The optics of the RGS allow spectroscopy of reasonably extended sources, up to a few arc minutes. The width of the spatial extraction mask is defined by the fraction of total events one wishes to extract. With the default pipeline parameter values, over 90% of events are extracted, assuming a point-like source.
Altering and optimizing the mask width for a spatially-extended source may
take some trial and error, and, depending on the temperature distribution of
the source, may depend on which lines one is currently interested in. While
AB Dor is not an extended source, the following example increases the
width of the extraction mask and ensures that the size of the background
mask is reduced so that the two do not overlap.
To adjust the region mask with rgsproc in the GUI:
To adjust the region mask with rgsproc in the Command Window:
where parameters are as they were decsribed previously, and
Observing extended sources effectively broadens the psf of the spectrum in the dispersion direction. Therefore, it is prudent to also increase the width of the PI masks using the pdistincl parameter in order to prevent event losses.