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Thomas Diehl, 12/18/2012 08:10 PM


SV StandardStar

To supplement the standard star fields that are setting at morning twilight, I've created json files for all the DES standard star "E region" fields: E1-A, E2-A, E3-A, E4-A, E5-A, E6-A, E8-A, and E9-A (E2-A and E4-A should just be duplicates of the previous E2-A and E4-A json files). I have placed them in the ~DECamObserver/ExposureScripts directory on observer2.ctio.noao.edu, as well as attaching them to the current message. (The file names follow the
format: stdstarField_<name>.json.)

Their coordinates have been adjusted to center them in the N4 CCD:
Field RA DEC
----- -------- ---------
E1-A 01:24:50 -44:33:40
E2-A 04:03:00 -44:41:45
E3-A 06:42:54 -45:05:06
E4-A 09:23:44 -45:21:02
E5-A 12:04:11 -45:24:03
E6-A 14:45:33 -45:15:34
E8-A 20:07:22 -44:37:01
E9-A 22:45:37 -44:22:47

I did some checks, and it looks like standard star fields E2-A, E4-A, E5-A, and E6-A -- in combination with the MaxVis and Stripe 82 standard star fields
-- should provide adequate standard star field coverage through February 14 (although we might want to supplement with another field or two for February).

Some suggestions for taking standard star field observations for the rest of the DES season (through mid-February):

1. For this first year of DES, it is very important to try to observe
at least one Stripe 82 standard star field under clear conditions each
night (and preferably the more Stripe 82 fields the better). Currently,
these are the only DES standard star fields with calibrated standard stars
covering all the CCDs over the full DECam focal plane. Since the Stripe 82
fields are getting hard to observe in the morning twilight, this means
trying to hit at least one Stripe 82 field in the evening twilight. If
sky conditions are not clear during evening twilight, one should try to
observe a Stripe 82 field under clear conditions in the middle of night,
before they all set too far into the West.

2. If no Stripe 82 fields can be observed during a clear period during the
night, the MaxVis standard star field is a less-preferred-but-still-adequate
second choice.

3. For some nights, due to clouds, #1 and #2 above will be impossible to achieve.
Data taken on these nights will have to be photometrically calibrated at a
later stage of the DESDM pipeline -- so, not a disaster, but a situation
that we prefer to avoid if possible, since it causes more work on the
data processing side of things.

4. To check which standard star fields are in a good position to observe
(airmass < 2.10 and moon separation > 15 deg), use the decamStdFieldsTimeDate.py
on observer2.ctio.noao.edu:

source ~/dtucker/bin/setup_StdStarFieldPicker.csh    (or .bash if you are using bash shell)
decamStdFieldsTimeDate.py --help
decamStdFieldsTimeDate.py --UT='2012/12/19 00:43'

5. It is usually better to observe your high-airmass standard star field
first, since generally its airmass will be changing the fastest.

Many thanks for your help, and best wishes for good observing!