[vsnet-chat 1263] Re: H/T chart vs. VT mags...

[Taichi Kato <tkato>]

Re: [vsnet-chat 1258] Re: H/T chart vs. VT mags...

Fraser Farrell wrote:

> (2) Knowing that the V mag is calculated from the mean Hpmag, calculate 
> the "offset" as:  offset = (V - Hpmag[mean])

   The Johnson V magnitudes in the Hipparcos Catalogues are from various
sources.  Many of them are from Hp and V-I color, some are from Tycho
observations, and some are from ground-based observations.  It would be
recommended to check the flag of the source of the V magnitude (in VSNET
H/T-based charts, we disregarded ground-based ones).

> This procedure (naively) assumes that the colour doesn't change between 
> max and min.  Also note that Hipparcos missed observing the full range 
> of many variables.

    We've recently had the same discussion in our local discussion group
on "what the representative magnitude of variable stars means in the Hipparcos
Catalogue".  It's enjoyable to check the represetative (median) magnitude
of some Mira stars.

Regards,
Taichi Kato

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