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RCW108CXO - RCW 108 Star Formation Region Chandra X-Ray Point Source Catalog

HEASARC
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Overview

This table contains some of the results of an approximately 90 ks Chandra observation of a complex region that hosts multiple sites of recent and active star formation in ARA OB1a. The field is centered on the embedded cluster RCW 108-IR and includes a large portion of the open cluster NGC 6193. The authors detected over 420 X-ray sources in the field and combined these data with deep near-IR, Spitzer/IRAC and Midcourse Space Experiment (MSX) mid-IR data. They find that about 360 of the X-ray sources have near-IR counterparts. They divide the region into five parts based on the X-ray point source characteristics and extended 8 micron emission. The most clearly defined regions are the central region, identified by embedded sources with high luminosities in the both the near-IR and X-ray as well as high X-ray temperatures (~3 keV), and the eastern region, identified by low extinction and ~1 keV X-ray temperatures. Other regions, identified by their directional relationship to RCW 108-IR, are less uniform, representing combinations of the first two regions, independent star formation epochs, or both. The cluster members range in X-ray luminosity from 10^29 to 10^33 erg s^-1. Over 18% of the cluster members with over 100 counts exhibit flares. All sources with over 350 counts are variable. Overall about 10% (16% in RCW 108-IR) appear to have optically thick disks as derived from their position in the (J - H), (H - K) diagram. The disk fraction becomes much higher when IRAC data are employed. The largest fraction of X-ray sources is best described as possessing some disk material via a more detailed extinction fitting. The authors fit the bulk of the X-ray spectra as absorbed Raymond-Smith-type plasmas, and find that the column to the RCW 108-IR members varies from 10^21 to 10^23 cm^-2. They find that the field contains 41 candidate O or B stars, and estimate that the total number of pre-main-sequence stars in the field is about 1600 +/- 200. Approximately 800 are confined to the 3' (~1.1 pc) central region.

The field was observed by Chandra on 2004 October 25 starting at 02:37 UT for 92.2 ks of total time and 88.8 ks of so-called "good-time" (ObsId 4503). The ACIS was used in the nominal imaging array (chips I0-I3) which provides a field of view of approximately 17' by 17' (~6.5 pc on a side). The aimpoint was at RA, Dec = 16:39:58.7, -48:51:54.4 (J2000.0). In addition, the S2 and S3 chips were on and located over IRAS 16379-4856. About 20 point sources were detected associated with this object; however, the analysis of these data is not presented here because they are far off-axis.


Catalog Bibcode

2008AJ....135..693W

References

X-ray and IR Point Source Identification and Characteristics in the Embedded,
Massive Star-Forming Region RCW 108.
    Wolk, S. J., Spitzbart, B. D.,  Bourke, T. L., Gutermuth, R. A.; Vigil,
    M., Comeron, F.
   <Astron. J., 135, 693-721 (2008)>
   =2008AJ....135..693W

Provenance

This table was created by the HEASARC in June 2008 based on electronic versions of Tables 1, 2, 5, 7, 10 and 11 from the reference paper which were obtained from the Astronomical Journal web site.

Parameters

Source_Number
A unique identification number for each X-ray source in the catalog.

Alt_Name
An alternative name for the X-ray source using the '[WSB2008]' prefix (for Wolk, Spitzbart, Bourke 2008) and the value of the source number parameter, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects, e.g., '[WSB2008] 5'.

Name
The recommended IAU-style name for the X-ray source using the 'CXOWSB' prefix registered with the CDS Dictionary of Nomenclature of Celestial Objects, e.g., 'CXOWSB JHHMMSS.S-DDMMSS'. Notice that in Tables 1 and 2 of the reference paper these names are given with an extra figure of precision in Declination, e.g., 'CXOWSB JHHMMSS.S-DDMMSS.S'.

RA
The Right Ascension of the centroid of the Chandra source in the selected equinox as taken from the WavDetect analysis (see Section 2.1 of the reference paper). The RA was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original Table 1, and to a precision of 0.001 seconds of time in the original Table 2.

Dec
The Declination of the centroid of the Chandra source in the selected equinox as taken from the WavDetect analysis (see Section 2.1 of the reference paper). The Dec was given in J2000.0 coordinates to a precision of 0.01 arcseconds in the original Tables 1 and 2.

LII
The Galactic Longitude of the X-ray source centroid.

BII
The Galactic Latitude of the X-ray source centroid.

Off_Axis
The off-axis angle of the X-ray source, in arcminutes (converted by the HEASARC from the value given in arcseconds in the original tables).

Raw_Counts
The raw counts in the X-ray source. At each source position an extraction ellipse was calculated following Wolk et al. (2006, AJ, 132, 1100) updated for the appropriate satellite roll angle. This provides an extraction ellipse containing 95% of the source flux. The numbers of counts in this region are listed in the raw_counts parameter.

Counts
The net counts in the X-ray source. For each source, a background ellipse is identified. The background is an annular ellipse with the same center, eccentricity, and rotation as the source. The outer radius is six times the radius of the source, and the inner radius is three times larger than the source. From this region any nearby sources are subtracted with ellipses three times the size of the source ellipse. The net counts are calculated by subtracting the background counts (corrected for area) and multiplying the result by 1.053 to correct for the use of a 95% encircled energy radius.

Num_Bayesian_Blocks
This is BB95, the number of Bayesian Blocks of greater than the 95% confidence required to describe the X-ray lightcurve. Any value greater than 1 indicates X-ray variability at or more than a 95% confidence level.

Significance
The X-ray source significance S given by the CIAO tool WavDetect. This is not in units of sigma, so no false alarm probability is associated. While the relative value of the significance is meaningful, it is not clearly defined in a statistical sense (V. Kashyap, private communication). This parameter is given only for the lower significance sources listed in Table 2 of the reference paper which have S <= 3.5, so that a null value implies S > 3.5.

Location
The location of the X-ray source in the field: East, West, North, South or Inner. These regions are depicted in Figure 5 of the reference paper.

Q_25
The bottom 25% energy quartile value, Q_25, i.e., the 25% quartile normalized energy value. In general, the quantile Q_x is defined as (E_x% - E_lo)/(E_hi - E_lo), where E_x% is the energy below which the net counts are x% of the total counts, and E_lo and E_hi are the lower and upper limits to the energy range considered (0.3 and 8.0 keV, respectively, in this case): see Section 3.3 of the reference paper for more details.

Q_25_Error
The uncertainty in the bottom quartile value.

Norm_Median
The normalized median energy m for the source, or Q_50. In general, the quantile Q_x is defined as (E_x% - E_lo)/(E_hi - E_lo), where E_x% is the energy below which the net counts are x% of the total counts, and E_lo and E_hi are the lower and upper limits to the energy range considered (0.3 and 8.0 keV, respectively, in this case): see Section 3.3 of the reference paper for more details.

Norm_Median_Error
The uncertainty in the normalized median energy.

Q_75
The top 75% energy quartile value, Q_75, i.e., the 75% quartile normalized energy value. In general, the quantile Q_x is defined as (E_x% - E_lo)/(E_hi - E_lo), where E_x% is the energy below which the net counts are x% of the total counts, and E_lo and E_hi are the lower and upper limits to the energy range considered (0.3 and 8.0 keV, respectively, in this case): see Section 3.3 of the reference paper for more details.

Q_75_Error
The uncertainty in the top quartile value.

Compressed_Median
The compressed median of the photon energy distribution including background subtraction, defined as log10 (m/(1-m)), where m = Q_50 is the normalized median energy or 50% quartile value given by m = (E_med - 0.3)/(8.0 - 0.3), E_med is the median energy in keV, and 0.3 keV and 8.0 keV are the lower and upper limits to the energy range considered (see Section 3.3 of the reference paper for more details).

Energy_Quartile_Ratio
The normalized quartile ratio of the photon energy distribution, 3 x (Q_25/Q_75), where Q_25 and Q_75 are the 25% and 75% quartile normalized energy values, respectively. In general, the quantile Q_x is defined as (E_x% - E_lo)/(E_hi - E_lo), where E_x% is the energy below which the net counts are x% of the total counts, and E_lo and E_hi are the lower and upper limits to the energy range considered (0.3 and 8.0 keV, respectively, in this case): see Section 3.3 of the reference paper for more details.

Reduced_Chi_Squared
The reduced chi-squared (Chi^2 per degrees of freedom) of the best-fit one-temperature (1T) absorbed Raymond & Smith (RS) plasma spectra model of the X-ray source photon distribution. These models were calculated with C statistics; it is unclear how the reduced chi-squared balue relates to the goodness of fit. The formal errors are unbiased; however, see Section 4 of the reference paper for more details.

NH
The best-fit 1T model absorbing hydrogen column density, in cm^-2.

NH_Error
The uncertainty in the best-fit model absorbing hydrogen column density, in cm^-2.

RS_kT_Limit
This flag is set to '>' if the quoted best-fit 1T RS model temperature is a lower limit rather than an actual value.

RS_kT
The best-fit absorbed 1T RS model temperature, in keV.

RS_kT_Error
The uncertainty in the best-fit absorbed 1T RS model temperature, in keV.

Absorbed_Flux
The absorbed (observed) flux of the X-ray source derived from the best-fit spectral model, in erg/s/cm^2, in the 0.3 - 8.0 keV energy range, presumably.

Flux
The unabsorbed (absorption-corrected) flux of the X-ray source derived from the best-fit spectral model, in erg/s/cm^2, in the 0.3 - 8.0 keV energy range, presumably.

Log_Lx
The logarithm of the X-ray luminosity of the source, in erg/s. This has been calculated using the unabsorbed X-ray flux in the 0.3 - 8.0 keV energy range, presumably, and an assumed distance to RCW 108 of 1.3 kpc.

NIR_Double_Flag
This flag parameter is set to 'a' to indicate that VLT adaptive optics data on the proposed near-infrared counterpart to the X-ray source indicate that it is a double.

RA_NIR_J2000
The J2000 Right Ascension of the near-infrared counterpart to the X-ray source.

Dec_NIR_J2000
The J2000 Declination of the near-infrared counterpart to the X-ray source.

CXO_NIR_Offset
The offset between the near-infrared counterpart and the X-ray source centroid position, in arcseconds.

Jmag
The J-band magnitude of the near-infrared counterpart to the X-ray source.

Jmag_Error
The uncertainty in the J-band magnitude of the near-infrared counterpart to the X-ray source.

Hmag
The H-band magnitude of the near-infrared counterpart to the X-ray source.

Hmag_Error
The uncertainty in the H-band magnitude of the near-infrared counterpart to the X-ray source.

Kmag
The K_S-band magnitude of the near-infrared counterpart to the X-ray source.

Kmag_Error
The uncertainty in the K_S-band magnitude of the near-infrared counterpart to the X-ray source.

NIR_Excess
The amount of infrared excess of the near-IR counterpart to the X-ray source using the reddening-free quantity: Q = (J-H) - 1.70(H-K_S. Values of Q < -0.10 are indicative of an infrared e xcess consistent with a disk. Overall about 33 of the over 330 X-ray sources with good infrared colors (10%) have Q < -0.10. There is some field-to-field variation: in RCW 108-IR the fraction is somewhat higher, 13 out of 81 (16%), the eastern and southern regions have the lowest fraction of low Q sources at about 6%, while the fractions in the west and north are 10% and 13%, respectively. From all of these assessments, it would appear that a relatively small fraction of sources have disks which are optically thick at K_S. However Q cannot distinguish among stars with less extreme optically thick disks. For this, mid-IR data are useful.

Vmag_Extinction
The V-band extinction of the near-IR counterpart to the X-ray source, calculated as per Section 6.2 of the reference paper.

Stellar_Model
The preferred model hypothesis for the near-IR counterpart of the X-ray source, namely, disk, M star or higher-mass star (see SectioThe uncertainty in then 6.2 of the reference paper for more details).

NIR_Flags
This parameter contains flags indicating the quality and/or source of the near-IR data. For photometry taken from 2MASS, it contains the 2MASS quality flags, e.g., AAA, UAB, UAU, AAU, etc, being the listed photometry codes for the JHK channels, respectively, where A means that the error < 10.9%, B, that the error < 15.6%, the E category includes detections where the goodness-of-fit quality of the profile-fit photometry was very poor, and U means an upper limit; otherwise, if the photometry is taken from the NTT or VLT data, the notations "NTT" or "VLT" are used, respectively.

CXO_IRAC_Offset
The offset Between the nearest IRAC counterpart and the X-ray source centroid position, in arcseconds.

IRAC_3p6_um_Mag
The Spitzer/IRAC 3.6-micron band magnitude of the IRAC counterpart to the X-ray source.

IRAC_4p5_um_Mag
The Spitzer/IRAC 4.5-micron magnitude of the IRAC counterpart to the X-ray source.

IRAC_5p8_um_Mag
The Spitzer/IRAC 5.8-micron magnitude of the IRAC counterpart to the X-ray source.

IRAC_8p0_um_Mag
The Spitzer/IRAC 8.0-micron magnitude of the IRAC counterpart to the X-ray source.

IRAC_3p6_um_Mag_Error
The uncertainty in the Spitzer/IRAC 3.6-micron band magnitude.

IRAC_4p5_um_Mag_Error
The uncertainty in the Spitzer/IRAC 4.5-micron band magnitude.

IRAC_5p8_um_Mag_Error
The uncertainty in the Spitzer/IRAC 5.8-micron band magnitude. #

IRAC_8p0_um_Mag_Error
The uncertainty in the Spitzer/IRAC 8.0-micron band magnitude.

IR_Class
The classification of the infrared counterpart to the X-ray source derived from the IRAC photometry, as discussed in Section 6.1 of the reference paper: I, II, or III.

Class
The HEASARC Browse object classification, based on the value of the ir_class parameter.


Contact Person

Questions regarding the RCW108CXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 13-Jun-2008