Standard Star Instructions¶

• Standard star fields are to be observed every evening and morning twilight that appear to be clear,
  where "clear" is determined by a quick visual inspection of the RASICAM image, of the TASCA image, or
  (!) of the sky itself.

• If possible, for each twilight period, 3 standard star fields should be observed: one at low airmass
  (X<1.25), on at medium airmass (X=1.25-1.65), and one at high airmass (X=1.65-2.10). It is generally
  better to observe the high-airmass field first, since its airmass will be changing the most rapidly.

• For half-nights, 1 or 2 fields -- preferably a low-airmass field and a high-airmass field -- should be
  observed just before switchover. (If only one field, a high-airmass field is preferred.)

• For evening twilight, use the DES/standard/Yzirg scripts (which start with Y-band and end with g-band);
  for morning twilight or pre-switchover, use the DES/standard/grizY scripts (which start with g-band and
  end with Y-band). (For those rare nights when we also observe in u-band, please use the corresponding
  "DES/standard/Yzirgu" and "DES/standard/ugrizY" scripts.)

• There are several useful scripts in the StdStarPicker package in the DECamObserver account on observer2,
  including decamStdFieldsTimeDate.py and decamStdFieldsQueryNextSet.py.

• To check which standard star fields are in a good position to observe (airmass < 2.10, moon separation
  > 15 deg, within Blanco horizon limits), use decamStdFieldsTimeDate.py:

  source ~/dtucker/bin/setup_StdStarFieldPicker.csh      (or .bash if you are using bash shell)

  decamStdFieldsTimeDate.py --help                       (for detailed help)
  decamStdFieldsTimeDate.py --UT=now                     (for a list accessible right now)
  decamStdFieldsTimeDate.py --UT='2013/09/17 00:43'      (for a list accessible at 00:43UT on Sept 17, 2013)

• To get a preferred triad of standard fields -- a low-airmass field, a medium-airmass field, and a
  high-airmass field -- for a given time and date, use decamStdFieldsQueryNextSet.py instead:

  decamStdFieldsQueryNextSet.py --help                   (for detailed help)
  decamStdFieldsQueryNextSet.py --UT=now                 (for a triad accessible right now)
  decamStdFieldsQueryNextSet.py --UT='2013/09/17 00:43'  (for a triad accessible at 00:43UT on Sept 17, 2013)

  (Warning: decamStdFieldsQueryNextSet.py will output a default json file, "stdstar.json".  Just ignore it.)

• For simplicity, a look-up table of preferred triads for the nights of August 30-Sepember 30, 2013,
  listing the preferred triad for each 15-min interval throughout those nights, can be found here:

The Standard Fields¶