[vsnet-chat 715] (fwd) on charts and sequences again

[Taichi Kato <tkato>]

From fidusz@zpok.hu Wed Jan 28 17:03 JST 1998
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Date: Wed, 28 Jan 1998 08:57:56 +0100
To: Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>
From: "FIDRICH Robert (Fidusz)" <fidusz@zpok.hu>
Subject: on charts and sequences again
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Dear VSNET and AAVSO Folks,

My points on the charts and sequences:

- I am not sure, hat we sould use V sequences for visual estimations. Since 

< mv = V + 0.2(B-V) for the dark-adapted visual response. .>

the V magnitudes would be not very good in case of comparisons 
with (B-V) > 0.5
Since red stars usually has (B-V)>2, so in the cases the sequences the
scatter could reach 0.5 magnitudes in visual magnitudes. So I don't think
the V magnitude is the best choice. My opinion then: if we know the color
index of the comparisons, we need to calculate mv using the  relations
f(b-r), f(B-V) etc. 

Since the use of different chart/sequence is the main cause of scatter in
many cases, for the stars already have AAVSO sequences, we should prefer
them until final standards to avoide scatter caused by different based
sequences. 

For NEW stars (I mean stras without AAVSO or other sequences earlier) we
can use HIP or Tycho V magnitudes for preliminary use, but we need to
convert them to mv as soon as possibble.

It is very problematic that sometimes AAVSO or others produces total
different charts for new stars. The mix of GSC, mpv, V and visual estimated
magnitudes in one chart is also problematic, but using there is the same
with different aged chart (in case of novae the sequences change several
times within a few month.) Since many observers has/knows the first version
of these charts, this could be the cause of large scatter. 
And we should not forget that many oservers has no possibility to
get/purchese many charts for same stars (since they already have a
chart...). And on the other hand the observers are also not informed if new
seuquences/charts were made. Why isn't the AAVSO Charts Catalogue not
published on the Web? I would very welcome all AAVSO charts on the Web/FTP
too.

(to be continued)

Kind regards,

Robert Fidrich
HAA/VSS

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