[vsnet-chat 3636] Fw: Overobserving

[Jan Hers <janhers@pixie.co.za>]

I am in full agreement with Sebastian that long period variables should not
be observed every night, but the reasons are somewhat different.

Each observation, of whatever kind, carries with it a certain amount of
error, which is generally unknown at the time it was made. So if one draws a
light curve from observations made, say, once a week, one may get a nice
clean picture - but it isn't necessarily correct!   If  observations had
been made every night, the curve might show numerous ups and downs.  And
when they are combined with observations from many other observers , which
used different eyes and different telescopes  in different places and under
different weather conditions, the ups and downs will become even more
noticeable. The result will therefore be a light curve which looks very
messy indeed, but if the all the values are averaged the result is likely to
be very good.

However, there may be another problem. If one observer reports his results
every  night, while seven other observers report observations made  once a
week, it means that the one observers' data will be given as much weight  as
that of all the others put together , which of course is highly undesirable.
This then is the main reason why observers are advised not to over-observe
LPV's.

Kind regards,
Jan Hers

>                   About the recent discussion on overobservations for mira
> stars, I agree with the notion of not making estimates every night.
> It's no use because of the long periods= the star is not going to vary in
> just one day. The star is going to stay the same and maybe observational
> error on our part will ruin a pretty nice lightcurve filling it with noise
> that could have been avoided if we were patient enough to wait for the
star
> to actually vary.
> Given the large amplitude is not useful trying to detect small variations
> since they will disappear in the resulting lightcurve.
> And also given its large amplitude, the star is going to vary if we give
> time to it. Just five or seven days and we will note the difference and
our
> lightcurve won't have false up and downs.

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