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Douglas Tucker, 08/29/2013 12:26 PM


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.
  • For evening twilight, the standards can begin when the Sun is 8.5 deg below the horizon, or about 45
    minutes before the end of Astronomical (18-deg) Twilight.
    If there is a late state, standards can
    continue until the start of Astronomical Twilight; after the end of Astronomical Twilight twilight,
    survey science observations must begin.
  • For morning twilight, the standards should finish before the Sun is 8.5 deg below the horizon, or
    no later than* 20 minutes before the start of Astronomical (18-deg) Twilight.
  • 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.)
  • The list of DES standard star fields can be found here: The Standard Fields. Note that they
    are broken into 3 types: a "Golden" sample, a "Silver" sample, and a "Bronze" sample. The "Golden"
    sample fields, which have photometrically calibrated standards in all 5 DES filters (grizY) over the full
    DECam focal plane, take precedence. The "Silver" and "Bronze" either are missing calibrated Y-band
    data or do not have calibrated standards just yet over the full DECam focal plane. Always make sure
    that at least one "Golden" (SDSS) standard star field is observed each clear night.
  • 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 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 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:

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

  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:
    listOfStdsByUT.Sept2013.txt

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