray spectra of (left) A-29, (middle) A-31, and (right) BF-36. Black and gray linesindicate spectra of the flare and quiescent phases, respectively. The upper panels show the datapoints (crosses) and the best-fit MEKAL models (solid line). For A-29 and A-31, we show thebest-fit models with the assumed 5 keV temperature. The lower panels are the data residuals fromthe model.6.5.4 Possible origin of A-29, A-31, and BF-36A-29A-29 is found near the center of the 850 µm core SMM J16264−2424 with the separation angleof ∼11 ′′ . This is larger than the position accuracy of Chandra but is comparable to that of thebeam size of the 850µm observation (∼14 ′′ , SCUBA). Assuming a uniform density core, the columndensity of SMM J16264−2424 is estimated to be ∼10 23 cm −2 from the radio flux (Johnstone et al.,2000), which is consistent with the X-ray-determined N H of A-29 (∼ 2×10 23 cm −2 ) within largeuncertainty for both the values. It is hence highly possible that A-29 is located in or behind SMMJ16264−2424. Using the LogN–logS relation by Mushotzky et al. (2000), we estimate the chanceprobability to detect a background AGN within the ∼11 ′′ radius to be ∼5 %. Although this valueis relatively large, A-29 shows a clear X-ray flare typical of low-mass stars but not seen in usualAGNs (Figure 6.19). No NIR counterpart of K < 15 mag, the association with the sub-millimetercore SMM J16264−2424, and the large absorption lead us to conclude that the origin of A-29 is anembedded star younger than class I.A-31A-31 is located within ∼2 ′′ from the center of the 3 mm clump KSHK-A (Kamazaki et al., 2001),the central source of millimeter/sub-millimeter clump SM1/SMM J16264−2423 (Johnstone et al.,2000). Taking into account of the physical size of KSHK-A (∼4 ′′ ) and position uncertainty ofChandra and the Nobeyama Millimeter Array interferometer observation (∼5 ′′ ), we can conclude
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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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¨28 CHAPTER 4. INSTRUMENTATIONspli
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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
Page 123 and 124: 8.2. CORRELATION BETWEEN THE FLARE
Page 125 and 126: 8.3. MAGNETIC RECONNECTION MODEL 11
Page 127 and 128: 8.5. EFFECT OF THE QUIESCENT X-RAYS
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 137: Fig. A.4.— Same as Figure A.1, bu
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Page 145 and 146: Appendix CModeling of the FlareIn t
Page 147 and 148: 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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