Standard Star Instructions » History » Version 63

Version 62 (Douglas Tucker, 08/05/2014 06:34 PM) → Version 63/124 (Thomas Diehl, 08/29/2014 01:28 PM)

h1. Standard Star Instructions

_(Author: Douglas Tucker; Created: 29 Aug 2013; Updated: 28 Sep 2013; Updated 5 Aug 2014)_

_*To cut to the chase, it is simplest just to run the kentools commands "ephem" and "standards"
described in the [[Introduction to kentools]] to find the appropriate triads of standard fields
to observe. If, however, you prefer tabulated lists, read the following and see the standard
star look-up tables for each month below. Don't bother with standards if the sky is noticeably
cloudy, though.*_

* 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 about 45 minutes before the end of Astronomical (18-deg)
Twilight. If there is a late start, standards can continue until the end of Astronomical Twilight;
after the end of Astronomical Twilight twilight, survey science observations must begin.

* For morning twilight, the standards should start 25 minutes after 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.
_[Added 16 Dec 2013:]_ If you are comfortable doing so, you can try to arrange the observing sequence
of the intermediate- and low-airmass fields so as to reduce slew time.

* 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.)

* The script *DES/defocus_nightly.json* should be appended to the last evening standard. No "breaK" is needed.
The script stays on the last standard field, defocuses, takes a single r-band image and refocuses. Obstac can
continue on from this point without trouble. If this script *fails* and the camera is out of focus press the
z-trim button on the ICS screen. This nightly defocus script should be run about once a week. Keep track
in elog and announce at the 4 o'clock meeting.

* 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 *(Note: the kentools
command "standards" is a wrapper for this python script)*:

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, look-up tables -- one for each month of DES Year 2 Operations -- listing the preferred
triad for each 15-min interval throughout each night, can be found here:*

> * "*listOfStdsByUT.Aug2014.txt*":

> * "*listOfStdsByUT.Sep2014.txt*":

> * "*listOfStdsByUT.Oct2014.txt*":

> * "*listOfStdsByUT.Nov2014.txt*":

> * "*listOfStdsByUT.Dec2014.txt*":

> * "*listOfStdsByUT.Jan2015.txt*":

> * "*listOfStdsByUT.Feb2015.txt*":

(Old Year 1 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.)

* _*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.*_

h2. Attachments