Region masks

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:

1)

Call rgsproc in the ``Available Tools'' panel of the Hera GUI.

3)

Next to ``(re)start processing at'', use the pull-down menu to select ``4:spectra''. Next to ``percent of cross-dispersion PSF included'' and ``percent of cross-dispersion PSF excluded from the background'', enter 99. Next to ``percent of pulse-height distribution included'', enter 95.

4)

Click ``Run''.

To adjust the region mask with rgsproc in the Command Window:

rgsproc orders='1 2' entrystage=4:spectra finalstage=5:fluxing bkgcorrect=no
$$ xpsfincl=99 xpsfexcl=99 pdistincl=95

where parameters are as they were decsribed previously, and

xpsfincl - include this fraction of point-source events inside the spatial source extraction mask
xpsfexcl - exclude this fraction of point-source events from the spatial background extraction mask
pdistincl - include this fraction of point-source events inside the pulse height extraction mask

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.