[vsnet-chat 328] Re: V1830 Sgr & Sequences

[Stan Walker <astroman@voyager.co.nz>]

At 05:11 PM 5/18/97 +0200, Berto Monard wrote:
>Hi,
>the RASNZ chart of V1830 Sgr shows this variable very close to a
>star of magnitude 12.0 (Vogt). I have questioned the accuracy of
>this magnitude on some earlier occasion and have used the
>VSNET sequences, which give this star 12.55. 
>Having a limiting magnitude of around 12.6 I never saw this star
>'with confidence'. ... Could it be V1830 Sgr?
>On the other hand, re my ignorance, if this star exists and be
>considered 12.0, previous outbursts of V1830 Sgr, reported at 12.2,
>would have actually been around 12.8. This could explain why I
>never saw such an outburst!  

Greetings, All,

Thanks to Bruce Sumner and Berto I can now place this star as the fainter of
the two semi-merged images on my CCD frames. It's about 9" from the above
star for which Bruce gives GSC 6851 1802, V=12.03, B-V=1.62 (Vogt 1977).
Thus both Downes & Shara and the VSNet charts place it rather too far south
which, in this very crowded field (average separation at magnitude 16 is
about 10"), is confusing. It's correct on Bill Gray's Guide charts.

After comments at PEP5 I allow the images to defocus a little to spread them
over more pixels. But they spread out a little anyway. Hence the merging.
Most visual observers should see this as a close double at maximum. Berto's
comments about the magnitude are interesting. With a B-V of 1.62 this could
be in the region where stars are usually low amplitude variables but in this
field there would be a lot of reddening and this star is probably G or K.
Did Vogt give a U-B which could allow this to be estimated?

I'm using unfiltered CCD with an ST6 which is normal for CVs. But the
response is obviously red-biased which is why the 12.03 comes out at 10.
Should V1830 still be around on the next clear night I'll take a couple of
frames in B and V using the Bessell filters to get a good value for both stars. 

Can I draw attention to Joe Patterson's call re V803 Cen? At present the
minima are over NZ but are shifting eastward. It varies between 13.3 and
14.7 and a couple of visual measures each night would greatly assist in
catching all cycles. 

Regards,
Stan Walker

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