[vsnet-chat 3367] Re: V382 Vel comparison stars

[Brian Skiff <bas@lowell.edu>]

     Let me offer yet another reminder to look at the errors shown for the photometry
for each star in the Tycho-2 catalogue.  If these internal errors exceed 0.05 mag. in
either BT or VT, then the magnitudes are not reliable, period.  Thus the faint star
in the V382 Vel that disagrees between the AAVSO cahrt and Tycho-2 might indicate
an error in Tycho-2, not the AAVSO chart, since the Tycho-2 error for that star
is likely to be ~0.2 mag.  Again, also see Figure 6 of the Tycho-2 contruction paper,
where the authors admit that these internal photometric errors are _underestimated_
by 50 percent---in other words, if the error is given as say 0.09 mag., the true error
is actually 0.135 mag.
     Once more:  any Tycho-2 star where the error on the photometry is 0.05 mag. or
larger should not be trusted.  Look at the errors on every star, even those brighter
than V mag. 10.

\Brian

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