[vsnet-chat 708] Re: Charts and Sequences

[Taichi Kato <tkato>]

Steve H. Lucas wrote:

> When all the visual data points (all observations) regarding phase-decay
> magnitudes of a particular supernova event are graphed, an extreme amount
> of scatter is noted. However, in one particular event standarized
> comparison sequences where used verses a published mean visual light curve
> (Doggett and Branch, AJ.,_,90_,2303, 1985)....the event was SN 1991T, and
> here are some statistics when that standardization was employed*:
> 
> ...
> 
> In conclusion, I would like to mention that while the work of large well
> organized Variable Star organizations are extremely valuable to the
> astronomical community, there are small groups of us who value our work as
> well, and open communication is how we attempt to better our contributions.

   I did the same thing for Nova Cas 1993 (V705 Cas) and Nova Cas 1995 (V723
Cas), for both of which a good V, b-y sequences were very timely provided
by Brian Skiff.  The results were remarkable, in spite of the expected
intrinsic scatter of individual eyes to these emmision line objects, yielding
almost always less than 0.1 mag r.m.s. scatter (in nightly bins) between
different observers from different countries.  These visual nightly averages
were also in very good agreement with averaged photoelectric V (systematic
error almost always less than 0.1 mag).  The results well confirmed the
usefullness of visual photometry, as an ensemble, when standardization was
employed.

   The opposite case can be found in Nova Sco 1997, for which no reliable,
established, sequence was supplied.  The light curve shows a considerable
amount of scatter up to 0.8 mag.  Nova researchers always complain about
these errors, and this is the chief reason for researchers to hesitatingly
use visual estimates.  (I also wonder whether some "published" early
observations have had any chance to be standardized.  Light curve drawn
from IAUCs and our own estimates sometimes show queer features -- e.g.
a sharp drop in magnitude in the early decline of V394 CrA).

   Another opposite case can be found in AC Her, a well-observed RV Tau
star which must have many fans even in this forum.  The scatter in this
star never becomes less than 0.3 mag, no comparable results to Novae
Cas cases even after applying correction to individual observer.  I suspect
this stems from a "bad" sequence -- the badness of the existing charts can
be easily realized simply by comparing with H/T magnitudes.  Some observer
prefers a set of comparison stars, another observer another set, usually
from a selection of the whole supplied sequence.  The different offsets
(or the "noise") of individual comparison star to the standard system
produce such random, preference-dependent, difficult-to-correct, errors.
Obviously visual observations could do better, and could better contribute
to science.  Necessary tools coming, it is up to decision.

Regards,
Taichi Kato

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