FAQ

Q: If fcmaker is not an official ESO tool, will the fcmaker charts still be accepted in Phase 2?

A: fcmaker is developed by an ESO Fellow with duties on UT4 at the VLT, but it is not an official ESO tool. Still, the fcmaker charts match all the official ESO requirements for finding charts, and were fine-tuned to meet the specific needs of the telescope operators and night astronomers during operations. The hope is that the inclusion of fcmaker finding charts in OBs will thus remain tolerated. Even for those instruments for which the use of the GuideCam Tool may be compulsory, I would still encourage the use of fcmaker once the OB has been finalized.

Q: How does fcmaker deal with proper motions?

A: fcmaker relies on astropy.coordinates.SkyCoord.appl_space_motion() routine to propagate proper motion between epochs. This routine assumes that the target is moving in a straight line. It also requires a distance along-the-line-of sight. In comparison, the VLT propagate proper motions by assuming that the target moves along a Great Circle on the sky, and thus does not require a line-of-sight distance.

By default, fcmaker assumes a distance of 1 AU (fcm_m.ephem_d) for targets with an ephemeris files, which by-and-large are found within the Solar System. For targets with proper motions defined as arcsec/year (either GAIA DR2 entries or the target set by the user), fcmaker assumes a default distance of 100 pc (fcm_m.default_pm_d). The error associated with these choices will remain negligible in most cases, particularly if user-provided coordinates are at recent epochs.