Dark Energy Survey » Science Verification

h1. 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(2000)   DEC(2000)

    -----     --------   ---------

    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!