[vsnet-chat 1244] Re: H/T chart vs. VT mags...

[Taichi Kato <tkato>]

Re: [vsnet-chat 1237] H/T chart vs. VT mags...

Dear Robert and others,

> I thougth these chart were made using the Hipparchos and Tycho catalgues,
> but the sequences show large differences compared with the 
> VT mags or Hp mags. from the Guide6.

   These charts used standard (Johnson) V magnitudes in Hipparcos and Tycho
catalogues, after disregarding ground-based (HIP) and Tycho measures with
unreliable flags.  VT mags are a Tycho-specific system, having a central
wavelength close to V but shorter, and a narrower bandwidth, and not
Johnson V.  Hp mags are a Hipparcos-specific system, having a much broader
passband than V and B.  Many stars are far off in Hp from V, so please
never use Hp mags for comparison.

Regards,
Taichi Kato

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