I've begun observing EF Peg, measuring with VPhot. I choose the Varible Star Index, and EF Peg is easily identified. So I measure and create a report.
But when I look at the all recent observations, mine are at odds with the others. While mine are at >13 mag, others very close to mine in time, is <14. So... am I doing something wrong here, or what might be going on? Two of my observations are available here:
Grateful for any help on this.
Easier to just share a few images to me to check (MZK). Know how to share in VPhot? I'll take a look.
Were the other magnitudes from "one" observer or many? Safety in numbers?
Thanks, I was not aware of that!! However, I think I should be able to see the companion - I mean, 5" is not THAT close, and I have a pixel scale of 1.42 arcsec/pixel with this setup. So that might mean that I only see the companion then?
I looked at your image and confirmed what Patrick stated above.
VPhot places the aperture on top of the "adjacent" bright 126 comp star. Both you and PJEE (CCD Observers) both reported its magnitude rather than the true EF Peg target which apparently is much fainter according to all the visual observers.
In fact, 5" is quite close. How big is the measurement aperture you are using for this star? I bet it is a few pixels in radius. 3 pixels would be 4.5" at your pixel scale.
VPhot uses a default search radius of 5 pixels around the RA/Dec. Therefore, it virtually always places the centroid on the adjacent much brighter 126 comp star.
This is referred to as a "double trouble" star. There are several that are known and there was, at one time, a campaign to measure and warn observers about such targets. Such targets "require" extra diligence on the part of CCD observers to make sure that they "shrink" the search radius setting in VPhot (or any similar software) AND make special effort to readjust the aperture centroid to move it to the nearby and currently much fainter "true" EF Peg.
This will ALWAYS take extra care. In fact, I suspect based on my look at your image that you cannot currently identify this target even though it is just far enough away from the bright comp to be resolved. It is just too faint right now to be detected reliably. It is certainly there BUT just to faint to pick out of background.
EF Peg ranges from 10.7 to 18.5 mag and is a UGSU star. Most of the time it will be below your mag limit unless it goes into outburst. I suspect when it gets brighter you might have success? Try later / wait until an outburst. ;-)
BTW, both you and OJEE should delete your reported magnitudes for this star, since they are really mags of the 126 comp!
Great. Yes, I used an aperture of 3 pixels, and have difficulties seeing any indication of a double here (as opposed to V0627 Per, where it is clearly visible but very difficult to resolve).
I could delete my observation - or maybe mark it ias "fainter than" the now reported magnitude? Which is best?