[vsnet-chat 5974] Re: [AAVSO-DIS] Charts and more

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

Re: [AAVSO-DIS] Charts and more

> It would be more useful to include B-V for each star. First of all, B-V
> has a better correlation with visual response than just spectral type.
> Second, as B-V approaches the limits approximately +0.6 < B-V or B-V <
> -0.1, the visual response tends to diverge more rapidly from V. Sometimes
> there is no choice but to include these "borderline" comp stars (or
> sometimes even "red" stars B-V > +1), due to a lack of any others to make
> a suitable sequence. It is important to at
> least alert the observer to this fact, so the appropriate care can be
> applied for the estimate.

   It would be a meaningful question whether this color choice prescription
should apply to all variable stars with different colors.  This is because
in many? (at least in some) variable star handbooks, observer are suggested
to use comparison stars having similar color to the variable stars, and
at least some observers indeed search for M-type stars for comparison of
Mira-type stars.  In my opinion, this is a "visual counterpart" of the
unfiltered CCD band matter.  I would therefore suggest to consistently
use bluer (e.g. 0.0 < B-V < 1.0) comparison stars whenever possible for
all sorts of stars, and visual color-term correction should be applied
(when necessary) according to the object's color.

Regards,
Taichi Kato

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