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RASSDSSTAR - ROSAT All-Sky Survey and SDSS Sample of X-Ray Emitting Stars

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Overview

The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. Combining the RASS Bright and Faint Source Catalogs yields an average of about three X-ray sources per square degree. However, while X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. The authors use optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709 stellar X-ray emitters cataloged in the RASS and falling within the SDSS Data Release 1 footprint. Most of these are bright stars with coronal X-ray emission unsuitable for SDSS spectroscopy, which is designed for fainter objects (g > 15mag). Instead, the authors use SDSS photometry, correlations with the Two Micron All Sky Survey (2MASS) and other catalogs, and spectroscopy from the Apache Point Observatory 3.5 m telescope to identify these stellar X-ray counterparts. Their sample of 707 X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected samples of such stars. The authors derive distances to these stars using photometric parallax relations appropriate for dwarfs on the main sequence, and use these distances to calculate their X-ray luminosities L_X. They also identify a previously unknown cataclysmic variable (CV) as a RASS counterpart.

Much more information on the SDSS is available at the project's web site at http://www.sdss.org/.


Catalog Bibcode

2009ApJS..181..444A

References

X-Ray-Emitting Stars Identified from the ROSAT All-Sky Survey and the Sloan
    Digital Sky Survey
    Agueros M.A., Anderson S.F., Covey K.R., Hawley S.L., Margon B.,
    Newsom E.R., Posselt B., Silvestri N.M., Szkody P., Voges W.
   <Astrophys. J. Suppl. 181, 444-465 (2009)>
   =2009ApJS..181..444A

Provenance

This table was created by the HEASARC in April 2009 based on the the machine-readable version of Table 4 from the reference paper which was obtained from the ApJ web site.

Parameters

Name
The RASS X-ray source designation using the recommended '1RXS J' prefix and based on the J2000 equatorial coordinates of the X-ray source.

RA
The Right Ascension of the RASS X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 decimal degrees in the original table.

Dec
The Declination of the RASS X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 decimal degrees in the original table.

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

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

Error_Radius
The positional uncertainty of the RASS X-ray source, in arcseconds. This is the total positional error (1-sigma error) and includes a 6 arcseconds systematic error.

Count_Rate
The vignetting-corrected count rate of the RASS X-ray source, in ct/s (0.1-2.4 keV energy band).

Count_Rate_Error
The uncertainty in the RASS X-ray count rate, in ct/s.

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

HR1
The first hardness ratio of the RASS X-ray source, defined as HR1=(B-A)/(B+A), where A are the counts in the PHA channels range 11-41 (0.1-0.4 keV) and B are the counts in the PHA channels range 52-201 (0.5-2.0 keV). For more information, see Voges et al. (1999, A&A, 349, 389).

HR1_Error
The uncertainty in the hardness ratio, HR1.

HR2
The second hardness ratio of the RASS X-ray source, defined as HR2=(D-C)/(D+C), where C are the counts in the PHA channels range 52-90 (0.5-0.9 keV) and D are the counts in the PHA channels range 91-201 (0.9-2.0 keV). For more information, see Voges et al. (1999, A&A, 349, 389).

HR2_Error
The uncertainty in the hardness ratio, HR2.

Source_Extent
The amount is specified by which the RASS X-ray source image exceeds the instrumental point spread function, in arcseconds.

Extent_Likelihood
The likelihood of the RASS X-ray source extent. If this > 9999.9, it was set to 9999. For more information, see Voges et al. (1999, A&A, 349, 389).

Detect_Likelihood
The likelihood of the RASS X-ray source detection. If this > 9999.9, it was set to 9999. For more information, see Voges et al. (1999, A&A, 349, 389).

SDSS_Name
The SDSS designation of the suggested optical counterpart to the RASS X-ray source, in the usual style based on its J2000 optical position.

SDSS_RA
The Right Ascension of the SDSS optical counterpart in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 degrees, in the original table.

SDSS_Dec
The Declination of the SDSS optical counterpart in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 degrees, in the original table.

SDSS_RASS_Offset
The offset between the SDSS and RASS positions, in arcseconds.

Umag
The u-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source. The authors caution that any SDSS photometry for objects brighter than g ~ 14 is suspect, and should be used only once the objects' SDSS flag values (the sdss_flags parameter in this table) have been checked.

Umag_Error
The uncertainty in the u-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source.

Gmag
The g-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source. The authors caution that any SDSS photometry for objects brighter than g ~ 14 is suspect, and should be used only once the objects' SDSS flag values (the sdss_flags parameter in this table) have been checked.

Gmag_Error
The uncertainty in the g-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source.

Rmag
The r-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source. The authors caution that any SDSS photometry for objects brighter than g ~ 14 is suspect, and should be used only once the objects' SDSS flag values (the sdss_flags parameter in this table) have been checked.

Rmag_Error
The uncertainty in the r-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source.

Imag
The i-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source. The authors caution that any SDSS photometry for objects brighter than g ~ 14 is suspect, and should be used only once the objects' SDSS flag values (the sdss_flags parameter in this table) have been checked. The HEASARC has set imag for 4 entries which had imag ~ 0.0 in the original table to null values.

Imag_Error
The uncertainty in the i-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source.

Zmag
The z-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source. The authors caution that any SDSS photometry for objects brighter than g ~ 14 is suspect, and should be used only once the objects' SDSS flag values (the sdss_flags parameter in this table) have been checked. The HEASARC has set zmag for 4 entries which had zmag ~ 0.0 in the original table to null values.

Zmag_Error
The uncertainty in the z-band PSF magnitude of the SDSS optical counterpart to the RASS X-ray source.

SDSS_Flags
The SDSS photometry flags for the SDSS optical counterpart to the RASS X-ray source. These flags were written in hexadecimal, and a full description of them is available at http://cas.sdss.org/astro/en/help/browser/enum.asp?n=PhotoFlags. The HEASARC notes that some of these values in the original table from the reference paper have inconsistent values such as '1.57E+015', apparently due to the original 16-character strings having been corrupted. These values have been retained in the present HEASARC version of this table.

TwoMASS_Name
The 2MASS designation of the suggested infrared counterpart to the RASS X-ray source, in the usual style based on its J2000 infrared position.

TwoMASS_RA
The Right Ascension of the 2MASS infrared counterpart in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 degrees, in the original table.

TwoMASS_Dec
The Declination of the 2MASS infrared counterpart in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 degrees, in the original table.

SDSS_2MASS_Offset
The offset between the SDSS and 2MASS positions, in arcseconds.

Jmag
The J-band magnitude of the 2MASS infrared counterpart to the RASS X-ray source.

Jmag_Error
The uncertainty in the J-band magnitude of the 2MASS infrared counterpart to the RASS X-ray source.

Hmag
The H-band magnitude of the 2MASS infrared counterpart to the RASS X-ray source.

Hmag_Error
The uncertainty in the H-band magnitude of the 2MASS infrared counterpart to the RASS X-ray source.

Ks_Mag
The K_s-band magnitude of the 2MASS infrared counterpart to the RASS X-ray source.

Ks_Mag_Error
The uncertainty in the K_s-band magnitude of the 2MASS infrared counterpart to the RASS X-ray source.

TwoMASS_Flags
The three-character 2MASS photometry flag for the infrared counterpart to the RASS X-ray source, one per band [JHK]. This parameter provides a summary of the net quality of the photometry in each band, as derived from the Read Flag, measurement uncertainties ([JHK]cmsig), scan signal-to-noise ratios ([JHK]snr), frame-detection statistics, and profile-fit reduced chi-squared values, as follows:

      X: There is a detection at this location, but no valid brightness
         estimate can be extracted using any algorithm. The default magnitude
         is null.
      U: Upper limit on magnitude. Source is not detected in this band, or it is
         detected, but not resolved in a consistent fashion with other bands.
      E: This category includes detections where the goodness-of-fit quality of
         the profile-fit photometry was very poor, or detections where psf fit
         photometry did not converge and an aperture magnitude is reported, or
         detections where the number of frames was too small in relation to the
         number of frames in which a detection was geometrically possible.
      A: Detections in any brightness regime where valid measurements were made
         with [JHK]snr > 10 AND [JHK]cmsig < 0.10857.
      B: Detections in any brightness regime where valid measurements were made
         with [JHK]snr > 7 AND [JHK]cmsig < 0.15510.
      C: Detections in any brightness regime where valid measurements were made
         with [JHK]snr > 5 AND [JHK]cmsig < 0.21714.
      D: Detections in any brightness regime where valid measurements were made
         with no [JHK]snr OR [JHK]cmsig requirement.
  

Log_Fx_Over_Fj
The logarithm of the ratio of the RASS X-ray to the 2MASS J-band fluxes, calculated from the X-ray flux f_x and the J-band magnitude J using log (f_x/f_J) = log (f_x) +0.4J + 6.30. (See Section 4.1.3 of the reference paper for more details). The X-ray flux (0.1-2.4 keV) was itself calculated from the quoted RASS count rate assuming a conversion factor of 1 x 10-11 erg cm-2 ct-1, as discussed in Section 4.1.1 of the reference paper.

Abs_Ks_Mag
The synthetic absolute K_S-band magnitude M(K_s) of the infrared counterpart to the RASS X-ray source, derived from the estimated distance to the source and the apparent K_s-band magnitude.

Abs_Ks_Mag_Error
The uncertainty in the synthetic absolute K_S-band magnitude M(K_s).

Distance
The estimated distance, D, to the star, in parsecs. This was calculated as discussed in Section 5.1 of the reference paper, and included the assumption that the star was on the main sequence, i.e., was a dwarf.

Distance_Error
The uncertainty in the distance, in pc.

Lx
The RASS X-ray luminosity L_x of the source, in erg/s, calculated from the adopted distance D in pc and the calculated 0.1-2.4 keV flux f_x in erg s-1 cm-2 using the standard relation L_x = 1.20E38 f_x D2.

Lx_Error
The uncertainty in the RASS X-ray luminosity, in erg/s.

APO_Obs_Date
The date on which the source was observed at the Apache Point Observatory (APO). For stars which were observed more than once, the date listed is that of the first APO observation. The details of the APO spectroscopic sample are presented in Section 4.2 of the reference paper

Spect_Type
The derived stellar spectral type.

SIMBAD_Name
The SIMBAD identification for the stellar counterpart to the X-ray source.

SIMBAD_RA
The Right Ascension of the SIMBAD counterpart to the RASS X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 degrees, in the original table.

SIMBAD_Dec
The Declination of the SIMBAD counterpart to the RASS X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 10-6 degrees, in the original table.

SDSS_SIMBAD_Offset
The offset between the SDSS and SIMBAD positions, in arcseconds.

Bmag
The SIMBAD B-band magnitude of the stellar counterpart to the RASS X-ray source.

Vmag
The SIMBAD V-band magnitude of the stellar counterpart to the RASS X-ray source.

Log_Fx_Over_Fv
The logarithm of the ratio of the RASS X-ray to the SIMBAD V-band fluxes, calculated from the X-ray flux f_x and the V-band magnitude V using log (f_x/f_V) = log (f_x) +0.4V + 5.37. (See Section 4.1.1 of the reference paper for more details). The X-ray flux (0.1-2.4 keV) was itself calculated from the quoted RASS count rate assuming a conversion factor of 1 x 10-11 erg cm-2 ct-1, as discussed in Section 4.1.1 of the reference paper.

SIMBAD_Class
The SIMBAD classification of the stellar counterpart to the RASS X-ray source, as follows:

      ** = double star system;
     *i* = multiple star system;
       * = star;
     PM* = high proper-motion star;
     WU* = W UMa-type eclipsing binary;
     LM* = low-mass star (< 1 MSun);
     BY* = BY Dra-type variable;
     Al* = Algol-type binary;
      V* = variable star;
       X = X-ray source;
     bL* = beta Lyr-type eclipsing binary;
     SB* = spectroscopic binary;
     Rad = radio source;
     RR* = RR Lyrae star;
      iC = star in a cluster;
      EB = eclipsing binary.
  

Source_Notes
This field can contain additional note(s) concerning some of the sources, including the spectral type derived from APO observations for stars with types listed in SIMBAD and/or the Flesch & Hardcastle (2004, A&A, 427, 387) or Parejko et al. (2008, AJ, 135, 10) classification for the source counterpart, as well as the following codes:

     RM = a random match between the Flesch & Hardcastle (2004) source catalogs
          is most likely in this case;
     SX = a stellar source;
    SX? = a probable stellar source;
      X = an unclassified X-ray source;
      G = a galaxy;
      R = a radio source;
      U = the source is an unclassifiable galaxy in the Parejko et al. (2008)
          catalog;
      T = a transition object;
    HII = a star-forming galaxy;
      E = an emission galaxy;
     UE = the emission is unclassified;
     CC = close companion (<~ 5 arcsec) star.
  

Class
The HEASARC Browse object classification, based only on the value of the spect_type parameter. Notice that the additional information on the nature of the source which is available in the source_notes parameter for some of the entries was not used to populate class values.


Contact Person

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

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