[vsnet-chat 7551] Re: variable in OTJ16... field?

[substellar at Safe-mail.net]

-------- 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>
Cc: vsnet-chat at ooruri.kusastro.kyoto-u.ac.jp
Subject: [vsnet-chat 7550] Re: variable in OTJ16... field?
Date: Mon, 12 Jul 2010 13:37:50 +0100

> I've measured GSC 967 944 (V= 13.36) and GSC 967 756 (V=14.10) which are both 
> between 2 and 3 arcmin from GSC 967 904 in the direction of the brighter star 
> John mentions. These have SDs of 0.007 and 0.009 respectively over a 3.2 hr run. 
> Over the same run GSC 967 904 had a SD of 0.033.

Thanks for that.

Well, there you go.  I'd be happier if period search was done on the other stars, but with standard deviations of 0.007 and 0.009 I doubt you'd find much if any period, so it looks safe enough.

Given the 0.17 day period, and a confirmation of it, some sort of near sinusoid shape to the lightcurve (well, it was described as humping), and the Galactic Latitude, SX Pheonix type variable is preferred over delta Scutid and beta Cepheid.  That's somewhat dependent on period confirmation, though.  Actually, if it's asymmetic in shape that's maybe a better clue.

However, the 2MASS colour of J-Ks 0.566 contradicts this, and there seems no easy solution to that even taking interstellar extinction into account, which appears to be very low here, and those no reason for this sort of variable to have a near infrared excess.

0.17 days is too fast for a normal situation main sequence or giant star rotator, but if you double it to 0.34 days, in order to get two minima, one each for superior and inferior conjunction, an ellipsoidal variable of spectral type G to K is not precluded.  I get telled sometimes that ellipsoidal variables are perforce also EW contact binaries at low inclination, but I'm not good at geometry, so I couldn't say.

That'd fit the 2MASS colours better.

More lightcurve and more cycles might help distinguish between the two possibilities, and then again you may never be able to tell which it is.  Consistently different depth minima can occur even in EW stars, but with the likely noise level and a 0.08 magnitude range amplitude you may not be able to discern whether or not this is the case.

But it isn't "humping"...  It's either pulsating or mutually (self-)eclipsing.

There may be other alternatives that I am neither aware of and/or unfamiliar with.

Cheers

John