Affiliation
American Association of Variable Star Observers (AAVSO)
Sun, 10/12/2014 - 15:48
I am trying to make sure that I understand VPhot correctly before submitting any observations. I am using a star cluster to practise on with 27 target stars. When I save a sequence with 1 Comp Star and 1 Check Star , clear it, and then immediately reload the same sequence using the same image - I get 22 targets, 7 Comp Stars and no Check Stars. I am obviously doing something incorrectly - any guidance would be helpful. I am assuming that I will be able to use the same saved sequence on a different image using the same telescope with a different filter.
Thanks
Len Adam
Hi Len,
"I am trying to make sure that I understand VPhot correctly before submitting any observations. I am using a star cluster to practise on with 27 target stars. When I save a sequence with 1 Comp Star and 1 Check Star , clear it, and then immediately reload the same sequence using the same image - I get 22 targets, 7 Comp Stars and no Check Stars. I am obviously doing something incorrectly - any guidance would be helpful."
The easiest way to tell if you have saved your sequence correctly is to name it, save it, close that image, open another (same FOV and the same filter) and check to see if your sequence is listed in the drop down list in the upper left of the image window.
[Hint: You have to click on the save button when saving in VPHOT. You can't just type in a name and hit enter or return.]
"I am assuming that I will be able to use the same saved sequence on a different image using the same telescope with a different filter."
No- you must save different sequences for each specific filter. You cannot use your V sequence to measure R band images.
Mike Simonsen
Mike - thanks for the response. I have set up a temporary web page on my site with an explanation of the problem I am having with appropriate images to illustrate what happens. I would appreciate if you could have a look at this to give me your views.
Here is the link.
Thanks
Len Adam
Looked on your web page. The comp and check have silver apertures. They are saturated (SNR~2000). They are not used. That is why the check is 0. Take shorter images.
Why did you discard the second aavso comp? Use it as the check. Click on that comp on image and change comp box to check box. Update. Save seq.
You can use the same sequence for all filters assuming they have BVRI magnitudes. AAVSO comps usually do and you can generally trust mags better than other catalogs!
Ken
Ken/Mike
Much embarassment - that is it. Some pixels were 65535!
I had taken 60s B and V images at the same time and they work exactly as you outlined.
The sequence I had previously saved with more target stars worked also.
I noted the point about using the second comp star as a check.
I also take the point about the AAVSO magnitudes being more reliable and more likely to have the BVRI mags available.
Another lesson learned. (Well several!)
Thank you both for your time and support.
Len Adam