[Aavso-photometry] GJ 436 Campaign Web Page

[Wolfgang Renz]

Hi Arne

Does the 15arcsec companion of the 114 comp also have BVRcIc data ?
Then the ones with wide-field setups and low resolution might be able to
subtract it out if it can not be resolved well.
(haven't seen a SRO calibration file for GJ 436 or ASAS 182611+1212.6 yet)

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message ----- 
From: "arne" <arne at aavso.org>
To: "Robin Leadbeater" <robin at leadbeaterhome.fsnet.co.uk>
Cc: <aavso-photometry at aavso.org>
Sent: Saturday, June 09, 2007 2:45 AM
Subject: Re: [Aavso-photometry] GJ 436 Campaign Web Page


> 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
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