CRDS File Structure Explanation
HST Reference Data
Like most other HST data, the reference data are FITS files. In the case of legacy instruments and WFPC2, reference files and science data are in "waiver" FITS format. In both cases, this reference data can contain information in the form of tables or images
For a detailed discussion of understanding and working with these file types, see the HST Data Handbook.
Each operational reference file past or present has a unique name. The file name root has the format YMDHHMMSI_suffix.fits where each of the first eight values are known as the root name and selected according to the rules provided in the following table:
| Value | Description | Rule |
|---|---|---|
| Y | denotes the year | Values A to Z or 0 to 9; where 1990=A and 2015=0 |
| M | denotes the month | Values 1 to C, where January = 1 |
| D | denotes the day of the month | Values 1 to V |
| HH | denotes the hour | Values 00 to 23 |
| MM | denotes the minutes | Values 00 to 59 |
| S | denotes seconds | Values 0 to T |
| I | denotes the instrument | j=ACS, n=NICMOS, u=WFPC2, o=STIS, f=FGS, l=COS, i=WFC3, v=HSP, w=WFPC, x=FOC, y=FOS, z=GHRS, m=multiple |
The reference file type defines the file suffix appended to the unique root name. For example, p9e1544dj_drk.fits is an ACS file (the last character in the rootname is j); it is a dark file (has suffix drk); it was named on 14 September 2005 at 15 hours 44 minutes 26 seconds.
JWST Reference Data
JWST reference files can be in either FITS, ASDF, or JSON format; with extension fits, asdf and json, respectively. Their names are sequential and generated during the file delivery process by the CRDS delivery tools. These have the form: jwst_instrument_type_####.ext. Here a few examples:
jwst_nircam_flat_0112.fits
jwst_nircam_wavelengthrange_0003.asdf
jwst_nirspec_extract1d_0006.json
Pysynphot Instrument Reference Data
Synphot throughput and emissivity reference files are all FITS tables which have two of more colums. These columns should have the following type of data
- column 1: wavelength
- column 2: throughput (default)
- column 3 to n: throughput for different parameterized values (e.g. MJDs)
- Note:
-
- wavelengths must be in increasing order
- there must be no duplicate wavelengths
- there must be no wavelengths with negative or zero values
These have a sequential naming convention too. HST instrument related files have the format instrument_component_[wavelenght]_####_suffix.fits; where #### increases with each new file and suffix can be syn for throughput files or th for emissivity files.