[vsnet-chat 7549] Re: variable in OTJ16... field?

[substellar at Safe-mail.net]

Alrighty, we're looking good now.

Only one level of paranoia left.  The amplitude's still a bit low for my liking, but not unprecedented (and fewer low amplitude examples known for a variability type can simply be a consequence of pre-CCD era selection effects).

There is an F8 star lying at 8 arcminutes distance and of 8th magnitude.  All the eights.

This is probably outside all observers field of view when they image the UGSU?  No stray light at all possible into the background even if it is off the field of view?  This is six magnitudes brighter than the target star, and probably even more above the faint limit of the images.

This is probably worrying needlessly, and being overcautious.  That the star is F8 and has a radial velocity of -65 km/s and a proper motion of about 100 mas/y does make it suitable to be an SX Phe star though, albeit a brightish one, and the spectral type (if accurate) being possibly a bit too late for said.

So it's unlikely to be interfering, really.

But how to conclusively exclude it from consideration?  Well, of course it could be measured itself, but it's a bit bright and all that.

And this sort of thing can be tested for as a possibility by using the already available data.

If it was affecting the background signal then one of the other 14th magnitude stars lying between it and GSC 967 904, and there are a few, would also be displaying the same signal as GSC 967 904, and it wouldn't be due to interference from GSC 967 904.

This is probably somewhat over the top extra caution, but with low amplitude stuff a simple means of checking for integrity of signal is to check that neighbouring similar field stars are constant or whether they also have this signal.  If you have a low amplitude signal you are not sure about, check to see if the nearest twin also carries the same signal.

I've checked the ASAS3 data for the F8 star, it doesn't seem to have any periodicity around that value, or any value up to 0.2 days, however the noise level is about 0.1 V anyway, so that's not conclusive.

Cheers

John

-------- Original Message --------
From: "David Boyd" <drsboyd at dsl.pipex.com>
Apparently from: vsnet-chat-bounces at ooruri.kusastro.kyoto-u.ac.jp
To: <substellar at Safe-mail.net>, <novak at hvezdarna.cz>, <vsnet-chat at ooruri.kusastro.kyoto-u.ac.jp>
Subject: [vsnet-chat 7548] Re: variable in OTJ16... field?
Date: Mon, 12 Jul 2010 10:19:49 +0100

> I've just analysed 5 nights (5-9 July) data from Bart and myself on the putative 
> new variable GSC 967 904. All from essentially one longitude so there are strong 
> aliases. It looks like a genuine variable unrelated to the nearby superhumper.
> 
> The sinusoidal fitting methods in Peranso all favour a single cycle period of 
> 0.169d with amplitude 0.08mag. ANOVA seems to prefer a longer double cycle 
> period. No colour information seems to be available yet.
> 
> Regards,
> David