[vsnet-chat 736] Re: USNO-A

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

Dear Dr. Henden,

    Thank for your time and comment.  Yes, I wish I will ask Dr. Monet
also, on the present and future nomenclature recommendation; as a matter
of fact, I am just waiting from him for a permission to the non-private
usage of an extract version of USNO A1.0 dedicated for variable star
researches, particularly as a portable tool for observing.  I will ask him
about the USNO catalog more, when I have an answer, since efficiency of
this kind of extraction also strongly depends whether the "running number"
nomenclature is necessary or not.  Omitting the running number will increase
the number of stars containable in the same media to about 15%.

> I personally still strongly prefer a coordinate-based nomenclature so that
> someone doesn't have to have a copy of the particular catalog (or the
> original paper) in order to locate objects.

    In referring to the USNO catalog (except for reporting already designated
one in the IAUC), I always accompany entries with coordinates to the last
significant digit of the original catalog, so that a reader can uniquely
identify or call it.

On the photometric calibration:

>   I don't have any favorite transformations, so your transformation to
> V is as good as any.  You should compare it to the GSC magnitudes since
> they are supposedly V-like, or (as I'm sure you have already done) to PEP or
> CCD sequences.

    Yes, the transformation equation has been derived from comparisons
with the secondary CV sequences of yours(!), and of Misselt etc.  For some
other fields, this equation-based, USNO-based charts look roughly acceptable,
with some occasional zero point errors (and the effect of blending), but
in terms of color, the derived artificial V sequence seems usable for
visual observation, with the same precautions as we have noticed during the
8-year experience with the GSC.  I suppose the most needed magnitude range
(below V=13) might be well covered in the linear part of photographic
response.

    Also thank you for your information on the relation between USNO r and Rc.
This would be quite helpful for amateur CCD observers who wish to use the
USNO catalog for casual comparisons (though not for actual photometry).

Regards,
Taichi Kato

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