First, the format of this catalog is ASCII and one can get the related column according to the following fits file head. Here we give a brief description of these columns column 1,2,3: Optical Group id, central galaxy id of this group, and the (central) galaxy id in NYUVAGC cataloge (see Yang et al. 2007,08,09 for detail) column 4: multi-z flag b1, b1=0 means clean (or isolated) detection,fmulti=1.0, the nearest neighbor detection is farther than 0.5*r200, b1=1,2,3...n refers to there are n nearest neighbor detections within 0.5*r200, and ordered by their redshift z. column 5: multi-z flag b2, for the i-th cluster (or group or detection) with b1=j+1, if b2/=0 then the former (i-1)th cluster (has lower redshift) with b1=j locate in 0.5*r200 of the i-th cluster. column 6: multi-z flag b3, b3(i+1)=1 means the i-th cluster has larger min{Rx,0.5*r200} than the former (i-1)th cluster (has lower redshift). column 7: mass sequence id for central, the k-th most massive galaxy in a group, k<=4. column 8: O-X offset, the offset (in arcmin) between the optical galaxy and X-ray cluster center. column 9,10: RA_X,DEC_X, the position of X-ray cluster (in J2000 deg.) column 11: cts, the X-ray photons count rate (1/s, in 0.1-2.4keV) in detection radius 0.5*r200 column 12: cts_error, error for the count rate column 13: Rx the radius of the extended X-ray source, here Rx = 0.5*r200 column 14: flux, the X-ray flux (in 10^(-12)erg/cm^2/s) column 15: LX, the X-ray luminosity of a cluster in 0.1-2.4keV (in 10^44 erg/s) column 16: LB, the bolometric luminosity (derived from LX) (in 10^44 erg/s) column 17: ext_corr, the beta model correction factor for the 'missing' fraction of the total projected source emission column 18: sigma, the velocity dispersion(in km/s) derived from the optical halo mass (see Yang et al. 2007, Eq.6) column 19: N, the number of galaxies in the group column 20: T, the gas temperature(in keV) of the group derived from the velocity dispersion sigma, (see White et al. 1997 or Shen et al. 2008,Eq.2) column 21: log(NH), NH is in 1/cm^2, the Galactic hydrogen column density column 22: Aexpo, the average exposure time on the detection (in seconds) column 23: z, the optical spectroscopic redshift of the central galaxy column 24: APR500, the aperture of r500 (in arcmin) column 25: S/N, the signal to noise ratio of the X-ray detection column 26: f_multi, the flux fraction of a X-ray source in a multi-cluster detection, see Eq.5 in this paper. fits file head: ============================================================== XTENSION= 'TABLE ' / ASCII table extension BITPIX = 8 / 8-bit ASCII characters NAXIS = 2 / 2-dimensional ASCII table NAXIS1 = 258 / width of table in characters NAXIS2 = 64646 / number of rows in table PCOUNT = 0 / no group parameters (required keyword) GCOUNT = 1 / one data group (required keyword) TFIELDS = 26 / number of fields in each row TTYPE1 = 'Group id' / label for field 1 TBCOL1 = 1 / beginning column of field 1 TFORM1 = 'I7 ' / Fortran-77 format of field TTYPE2 = 'galaxy id' / label for field 2 TBCOL2 = 9 / beginning column of field 2 TFORM2 = 'I7 ' / Fortran-77 format of field TTYPE3 = 'NYUVAGC id' / label for field 3 TBCOL3 = 17 / beginning column of field 3 TFORM3 = 'I7 ' / Fortran-77 format of field TTYPE4 = 'multi-z flag b1' / label for field 4 TBCOL4 = 25 / beginning column of field 4 TFORM4 = 'I2 ' / Fortran-77 format of field TTYPE5 = 'multi-z flag b2' / label for field 5 TBCOL5 = 28 / beginning column of field 5 TFORM5 = 'I2 ' / Fortran-77 format of field TTYPE6 = 'multi-z flag b3' / label for field 6 TBCOL6 = 31 / beginning column of field 6 TFORM6 = 'I2 ' / Fortran-77 format of field TTYPE7 = 'mass sequence id for central' / label for field 7 TBCOL7 = 34 / beginning column of field 7 TFORM7 = 'I2 ' / Fortran-77 format of field TTYPE8 = 'O-X offset' / label for field 8 TBCOL8 = 37 / beginning column of field 8 TFORM8 = 'F10.6 ' / Fortran-77 format of field TUNIT8 = 'arcmin ' / physical unit of field TTYPE9 = 'RA_X ' / label for field 9 TBCOL9 = 48 / beginning column of field 9 TFORM9 = 'F11.5 ' / Fortran-77 format of field TUNIT9 = 'deg.(J2000)' / physical unit of field TTYPE10 = 'DEC_X ' / label for field 10 TBCOL10 = 60 / beginning column of field 10 TFORM10 = 'F11.5 ' / Fortran-77 format of field TUNIT10 = 'deg.(J2000)' / physical unit of field TTYPE11 = 'cts ' / label for field 11 TBCOL11 = 72 / beginning column of field 11 TFORM11 = 'F14.9 ' / Fortran-77 format of field TUNIT11 = '1/s ' / physical unit of field TTYPE12 = 'cts_error' / label for field 12 TBCOL12 = 87 / beginning column of field 12 TFORM12 = 'F14.9 ' / Fortran-77 format of field TUNIT12 = '1/s ' / physical unit of field TTYPE13 = 'Rx ' / label for field 13 TBCOL13 = 102 / beginning column of field 13 TFORM13 = 'F6.1 ' / Fortran-77 format of field TUNIT13 = 'arcmin ' / physical unit of field TTYPE14 = 'flux ' / label for field 14 TBCOL14 = 109 / beginning column of field 14 TFORM14 = 'F14.8 ' / Fortran-77 format of field TUNIT14 = '1.e-12 erg/cm^2/s' / physical unit of field TTYPE15 = 'LX ' / label for field 15 TBCOL15 = 124 / beginning column of field 15 TFORM15 = 'F14.8 ' / Fortran-77 format of field TUNIT15 = '1.e44 erg/s' / physical unit of field TTYPE16 = 'LB ' / label for field 16 TBCOL16 = 139 / beginning column of field 16 TFORM16 = 'F14.8 ' / Fortran-77 format of field TUNIT16 = '1.e44 erg/s' / physical unit of field TTYPE17 = 'ext_corr' / label for field 17 TBCOL17 = 154 / beginning column of field 17 TFORM17 = 'F14.8 ' / Fortran-77 format of field TTYPE18 = 'sigma ' / label for field 18 TBCOL18 = 169 / beginning column of field 18 TFORM18 = 'F14.8 ' / Fortran-77 format of field TUNIT18 = 'km/s ' / physical unit of field TTYPE19 = 'Ngal ' / label for field 19 TBCOL19 = 184 / beginning column of field 19 TFORM19 = 'I4 ' / Fortran-77 format of field TTYPE20 = 'T ' / label for field 20 TBCOL20 = 189 / beginning column of field 20 TFORM20 = 'F5.2 ' / Fortran-77 format of field TUNIT20 = 'keV ' / physical unit of field TTYPE21 = 'log(NH) ' / label for field 21 TBCOL21 = 195 / beginning column of field 21 TFORM21 = 'E9.2 ' / Fortran-77 format of field TUNIT21 = 'cm^-2 ' / physical unit of field TTYPE22 = 'Aexpo ' / label for field 22 TBCOL22 = 205 / beginning column of field 22 TFORM22 = 'F9.1 ' / Fortran-77 format of field TUNIT22 = 's ' / physical unit of field TTYPE23 = 'z ' / label for field 23 TBCOL23 = 215 / beginning column of field 23 TFORM23 = 'F11.7 ' / Fortran-77 format of field TTYPE24 = 'APR500 ' / label for field 24 TBCOL24 = 227 / beginning column of field 24 TFORM24 = 'F10.5 ' / Fortran-77 format of field TUNIT24 = 'arcmin ' / physical unit of field TTYPE25 = 'S/N ' / label for field 25 TBCOL25 = 238 / beginning column of field 25 TFORM25 = 'F10.5 ' / Fortran-77 format of field TTYPE26 = 'f_multi ' / label for field 26 TBCOL26 = 249 / beginning column of field 26 TFORM26 = 'F10.5 ' / Fortran-77 format of field EXTNAME = 'OTX-Catalog' / name of this ASCII table extension END