ASTROMET/TRANSFORM

This command computes the astrometric transformation parameters for the input data set using a least-square fitting algorithm. The input data is assumed to be two MIDAS tables with fixed columns names. The accuracy has been tested on standard stars, and in real life on many objects including comet Shoemaker-Levy 9, leading to very accurate impact times. ASTROMET/TRANSFORM only computes the transformation parameters. Other commands (see below) should be used to actually do the transformations, to edit the data, or to display the residuals.

The first input MIDAS table should contain the coordinates of the standard stars in RA and Dec. It should contain the following columns:

• :PPM Integer column (I6) containing the identifier of the standards;
• :R_A Real column containing the right ascension in degrees;
• :DEC Real column with the declination in degrees;
• :MAG Real column with the magnitude;
• :PMA Real column with the proper motion in RA in arcsec/year (NOT time_second);
• :PMD Real column with the proper motion in Dec in arcsec/year.

A possible way to produce this table is to use StarCat, with the MIDAS table output option, in the PPM catalogue.

The second MIDAS table should contain the XY measurements of the standards and should have, as a minimum, the following columns:

• :IDENT Character columns (A16) which must contain a character string; leading letters (e.g. PPM) are ignored;
• :XCEN Real column to contain the X measurement;
• :YCEN Real column to contain the Y measurement.

The remaining parameters are: the coordinate of the center, the epoch of the plate and the reference epoch of the catalogue, two instruments flag, a tolerance on the measurements, and a selection flag. These parameters are described in the help file of the command (HELP ASTROMET/TRANSFORM).