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: http://xmm.vilspa.esa.es/sas/5.4.1/doc/asmooth/node10.html
Дата изменения: Fri Jan 10 22:48:37 2003 Дата индексирования: Sat Dec 22 09:04:01 2007 Кодировка: |
In asmooth at present sources can be removed and the local background interpolated over their positions. This is achieved by the internal addition to inmaskset of holes at the source locations. The result is a smoothed map of the background, suitable as input to eboxdetect in map mode in place of the usual spline map.
To create such a map, the user should supply asmooth, via the parameters withsrclistset and srclistset, with a list of sources produced by either eboxdetect or emldetect. The source loist can be filtered (eg to use sources with only a single value of ID_BAND) using a filtering expression supplied via the parameter expression. Source positions and count rates are obtained from columns whose names are supplied via racol, deccol and ratecol. For each source, asmooth calculates an elliptical boundary, being the locus at which the point spread function (PSF) of the source decreases to some constant value times the value of the local background. The 'constant' is supplied by the user via bkgfraction; the local background value is read from the column in the source list named in parameter bkgratecol. A mask is constructed equal to the input mask minus holes corresponding to the elliptical loci. This is used to weight the convolution, as described above. The mask is available for inspection via the parameters writecheesemaskset and writecheesemaskset.
Note that at present the PSF used is only approximately correct.