Improved ROSAT/WFC calibration and ROSAT/WFC Pointed Phase Source Catalogue *************************************************************************** Work on a ROSAT/WFC Pointed Phase Source Catalogue based on the processing of the ROSAT/WFC data performed in Tuebingen has recently been completed (Kreysing, Brunner, Staubert, 1995, submitted to A&A Supp.). The catalogue covers all pointed ROSAT/WFC observations from the time period June 20th, 1990 to July 15th, 1994. It lists 1016 individual detections, corresponding to 321 detected sources. A continuously updated version of the catalogue is kept on this archive. A subset of 242 observations of non-variable White Dwarfs from this catalogue which were observed repeatedly (both in the ROSAT/WFC All Sky Survey and/or during the pointed phase) were used to calibrate the temporal change of the WFC efficiencies. Results from a simultaneous fit to all available data points are given in the table below. The table lists the degradation history of the effective areas for the S1 and S2 filters, normalized to the beginning of the mission. As a comparison, values from the most recent WFC Master Calibration File (MCF-12) issued September 1993 by the UK Data Centre are also given. Details on the improved calibration may be found in Kreysing, Brunner, Staubert (1995; submitted to A&A Supp.). Note that WFC effective area tables (OPAEFF.TBL) distributed from Tuebingen so far are already corrected for the degradation of the WFC efficiency by interpolating the MCF-12 efficiencies for the date of each observation ! To make use of the improved calibration for your old datasets, simply apply the correction factors given in the last two columns, below, to the effective areas already available to you (linear interpolation between the dates listed will be sufficient). Effective area tables issued with future WFC observations will already incorporate the improved calibration. WFC efficiencies for filters S1 and S2 (normalized to beginning of mission) *************************************************************************** Old calibration Improved calibration Correction (MCF-12/UKDC) (Tuebingen) factors Date MJD S1 S2 S1 err 1) S2 err 1) S1 S2 01-Jun-90 48043 1.0 1.0 1.0 - 1.0 - 1.0 1.0 08-Jul-90 48080 1.0 1.0 0.945 0.06 1.009 0.18 0.945 1.009 26-Jan-91 48282 2) 0.685 0.830 0.664 0.03 0.758 0.11 0.969 0.913 03-Mar-91 48318 0.120 0.297 0.175 0.02 0.138 0.03 1.458 0.465 13-Mar-91 48328 0.1128 0.154 - - - - - - 08-May-91 48384 0.0738 0.110 0.049 0.005 0.112 0.02 0.664 1.018 09-May-91 48385 0.182 0.310 0.190 3) - 0.200 3) - - - 19-Jun-91 48426 0.136 0.198 0.150 0.01 0.178 0.03 1.103 0.899 18-Oct-91 48547 0.112 0.137 0.112 0.008 0.135 0.02 1.000 0.985 12-Jan-92 48633 0.140 0.185 0.125 0.009 0.155 0.02 0.893 0.838 10-Jun-92 48783 0.140 0.185 0.131 0.008 0.169 0.03 0.936 0.914 23-Jan-93 49010 0.145 0.187 0.128 0.007 0.157 0.02 0.883 0.840 21-Feb-93 49039 0.145 0.187 - - - - - - 22-Mar-93 49068 0.145 0.187 - - - - - - 30-Jun-93 49168 0.145 0.187 0.122 0.007 0.157 0.02 0.841 0.840 15-May-94 49487 0.145 0.187 4) 0.111 5) - 0.157 5) - 0.766 0.840 1) 1-sigma errors from chi-square fit to 242 observations of WDs 2) corresponds to survey day 180 (end of the All Sky Survey) 3) estimated value, no calibration source available 4) extrapolated MCF-12 values 5) value of fitting function at end of calibration dataset; no error determined