The task ommag converts the count rates to magnitudes in the appropriate instrumental bandpasses. The rates are taken from a source-list produced by omdetect or from a time series produced by evselect. The output file will be a FITS file identical to the input source-list or time-series except that the count-rates have been converted into instrumental magnitudes (in the specified filter bandpass: U, B, V, UVW1, UVM2, UVW2) and then written as an extra column in the original FITS file. The programme also calculates the limiting magnitude and writes the value in the FITS header.
Since SAS 5.4, flux conversion factors for U, B, V, UVW1, UVM2
and UVW2 filters are added in
the keyword in the COLORMAG extension of the CCF file, OM_COLORTRANS.
These flux conversion factors help users to get a rough direct estimation of
flux (expressed in erg/cm/s/Å)from count rates.
For each filter, the flux (in erg/cm/s/Å) can be obtained multiplying the count rates (counts/s) from SAS by the following values:
These flux conversion values have been obtained from observations of white
dwarfs standard stars. They reflect the current status of the OM
calibration, and are therefore constantly verified and updated. The
users should make sure that the most updated calibration is always
It should also be pointed out that these flux conversion numbers can only provide an approximated measurement of the flux without an a priori knowledge of the spectral type. For a more accurate determination of the flux, the users will find in our SAS watchout page updated values of the flux conversion factors for a given spectral type.