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J/PASJ/55/653    Chandra X-ray flares in rho Ophiuchi    (Imanishi+, 2003)

A systematic study of X-ray flares from low-mass young stellar objects in the rho Ophiuchi star-forming region with Chandra. Imanishi K., Nakajima H., Tsujimoto M., Koyama K., Tsuboi Y. <Publ. Astron. Soc. Jap., 55, 653 (2003)> =2003PASJ...55..653I
ADC_Keywords: YSOs ; Stars, pre-main sequence ; Stars, flare ; X-ray sources Keywords: ISM: clouds - ISM: individual (rho Ophiuchi cloud) - stars: flare - stars: pre-main-sequence - X-rays: stars Abstract: We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the ρ Ophiuchi star-forming cloud. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Description: The Chandra X-ray Observatory (Weisskopf et al., 2002PASP..114....1W) observed the central region of Oph twice with a deep exposure of the ACIS-I array, consisting of four abutted X-ray CCDs. The first observation (here and after, obs. BF) covered the south-east 17.4'x17.4' area, including cores B, C, E, and F, while the second observation (obs. A) covered the north-west area centered on core A (Loren et al., 1990ApJ...365..269L). Although some of the ACIS-S chips were simultaneously in operation, we do not use these data because large off-axis angles cause a degeneration of the sensitivity and position determination. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 150 306 Chandra X-ray sources in the rho Oph region table3.dat 137 204 Identifications of the X-ray sources
See also: B/chandra : The Chandra Archive Log (CXC, 1999-) J/A+A/359/113 : X-ray and IR study of Rho Oph dark cloud (Grosso+, 2000) J/ApJ/438/813 : Stellar population in ρ Oph cloud core (Strom+, 1995) J/ApJ/630/381 : Mid-IR imaging in ρ Oph (Barsony+, 2005) J/ApJS/112/109 : Rho Oph Near IR Positions and Photometry (Barsony+, 1997) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 5 A5 --- [INT2003] Source designation (G1) (1) 7- 8 A2 --- n_[INT2003] Note on [INT2003] (2) 10- 16 F7.1 ct Count Background-subtracted ACIS-I counts (3) 17- 19 A3 --- n_Count Note on Count (4) 21- 22 I2 h RAh Right ascension (J2000) 24- 25 I2 min RAm Right ascension (J2000) 27- 31 F5.2 s RAs Right ascension (J2000) 33 A1 --- DE- Declination sign (J2000) 34- 35 I2 deg DEd Declination (J2000) 37- 38 I2 arcmin DEm Declination (J2000) 40- 43 F4.1 arcsec DEs Declination (J2000) 45 A1 --- l_<kT> Limit flag on <kT> 46- 50 F5.2 keV <kT> ? Time-averaged temperature 52 A1 --- l_kTl Limit flag on kTl 53- 56 F4.2 keV kTl ? 90% confidence lower limit of kT 58- 62 F5.2 keV kTu ? 90% confidence upper limit of kT 63 A1 --- n_<kT> [f] f for fixed 65- 68 F4.1 [cm-3] log<EM> ? Mean emission measure 70 A1 --- l_logEMl Limit flag on logEMl 71- 74 F4.1 [cm-3] logEMl ? 90% confidence lower limit of logEM 76- 79 F4.1 [cm-3] logEMu ? 90% confidence upper limit of logEM 81- 86 F6.3 10+22cm-2 NH ? Absorption hydrogen column density 88 A1 --- l_NHl Limit flag on NHl 89- 95 F7.3 10+22cm-2 NHl ? 90% confidence lower limit of NH 97-102 F6.2 10+22cm-2 NHu ? 90% confidence upper limit of NH 103-109 F7.2 10-17W/m2 Flux ? Observed flux in 0.5-9.0keV 111-118 F8.3 10+22W <LX> ? Mean absorption-corrected X-ray luminosity in 0.5-9.0keV 120-123 F4.2 --- Chi2 ? Reduced χ2 for the spectral fittings 125-127 I3 --- DOF ? Degree of freedom 129-150 A22 --- Com Comments
Note (1): Different measurements are made for the same source (the name and position of the source are repeated). Note (2): Notes as follows: a = We determine spectral parameters with fixed temperatures of 1keV and 5keV (see text). For sources which only show the parameters for kT=1 or 5keV, no good fitting is obtained for the other temperature. b = We assume the same abundances as the ``F2'' phase in Imanishi et al. (2002ApJ...572..300I). The quiescent spectrum is not obtained because the decay phases of the two flares occupy all of the light curve. d = No spectral fit is done due to the limited statistics e = Abundances are free parameters (see sub-subsection 4.8.1 in Paper I, Imanishi et al., 2001ApJ...557..747I and Imanishi, 2003, PhD Thesis, Kyoto University) f = We make the flare spectra with a bit larger time scale in order to obtain as good statistics as possible. Errors of <EM> for A-29 in the quiescent are not determined because of the limited statistics g = The spectra show possible edge absorption of neutral Ca or warm Ar. The non-thermal model also well reproduces the spectra (Hamaguchi, Imanishi, 2002, PASJ, submitted) h = We assume the same temperature because of the limited statistics. i = These show non-thermal spectra (Imanishi, 2003, PhD Thesis, Kyoto University) k = Imanishi et al. (2002ApJ...572..300I) proposed two-temperature model with an unusual abundance pattern l = Foreground star. The distance is 60pc (Festin, 1998A&A...336..883F) m = The best-fit value of <kT> is not determined (larger than 10keV), hence we assume 10keV temperature for the estimation of the other parameters. n = NH and reduced-chi2 are estimated by the simultaneous fittings with the identical sources in obs. A. Note (3): X-ray counts in 0.5-2.0keV, 2.0-9.0keV, and 0.5-9.0keV for soft-band, hard-band, and the other sources, respectively. The soft-band and hard-band sources are indicated by the prefixes "S" and "H". Note (4): Note on Count as follows: (m) = denotes sources with marginal detections (the confidence level <99.9%, see subsection 3). Although the confidence levels of A-48 and A-H2 are significant enough, we regard them as marginal sources because of the larger source size (A-48) and severe contamination from A-2 (A-H2). ++ = The pile-up effect is not corrected
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 5 A5 --- [INT2003] Source designation (G1) 7- 10 F4.2 arcsec o2MASS ? Offset between the Chandra and nearest 2MASS sources (Cat. II/246) 11- 13 A3 --- n_o2MASS [(R)# ] Note on o2MASS (2) 15- 25 A11 --- RNames Radio source names, separated by comma (3) 27- 33 A7 --- PSPC X-ray source detected by ROSAT/PSPC (Casanova et al., 1995ApJ...439..752C, ROXR1 NN or ROXR1 CNN) 35- 37 A3 --- HRI X-ray source detected by ROSAT/HRI (Grosso et al., 2000, Cat. J/A+A/359/113, ROXRA NN or ROXRF NN) 38 A1 --- n_HRI [*] From Grosso (2001A&A...370L..22G) 40- 41 A2 --- ASCA X-ray source detected by ASCA (Katama et al., 1997PASJ...49..461K, ROXA NNA or ROXA CN) 42 A1 --- n_ASCA [+] +: From Tsuboi et al., 2000ApJ...532.1089T 44- 45 I2 --- [IKT2001] ? Chandra sources already listed in Paper I, Imanishi et al., 2001ApJ...557..747I 47-121 A75 --- ONames Other names (4) 122 A1 --- n_ONames [+S] Note on ONames (5) 124-136 A13 --- Class Classification of the source (6) 137 A1 --- n_Class [a] a: From NIR spectroscopy (7)
Note (2): Note on o2MASS as follows: (R) = for sources having a radio counterpart only, the offset between the Chandra and radio sources (Andre et al., 1987AJ.....93.1182A) are shown. # = Offset from a nearest NIR source in Greene and Young (1992ApJ...395..516G). Note (3): S, R, and L indicate sources listed as follows in: R = Andre et al. (1987AJ.....93.1182A) (ROC NN) S = Stine et al. (1988AJ.....96.1394S) (SFAM NN) L = Leous et al. (1991ApJ...379..683L) (LFAM NN) Lp denotes possible radio sources in LFAM. Note (4): Source names used in the literature; abbreviations for names are: SR: Struve, Rudkjobing, 1949ApJ...109...92S DoAr: Dolidze, Arakelyan, 1959AZh....36..444D ROXs: Bouvier, Appenzeller, 1992A&AS...92..481B S: Grasdalen et al., 1973ApJ...184L..53G YLW: Young et al., 1986ApJ...304L..45Y GY: Greene, Young, 1992ApJ...395..516G WL: Wilking, Lada, 1983ApJ...274..698W VSSG: Vrba et al., 1975ApJ...197...77V GSS: Grasdalen et al., 1973ApJ...184L..53G Elias: Elias, 1978ApJ...224..453E BBRCG: Barsony et al., 1989ApJ...346L..93B CRBR: Comeron et al., 1993ApJ...416..185C SKS: Strom et al., 1995, Cat. J/ApJ/438/813 IRS: Wilking et al., 1989ApJ...340..823W ISO: Bontemps et al., 2001, Cat. J/A+A/372/173 For sources having NIR counterpart only in the 2MASS catalog, we alternatively show the 2MASS source names. Note (5): Note on ONames as follows: + = The position of GY5 (Greene, Young, 1992ApJ...395..516G) is slightly shifted (∼2.3") from the 2MASS source. S = A candidate of HH object (Gomez et al., 1998AJ....115.2018G). Note (6): Source classifications as follows: I = class I YSO (infall envelope and accretion disk) II = class II YSO (accretion disk) III = class III YSO (remnant or absent accretion disk) IIIc = class III candidate (table 5 in Bontemps et al., 2001, Cat. J/A+A/372/173) BD = brown dwarf BDc = brown dwarf candidate (Imanishi et al., 2001ApJ...563..361I) F = foreground star (Festin, 1998A&A...336..883F). Unclassified NIR sources are indicated by "?", and sources with no NIR counterpart are called "unidentified sources", and have a blank field. For BD/BD_cs, we show the available IR classification in Bontemps et al. (2001, Cat. J/A+A/372/173) in the parentheses. Note (7): Wilking et al. (1999AJ....117..469W) derived for these M dwarfs masses higher than the hydrogen burning limit.
Global notes: Note (G1): The sources of the first observation are labelled A-NN (NN=1 to 84), A-HN (N=-1-5) for the hard (2.0-9.0keV) band, A-SN (N=-1-5) for the soft (0.5-2.0keV) band. The sources of the second observation are labelled BF-NN (1-98), BF-HN (N=1-4) for the hard (2.0-9.0keV) band, BF-SN (N=1-8) for the soft (0.5-2.0keV) band.
History: From electronic version of the journal
(End) James Marcout, Patricia Bauer [CDS] 21-Nov-2003
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