2.2. Reading HST FITS files

To analyze the data of the first generation HST instruments as well as from WFPC2, it is strongly recommended that it be read from its original FITS format and stored in GEIS format on disk. NICMOS and STIS data should remain in FITS format.

The task stsdas.fitsio.catfits can be used to list the contents of a tape. An example of such listing is:

The suggested parameters to read a FITS tape with the stsdas.fitsio.strfits task are:

As mentioned above, the header contains all the information about the observation. Important parameters can be listed using the stsdas.toolbox.headers.imininfo task; resulting in, for example for a WFPC2 image:

and for an FOS spectrum:

2.2.1 Other HST files

Besides the science headers described above, there are others that contain further information about the observation:

• The Standard Header Packet (extension shh) contains information about the ephemerides of the observation, the positions of the Sun and the Moon during the observation, engineering data and other proposal information.
• The Unique Data Log (extension ulh) contains data from the satellite like temperatures in different positions, voltages, gains, etc.
• The Observatory Logfiles are binary tables (extension cmi and cmj) with information about the name and positions of the guide stars used in the observation, any loss of lock time if any and the jitter information.

2.2.2 Association Data

The most recent instruments installed on board of HST, NICMOS and STIS, have the characteristics that to create a useful science observation several exposures are combined. These individual exposures constitute an association that can then be worked on (read, calibrated, archived and analyzed) together rather than as separate observations. In the case of NICMOS an association is the collection of all the observations of the source and the sky that are executed as part of an observation. NICMOS and STIS data should always remain in FITS format and not be read to other formats. The syntax to operate with these files is:

Please refer to the HST Data Handbook for more details about these files.

2.2.3 Other programs that read FITS files

Table 2 lists other programs, besides the STSDAS task mentioned, IDL, MIDAS, Figaro that can read FITS files (although most do not read group-formatted data)