In addition to the RASS, we performed a raster scan of pointed ROSAT observations covering the Lupus 1-3 subgroups. The journal of these pointed observations is given in Tables 1 (click here), 2 (click here), and 3 (click here). The reduction of these data was performed using EXSAS. The first step consisted in merging the photon event tables (PETs) of the individual observations, containing the data for each registered X-ray photon during the observation, into one single PET for each of the three observed Lupus subgroups. Then on each of these three PETs, like for the RASS data, source detection was performed seperately in the five different energy bands mentioned above. After application of both local and map source detection algorithms, detected sources were merged and tested with a maximum likelihood technique (Cruddace et al. 1988).
In a pointed ROSAT observation
the size of the point spread function increases from the center of the
field of view outwards, while in the survey it retains a constant value, thus
demanding somewhat different settings of the parameters of the
source detection algorithms (the main difference being the size of the
sliding window). As our raster scan
did not conform to either of these two cases, we tried a variety of parameter
settings, judging the results by visual inspection of the X-ray images. We
obtained the best results for a combination of the window size for
pointed observations, a constant value for the FWHM of the
point spread function (60 arcsec)
in the maximum-likelihood test, and
a conservative value of 
.
This procedure yielded 70 X-ray sources in Lupus 1, 52 sources in Lupus 2 and 96 sources in Lupus 3. To these sources the same selection procedure was applied as to the RASS sources. I.e. we excluded sources with a counterpart of known nature in the SIMBAD database and selected candidate sources for optical follow-up observations, according to the same criteria as mentioned above for the RASS source list.