chandra_aca.drift.get_fid_offset

chandra_aca.drift.get_fid_offset(time, t_ccd, drift_pars=None)

Compute the fid light offset values for a given time and temperature.

The time and t_ccd inputs can be either scalars or arrays.

Parameters:

timeCxoTimeLike format

Time for offset calculation.

t_ccdfloat

ACA CCD temperature in degrees Celsius.

drift_parsdict, optional

ACA drift model parameters. If not supplied, the default parameters are used.

Returns:

tuple

A tuple containing the y-angle and z-angle offsets (in arcseconds) to apply additively to the nominal (FEB07) fid positions.

Notes

The apparent fid light positions change in accordance with the ACA alignment drift as a function of time and temperature. This is captured in the ACA aimpoint drift model. This function uses that model to provide the offsets in y-angle and z-angle (arcsec) to apply additively to the nominal fid positions.

The y_offset and z_offset values in this function were calibrated using the 2022-11 aimpoint drift model and the FEB07 fid characteristics. See sot/fid_drift_mon