Guidelines for imaging data products
The table below contains the minimum set of information ('data items') requested for image headers (example header).
Providing these metadata in the FITS header and mapping it to the appropriate data items will enable users to fully characterise the data and to query for this information.
For each data item the table includes a description and a FITS header keyword suggestion. Keywords may assume different names as long as there is a one-to-one correspondence. The colour of each line indicates whether that item is:
| required | , | highly recommended | or | optional |
| Data item | Description | FITS keyword | |
|---|---|---|---|
| Curation | |||
| Facility | The observatory or facility where the data was obtained | ORIGIN | |
| Telescope | Telescope name. Please use the TELESCOPE key values from the raw frames (if present) | TELESCOP | |
| Creator | Name of PI/Co-I | PI-COI | |
| Collection | Proposal ID (identifier of the original proposal) or name of data collection | PROG_ID | |
| Photometric calibration | (uncalibrated, relative, absolute) | FLUXCAL | |
| Astrometric calibration | (uncalibrated, relative, absolute) | SPATCAL | |
| Software reference | Description of software/pipeline used for processing (e.g. MVM, IRAF, etc.), with version | PROCSOFT | |
| Bibliographic reference | Please use a format like 2006A&A...454..423V | BIBREF | |
| Instrument | |||
| Instrument name | Please use instrument values from the raw frames or as specified in the proposal | INSTRUME | |
| Filter name | Please use the filter values from the raw frames or as specified in the proposal | FILTER | |
| Instrument mode | Instrument mode (partly identifying optical path) as specified in the proposal(1) | INS_MODE | |
| Observation | |||
| Effective exposure time | Effective exposure time (flux rescaled) [s] | EXPTIME | |
| Total exposure time | Total exposure time [s] | TEXPTIME | |
| Unit of pixel values | (ADU, ADU/s) | BUNIT | |
| Number of frames | Number of combined frames | NCOMBINE | |
| Minimum flux | Min. physical value across image in BUNIT | DATAMIN | |
| Maximum flux | Max. physical value across image in BUNIT | DATAMAX | |
| Effective gain | Detector sensitivity in no. of electrons/count | GAIN | |
| Comments | Further explanations about this data product | COMMENT | |
| Target | |||
| Target name | Target name | OBJECT | |
| RA of the target | Right Ascension of target | RA_TARG | |
| DEC of the target | Declination of target | DEC_TARG | |
| Target position error | Positional uncertainty of target coordinates ["] | ERR_TARG | |
| WCS | |||
| NAXIS1 | Number of bins along axis 1 | NAXIS1 | |
| NAXIS2 | Number of bins along axis 2 | NAXIS2 | |
| CD1_1 | Linear transformation matrix element 1,1 | CD1_1 | |
| CD1_2 | Linear transformation matrix element 1,2 | CD1_2 | |
| CD2_1 | Linear transformation matrix element 2,1 | CD2_1 | |
| CD2_2 | Linear transformation matrix element 2,2 | CD2_2 | |
| CRPIX1 | Pixel coordinate of reference point | CRPIX1 | |
| CRPIX2 | Pixel coordinate of reference point | CRPIX2 | |
| CRVAL1 | Coordinate value of reference point | CRVAL1 | |
| CRVAL2 | Coordinate value of reference point | CRVAL2 | |
| CTYPE1 | (Longitude) Axis type(3) | CTYPE1 | |
| CTYPE2 | (Latitude) Axis type(3) | CTYPE2 | |
| CUNIT1 | Unit of axis 1 | CUNIT1 | |
| CUNIT2 | Unit of axis 2 | CUNIT2 | |
| Equinox | Equinox of WCS coordinate system | EQUINOX | |
| Reference frame | Frame of reference for equatorial coordinate system (FK5, ICRS) | RADECSYS | |
| Reference catalogue | Reference source for WCS (GSC2, USNO, ...) | ASTRCAT | |
| Spatial accuracy | RMS error of astrometric solution ["] | ASTRERR | |
| Characterisation | |||
| Start date time | Observation start date time of first exposure [MJD] | MJDSTART | |
| Stop date time | Observation end date time of last exposure [MJD] | MJDEND | |
| Seeing | Atmospheric seeing condition ["] | SEEING | |
| Seeing error | Atmospheric seeing error ["] | SEEINERR | |
| Photometry | |||
| Photometric magnitude system | (AB, VEGA) | PHOTSYS | |
| Photometric zero point | mag = -2.5log(ADU)+ZP+2.5log(T) where T=effective exposure time | PHOTZP | |
| Photometric zero point error | Error in photometric zero point [mag] | PHOTZPER | |
(1) An explicit list may appear here at a later time
(2) See 'Representations of celestial coordinates in FITS', Calabretta, M. R. and Greisen, E. W., 2002A&A...395.1077C