[vsnet-chat 5980] Charts and more (you're losing accuracy !)

["Sebastian Otero" <varsao@fullzero.com.ar>]

>    From the very beginning of new availability of modern catalogs, VSNET
> has used to do (two decimal V magnitudes and B-V colors) even with the
charts
> for visual reference purposes.

Something logic and welcome.

> 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.

But for me this is one step backwards again...
Different colors are a more serious matter than this. I've written too much
already about cones and rods issues but color term corrections are totally
dependent on the use every person makes of his/her own eyes.
So we have now: V comparison star magnitudes and B-V colors.. So the logical
step further is: observing technics that give observations close to V.
I have conducted an experiment in the Telescopium area last year.
I used 34 stars and observed them three times in different days.
I used white comparison stars.

1) The first time I used averted vision in trying to become an "average
observer".
The result showed my color coefficient as:
v-V= 0.1125 (B-V) + 0.0125

2) The second session was made with direct vision. Things changed completely
and the relation found was:
v-V= -0.002 (B-V) + 0.0175
So response is pretty close to V unlike the other type of vision.

3) The last try was with the "Otero Method" ;-)). Use of different types of
vision depending on star's color and self-calibration according to color,
but also to sky brightness, instrument used and brightness of the variable
as some of the more important factors.

The final results are as follows:

After correcting for the coefficients in sessions 1 and 2, the final V
converted results checked against GCPD data are:

AVERTED VISION:   mean error 0.063 with random errors up to 0.19 magnitudes.
DIRECT VISION:      mean error 0.040 with random errors up to 0.11
magnitudes.
OTERO METHOD:    mean error 0.034 with random errors up to 0.08 magnitudes.

This didn't surprise me.
It's known that averted vision is sensitive but no selective. You can see
much more but seing is not estimating brightness.
So I did become an average observer by using this crap...

There is no color-related problems with my method. There may be an error of
0.05 in a white star or in a red star. It has more to do with the distance
of the observed star to the comparison stars , with magnitude difference and
with intrinsic human error than with color matters.
So it's a fact that a self-calibration technique is not only a way of
reducing the waste of time in personal colr-term corrections in HQ's but a
way of improving accuracy.
Every comparison star with a V mag. measured is useful. (In fact, a couple
of similar V mag. with different colors are recommended for the
self-calibration I mentioned)
The blue comparisons issue that I'm tired of reading/hearing about, implies
the use of averted vision that is a bad choice for making brightness
estimates.
Don't say "human eyes are blue sensitive". Just rods are. Rods are part of
the eye but not the whole of it.
We are able to use the eye as we want in order to make the response we
desire. We just need to teach it and it learns quickly ;-))

I realize that discussions about this topic come and go all the time but
nothing seems to change in time and most of the observers like to chat about
these issues only to make complains and then go on as if there wasn't any
other choice than to give in to the lack of accuracy of visual observations.
I also see that most of the observers simply don't want to change anything
because they're comfortable the way they have always worked.
I'm not against that. But they are making choices.
Any data-checking or any comparison will make them see that in fact there
are better ways to do it.
IT IS A CHOICE.
So don't say everywhere that things can't be improved. We have the
resources, accurate magnitudes, colors, observing technics.

It's a little annoying to read about the same topics year after year when I
found a way to make it better and I have already told everybody about it...
I think my next step will be silence...
I still conitnue to write a handbook about it. It's a neverending task (lack
of time and new things to add all the time) but there are several pages
devoted to these issues.
For now it is only in Spanish but I plan to make a translation eventually.
However my priority is to have it ended for Latin American observers that
are finding it interesting and my colleagues here that see the point in
hving visual data already reported in a standard system (or comparable to
it).and with better accuracy.
I'll be including several exercises, experiments, charts and examples to do
it a practical thing.
Although you may not understand this evrsion, I'm sure you'll find
interesting the R Sct and omicron 1 Centauri fields used here for the
"Calibration Pairs" consisting of two stars of the same magnitude, one
blue-white and the other orange.
The exercise consists in observing both stars with the type of vision
necessary for the two to become equally bright.
This is the best way to know HOW you should observe stars of different
colors to become close to V.

It's very comforting to be reporting observations that you know that are
directly comparable to other data.
I don't want to bother anyone with these comments and suggestions. I think
that results are the best proof to try to make a change and I'd like to
share the tools that helped me in my work with everybody willing to use them
if they consider them useful.
Well, the most recent (very uncomplete yet) version of my handbook in
Spanish is at:
http://ar.geocities.com/varsao/  in the main page click on the link "Manual
de Tecnicas de Observacion de Variables" to find a .doc version.

Best wishes,
Sebastian.



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