[vsnet-chat 3888] RE: [vsnet-id 325] Info on a LMC star

["Sebastian Otero" <varsao@fullzero.com.ar>]

Thanks, Brian:
                      As you said the star is double and there is a 11.5
magnitud companion. Taken together the 10.6/ 10.7 value from the GCPD
(supposing it is for the primary and not for AB) and the 11.5 (approximate
mag) star make a 10.2/10.3 star. That's what I observed (10.25).
However, I'll keep watching it.
Catalogues are full of mistakes like this: combined brightness is presented
as A brightness or the opposite. But one never knows and maybe both 10.96
and 10.64 are for the same VARIABLE star....

Let's observe.
Thanks again. I know what to do next time.

Sebastian.


>      It is very helpful in such cases to look at a picture rather than
> trying to parse out what's going on from catalogues alone.  Try using thhe
> Goddard SkyView utility:
>
> http://skyview.gsfc.nasa.gov/cgi-bin/skvadvanced.pl
>
> o  key in the coordinates
> o  click on "Digitized Sky Survey" in the next set of windows
> o  under "optional parameters", toggle "Grid" to 'yes'; change the image
>    size (degrees) to 0.1
> o  submit the request
>
> ...this will bring up a new window with (in this case) a short-exposure
> image of the relevant region.  As you can see from comparing coordinates
> with the grid, the Tycho-1 detection is bogus, and Tycho-2 is correct,
> and yes, it's a double star.  The Tycho-2 photometry is probably simply
> wrong.  Any star with photometric uncertainty > 0.05 mag. (on either
color)
> in Tycho-2 should be treated as an approximate value.  In this case, the
> uncertainty is +/- 0.173 on VT.  Remember also that these errors are
> _underestimated_ by half according to the people who built the catalogue.
>
> \Brian


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