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RASS2FOID - ROSAT All-Sky Survey Two Selected Fields Optical Identifications Catalog



The optical identification of large number of X-ray sources such as those from the ROSAT All-Sky Survey is challenging with conventional spectroscopic follow-up observations. The authors have investigated two ROSAT All-Sky Survey fields of size 10 degrees by 10 degrees each, one at a galactic latitude b = 83o (26 Com), the other at b = -5o (gamma Sge), in order to optically identify the majority of sources. They used optical variability, among other more standard methods, as a means of identifying a large number of ROSAT All- Sky Survey sources. All objects fainter than about 12th magnitude and brighter than about 17th magnitude in or near the error circle of the ROSAT positions were tested for optical variability on hundreds of archival plates of the Sonneberg field patrol.

The reference paper contains probable optical identifications of altogether 256 of the 370 ROSAT sources analyzed. In particular, the authors found 126 active galactic nuclei (some of them may be misclassified cataclysmic variables, CVs), 17 likely clusters of galaxies, 16 eruptive double stars (mostly CVs), 43 chromospherically active stars, 65 stars brighter than about 13th magnitude, 7 UV Ceti stars, 3 semi-regular or slow irregular variable stars of late spectral type, 2 DA white dwarfs, 1 Am star, 1 supernova remnant, and 1 planetary nebula. As expected, nearly all active galactic nuclei are found in the high-galactic latitude field, while the majority of CVs is located at low galactic latitudes. The authors identify in total 72 new variable objects. X-ray emission is, not unexpectedly, tightly correlated with optical variability, and thus their new method for optically identifying X-ray sources is demonstrated to be feasible. Given the large number of optical plates used, this method was most likely not more efficient than, for example, optical spectroscopy. However, it required no telescope time, only access to archival data.

This table contains the optical spectroscopic and photometric properties of the 722 possible optical counterparts to the 370 ROSAT point sources found by the authors in the 2 examined fields above a maximum likelihood threshold of 8. It is essentially the union of the 314 counterparts which were listed in Table 8 (26 Com field) of the reference paper with the 408 counterparts listed in Table 9 (gamma Sge field) of that paper. We have removed 12 entries from Table 8 for which no optical counterpart was found (1033, 1050, 1060, 1085, 1091, 1103, 1129, 1166, 1177, 1190, 1217 and 1237), 1 additional entry from the same table (1071) where the X-ray emission is more likely associated with galaxy cluster gas emission rather than an individual galaxy in that cluster, and 7 entries from Table 9 (source numbers 2087-2091 and 2093-2094 which are detections of flux enhancements of an extended supernova remnant (SNR 053.6-02.2), for a total of 20 removed, since none of these entries had any positional or optical data given in the original tables.

The combined lists of the X-ray sources which were given in Table 1 (26 Com field) of the reference paper and Table 2 (gamma Sge field) of that paper are available in the HEASARC table RASS2FXRAY (to which the present table is linked).

Catalog Bibcode



Optical counterparts of ROSAT X-ray sources in two selected fields at
low vs. high Galactic latitudes.
    Greiner J., Richter G.A.
    <Astron. Astrophys. 575, A42 (2015)>
    =2015A&A...575A..42G        (SIMBAD/NED BibCode)


This table was created by the HEASARC in April 2015 based on CDS catalog J/A+A/575/A42 files table8.dat and table9.dat.


A unique identification number for each X-ray source in the catalog. In the original two tables. The source numbers were unique within each table but are not when combined, as they are in the present HEASARC version. To break this degeneracy, the HEASARC has created a unique X-ray source number by adding 1000 to the original Tables 1 and 8 (26 Com field) source number values and 2000 to the original Tables 2 and 9 (gamma Sge field) source number values. X-ray sources for which no counterpart was found within the search radius or the counterpart appeared to be a flux enhancement of an extended object rather than a distinct source, have been deleted from this table, as discussed in the Overview section above.

This parameter contains the optical counterpart(s) identification for the X-ray sources in the usual style, 'a' , 'b', ... up to 'j' in the case of the X-ray source number 2039 which has 10 possible optical counterparts.

The optical counterpart name created by the HEASARC in the style recommended by the Dictionary of Nomenclature of Celestial Objects, viz., the prefix '[GR2015] Com' for the sources in the 26 Com field or the prefix '[GR2015] Sge' for the sources in the gamma Sge field (where GR2015 stands for Greiner, Richter 2015) combined with the original source numbers and counterpart identifiers from Tables 8 and 9 of the reference paper. Thus, the first counterpart ('a') to the first X-ray source (1) in Table 8 of the reference paper has been named '[GR2015] Com 1a' in this HEASARC table (and been given the unique source number of 1001 herein as discussed above), and the last counterpart ('b') to the last X-ray source (132) in Table 9 of that paper has been named '[GR2015] Sge 132b' in this HEASARC table (and been given the unique source number of 2132 herein).

The Right Ascension of the optical counterpart to the X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 0.1 seconds of time in the original tables.

The Declination of the optical counterpart to the X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 1 arcsecond in the original tables.

The Galactic Longitude of the optical counterpart to the X-ray source.

The Galactic Latitude of the optical counterpart to the X-ray source.

The angular distance between the X-ray source centroid and counterpart positions, in arcseconds.

The designation of the optical counterpart (or a previous X-ray source designation in a few cases), often from the Guide Star or HD Catalogs.

This flag is set to 'C' for optical counterparts which are found to be constant on all of the plates, to 'C?' for objects for which there could be small amplitude variations which are marginal in the authors' data, to 'V' for variable objects, or to 'V?' for possibly variable objects. A void place means that the object was not tested for variability, for example, bright stars (mostly HD stars), and very faint stars below the plate limit.

The variable star designation, it the object is variable and one already exists. The preferred designation is that from the General Catalogue of Variable Stars and its supplements (GCVS, Moscow). If not named therein, the preliminary designation of newly discovered Sonneberg variables as given by the usual S-number is used (some prominent cases among the ~ 70 new variables discovered in this work have already been published by the authors separately, and have already received an IAU variable star name). In a few cases, the number in the New Catalogue of Suspected Variable Stars (NSV Catalogue, Moscow 1982) is given.

The object type and type of variability corresponding to the nomenclature of the GCVS for the optical counterpart coded as follows:

    Code  Meaning

      G = galaxy
      GCl = cluster of galaxies
      AGN = active galactic nucleus
      AGN? = supposed AGN only by reason of its blue color, though in single
              cases it may be a white dwarf or a cataclysmic variable.

      If possible, further sub-classification of AGN:

      	QSO = quasi-stellar object
      	BLL = BL Lacertae object
      	SY = Seyfert galaxy
      	ULX = ultra-luminous X-ray source

      CV = cataclysmic variable

      If possible, further specification of the CV:

  	UGSU = SU UMa type
          AM = AM Her type
          NC = very slow nova
          E = eclipsing variable
          EA = Algol type
          EB = Beta Lyrae type

      CA = chromospherically active star.

      If possible, further subclasses are specified:

          RS = RS CVn
          BY = BY Dra
          UV = UV Cet type

      LB resp. SRB = slowly irregular resp. semi-regular variable of late
                     spectral type
      PN = planetary nebula

The spectral type of the optical counterpart, generally taken from Simbad. A value of 'FG' means an F- or G-type star according to the objective prism spectra taken with the Hamburg Schmidt telescope on Calar Alto (Bade et al., 1998, A&AS, 127, 145).

The USNO B magnitude of the optical counterpart to the X-ray source.

The USNO V magnitude of the optical counterpart to the X-ray source.

The USNO R magnitude of the optical counterpart to the X-ray source.

The range or amplitude of the optical variability of the counterpart to the X-ray source.

The logarithm of the X-ray to optical flux ratio for the specified counterpart to the X-ray source. This ratio is somewhat arbitrary for variable sources, since the catalogued V (or B) band value is used and this is not contemporaneous with the X-ray observation.

The HEASARC Browse object classification of the optical counterpart to the X-ray source. This is based on the spectral type (spect_type value) if given, else on the source_type.

Contact Person

Questions regarding the RASS2FOID database table can be addressed to the HEASARC Help Desk.
Page Author: Browse Software Development Team
Last Modified: Wednesday, 23-Nov-2022 19:36:44 EST