[vsnet-chat 695] Re: on chart and seuences (Fidrich)

[Taichi Kato <tkato>]

Robert Fidrich wrote in vsnet-chat:

> I downloaded some TAC/HIC/HIP charts.
> Could someone inform me what kind of source of these chart are originated
> (I mean the sequences?) There was no info in the SIMBAD about TAC as 
> "KVI" (Istvan Kovacs) informed me.

   TAC is an abbreviation of "Twin Astrographic Catalog", which Dr. Skiff
introduced us earlier.  More information is available from the URL
http://aries.usno.navy.mil/ad/tac.html.

   TAC being based on photographic calibration, HIC combination of many
(probably of different degree of quiality) authors, HIP would be the best
choice among them.

   We should in future finally fix all the variable star charts to conform
some standard system, for which I think the present Johnson V is generally
acceptable (within intrinsic errors of visual estimates).  From this
standpoint, the VSOLJ (Variable Star Observers League in Japan) volunteers
have decided to use the V-sequence (from Hipparcos, Tycho; secondary
photometric sequences published by Skiff, Henden, Honeycutt etc. when
available; prelimnary Ouda V-sequence i.e. VSNET charts etc.).  After
this resolution at the Annual Meeting of the VSOLJ, I have tried to redraw
my variable star charts (brighter variables) in H/T = Hipparcos/Tycho scales.
Now I report all my visual observations on H/T basis (thanks to the small
apeture not to go deeper than Tycho can achieve!).  Dr. Mattei, when I meet
at that meeting, expressed the AAVSO is also preparing to re-scale the
existing charts on Tycho basis.  Though it would be a tough task to fill
the fainter end of H/T standards, we should finally have to fix the sequences
in less than a decade.  For the meantime, it would be advisable to report
the sequence the observation depends on.

   It will be also a tough task to convert preexisting observations on
old scales to new V-scale.  We still don't have a good idea how to
systematically convert them (however, I partly tried on my own).
Considering many number of observations having no specifications which
comparison stars were exactly used, I think it might be an acceptable solution
to derive a conversion formula (or table) from a sequence to the V scale for
each object.

   For more reason or another, the VSOLJ volunteers have been undertaking
to uniquely idetifying comparison stars (often called by magnitudes only)
by giving DM, GSC, or USNO numbers.  This procedure would facillitate future
comparison between sequences.  Something in the RX And field (one of the
most frequently used comparison stars) may be permanently given a name
GSC2807.1483 (this star is identical with GSPC P194-S, having a V magnitude
of 11.85), to which aliases are given as inidividual-chart-dependent names
(like VSOLJ(b)).

   What about this idea?

Regards,
Taichi Kato

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