[vsnet-chat 3887] Re: [vsnet-id 325] Info on a LMC star

[Brian Skiff <bas@lowell.edu>]

     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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