So I am nearly complete with a comprehensive telescope data analysis pipeline for Comet observations which uses APASS to calibrate the stars across the entire sky. However, I want to make sure I have a backup calibration method in case my comets happent to be in a region where the APASS photometry is not especially reliable (or perhaps even absent entirely!).
With that said, are the standard star fields used by APASS listed anywhere? In particular, would it be possible to get a list of names and coordinates of those fields? I will be doing nightly observations year round (primarily from the northern hemisphere telescope, but from time to time there will be southern hemisphere observations as well), so I will need standard fields observable across the entire sky.
Any information regarding the standard star fields would be greatly appreciated, so that I can then apply this calibration across the entire sky.
Steven Ehlert
Hi Stephen,
The APASS fields will be listed in the first APASS paper, but unfortunately, that won't happen until January. What I tried to do is find (a) fields that could be seen by both the northern and southern telescopes; (b) had Landolt standards for calibrating B,V and (c) had Sloan standards for calibrating g,r,i. Luckily, those conditions were easily met, since Landolt had calibrated equatorial fields and the Smith, et al. paper calibrated stars surrounding Landolt equatorial standards. I picked 13 regions spaced about every 2 hours in right ascension for the calibration. Those fields were:
10006 00:53:20
10012 01:57:20
10018 03:01:20
10023 03:54:40
10040 06:56:00
10051 08:53:20
10057 09:57:20
10068 11:54:40
10073 12:48:00
10089 15:38:40
10101 17:46:40
10106 18:40:00
10123 21:41:20
Each field has Declination 00:00:00 and field size 2.9x2.9 degrees. A typical night will visit about 12 fields at high and low airmass, with perhaps 300 stars used for the calibration. I then use the Landolt standards at +45 and -50 declination as cross-checks on the data quality. DR8, which fills in most of the northern missing fields, should be released shortly.
Arne
Thank you so much for this- this is exactly what I was looking for! Obviously this is just a backup for when I cannot use the stars within the field of view as "standards", but I need to make sure I have the most accurate and precise calibration possible for every field so it will be wise to get these data every night. I will also want to test to see what sort of systematics I may expect based on different calibration techniques.
Your mention about DR8 brought up another set of questions I wanted to ask you: is it possible to get the entire survey on my hard disk when it is released? Right now I am using the UCAC-4 version of APASS for my calibration, but it is probably prudent for me to try and get my hands on DR7 or DR8 for the calibration I need, but ideally I would have the entire catalog on hand so I could match it up to my fields of view without having to bug you with too many queries. Do you share the catalog with people who ask nicely?
Thanks again for all of your help in making my calibration so much more effective!
Steven Ehlert
Hi Arne,
I'll second a request to have the full DR8 via an FTP download (or by sending a USB flash drive). I know HQ doeesn't want to get bogged down with such requests but in my asteroid work (gasp!), I can't always access the on-line version or it's too slow.
Thanks.
Down to counting the minutes yet?
Clear Skies,
Brian D. Warner (WAB)
Hi Steven and Brian,
Now that APASS is being supported by NSF, it will be more available. I'll be bringing flash drives to the AAS meeting with the most recent APASS on them, and will also give on the APASS webpage the download address on the Cloud where you can retrieve the most recent version when it is available. I won't do that for DR7 since it is just about ready to be obselete. If you do check APASS against some other catalog to look for systematics, I'd always be interested in hearing the results. I compare against CMC14/15, SDSS, ASAS and several other catalogs internally. There will be some systematics at the 0.03mag level until we do the global solution next year.
Arne