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J/AJ/132/1100       X-ray and IR sources in RCW 38           (Wolk+, 2006)

X-ray and infrared point source identification and characteristics in the embedded, massive star-forming region RCW 38. Wolk S.J., Spitzbart B.D., Bourke T.L., Alves J. <Astron. J., 132, 1100-1125 (2006)> =2006AJ....132.1100W
ADC_Keywords: H II regions ; Infrared sources ; X-ray sources Keywords: H II regions - ISM: individual (RCW 38) - stars: formation - X-rays: stars Abstract: We report on results of a 96.7ks Chandra observation of one of the youngest, most embedded, and most massive young stellar clusters studied in X-rays: RCW 38. We detect 460 sources in the field, of which 360 are confirmed to be associated with the RCW 38 cluster. The cluster members range in luminosity from 1030 to 1033.5ergs/s. Over 10% of the cluster members with over 100 counts exhibit flares, while about 15% of the cluster members with over 30 counts are variable. Of the sources identified as cluster members, 160 have near-infrared (NIR) counterparts either in the Two Micron All Sky Survey database or detected via Very Large Telescope observations. Of these, about 20% appear to have optically thick disks. An additional 353 members are identified through NIR observations, of which at least 50% possess optically thick disks. We fit over 100 X-ray sources as absorbed Raymond-Smith-type plasmas and find that the column to the cluster members varies from 1021.5 to 1023cm-2. We compare the gas to dust absorption signatures in these stars and find NH=AV(2x1021)cm-2. We find that the cluster contains 31 candidate OB stars and is centered about 10" (0.1pc) west of the primary source of the ionization, the O5 star IRS 2. The cluster has a peak central density of about 400 X-ray sources/pc2. We estimate that the total cluster membership exceeds 2000 stars. Description: Chandra observed RCW 38 on 2001 December 10-11 for 96.7ks (ObsID 2556), using Advanced CCD Imaging Spectrometer (ACIS) chips 0, 1, 2, 3, 6, and 7 in very faint mode. The ACIS combines the ability to image X-rays at a 0.492" plate scale with moderate spectral resolution (R∼3050) and time tagging every 3.2s. The combined field of view (FOV) of the four chips in the imaging array is 16.9'x16.9'. The aim point of the array was 8:59:19.20, -47:30:22.0 (J2000.0), and the satellite roll angle (i.e., orientation of the CCD array relative to the north-south direction) was 51°. The roll angle was selected so that photons from the H II region Bran 213A would strike the ACIS spectroscopic array, whereupon chips 6 and 7 were also turned on. While the H II region was clearly detected, these data are not discussed here, since the mirror point-spread function (PSF) is considerably degraded far off-axis. The focal plane temperature was -119.7°C. The radiation environment was benign. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 59 460 X-ray sources detected in the RCW 38 field table2.dat 44 354 Quartile values of probable cluster members table3.dat 44 99 Quartile values of probable non-members table6.dat 49 187 Cluster members fit with 1 temperature spectra table7.dat 49 159 Faint cluster members fit with 1 temperature spectra table8.dat 49 23 X-ray spectral fits to bright non-member X-Ray sources table9.dat 49 70 X-ray spectral fits to faint non-member sources table10.dat 90 292 IR photometry of X-ray sources (members) table11.dat 90 56 IR photometry of X-Ray sources (non-members) table12.dat 95 364 IR Photometry in the VLT field (non-X-ray sources) table13.dat 70 31 Candidate OB stars in RCW 38
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 3 I3 --- [WSB2006] Running source number 5- 19 A15 --- CXOJ Source name 21 I1 h RAh Hour of Right Ascension (J2000) 23- 24 I2 min RAm Minute of Right Ascension (J2000) 26- 30 F5.2 s RAs Second of Right Ascension (J2000) 32 A1 --- DE- Sign of the Declination (J2000) 33- 34 I2 deg DEd Degree of Declination (J2000) 36- 37 I2 arcmin DEm Arcminute of Declination (J2000) 39- 42 F4.1 arcsec DEs Arcsecond of Declination (J2000) 44- 48 F5.1 arcsec OffAxis Off-axis distance 50- 55 F6.1 ct Ncts Net counts (1) 57 I1 --- B95 Number of intervals of constant flux at 95% significance (2) 59 I1 --- B99 Number of intervals of constant flux at 99% significance (2)
Note (1): Background subtracted and corrected for the aperture size. Note (2): More than one interval indicates a variable source.
Byte-by-byte Description of file: table[23].dat
Bytes Format Units Label Explanations
1- 3 I3 --- [WSB2006] Running source number 5- 8 F4.2 --- Q25 The 25% quartile value 10- 13 F4.2 --- e_Q25 Error in Q25 15- 18 F4.2 --- m The median quartile (=Q50) 20- 23 F4.2 --- e_m Error in m 25- 28 F4.2 --- Q75 The 75% quartile value 30- 33 F4.2 --- e_Q75 Error in Q75 35- 39 F5.2 [-] log(m/(1-m)) Log of the m/(1-m) value 41- 44 F4.2 --- Ratio The 3*Q25/Q75 ratio
Byte-by-byte Description of file: table[6789].dat
Bytes Format Units Label Explanations
1- 3 I3 --- [WSB2006] Running source number 5- 9 F5.2 --- chi2/dof The chi^2^ per d.o.f. (1) 11- 15 F5.2 10+22cm-2 NH Model hydrogen column density 17- 21 F5.2 10+22cm-2 e_NH ? Error in NH 23 A1 --- l_kT Limit flag on kT 24- 29 F6.2 keV kT Raymond-Smith model temperature 31 A1 --- f_kT Indicates lower limit on the error in kT 32- 36 F5.2 keV e_kT ? Error in kT 38- 43 F6.2 [mW/m2] logF Log of the unabsorbed flux in units of ergs/cm2/s 45- 49 F5.2 [10-7W] logL ? Log of the luminosity in units of erg/s (2)
Note (1): Goodness of fit to an absorbed one-temperature Raymond-Smith plasma. Note (2): Calculated based on the derived unabsorbed flux and the cluster distance of 1.7kpc.
Byte-by-byte Description of file: table1[01].dat
Bytes Format Units Label Explanations
1- 3 I3 --- [WSB2006] Running source number 5- 28 A24 --- IRName Infrared identification 30- 33 F4.2 --- Offset X-ray and IR position offset 35- 40 F6.3 mag Jmag ? The J band magnitude 42- 46 F5.3 mag e_Jmag ? Error in Jmag 48- 53 F6.3 mag Hmag ? The H band magnitude 55- 59 F5.3 mag e_Hmag ? Error in Hmag 61- 66 F6.3 mag Kmag ? The K band magnitude 68- 72 F5.3 mag e_Kmag ? Error in Kmag 74- 78 F5.2 mag AV ? The V band extinction 80- 86 A7 --- Model Type of emitting surface assumed (1) 88- 90 A3 --- Flags Additional flags (2)
Note (1): Model flag as follows: M STAR = a cool M star photosphere; bright = a higher mass star photosphere; Bright = a star + disk combination; GK STAR = inferred spectral type on the main sequence. Note (2): If the source is from 2MASS then these are the 2MASS flags. If the source is from VLT then there is no color correction.
Byte-by-byte Description of file: table12.dat
Bytes Format Units Label Explanations
1- 3 A3 --- --- [VLT] 5- 24 A20 --- IRName Infrared identification (JHHMMSS.ss+DDMMSS.s) 26- 27 I2 h RAh Hour of Right Ascension (J2000) 29- 30 I2 min RAm Minute of Right Ascension (J2000) 32- 37 F6.3 s RAs Second of Right Ascension (J2000) 39 A1 --- DE- Sign of the Declination (J2000) 40- 41 I2 deg DEd Degree of Declination (J2000) 43- 44 I2 arcmin DEm Arcminute of Declination (J2000) 46- 50 F5.2 arcsec DEs Arcsecond of Declination (J2000) 52- 57 F6.3 mag Jmag The J band magnitude 59- 63 F5.3 mag e_Jmag Error in Jmag 65- 70 F6.3 mag Hmag The H band magnitude 72- 76 F5.3 mag e_Hmag Error in Hmag 78- 83 F6.3 mag Kmag The K band magnitude 85- 89 F5.3 mag e_Kmag Error in Kmag 91- 95 F5.2 mag AV The minimum V band extinction
Byte-by-byte Description of file: table13.dat
Bytes Format Units Label Explanations
1- 3 I3 --- [WSB2006] ? Running source number 5- 11 A7 --- VLT VLT number for the two VLT-only sources (VLT NNN) 13- 14 I2 h RAh Right ascension (J2000.0) 16- 17 I2 min RAm Right ascension (J2000.0) 19- 23 F5.2 s RAs Right ascension (J2000.0) 25 A1 --- DE- Declination sign (J2000.0) 26- 27 I2 deg DEd Declination (J2000.0) 29- 30 I2 arcmin DEm Declination (J2000.0) 32- 35 F4.1 arcsec DEs Declination (J2000.0) 37- 41 F5.1 arcsec OffAxis Distance from the cluster center 43- 46 F4.1 mag AV(IR) ?=- V band extinction derived from the IR method 48- 52 F5.1 mag AV(NH) ?=- V band extinction derived from the X-ray method 54- 58 F5.2 mag KsMAG ?=- Absolute Ks magnitude 60- 63 F4.2 [solLum] logLbol Bolometric luminosity 65 A1 --- l_log(LX/Lbol) Limit flag on log(LX/Lbol) 66- 70 F5.2 [-] log(LX/Lbol) X-ray-to-bolometric luminosity ratio
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 25-Apr-2008
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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