[vsnet-chat 681] T Phe comp stars

[bas@lowell.Lowell.Edu (Brian Skiff)]

     That the T Phe Landolt comparison star B is the variable RW Phe I think
is a "known", at least among professionals---it is listed correctly as such
in SIMBAD.  If this information (and the sequence itself) are not known by
amateur variable-star organizations, then it's good to get it out.  As an
aside, I have determined accurate (1") positions and IDs for all the 1100-odd
Landolt stars.  Most of the positions he published are inaccurate or simply
wrong, since they were computed from the rough Selected Area durchmusterungen
lists.  The positions and notes files can be obtained at:

http://ftp.lowell.edu/pub/bas/starcats/landolt.all
                                 ... /landolt.notes

     Landolt T Phe star C is an O-type subdwarf, and not likely to be
substantially variable.  Many of these stars are rapidly-oscillating with
very short periods at amplitudes of a percent or less, but that is not a
concern for visual observers (nor many CCD observers).
     The visual color term is _roughly_:  m(vis) = V + 0.2(B-V).  Thus in
the case of the O subdwarf versus the red star D (evidently an early-M giant
by its UBV colors), you would expect the blue star to be unnoticeably
brighter visually than in V, and the red star to appear some 0.3 mag. fainter
than V.  This reduces the apparent brightness difference to only 0.9-1.0,
so the discrepancy with Harvard numbers should be quiet noticeable to visual
observers.
     Finally, it is worth noting that in most of the southern sky (south of +3
Dec), the GSC magnitudes are on a blue-ish scale, so red stars will come out
too faint relative to V, and (extremely) blue stars will be a bit bright, just
as Mati found for stars C and D.

\Brian Skiff

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