[vsnet-chat 3657] re Overobserving

[crawl@zoom.co.uk]

Taichi Kato wrote:

>Well, you seem to be very much inclined to
>character-based data examination ;-)  Almost the same thing can be more
>easily performed using a GUI light curve viewer/editor.  Just a few
>mouse clickes are usually necessary.

Such a GUI device sounds glorious... ...I've never found a fully usable
one, and don't know how to write one, and so have to compromise on the
matter with next best attempts.

Sometimes the sheer size of the data makes things difficult... ...T Cas for
instance has about 30,000 observations for it (and that is _excluding_ the
AAVSO data which I do not have access to!)  Even using AVE, chopping up 80
years worth of T Cas data consisting of 30,000 datapoints gives very small
"windows" on the data from which to make judgement upon.

>   If the observer observed by a constant above the rest of observers,
>the difference can be easily corrected using a constant correction
>(self-evident).  Otherwise, the cause of deviation needed to be more
>rigorously examined.

Yes, it is self-evident, but as Stan pointed out, it needs to be done on
almost a per observer per star per night basis... ...though that's up to
how rigorour the analyst feels they want to be, I suppose ;^)  However,
your FG Sge comments suggest that just some simple global corrections can
make quite a difference.

The rigorous examination to cure such problems just isn't done that much
anymore... ...I think a lot of organisations have enough trouble just
finding enough time for the reports archived in the first place!

>   This is an example of a caveat to non-Pogson-type (I don't know the
>exact terminology) visual estimates.

The BAA call it the "fractional method" I think.  I better not get in to an
argument on various methods... ...I _personally_ have some suspiscion re
the smoothing caused by utilising the Pogson method, as I never got good
enough to split things into tenths of a magnitude.  Sebastian as of course
shown that it is quite possible, but it is very dependant on the quality of
the sequence, which itself is dependant on the available nearby stars!

So, I don't think any scheme is better than any other, just different in
what happens when it is plotted on a folded lightcurve.

>   However, the dramatic effect of corrections appear is to the human
>eye on the corrected light curve, rather than the power spectrum [and is
>quite natural.]  Without corrections of personal biases, I found it hard
>to detect visually modulations (before that fading) in the combined light
>curve of FG Sge, but they dramatically appeared after simple corrections!
>
>   This suggest that the most of noise (what looks like noise to human
>eyes) is caused by personal biases, presumably caused by different comparison
>stars or personal preference.

Aah...  it seems I am concentrating my thoughts too much in the area of LPV
overobserving, which is where the original thread set off from, but of
course things have travelled a bit since then!

Obviously, from what you say, what is done appears to depend on what sort
of information you are hoping to gain with respect to what sort of star.


Anyway, in sum, I still think people _cannot_ overobserve, for what is seen
is a function of how often the star is looked at.  I think quite a few
emails have come to this conclusion, though some still will not "like"
"overobserving".

On the other hand it seems some of us just don't trust "pre-processing" of
raw visual data, whilst others have had improved results by doing so.  The
bottom line seems to be that it really depends on what you are looking for.

I've found this an interesting thread, and I've learnt some stuff.  Sorry
if others out there have got bored.

Cheers

John

John Greaves
UK

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