XMM-Newton Science Analysis System: User Guide

5.9 Treatment of multiple RGS sources

Figure 45: An example of two sources in the RGS aperture. In this observation of YY Gem and Castor, it was already known from previous work that the two stars are bright, so the aperture was aligned perpendicular to the line joining the stars to allow maximum separation of the two spectra.

In the rare cases when two or more sources appear in the RGS aperture, rgsproc should be instructed to calculate the required number of spectra and modify its treatment of the background. In all such cases encountered so far, such as the observation of the active stars YY Gem and Castor shown in Fig. 45, the spectra have been well enough separated so that their selection regions can be treated independently. The current tools do not allow simultaneous estimates of overlapping spectra. It is not possible initially to specify more than one source, so a step-by-step approach is required adding sources one at a time with rgssources and setting source and background parameters accordingly before rerunning rgsproc to recalculate the spectra. Having accurate SIMBAD [22] coordinates for the brighter YY Gem and weaker Castor (not forgetting Castor's high proper motion), the sequence of events might be as follows to make spectra for both stars and exclude both from the background

 rgsproc withsrc=yes srclabel=YYGem \
                     srcstyle=radec srcra=113.655858 srcdec=+31.869386

 rgssources srclist=P0123710201R1S004SRCLI_0000.FIT addusersource=yes \
            label=Castor ra=113.649428 dec=+31.888276

 rgssources srclist=P0123710201R2S005SRCLI_0000.FIT addusersource=yes \
            label=Castor ra=113.649428 dec=+31.888276

 rgsproc entrystage=4:spectra procsrcsexpr='INDEX==3||INDEX==4' \
                              exclsrcsexpr='INDEX==3||INDEX==4'