Catalogues

 

A catalogue file is a list of target names and positions in the format used by the WHT TCS. A catalogue is simply a text file of positional information in free format with spaces as separators. All data for an entry should be on one line of the file. Anything following an asterisk or exclamation mark is treated as a comment and is ignored. Do not use tab, control or other peculiar characters. The parameters must be in the order: Name, Right Ascension, Declination, Equinox, proper motion in right ascension, proper motion in declination, Epoch, Parallax, Radial velocity. The first four parameters are mandatory and the remainder are optional with sensible defaults. The formats and units of the necessary parameters are as follows:

• Name--up to 20 characters. Embedded spaces are allowed, but if they are used, then the name must be enclosed in double quotes (e.g. "NGC 7027").
• Right ascension--hours, minutes, seconds, separated by spaces.
• Declination--degrees, minutes, seconds, separated by spaces.
• Equinox--for mean positions, a leading letter indicates the coordinate system:
  * B implies mean pre-IAU76 or FK4
  * J implies mean post-IAU76 or FK5

  The letter is followed immediately by a number indicating the epoch of the mean equator and equinox of that system (e.g. B1950.0 or J1987.5).
  * For apparent positions this field should contain the word APPARENT (abbreviable to A). In order to maintain strict compatibility with the WHT TCS, no epoch is specified, and the DATE command should be used to set the epoch of observation.

The formats, units and defaults of the optional parameters are as follows:

• Proper motions--in right ascension (seconds of time per year) and declination (arcseconds per year). Default to zero if not specified.
• Epoch of position--(year). This should not be confused with the equinox. The epoch of observation is used in conjunction with the proper motions to correct for the space motion of the object. If the epoch is not specified, then it is assumed to be the same as the equinox.
• Parallax--(arcseconds). Generally negligible. Defaults to zero if not specified.
• Radial velocity--(km s$-1$, positive for a receding object). Generally unimportant. Defaults to zero if not specified.

Examples of catalogue files are:

• The simplest possible catalogue contains only name, right ascension, declination and equinox:

    3C567    12 34 56.78  -01 23 45.6  B1950 
    NGC123   00 12 46.6    05 34 56    J1987.5 
    COMET    12 12 12.12  +12 12 12.1  A

• A more complicated entry might include proper motions:

    SP1  00 31 22.2  -12 24 21  B1950.0  0.011 -0.17

• The ultimate in complexity has parallaxes and radial velocities too:

    S01-07  00 50  7.596  -10 38 39.54  J2000  -0.01531 -0.2287 2000  .059    8 
    S01-22  01 06  7.724  -23 59 33.07  J2000  -0.00225 -0.0409 2000  .000    0