Files Used by the System

When the data acquisition system obtains a raw data frame from the control system, it writes it to an integration file whose name is of the form iyymmdd_oooo_iiii where `yymmdd' is the UT date, `oooo' the observation number and `iiii' the integration number. Integration files are, therefore, frames taken at a single detector position and are written to the directory $idir/. If a single integration is reduced, the result is written to a reduced integration file whose name is of the form riyymmdd_oooo_iiii, written to the directory $ridir/.

In CGS4, however, the spectrum may be oversampled by combining several integrations at different detector positions. A description of the instrument configuration during an observation is held in an observation file whose name is of the form oyymmdd_oooo in the directory $odir/. This information is combined with the data in the integration files to produce a reduced observation of size elements where n is the oversampling factor and is the readout area. This reduced observation, whose name is of the form royymmdd_oooo, is held in the directory $rodir/. The reduced observation file contains the reduced data for a single observation.

When observing astronomical objects, individual observations may be of OBJECT or SKY. Any number of OBJECT and SKY observations relating to one particular astronomical object may be combined together into a reduced group whose name is of the form rgyymmdd_gggg, where `gggg' is a unique group number, which is the first observation in the group as defined by the data acquisition system, held in the directory $rgdir/. These reduced group files contain sky-subtracted data. These files may be manipulated further by the automatic data reduction sequence to provide enhanced sky-subtraction for point sources and to ratio by a standard star. Depending upon the options selected the prefixes _pf, _dbs, _spc, _imspc may be appended to the reduced group filenames. For example, a group called rg920530_17 which is divided by a standard will produce a group called rg920530_17_dbs. If the same group is `polysky-ed', divided by a standard and a spectrum is extracted, two files will be created named rg920530_17_pf_dbs_spc and rg920530_17_pf_dbs_imspc. The Unix file clobbering mechanism should ensure that only one version of each file exists at any one time.

The system will clear up any temporary files upon receipt of an ENDGROUP command in the data reduction queue. The data acquisition system places such a command in the queue automatically but the data reduction system does not.

The data reduction system uses two other types of file. Wavelength calibrated CALIBR frames are held in files of type cayymmdd_oooo in the $rodir/ directory. Standard star observations are held in files whose names are of the form styymmdd_gggg, held in the $rgdir/ directory.

Note that the files contained in $idir/ and $odir/ are never over-written whereas the files in $ridir/, $rodir/ and $rgdir/ may be over-written by re-reducing the data.