Standard Star Instructions » History » Version 34

Version 33 (Douglas Tucker, 08/29/2013 12:44 PM) → Version 34/124 (Douglas Tucker, 08/29/2013 12:45 PM)

h1. 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 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 finish before the Sun is 8.5 deg below the horizon, or
_no later than 20 minutes after 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 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:

h2. Attachments