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ORIONFFCXO - Orion Flanking Fields Chandra X-Ray Point Source Catalog

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Overview

This table contains the results of Chandra observations of two flanking fields (FFs) in Orion outside the Orion Nebula Cluster (ONC), in the form of a catalog of 417 sources, which includes X-ray luminosity, optical and infrared photometry, and X-ray variability information. 91 variable sources were found, 33 of which have flarelike light curves, and 11 of which have a pattern of a steady increase or decrease over a 10 hour period. The optical and infrared photometry for the stars identified as X-ray sources are consistent with most of these objects being pre-main-sequence stars with ages younger than 10 Myr.

The two flanking fields in Orion were observed with the Advanced CCD Imaging Spectrometer (ACIS) detector on board the Chandra X-Ray Observatory. The north Orion flanking field (NOFF) is centered at a J2000 RA and Declination of 05:35:19, -04:48:15, which is about 36' (~5 pc, at a distance of 470 pc) north of the Trapezium cluster and was observed on 2002 August 26 with a total exposure time of 48.8 ks. The south Orion flanking field (SOFF), centered at a J2000 RA and Declination of 05:35:06, -05:40:48, which is about 17' (~ 2.5pc, at a distance of 470 pc) south of the Trapezium cluster, was observed on 2002 September 6 with a total exposure time of 47.9 ks.

The data analysis for these observations was performed in the same manner as described in Ramirez et al. (2004, AJ, 127, 2659) for a similar observation of a field in NGC 2264, which should be consulted for the full details. (See also the help file for the HEASARC version of the catalog from the latter reference available at /W3Browse/chandra/ngc2264cxo.html ).


Catalog Bibcode

2004AJ....128..787R

References

Chandra X-ray observations of young clusters. II. Orion flanking fields data.
    Ramirez S.V., Rebull L., Stauffer J., Strom S., Hillenbrand L., Hearty T.,
    Kopan E.L., Pravdo S., Makidon R., Jones B.
   <Astron. J., 128, 787-804 (2004)>
   =2004AJ....128..787R

Provenance

This table was created by the HEASARC in February 2007 based on the CDS table J/AJ/128/787, files table1.dat, table3.dat and table4.dat. It does not include the results from the spectral analysis of 44 bright X-ray sources which were presented in Table 2 of the reference paper.

Parameters

Field_Name
The flanking field name, being 'NOFF' for the North Orion flanking field and 'SOFF' for the South Orion flanking field.

Source_Number
A running number for the X-ray source in order of increasing J2000.0 Right Ascension separately within each flanking field, with sources in the North flanking field having a prefix of 'N' and those in the South one having a prefix of 'S'.

Name
The name of the X-ray source using the 'CXORRS J' prefix registered with the CDS Dictionary of Nomenclature of Celestial Objects and the trincated J2000.0 coordinates of the source (HHMMSS.s-DDMMSS).

Alt_Name
An alternative name for the X-ray source recommended by the CDS Dictionary of Nomenclature of Celestial Objects using the prefix of '[RRS2004] NOFF W' for objects in the North flanking field or '[RRS2004] SOFF W' for objects in the South flanking field (where RRS2004 stands for Ramirez, Rebull and Stauffer, 2004), together with the numerical part of the source number.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table. From a comparison of the original Chandra positions for sources with off-axis angles of less than 5 arcminutes with their 2MASS counterpart sources, the authors determined a mean offset in Right Ascension of -0.09" +/ 0.02" for the NOFF sources, and of +0.09" +/- 0.03" for the SOFF sources, which has been corrected for in the values given here so as to put the positions in the same reference frame as their 2MASS counterparts.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.001 arcseconds in the original table. From a comparison of the original Chandra positions for sources with off-axis angles of less than 5 arcminutes with their 2MASS counterpart sources, the authors determined a mean offset in Declination of -0.14" +/ 0.03" for the NOFF sources, and of -0.28" +/- 0.03" for the SOFF sources, which has been corrected for in the values given here so as to put the positions in the same reference frame as their 2MASS counterparts.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Off_Axis
The off-axis angle of the X-ray source from the aimpoint of the observation in which it was found, in arcminutes.

Extraction_Radius
The count extraction radius used for the X-ray source, in arcseconds.

PSF_Fraction
The enclosed fraction of the point-spread function (PSF) used in the count rate computation.

Exposure
The effective exposure time for the X-ray source, in seconds.

Count_Rate
The net background- and vignetting-subtracted count rate of the X-ray source in ct/s.

Flux
The flux of the X-ray source in the 0.3 to 8.0 keV energy range, in ergs/s/cm2. The authors used the X-ray fluxes of the bright sources obtained from a spectral analysis using 2-T absorbed XSMEKAL thermal emission models to compute X-ray flux-weighted conversion factors between count rates and X-ray fluxes for all of the sources in each field, namely (6.58 +/- 0.13) x 10-15 erg/cm2/s per (count/ks) for the NOFF sources and (6.72 +/- 0.20) x 10-15 erg/cm2/s per (count/ks) for the SOFF sources.

Log_Lx
The logarithm of the X-Ray luminosity, in ergs/s, for the X-ray source, using the X-ray flux and an assumed distance of 470 pc to Orion.

Prob_Constant
The constant-source probability P_c as derived from the chi-squared value found when comparing the actual light curve with a constant source, in percent. Sources with P_c < 90% are the most likely to be variable. The authors defined a variable source as those having 2500 s bin light curves with P_c < 90% and 5000 s and 7500 s bin light curves with reduced chi-squared values > 2.5. There are 91 variable sources that meet these criteria and have a 'v' value in the comment_flags parameter. There are 33 variable sources which show a flare shape, defined as a rapid increase and a slow decrease in the X-ray flux, indicated with an additional 'f' in the value of the same parameter. There are 16 sources which show a possible flare pattern, described as an increase in X-ray flux happening at the end of an observation, or a decrease in X-ray flux occurring at the beginning of an observation, indicated with an additional 'p' in the value of the comment_flags parameter. There are 11 sources that show steady increase or decrease in their X-ray flux, and are indicated with an additional 's' in the value of the comment_flags parameter.

Comment_Flags
This parameter contains flags encoding information aout the variability of the source as well as other properties, as follows (a more detailed explanation on the v, f, p and s values is given above, in the text for the prob_constant parameter):

  v = Variable star
  f = Flarelike light curve
  p = Possible flare in the light curve
  s = Steady increase or decrease in the light curve
  c = Source confusion:
      There were cases in which two optical/near-IR counterparts were
      located within the extraction radius, which is a measure of the
      size of the PSF in the Chandra field. This was the case for nine
      X-ray sources which were matched to the closest counterpart in each case
  X = Source detected only in X-rays:
      There are 61 X-ray sources that do not have optical or infrared
      counterparts
  

Ctrpart_Name
The name of the proposed optical/infrared counterpart to the X-ray source, where sources beginning with 'Par' are from the Parenago (1954, CDS Cat. <II/171>) Catalog, those beginning with 'R01' are from the Rebull (2001, CDS Cat. <J/AJ/121/1676>) Catalog, those beginning with 'CHS' are from the Carpenter et al. (2001, CDS Cat. <J/AJ/121/3160>) Catalog, and those beginning with '2MASS' are from the 2MASS Catalog. Other prefixes are:

        SMMV = Stassun et al., 1999, CDS Cat. <J/AJ/117/2941>
          JW = Jones & Walker, 1988AJ.....95.1755J
         H97 = Hillenbrand, 1997AJ....113.1733H
        HBJM = Herbst et al., 2001ApJ...554L.197H
  

RA_Ctrpart
The J2000.0 Right Ascension of the optical/IR counterpart to the X-ray source.

Dec_Ctrpart
The J2000.0 Declination of of the optical/IR counterpart to the X-ray source.

Vmag
The V-band magnitude of the optical/IR counterpart to the X-ray source. The sources of the optical and infrared photometry are discussed in Section 4.1 of the reference paper.

Ic_Mag
The I_c-band magnitude of the optical/IR counterpart to the X-ray source. The sources of the optical and infrared photometry are discussed in Section 4.1 of the reference paper.

Jmag
The J-band magnitude of the optical/IR counterpart to the X-ray source. The sources of the optical and infrared photometry are discussed in Section 4.1 of the reference paper.

Hmag
The H-band magnitude of the optical/IR counterpart to the X-ray source. The sources of the optical and infrared photometry are discussed in Section 4.1 of the reference paper.

Kmag
The K-band magnitude of the optical/IR counterpart to the X-ray source. The sources of the optical and infrared photometry are discussed in Section 4.1 of the reference paper.

Alt_Name_1
The name of the proposed optical/infrared counterpart to the X-ray source, if listed in the Parenago (1954, CDS Cat. <II/171>) Catalog, e.g., Par 1567.

Alt_Name_2
The name of the proposed optical/infrared counterpart to the X-ray source, if listed in the Rebull (2001, CDS Cat. <J/AJ/121/1676>) Catalog, e.g., R01 1413.

Alt_Name_3
The name of the proposed optical/infrared counterpart to the X-ray source, if listed in the Carpenter et al. (2001, CDS Cat. <J/AJ/121/3160>) Catalog, e.g., CHS 5807.

Alt_Name_4
The name of the proposed optical/infrared counterpart to the X-ray source, if listed in the 2MASS Catalog, e.g., 2MASS J05353104-0536069.

Other_Names
Other names for the proposed optical/infrared counterpart to the X-ray source, as follows:

        SMMV = Stassun et al., 1999, CDS Cat. <J/AJ/117/2941>; SMMV NNNN
        Tian = Tian et al., 1996, CDS Cat. <J/A+AS/118/503>; [TVZ96] NNN
       ROSAT = Gagne & Caillault, 1994, CDS Cat. <J/ApJ/437/361>; [GC94b] NNN
    Einstein = Gagne et al., 1995, CDS Cat. <J/ApJ/445/280>;[GCS95] NNN
         HBC = Herbig & Bell, 1988, CDS Cat. <V/73A>; HBC NNN
          JW = Jones & Walker, 1988AJ.....95.1755J; JW NNNN
         H97 = Hillenbrand, 1997AJ....113.1733H; [H97b] NNNNa
   Feigelson = Feigelson et al., 2002, CDS Cat. <J/ApJ/574/258>; [FBG2002] NNNN
        HBJM = Herbst et al., 2001ApJ...554L.197H
  

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 28-Aug-2012