[vsnet-newvar 1826] Re: GSC 6248:1255 Variability

["Ondrej Pejcha" <opejcha@volny.cz>]

> The star GSC 6248:1255 (in the field of V2540 Oph) appears
to be variable.  I
> used GSC 6248:1364 (V=11.05, Rc=10.66) and SAO 160704
(V=9.97, Rc=9.72) as
> comparison stars.  For reference, the Tycho 2 position
(J2000) is 17 37
> 22.694 -16 21 11.09 and photometry Bt = 13.160 and Vt =
11.422.  This is a
> red star (M type).  I did not find the star listed in the
GCVS.  My CCD
> measurements are:
>
> 20020213.584  11.76V  WJD
> 20020819.115  11.35V  WJD
> 20020819.101  9.27Rc  WJD
> 20020907.091  11.21V  WJD
>
> Assume an error of +/- 0.1 magnitude to account for lack
of color correction.

The field of V2540 Oph was observed at Brno observatory in
VRI during 2002 mostly by me, some observations also with
Petr Sobotka and Jan Skalicky. The star Doug mentions is
overexposed on I band frames, but can be well measured on R
and V frames. Here is a list of nightly averages of
differential magnitudes with respect to GSC 6248 1364 (V-C):

R band:
2452413.484744   -2.0581 0.0082  5
2452461.486586   -1.8167 0.0069  3
2452478.395457   -1.7443 0.0033  3
2452483.363241   -1.7603 0.0059  3
2452506.308848   -1.8347 0.0012  3
2452517.288041   -1.9262 0.0076  5
2452520.276873   -1.8321 0.0179  3
2452574.209109   -1.6174 0.0213  3

V band:
2452461.487938   0.3520 0.0164  3
2452478.397049   0.3800 0.0053  3
2452483.366422   0.4163 0.0043  3
2452484.325555   0.3703 0.0128  13
2452506.310779   0.4957 0.0173  3
2452517.290398   0.4278 0.0169  5
2452520.278407   0.4020 0.0114  3
2452574.207490   0.6024 0.0212  3

Column 1: JD
Column 2: Averaged magnitude, weighted according to
photometric errors
Column 3: rms scatter of averaged magnitudes
Column 4: number of observations

The last measurement should be taken with care as it was
obtained at very high airmass (~20 degs above the horizon).

The star is probably some kind of low amplitude semiregular
pulsator.

Best regards,

Ondrej Pejcha

P.S: I have searched my I band photometry of this field with
code similar to that of Pojmanski (Astro-ph/0005236). There
does not seem to be any other variable stars except for
V2540 Oph and GSC 6248 1255.

> Regards,
> Doug West
> http://hometown.aol.com/dwest61506/index.html
>

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