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LKHA101CXO - LkH-alpha 101 Star Formation Region Chandra X-Ray Point Source Catalog

HEASARC
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Overview

This table contains some of the results from a multiwavelength study of a partially embedded region of star formation centered on the Herbig Be star LkH-alpha 101. Using two 40 ks Chandra observations, The authors have detected 213 X-ray sources in the ~ 17' x 17' ACIS-I field. They combine the X-ray data with Two Micron All Sky Survey (2MASS) near-IR observations and Spitzer Space Telescope (SST) IRAC and MIPS 24-micron observations to obtain a complete picture of the cluster. A total of 158 of the X-ray sources have infrared counterparts. Of these, the authors find nine protostars, 48 Class II objects, five transition objects, and 72 Class III objects. From the Spitzer data, they identify an additional 10 protostars, 53 Class II objects, and four transition disk candidates which are not detected by Chandra. (These objects are not included in this HEASARC table which contains the multiwavelength data for only the 213 detected X-ray sources). The authors obtained optical spectra of a sample of both X-ray-detected and non-X-ray-detected objects. Combining the X-ray, Spitzer, and spectral data, they obtain independent estimates of cluster distance and the total cluster size - excluding protostars. The authors obtain consistent distance estimates of 510 (+100,-40) pc and a total cluster size of 255 (+50,-25) stars. They find the Class II:III ratio is about 5:7 with some evidence that the Class III sources are spatially more dispersed. The cluster appears very young with three sites of active star formation and a median age of about 1 Myr.

The field was observed by Chandra on 2005 March 6 starting at 17:16 UT for 40.2 ks of total time and 39.6 ks of the so-called good time (Chandra ObsID 5429). It was observed again on 2005 March 8 starting at 17:43 UT for essentially the same duration (Chandra ObsID 5428). The ACIS was used in the nominal imaging array (chips I0-I3) which provides a field of view of approximately 17' x 17'. The aimpoint was at RA, Dec = 04:30:14.4, +35:16:22.2 (J2000.0) with a roll angle of 281 degrees. In addition, the S2 and S3 chips were active; however, the analysis of these data is not presented here.

For purposes of point-source detection, the data from the two observations were merged into a single event list following established CIAO procedures to create a merged event list. To identify point sources, photons with energies below 300 eV and above 8.0 keV were filtered out from this merged event list. This excluded energies which generally lack a stellar contribution. By filtering the data as described, contributions from hard, non-stellar sources such as X-ray binaries and active galactic nuclei (AGNs) are attenuated, as is noise. A monochromatic exposure map was generated in the standard way using an energy of 1.49 keV which is a reasonable match to the expected peak energy of the stellar sources and the Chandra mirror transmission. The CIAO tool WavDetect was then run on a series of flux-corrected images binned by 1, 2, and 4 pixels. The output source lists were combined and this resulted in the detection of 231 sources. The authors defined false detections as any sources with < 4 net counts or any sources more than 5' off-axis with < 7 net counts. By this definition, 18 of the 231 detections were rejected as false detections. A post facto check confirmed that none of these (spurious) sources had an infrared counterpart.


Catalog Bibcode

2010ApJ...715..671W

References

X-ray and Infrared Emission from Young Stellar Objects Near LkH-alpha 101
     Wolk S.J., Winston E., Bourke T.L., Gutermuth R., Megeath S.T.,
     Spitzbart B.D., Osten R.A.
    <Astrophys. J. 715, 671 (2010)>
    =2010ApJ...715..671W

Provenance

This table was created by the HEASARC in July 2010 based on the versions of Tables 1, 2, 3, 7 and 9 from the paper which were obtained from the electronic ApJ web site.

Parameters

Source_Number
A unique running source number for each X-ray source in the catalog, where skips in the numeration scheme indicate where spurious X-ray detections have been removed (discussed in the Overview section above).

Name
The X-ray source designation, e.g., 'LkHa101CXO JHHMMSS.ss+DDMMSS.s', for sources in this table, using the IAU-style position-based designation for LkH-alpha 101 CXO-detected X-ray sources. Those X-ray sources with Spitzer counterparts, in addition to these X-ray names, can be equally identified using the Spitzer prefix, e.g., 'LkHa101SST JHHMMSS.ss+DDMMSS.s'.

RA
The Right Ascension of the X-ray source in the selected equinox. This was derived from the name for the source, which contains the RA given in J2000.0 equatorial coordinates to a precision of 0.01 seconds of time.

Dec
The Declination of the X-ray source in the selected equinox. This was derived from the name for the source, which contains the Dec given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Off_Axis
The offset of the X-ray source from the pointing axis, in \ arcminutes (converted from the arcseconds units given in the original table).

Raw_Counts
At each source position, an extraction ellipse was calculated following Wolk et al. (2006, AJ, 132, 1100) updated for the appropriate roll. This provides an extraction ellipse containing 95% of the source flux. The total counts in this region are contained in this parameter.

Counts
For each of the sources, a background ellipse was identified. The background is an annular ellipse with the same center, eccentricity, and rotation as the source extraction ellipse. The outer radius is 6 times the radius of the source, and the inner radius is 3 times larger than the source. From this region, any nearby sources are subtracted with ellipses 3 times the sizes 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.

CXO_2MASS_Offset
The positional offset between the X-ray source and its 2MASS counterpart, in arcseconds.

Jmag
The J-band magnitude of the 2MASS counterpart to the Chandra source.

Jmag_Error
The uncertainty in the 2MASS J-band magnitude of the 2MASS counterpart to the Chandra source.

Hmag
The H-band magnitude of the 2MASS counterpart to the Chandra source.

Hmag_Error
The uncertainty in the 2MASS H-band magnitude of the 2MASS counterpart to the Chandra source.

Kmag
The K-band magnitude of the 2MASS counterpart to the Chandra source.

Kmag_Error
The uncertainty in the 2MASS K-band magnitude of the 2MASS counterpart to the Chandra source.

TwoMASS_Flags
The 2MASS photometric quality flags for the J, H and K bands, respectively, where 'A'. 'B', 'C' and 'D' indicate decreasing quality of measurements and 'U' means that the quoted value is an upper limit. See the 2MASS documentation for further details.

CXO_Spitzer_Offset
The positional offset between the X-ray source and its Spitzer counterpart, in arcseconds.

IRAC_3p6_um_Mag
The Spitzer IRAC 3.6um magnitude of the mid-infrared (MIR) counterpart to the Chandra X-ray source.

IRAC_3p6_um_Mag_Error
The uncertainty in the Spitzer IRAC 3.6um magnitude of the MIR counterpart to the Chandra source.

IRAC_4p5_um_Mag
The Spitzer IRAC 4.5um magnitude of the mid-infrared (MIR) counterpart to the Chandra X-ray source

IRAC_4p5_um_Mag_Error
The uncertainty in the Spitzer IRAC 4.5um magnitude of the MIR counterpart to the Chandra source.

IRAC_5p8_um_Mag
The Spitzer IRAC 5.8um magnitude of the mid-infrared (MIR) counterpart to the Chandra X-ray source

IRAC_5p8_um_Mag_Error
The uncertainty in the Spitzer IRAC 5.8um magnitude of the MIR counterpart to the Chandra source.

IRAC_8p0_um_Mag
The Spitzer IRAC 8.0um magnitude of the mid-infrared (MIR) counterpart to the Chandra X-ray source

IRAC_8p0_um_Mag_Error
The uncertainty in the Spitzer IRAC 8.0um magnitude of the MIR counterpart to the Chandra source.

MIPS_24_um_Mag
The Spitzer MIPS 24um magnitude of the infrared counterpart to the Chandra X-ray source

MIPS_24_um_Mag_Error
The uncertainty in the Spitzer MIPS 24um magnitude of the IR counterpart to the Chandra source.

Kmag_Extinction
The K-band extinction of the infrared counterpart to the Chandra source, in magnitudes.

Broad_Type
The pre-main sequence star classification based on the infrared colors, (using the schema discussed in Section 2.2 of the reference paper), where '1' is protostar, 2 is pre-main sequence star with accretion disk, 3 is a diskless pre-main sequence star, and 'III/T' is a young star with a candidate transition disk. Objects calssed as 'gal' are likely background galaxies.

Source_Note
This parameter contains a 'b' flag for those stars that are within 90" of LkH-alpha 101. Their spatial proximity led to the conclusion that they were cluster members, despite their missing some IRAC data. For these stars, the 2MASS data played an enhanced role in determining their class identification. The star LkH-alpha 101 itself is flagged with 'LkHa 101'.

Spectral_Counts
The net X-ray counts used in the spectral fit. This can be less than the net counts (the 'counts' parameter) if data from only one of the two Chandra observations was used in the fit.

NH
The best-fit hydrogen column density, N_H, in cm-2.

NH_Error
The 1-sigma uncertainty in N_H, in cm-2.

Limit_kT
This parameter contains '>' if the quoted plasma temperature is a lower limit rather than an actual value.

kT
The best-fit plasma temperature, in keV, using an absorbed single-temperature (1T) spectra model. Counting the three coronal plasma models that the authors used (APEC, Mekal and Raymond-Smith) and the three possible data sets (the first observation, the second observation, and the combined observations), there were up to nine spectral fits performed for each source. Based on the results shown in Table 6 of the reference paper, the authors argue that the particular models are not too different in the result they provide. However, the Mekal models tend to be more deviant, hence they are a last choice. APEC was given primacy over Raymond-Smith primarily due to the inclusion of additional emission lines in APEC as it is a more recent model. Preference was given to fits with using the merged data set, then to models using APEC chi-data variance statistics from only one observation, and finally to models using C-statistics from only one observation.

Only fits using chi-data variance statistics with 0.5 < chi2 < 1.5 are included in this table. Such well-constrained fits were obtained for 88 sources. Table 8 of the reference paper contains 30 additional spectral fits which did not meet these rather rigorous criteria.

kT_Error
The 1-sigma uncertainty in the best-fit plasma temperature, in keV.

Obs_Flux
The absorbed (observed) X-ray flux of the source in the 0.3-8.0 keV band, in erg/s/cm2, as derived from the best-fit spectral model.

Flux
The unabsorbed X-ray flux of the source in the 0.3-8.0 keV band, in erg/s/cm2, as derived from the best-fit spectral model and the estimated absorbing column density.

Reduced_Chi_Squared
The reduced chi2 (chi2 per degree of freedom) of the spectral fit to the X-ray source. This is included for "cstat" models for completeness. It is unclear how chi2/dof relates to goodness of fit for these models. The formal errors are unbiased, however.

Spectral_Model
The spectral model and Chandra dataset used in the fit to the source spectrum. The model used for the fit is coded in two parts. The left-hand side (LHS) indicates the type of spectral model used. The right-hand side (RHS) indicates the Chandra data set. The overall model is written as LHS_RHS. Possible values for the LHS:

    cstat = C-statistics used for the fit with an initial guess of kT = 1 keV
            and N_H = 1021 cm-2.
      crs = c-stat used for initial guess with those input parameters and then
            refit using Raymond-Smith plasma for final fit.
    Mekal = again c-stat used for initial guess and then Mekal for final fit.
     APEC = cstat used for initial guess and then APEC for final fit.
  

Possible values for the RHS:

       29 = only data from the first observation (Chandra ObsID = 5429) were
            used in the fit.
       28 = only data from the second observation (Chandra ObsID = 5428) were
            used in the fit.
      all = data from both Chandra observations were used in the fit.
  

GL_Index
The Gregory & Loredo (1992, ApJ, 398, 146) GL-vary index for the X-ray light curve of the source, for sources with over 30 raw counts. The higher the value of this index, the greater the variability. Values greater than 7 indicate > 99% variability probability. See Section 3.2 of the reference paper for more details.

GL_Probability
The Gregory & Loredo (1992, ApJ, 398, 146) probability of variability for the X-ray light curve of the source, for sources with over 30 raw counts. See Section 3.2 of the reference paper for more details.

Num_Bayesian_Blocks
The number of Bayesian Blocks (BB) found for the X-ray light curve of the source. A value of > 1 indicates possible variability, with higher values implying greater variability. See Section 3.2 of the reference paper for more details.

Flare_Rates
The BB-derived X-ray flare rate(s) for the source, in units of 104/R x dR/dt s-1. One star (source number 77) was seen to flare twice, and another (source number 3) was seen to flare 5 times. See Section 3.2 of the reference paper for more details.

Class
The HEASARC Browse object classification, based on the infrared classification of the object (the broad_type parameter).


Contact Person

Questions regarding the LKHA101CXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 28-Jul-2010