[Aavso-photometry] GJ 436 Campaign Web Page

[arne]

Robin Leadbeater wrote:
> If  the purpose of the exercise is to determine the timing of the transits 
> to the highest precision, what  advantage does multiple measurements at 
> different wavelengths offer?
> 
> Concerning scintillation, I assume there must be some  break point dependent 
> on read out time and read noise that makes it more advantageous to filter to 
> increase exposure time rather than summing multiple short exposures post 
> event. Can anyone point me to an example of this calculation?
> 
The purpose is to not only determine the timing of the transits of GJ436b,
but also to look for other transiting exoplanets around this system.
Since the transit depths are likely to be small, it is easier to
combine people's datasets if they use filters, and if they transform
their data.  In order to transform, you need color information.
Since the colors of the comp stars and of the target star are known,
you can use those colors plus your transformation coefficients to
transform your single-filter measures, or you can take 2-filter
sets and transform with "live" data.  Either method works.  We
may use other stars in the field to obtain rough transformation
coefficients for those who have never done this before.  As mentioned
in the Alert Notice, this is a tough project!

It is highly recommended that you use a filter for these observations.
This is *very* different than CV observations.  You are dealing
with millimagnitude variations of a red star.  You have plenty of
light, so using a filter also gains you with longer exposure times
to beat down scintillation.  It is easier to work with a single
longer exposure than to have to sum groups of shorter exposures.
Why make more work for yourself?  However, to answer your question,
there is no difference between taking a single long exposure and taking
multiple short exposures that add up to the same length when it comes
to scintillation noise.  The multiple shorter exposures will have
more read noise, which may be important in this case.
Arne