[vsnet-obs 70105] Re: Comp stars for T Pyx (is HD 77938 a variablestar?)

[Sebastián Otero]

Hi, Robert,

----- Original Message ----- 
From: "Robert J. Modic" <robertjmodic at att.net>
To: <aavso-photometry at mira.aavso.org>; "VSNET-OBS" 
<vsnet-obs at ooruri.kusastro.kyoto-u.ac.jp>
Sent: Saturday, April 16, 2011 4:07 AM
Subject: [vsnet-obs 70101] Comp stars for T Pyx (is HD 77938 a 
variablestar?)


> Looking at some of the comp stars for T Pyx, I noticed that HD 77938 is 
> listed as a suspected variable star in some catalogs.
> However, the ASAS light curve for this star is flat with the normal
> scatter expected for a constant star.  I would like some clarification 
> about this star since its proximity to T Pyx makes it the only bright
> comp star that I can fit on the same CCD frame as the nova.


It is NSV 18130:
http://www.aavso.org/vsx/index.php?view=detail.top&oid=56565

If you check VSX you'll find that it is indeed a variable star, a red 
semiregular. Even though it is a NSV star if you have it flagged as "V" in 
VSX, that means it is a confirmed variable.
The paper by Tabur et al. (you'll find it on the VSX references section) 
found several periods.
One of those periods is the one with the largest amplitude in the several 
years of ASAS data (15.25 d.). But the amplitude is small (0.05 mag.) so the 
variability is lost among the mean magnitude variations in the phase plot. 
Total range is only 7.77 to 7.91 in V.

Given that it is also a red star (B-V 1.55, GCPD) and that T Pyx is blue in 
outburst, it doesn't seem to be a good choice as a comp star.

Cheers,
Sebastian