[vsnet-chat 4336] Re: [vsnet-campaign-be 107] Delta Scorpii rising again

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

Thom Gandet wrote:

>>Bravo!  It is exactly the kind of accurate visual photometry you
have been doing that can detect the small changes in luminosity
to make a major contribution to the study of these relatively small
amplitude blue stars.

I don't know what your techniques are, but you can read my posting
about Theta CrB this morning about how I do it and compare our
methods.
Techniques which can result in higher precision
observations are possible, and I think that close to an order of
magnitude improvement in the precision of visual observations is
possible.

And Lew Cook asked:

> I, for one, would be extremely interested to find out what
> Sebastian's techniques are. Such precision in visual photometry is
> truly commendable and praiseworthy. If he has developed a new
> technique, and would share it with the visual observing world, we
> would all be better off!


Thom, Lew and all:

As Sergio said, the main points are: a good sequence and a color-dependent
technique.
As Brian Skiff pointed out in the omega CMa case, the GCPD SHOULD BE the
source of photometry on bright stars.
With the GCPD we can prepare sequences for most of the naked eye and
binocular variables.
Nowadays, accurate V magnitudes and colours are available and if we don't
take advantage of this it is just because of laziness.
Specially considering that V has been adopted as the standard.
And I insist on that. All formulas or convertions between V and v relies on
everybody estimating the same way.
For those of us that have realizaed that we can see close to V whatever the
color, this convertion would ruin our observations.
Some people uses direct vision, others averted vision, others a mix. And
this is because nobody cares on the differencies.

We have discussed this topic before and I know most of the observers
disagree with my point of view but maybe just one can make some good use of
this method and then it will be worth.
Most of observers work under limitting magnitude conditions trying to detect
outbursts of faint objects. And that's the perfect case for applying averted
vision. Great. But it is the only case. We don't need accuracy for a
detection. Just need to go deeper. Exactly what our rods can give us.
But if we want to detect brightness differencies, meaning a positive
estimate of a bright star, cones are the main cells involved in this job. I
mean: direct vision.
"v" is the magnitude as seen with averted vision. I've seen it by myself.
Just look straight at the stars and you'll be doing something closer to V.
The important thing is that we don't have a switch to change from rods to
cells when we want it. It is the colour of the star that makes that
decission for ourselves. And a small change in the way we are looking at the
star may mean there are rods involved or they are not. It happens all the
time if we don't have in mind we have to do it in a certain way.
People just "look" and depending on how, it may mean more than 1 full
magnitude difference: the same as seen in the databases. (That pisses me off
and makes most of the work useless.)
I observe lots of small amplitude variables and can get lightcurves from
them. (NSV 20018 is one of the recent ones I am constructing and it is very
pretty although with a maximum amplitude of 0.3 mag.) But combining all
observers' data throw everything out to the garbage. And only because they
don't care about the colors and how they look at the stars.

Example:
Last night I observed it with direct vision (but I didn't know...) and the
red star was at 7.1. Tonight I didn't realize I was observing it with a
parafoveal vision and the estimate was 7.3. Tomorrow I will be looking at it
with averted vision (but I will never be aware of that) and the star will be
at 7.5. A perfect lightcurve.
The only thing to be ashamed of is that the star is actually RISING!!!

And even if we have observing techniques in mind. They must be colour
dependent (IF we want to be close to V).
The different types of vision to be applied are dependent on the brigthness
of the star and its color.
It is very different to look at a naked eye star than to look at a faint
telescopic star, since color response is greater if the intensity is
stronger.

Anyway, whatever the technique was, I am amazed that noone seems to have
laid down one night to estimate stars as a practice in order to check  their
own accuracy. This would be an investment rather than a waste of time.
Just find some stars similar in brightness and different in color. Observe
them with the V and B-V values right beside you. That's all. You now know
how an orange 5.15V mag star looks like and how a blue 5.15V magnitude star
looks like too.
You now make your eyes work for the stars to look the same. And you realize
in the act that you are looking at the orange star directly and the blue
star slightly out of focus. If you use averted vision for both the blue star
is brighter. If you use direct vision the orange star is brighter. (That
5.15 stars are actually in the NGC 3766 region in Centaurus. You also have a
5.42V pair as 52 and 54 comp. stars in the AAVSO chart for R Sct. (Very
close from each other))
You only need to go out and make this experiment yourself. Play a while.
Then you won't forget it. You'll know how to be sticked to V and you won't
waste your time regreating your observations are 0.7 mag. off the average.

It's obvious that if the comparison stars are the same colour, it would be
the ideal case.
The ideal case exists: it is called the delta Scorpii's case and that's why
the accuracy of my visual estimates is at the 0.03 mag. level (checked
against PEP(V)).
Similar comparison stars' magnitudes (1.62, 1.84, 1.86, 2.09) with similar
colors (most of them white-blue) and near the variable.
A dream, although AAVSO people have decided to use a different set of
distant an even orange comparison stars. Maybe they want to use the V-v
formula at any cost...
We can't waste the possibility of doing a better job as if it wasn't there.
We have all the elements to do it.
We can't stick to old stuff when the new one offers the chance of an
incredible degree of improvement.
At least I can't.

In short:
For naked eye stars: out of focus vision (I mean almost direct but with both
cones and rods involved, maybe "parafoveal") when different colors are
present, so the red star won't get too bright)
Actually all this techniques are important when the stars are not the same.
For instance, if both stars are blue, they will look okay whatever the
method you use.
But not averted vision. Accuracy is dead and buried that way. And white and
blue turns too bright. When you are at the limit of your scope the
difference is terrible!!

Binocular variables: the same approach for the brightest ones and when the
magnitude is fainter, we need to pay attention to the punctual image for the
red stars in order not to underestimate their brightness.
The key to my accuracy has always been to estimate the strength of the point
source in red stars comparing it with the bigger image of the blue star.
(blue stars tend to disperse because rods are involved, in the red star they
don't act so we need to concentrate on the cones activity to compensate the
effect).

This may sound strange and difficult to apply and to distinguish when and
how. But it's not. When you get used to it, you do it naturally and you
don't even think.
There are several examples to show the scatter that could be avoided:

V Hydrae, a superred star. I observe it at 6.6 right now. E . Eker at 8.5.
Nice lightcurve from our observations!!
The problem is... My binoculars' limitting magnitude is near 8.0. I look at
V Hya as a bright star through my 7X50's. Cones only work with a light
strong enough. I use direct vision so my cones are estimullated, so it is a
bright star. When R Lep is fainter than 8.0 I can not see it through my
bino's.

U Hydrae has risen from 5.1 to 4.8 during the last weeks. But it has jumped
from 6.3 to 5.2 to other observers. You'll understand why: the brighter the
star the stronger the color, so it gains intensity. If we use direct vision
all the time, we see that the star never gets that faint. BUT NO V-v will
account for that change since the color barely has intrinsically varied!!
The published amplitudes are not ALL wrong.
(Which reminds me of kappa CMa, quoted by Thom. Thom, OK the catalogued
range is 3.78 - 3.96, but the star is rather quite at 3.7 with small
outbursts to 3.6. Actually 3.58 - 3.75 according to my estimates, so the
catalogue is useless this time, as with L2 Puppis, catalogued as 2.6 - 6.2
and whose last maximum has barely reached 6.1 !!!!!!!)

For telescopic variables: concentrate more in the punctual image. the darker
the sky gets (with more magnification) the more difficult it gets not to
suffer from the undesired switch between one and other type of cells. So we
need to look at the center of red stars to compensate the grow in brightness
of bluer stars as seen in a darkest background.

THE KEY TO THIS is PRACTISING. You need to check your results against PEP(V)
measures. If you check your work you'll be reporting things that you know
that are useful.
People have been reporting a star that wasn't T Caeli for years and they
have seen it vary with an interesting lightcurve. If they had checked their
"work", they should have known that their error was greater than the
variations of most of the stars they were observing. They then should have
given up observing or they should have done something to improve the quality
of their observations.
Probably (and happily) the second option.
But for me, amateur observer, to see two lightcurves in the data of T Caeli
was a shame I won't forget. If noone cares about what they do and just want
to play the estimating game without knowing if they are doing right or wrong
(YES, THIS IS NOT AS PERSONAL AS MOST OF THE PEOPLE STATE..., some do it
well, some do it badly. If you want to be polite, be polite. But some of the
observers are wasting their times and ours... only because everybody is
afraid of hurting their feelings instead of teaching them how to do it
better !!!).

So take your time, take a look, check and check, and then..
Then you can call me jerk>>>: -))


Cheers,
Sebastian.





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