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RASSUSNOID - ROSAT All-Sky Survey Bright Source Catalog USNO A2 Cross-Associations

HEASARC
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Overview

The authors have quantitatively cross-associated the 18,811 ROSAT All-Sky Survey Bright Source Catalog (RASS/BSC) X-ray sources with optical sources in the USNO A-2 catalog, calculating the probability of unique association (P_id) between each candidate within 75" of the X-ray source position, on the basis of optical magnitude and proximity. They have generated catalogs of RASS/BSC sources for which P_id > 98%, P_id > 90%, and P_id > 50%, which contain 2705, 5492, and 11,301 unique USNO A-2 optical counterparts respectively down to the stated level of significance. Together with identifications of objects not cataloged in USNO A-2 due to their high surface brightness (M31, M32, ...) and optical pairs, they produced a total of 11,803 associations to a probability of P_id > 50%. They also include in this catalog a list of objects in the SIMBAD database within 10" of the USNO A-2 position, as an aid to identification and source classification. This is the first RASS/BSC counterpart catalog which provides a probability of association between each X-ray source and counterpart, quantifying the certainty of each individual association. The catalog is more useful than previous catalogs which either rely on plausibility arguments for association or do not aid in selecting a counterpart between multiple off-band sources in the field. Sources of high probability of association can be separated out, to produce high-quality lists of classes (Seyfert 1/2s, QSOs, RS CVns) desired for targeted study, or for discovering new examples of known classes (or new classes altogether) through the spectroscopic classification of securely identified but unclassified USNO A-2 counterparts. Low P_id associations can be used for statistical studies and follow-on investigation - for example, performing follow-up spectroscopy of the many low-mass stars to search for signatures of coronal emission, or to investigate the relationship between X-ray emission and classes of sources not previously well-studied for their X-ray emissions (such as pulsating variable stars). The authors find that a fraction ~65.8% of RASS/BSC sources have an identifiable optical counterpart, down to the magnitude limit of the USNO A-2 catalog which could be identified by their spatial proximity and high optical brightness.

Catalog Bibcode

2000ApJS..131..335R

References

Cross-Association of ROSAT/Bright Source Catalog X-Ray Sources with USNO A-2
Optical Point Sources
     Rutledge, R. E., Brunner, R. J., Prince, T. A., Lonsdale, C.
    <Astrophys. J. Suppl. Ser. 131, 335 (2000)>
    =2000ApJS..131..335R

Provenance

This table was created by the HEASARC in October 2009 based on electronic versions of Tables 9 (USNO counterparts for which P_id > 98%) and 10 (USNO counterparts for which 90% > P_id > 98%) of the reference paper which were obtained from the Astrophysical Journal web site.

HEASARC Implementation

This HEASARC table contains the USNO counterparts and their nearby SIMBAD cross-identifications to the RASS/BSC sources for which P_id > 98% (Table 9 of the reference paper),and for which 98% > P_id > 90% (Table 10 of the reference paper), but not the lower probability USNO counterparts (90% > P_id > 50% contained in Table 11 of the reference paper). The expected fractions of misidentified counterparts in these samples are 0.66%, 5.0%, and 32%, respectively. Notice that there are many cases where there are multiple SIMBAD cross-identifications for a single USNO A2 counterpart to a RASS/BSC X-ray source, and that these are listed as separate rows in this table.

Parameters

RASS_Name
The RASS name of the X-ray source, using the recommended '1RXS' prefix and the J2000 equatorial coordinates.

RA_Rass
The Right Ascension of the X-ray source in the selected equinox. This was constructed by the HEASARC from the position-based RASS name.

Dec_Rass
The Declination of the X-ray source in the selected equinox. This was constructed by the HEASARC from the position-based RASS name.

Count_Rate
The RASS/BSC PSPC count rate, in ct/s.

Count_Rate_Error
The 1-sigma uncertainty in the RASS/BSC PSPC count rate, in ct/s.

ID_Prob
The calculated fractional probability of unique association between the X-ray and the USNO A-2 objects.

Bmag
The USNO A-2 counterpart B-band magnitude.

Name
The name of a SIMBAD Object within 10 arcseconds of the USNO A-2 counterpart position. Notice that there are many cases where there are multiple SIMBAD cross-identifications for a single USNO A2 counterpart to a RASS/BSC X-ray source, and that these are listed as separate entries in this table.

RA
The Right Ascension of the USNO A-2 counterpart to the RASS/BSC X-ray source in the selected equinox. This was given in J2000 coordinates to an accuracy of 0.01 seconds of time in the original reference.

Dec
The Declination of the USNO A-2 counterpart to the RASS/BSC X-ray source in the selected equinox. This was given in J2000 coordinates to an accuracy of 0.1 arcseconds in the original reference.

LII
The Galactic Longitude of the USNO A-2 counterpart to the RASS/BSC X-ray source.

BII
The Galactic Latitude of the USNO A-2 counterpart to the RASS/BSC X-ray source.

SIMBAD_Type
The SIMBAD object type of the counterpart. Notice that there are many cases where there are multiple SIMBAD cross-identifications for a single USNO A2 counterpart to a RASS/BSC X-ray source, and that these are listed as separate entries in this table. The meaning of many of the types are listed below:

      * = Star
      ** = Stellar binary
      *iC = Star in Cluster
      **mul = multiple stellar system
      *Neb = Star in Nebula
      Clust. = Cluster
      CV = Cataclysmic Variable
      Ceph. = Cephied Variable
      DN = Dwarf Nova
      Ecl. Bin. = Eclipsing Binary (and type)
      Em. * = Emission line star
      HiPM* = High Proper-motion Star
      HMXB = High Mass X-ray Binary
      IR = Infra-red object
      Glob. Clust. = Globular Cluster
      Gal. = Galaxy
      GiG = Galaxy in Group of Galaxies
      LMXB = Low Mass X-ray Binary
      LSBG = Low Surface Brightness Galaxy
      PN = Planetary Nebula
      Rad. = Radio source
      Rot. Var. * = Rotationally Variable Star
      SN = SuperNova
      Spec. Bin. = Spectroscopic Binary
      Sy1 = Seyfert 1
      Sy2 = Seyfert 2
      TT = T-Tauri type star
      UV = Ultra-violet emission source
      V* = Variable Star
      WD = White Dwarf
      WR * = Wolf-Rayet Star
      X = X-ray source
      YSO = Young Stellar Object
  

SIMBAD_Smtype
The spectral or morphological classification of the SIMBAD object. For stars, this field contains the spectral type, while for galaxies it contains the Hubble type.

SIMBAD_Bmag
The B-band magnitude of the SIMBAD object.

SIMBAD_Vmag
The V-band magnitude of the SIMBAD object.

Comment_Code
This parameter is set to 'P' if the SIMBAD object had previously been identified as the counterpart to the RASS/BSC X-ray source.

Class
The HEASARC Browse object classification, based on the simbad_type and simbad_smtype parameter values.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 16-Oct-2009