[vsnet-chat 2851] Re: (fwd) TASS Variable Carbon Stars (Greaves)

[Brian Skiff <bas@lowell.edu>]

     It is best when one does this sort of catalogue match-up to _not_rely_
on the positions in the catalogues themselves unless they are more-or-less
primaryu astrometric catalogues themselves.  The CGCS is a good example:
plenty of the "accurate" positions there (those given to 0s.1/1" precision)
are off by a lot, say 30" or more.  What's really required is to check on
an image that the positions for all the candidates are correct and real.
You can do this easily using the Goddard SkyView server, for instance, which
allows a coordinate gird to be overlain on a DSS cutout.  Blind matching
of catalogues is guaranteed to lead you astray.
     In re: the TASS variable HD 88392, given the tendency for double-star
observers to underestimate delta-mag, it is probably the case that the
fainter companion of the pair is much fainter than mag. 12.7, probably 13.5
or fainter.  The Houk spectral type also is a little odd.  The temperature
type is about right for the Tycho-2 B-V, but given the modest but 
significant proper motion (-32/+19 mas per year in Tycho-2 --- 50 percent
larger in RA than in Tycho-1!), the "bright-giant" luminosity class (II) is
almost certainly wrong.  Just as a guess, it is possibly a metal-weak star,
which could have led her to give it a high luminosity in error.  The star is
unusually faint for an ordinary HD star, so Houk's plates probably have this
star's spectrum underexposed.

\Brian

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