Data Format

Formally, the raw data files produced by the PISCO data acquisition programme conform to the standards of FITS images or MIDAS bulk data frames and can, therefore, be treated with all MIDAS commands pertaining to images. By contrast, the content of these data files is very highly non-standard and is a mixture of spectrum-like images and tables (does not apply to calibration frames, cf. below).

As described in the PISCO Operating Manual, there are two types of data files:

Calibration frames

contain 8 lines with 32 data points each which correspond to the 32 positions of the half-wave plate. In the first seven lines, seven measurements are stored; the eigth line holds their normalised mean.

Normal data frames

also consist of 8 lines with 32 data points each. However, their contents is as follows:

Line 1:

raw data of channel X in the direct mode of the compensating phase plate.

Line 2:

raw data of channel Y in the direct mode of the compensating phase plate.

Line 3:

raw data of channel X in the rotated mode of the compensating phase plate.

Line 4:

raw data of channel Y in the rotated mode of the compensating phase plate.

Lines 5-7:

results of on-line reduction as described in the Operating Manual. They are not used by MIDAS.

Line 8:

not used at present.