[Aavso-photometry] Scintillation errors

[Thom Gandet]

What exposure times are you using Pedro?  (Sorry if I missed an earlier answer
to that question!)

Assuming Poisson limited data, to what extent are scintillation errors
exposure-time dependent?  I guess that question can translate to how much
would the scatter in Pedro's time-series scatter be reduced by, say, doubling
his exposure time?

I've seen sort of the same sort of effect here, and our seeing has been lousy
the last two years.


Regards,
Thom




At 04:55 PM 6/5/2005, Radu Corlan wrote:
> > > Pedro Pastor wrote:
> > >
> > > >I've done a high rate sampling on a Delta Scuti (NSV 3063). While
> > > >processing data I saw that, although single point data precision is
> > > >around 0.002 mag., data dispersion along the whole series is high.
> > > >
> > > >As long as my sampling rate was high, I thought of averaging measures
> > > >(every 5 points). Then, a big doubt rose in my mind. What would be
> > > >better to average: differential photometry data or raw images (in order
> > > >to raise SNR) and then calibrating the result image and get the
> > > >differential photometry measure?
>
>Pedro,
>
>do you know why your dispersion was much higher than the expected
>precision? i would suspect there are two probable causes: either
>atmospheric scintillation, or thin clouds or other "accidents".
>
>If it's scintillation (the calculated value is of the same order or
>magnitude as your error), i'd say you'll get very similar results
>whether you average images or reduced magnitudes.
>
>If on the other hand you had some transparency problems, you'll probably
>be better off by first getting the differential photometry data and then
>average that. If you plot the differential mag and a raw (instrumental)
>magnitudes vs time, the cause of the error becomes
>obvious: if both show about the same spread, and the graph appears
>uniform in time, you are probably scintillation limited. If increases in
>the spread of the differential value are accompanied by large changes in
>the raw magnitudes, you know you have thin clouds, a problem with flats,
>dust etc.
>
>Radu
>
> > > >
> > > >I've done some tests in order to compare both methods, but my results
> > > >don't shed any light on the question. Maybe both procedures are
> > > >equivalent?
> > > >
> > > >Could anybody provide me with some information (or results) about this
> > > >point?
> > > >
> > > >Thank you very much.
> > > >
>
>--
>Radu Corlan       rcorlan _at_ pcnet _dot_ ro
>
>    You can still escape the "Gates" of Hell!
>                  Use Linux!
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