I was recently observing V1084 Her, and I noticed that one of the stars in the sequence was far more variable then the others (here, labeled 122). I've attached the light curves here to illustrate what I'm talking about (this is through a luminance filter, although the comparison stars are V). So I removed it from my sequence, and decided I should maybe do what I can to get it removed from VSX by submitting it as a variable. I included some data from ASAS-SN, which I thought demonstrated a historical V fluctuation of several magnitudes (link).
Well, it was rejected by the VSX team, but they had a very helpful conversation with me (thanks Sebastian Otero!). I didn't know you could "Recompute" the light curve to get more data - when you do, it looks much more like a star that is basically constant in magnitude, but with scatter due to several rather natural sources (link). For example, there is a nearby bright star which is possibly being mis-identified by the algorithm.
Well, now I'm kind of interested in trying to pin down the nature of this star. From my conversation with the team, he did suggest reaching out on the forums to see if anyone else knew anything more about this source, or what I could to learn more about it. So, I'm taking all suggestions!
It seems like confirming the variability in a V-filter is a reasonable next step (since I've only done luminance so far) - I have access to the iTelescope network, so I can do that. I can use VSX for differential photometry in V and B, but I guess I could create sequences in other surveys for other filers and get some complete color indices that way. And I have access to a spectrometer, but I've never gone down to magnitude 12....I could try. And of course, I'll start observing the thing regularly to get more time-domain info.
Anyone have any other suggestions, or advice about the prospects here?
Hi Christopher
The first thing I notice is the very bright star in the field. Is there any way that you can get a reasonable signal from a 12th magnitude star while maintaining linearity given that there is such a bright star next to it?
Ray
Hi Ray, thanks for the reply.
The typical FWHM here is 3.55", whereas the stars are separated by 4.9' (see the image TYV-SS I attached to the main thread), so I don't think linearity is an issue. There is some bleed from the brighter star, but as long as the camera orientation is taken care of, I think you're ok. Do you agree?
Also, do you happen to be running a CCD and clocking 122 through the bright and perhaps over-exposed star to the east? If so, I wonder if some variability of the bright star shows up on comparison star 122. You might turn the camera 90 degrees and see if the variability of 122 goes away. Then depending on which way the CCD is bucket-brigading, comp 143 may become variable if the bright star remains overexposed. I likely have the CCD operation and geometry bollixed up, but it is a quick check.
Ray
These observations were taken with a remote telescope on the iTelescope network, so I can't turn the CCD. To check that I guess another telescope could be used for follow-up, but I think being close to the saturation limit will turn out to be the problem.
If you want to get 122 removed as a comparison star, submit your findings to the Sequence Team. They will take a look at it and remove if necessary.
Essentially, I was told by the VSX team that what I had produced was not enough to remove it from the sequence. I don't agree - if I had not been watching the stability it almost certainly would have changed my differential photometry results, so it seems like removing it while *not* declaring it "a variable" is a reasonable response. But anyway, they want more so that's what I'm trying now.
Hello Christopher,
Let's see if other people also have similar issues with this same star. Then removing it would be justified. If we can't find further evidence of variability, there would be no reason to do that.
And if it is not variable, the contamination issue should be investigated. The bright star is rather far away. For surveys like ASAS-SN it is not a surprise that there is light contamination because of its low resolution but for higher resolutions, it is not easy to understand. And since it is likely not an issue with the star itself, it shouldn't affect everyone in the same way.
We need more data. If there is anyone else having an issue we will remove it.
Was it this 122 the brightest of the comp stars used? Is saturation ruled out?
Cheers,
Sebastian
Apologies to Sebastian (and the others who are helping me here) - this source was indeed near saturation. I've reserved some time in a few weeks for a final check at a lower exposure time, but at least my initial suspicions should be discounted.
Sorry again, but thanks to everyone for their time and patience.