Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 03/22/2012 - 21:46
I was wondering if there is any easy way to bring APASS photometry into VPHOT? The variables in question are V718 Tau and V1235 Tau. My FOV is 20x30' and VPHOT only lists one comparison star far enough into the field to use (118). But there seems to be plenty of candidates in APASS withing 0.5 degrees of V718 Tau.
Hi Ed:
APASS may be made active on VPhot sometime after the next release. Geir and Arne will make the decision.
However, Geir had created this functionality many months ago and I know that it worked. The main issue that needs resolution is that too many comps are often present in a field! A way needs to be designed to select fewer comps on the basis of magnitude, color, or other parameter.
I hope I don't get in trouble for mentioning this!? The current server issue has potentially put a crimp on this plan/schedule?
In the interim, I have used seqplot to identify APASS comps and created my own sequence for a few targets.
Ken
Thanks for the reply, Ken. I can see the problem. I think I will try your method and see how it works. One way to extend the system might be to share use defined fields. I don't know enough about sharing to know if such a strategy would work. I can see problems with sharing was well.
Ed
Hi Ed,
I was wondering about the same thing (just 10 months later) and searched the AAVSO forums to find out. Guess not.
I use Aladin to display APASS stars (see attached). Didn't see alot of mention of Aladin in the forums either. Aladin is available here: http://aladin.u-strasbg.fr/aladin.gml
In Aladin, you can set up your own FOV and display a plethora of astronomic surveys including GCVS, VSX, all the big star (and non-stellar) surveys and, through file import, APASS stars.
Attached is a screenshot of Aladin centered on V0718 Tau with your 20'x30' FOV shown as a white rectangle, VSX stars indicated with red squares, and APASS stars indocated with green diamonds. While not integrated into VPhot, using Aladin this way makes it easier to assign comp and check stars from the APASS survey.
Steps to get this screenshot:
Aladin has so much capability (documentation is on the web site). You may find others uses for it, so give it a try. If you need some help, just ask.
Michael
I emailed Geir a few weeks ago and asked him about setting VPhot up to include APASS comps. With enough users asking (nicely) for this, he may be able to update his previous algorithm (1 year old) and get it working again. It was working for a few days at the beginning of last year. The major issue relates to filtering comps so that so many comps don't appear! That filter is what would take a lot of his programming time to accomplish.
So Geir, note that it is now on more than Ed's and my wishlist!!
Ken
Noted!
I'll talk to Arne about this again.
Geir
If I see this right APASS objects are still not available as comp stars for VPhot - is there any timeframe in view when to expect this?
Currently I use UCAC4 objects with V-mag values given assuming these are coming from APASS or A. Henden but there is a lot of steps required to define comp stars this way manually.
Wilfried
Hello Wilfried,
As long as your target star is included in the VSX you can request the "sequence team" (i.e Tim Crawford) to make a comp star set for use in VPhot. I most cases you'll have a custom made set (for your FOV, filters, etc.) in just a few days. In my experience most of the stars in the newly created sequences are APASS stars.
http://www.aavso.org/request-comparison-stars-variable-star-charts
If your target star is not in VSX you can ask that it be included after you've logged on to VSX.
Phil Sullivan
I can concur with Phil. APASS stars are available as comps. Refer to footnote (29) in the field photometry tables of VSP.