This is a first draft proposal of a pointing table. Please note that the format is likely subject to change.

POINTING extension

The POINTING extension is a binary FITS table that contains for a number of time stamps the pointing direction of the telescopes. A pointing is here defined as the centre of the field of view (or centre of the camera coordinates). In reality, all telescopes may point to different positions (for example for divergent pointing mode). The main purpose of the POINTING extension is to provide time dependent information on how to transform between celestial and terrestial coordinates.

See also HFWG Recommendation R3 for the OGIP standard.

Mandatory columns

  • TIME type: float64, unit: s
    • Time stamp of pointing.
  • RA_PNT type: float, unit: deg
    • Pointing Right Ascension (see RA / DEC).
  • DEC_PNT type: float, unit: deg
  • ALT_PNT type: float, unit: deg
  • AZ_PNT type: float, unit: deg

Mandatory header keywords

  • MJDREFI type: int, unit: days
    • Integer part of instrument specific MJD time reference
  • MJDREFF type: float, unit: days
    • Float part of instrument specific MJD time reference
  • TIMEUNIT type: string
    • Time unit (e.g. ‘s’)
  • TIMESYS type: string
    • Time system (e.g. ‘TT’, ‘MJD’, ‘JD’, ‘TJD’)
  • TIMEREF type: string
    • Time reference frame, used for example for barycentric corrections (options: ‘LOCAL’, ‘SOLARSYSTEM’, ‘HELIOCENTRIC’, ‘GEOCENTRIC’)
  • GEOLON type: float, unit: deg
    • Geographic longitude of array centre
  • GEOLAT type: float, unit: deg
    • Geographic latitude of array centre
  • GEOALT type: float, unit: m
    • Altitude of array center above sea level