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Standard Star Instructions » History » Version 64

Douglas Tucker, 08/21/2015 04:39 PM

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h1. Standard Star Instructions
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_(Author:  Douglas Tucker; Created: 29 Aug 2013; Updated: 28 Sep 2013; Updated 5 Aug 2014; Updated 21 Aug 2015)_
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_*To cut to the chase, it is simplest just to run the kentools commands "ephem" and "standards" 
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  described in the [[Introduction to kentools]] to find the appropriate triads of standard fields 
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  to observe.  If, however, you prefer tabulated lists, read the following and see the standard 
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  star look-up tables for each month below.  Don't bother with standards if the sky is obviously 
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  cloudy, though.  ("Obviously cloudy" == any clouds seen by eye outside higher than 20 degrees
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  above the horizon, or moderate to heavy clouds seen on the RASICAM or TASCA displays.  If in 
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  doubt, take a full complement of standards.)*_
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* Standard star fields are to be observed every evening and morning twilight (and, for half nights, 
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  at switchover) that appear to be clear, where "clear" is determined by a quick visual inspection 
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  of the RASICAM image, of the TASCA image, or of the sky itself.  If in doubt, assume the sky is 
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  clear and take a full complement of standards.
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* For evening twilight, the standards can begin about 45 minutes before the end of Astronomical (18-deg) 
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  Twilight.  If there is a late start, standards can continue until the end of Astronomical Twilight; 
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  after the end of Astronomical Twilight twilight, survey science observations must begin.
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* For morning twilight, the standards should start 25 minutes after the start of Astronomical (18-deg) Twilight.
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* If possible, for each twilight period, 3 standard star fields should be observed:  one at low airmass 
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  (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 
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  better to observe the high-airmass field first, since its airmass will be changing the most rapidly.
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  _[Added 16 Dec 2013:]_ If you are comfortable doing so, you can try to arrange the observing sequence
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  of the intermediate- and low-airmass fields so as to reduce slew time.
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* For half-nights, 1 or 2 fields -- preferably a low-airmass field and a high-airmass field -- should 
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  be observed just before switchover.  (If only one field, a high-airmass field is preferred.)
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* The list of DES standard star fields can be found here:  [[The Standard Fields]].  Note that they 
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  are broken into 3 types:  a "Golden" sample, a "Silver" sample, and a "Bronze" sample.  The "Golden"
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  sample fields, which have photometrically calibrated standards in all 5 DES filters (grizY) over the full
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  DECam focal plane, take precedence.  The "Silver" and "Bronze" either are missing calibrated Y-band
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  data or do not have calibrated standards just yet over the full DECam focal plane.  *Always make sure
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  that at least one "Golden" (SDSS) standard star field is observed each clear night.*
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* For evening twilight, use the *DES/standard/Yzirg* scripts (which start with Y-band and end with g-band);
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  for morning twilight or pre-switchover, use the *DES/standard/grizY* scripts (which start with g-band and 
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  end with Y-band).   (For those rare nights when we also observe in u-band, please use the corresponding 
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  "DES/standard/Yzirgu" and "DES/standard/ugrizY" scripts.)
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* The script *DES/defocus_nightly.json* should be appended to the last evening standard. No "break" is needed. 
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  The script stays on the last standard field, defocuses, takes a single r-band image and refocuses. Obstac can
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  continue on from this point without trouble. If this script *fails* and the camera is out of focus press the
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  z-trim button on the ICS screen. This nightly defocus script should be run about once a week. Keep track
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  in elog and announce at the 4 o'clock meeting.
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* There are several useful scripts in the StdStarPicker package in the DECamObserver account on observer2,
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  including decamStdFieldsTimeDate.py and decamStdFieldsQueryNextSet.py.
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* To get a full list of standard star fields that are in a good position to observe (airmass < 2.10, 
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  moon separation > 15 deg, within Blanco horizon limits), use decamStdFieldsTimeDate.py:
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<pre><code>
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  source ~/dtucker/bin/setup_StdStarFieldPicker.csh      (or .bash if you are using bash shell)
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  decamStdFieldsTimeDate.py --help                       (for detailed help)
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  decamStdFieldsTimeDate.py --UT=now                     (for a list accessible right now)
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  decamStdFieldsTimeDate.py --UT='2013/09/17 00:43'      (for a list accessible at 00:43UT on Sept 17, 2013)
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</code></pre>
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* To get a preferred triad of standard fields -- a low-airmass field, a medium-airmass field, and a
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  high-airmass field -- for a given time and date, use decamStdFieldsQueryNextSet.py *(Note:  the kentools
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  command "standards" is a wrapper for this python script)*:
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<pre><code>
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  source ~/dtucker/bin/setup_StdStarFieldPicker.csh      (or .bash if you are using bash shell)
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  decamStdFieldsQueryNextSet.py --help                   (for detailed help)
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  decamStdFieldsQueryNextSet.py --UT=now                 (for a triad accessible right now)
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  decamStdFieldsQueryNextSet.py --UT='2013/09/17 00:43'  (for a triad accessible at 00:43UT on Sept 17, 2013)
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  (Warning: decamStdFieldsQueryNextSet.py will output a default json file, "stdstar.json".  Just ignore it.)
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</code></pre>
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* *For simplicity, look-up tables -- one for each month of DES Year 2 Operations -- listing the preferred 
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   triad for each 15-min interval throughout each night, can be found here:*
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> * "*listOfStdsByUT.Aug2015.txt*":https://cdcvs.fnal.gov/redmine/attachments/19418/listOfStdsByUT.Aug2015.txt 
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> * "*listOfStdsByUT.Sep2015.txt*":https://cdcvs.fnal.gov/redmine/attachments/19419/listOfStdsByUT.Sep2015.txt
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> * "*listOfStdsByUT.Oct2015.txt*":https://cdcvs.fnal.gov/redmine/attachments/19420/listOfStdsByUT.Oct2015.txt
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> * "*listOfStdsByUT.Nov2015.txt*":https://cdcvs.fnal.gov/redmine/attachments/19421/listOfStdsByUT.Nov2015.txt
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> * "*listOfStdsByUT.Dec2015.txt*":https://cdcvs.fnal.gov/redmine/attachments/19422/listOfStdsByUT.Dec2015.txt
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> * "*listOfStdsByUT.Jan2016.txt*":https://cdcvs.fnal.gov/redmine/attachments/19423/listOfStdsByUT.Jan2016.txt
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> * "*listOfStdsByUT.Feb2015.txt*":https://cdcvs.fnal.gov/redmine/attachments/19424/listOfStdsByUT.Feb2015.txt
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(Old Year 1 and Year 2 versions can be found in the attached files below.  Note that the tables vary year-to-year, since Moon-avoidance is built into these tables and the Standard Star Picker tool from which these tables were derived.)
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* _*You can also just run the the kentools commands "ephem" and "standards" described in the [[Introduction to kentools]] to find the appropriate triads of standard fields to observe.  This is usually the simplest option.*_
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h2. Attachments