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Douglas Tucker, 08/29/2013 11:22 AM

Standard Star Instructions

(Author: Douglas Tucker, 29 Aug 2013)

  • 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 and
  • To get a full list of standard star fields that are in a good position to observe (airmass < 2.10,
    moon separation > 15 deg, within Blanco horizon limits), use

  source ~/dtucker/bin/setup_StdStarFieldPicker.csh      (or .bash if you are using bash shell) --help                       (for detailed help) --UT=now                     (for a list accessible right now) --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

  source ~/dtucker/bin/setup_StdStarFieldPicker.csh      (or .bash if you are using bash shell) --help                   (for detailed help) --UT=now                 (for a triad accessible right now) --UT='2013/09/17 00:43'  (for a triad accessible at 00:43UT on Sept 17, 2013)

  (Warning: 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