[Aavso-photometry] Help locating Article

[Wolfgang Renz]

Hello Tim

I've seen a simillar technique applied by Christian Buil  for
photometry of the exo planet HD209458 (V=7.64, B-V=0.58)
in 2001 with his C8 and Audine CCD camera.
He used it to weaken the signal of HD 209458 by ~ 3 mag to
the range of the much fainter available comp stars by covering
half "of the CCD windows by an small piece of an exposed
diapositive slide photographic film".
See: "Tentative detection of the extrasolar planet of the HD209458
system" http://astrosurf.com/buil/us/exop/209458.htm


Ron Bissinger used a simillar, but larger mask (see email below)
to cover the main chip but to leave the guide chip uncovered.
[But 60 sec exposure time might be already pretty long.]


Clear skies
  Wolfgang

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



----- Original Message ----- 
From: "Tim Crawford" <tcarchcape at yahoo.com>
To: <aavso-photometry at mira.aavso.org>
Sent: Sunday, December 05, 2004 2:50 AM
Subject: [Aavso-photometry] Help locating Article

> Trying to locate a copy of the following article:
> 
> A Search for Planetary Transits of the Star HD 187123
> by Spot Filter CCD Differential Photometry
> 
> Castellano, T. 2000, PASP,112,821C
> 
> Can anyone help with this search?  Apparently PASP
> will not let me download as I am not a  member of a
> "subscribing institution."
> 
> CS 
> Tim Crawford (CTX)



----- Original Message ----- 
From: <RBissinger>
To: <Tonny.Vanmunster>; <transitsearch at ucolick.org>
Sent: Saturday, December 04, 2004 2:25 AM
Subject: Re: [TransitSearch] Baseline photometry of HD 74156 at CBA BelgiumObservatory - results

> I too have had the same problem with my ST-10XME and 35cm C14: too many
> photons.  Only a few seconds and the camera will saturate with a mag 7 star.
> The problem I had with using a screw-in neutral density filter is that they
> also reduce the light to the guide chip, and often I found I could not
> autoguide.
> 
> One could use a separate guide scope and autoguider, but I came up with a
> simpler, if less elegant, solution that works with the SBIG dual chip
> cameras.  I obtained some Kodak Wratten neutral density gel filter material
> (available from most high end photo shops or mail order - B&H Photo in the
> US, for example) and cut it into a semicircle that would only cover the
> imaging chip and leave the guide chip uncovered.  I used 1.0 factor
> material, meaning that it transmits only 10% of the light.  I mounted the
> material in a scissor-cut cardboard mount and placed it between the CCD
> camera window and the focal reducer and/or nosepiece.  The imaging chip is
> covered; the guide chip is uncovered.  The material does cause a slightly
> different focus for each chip but that is not really a problem.  The slight
> distortions and internal reflections introduced by the gel filter are
> removed with flat fielding.  With mag 7 stars I can get around 60 second
> exposures using the filter.
> 
> I have also prepared a similar filter for brighter stars, mag 5 to 6, using
> 2.0 factor material which transmits only 1%.  These have worked well for
> transit work...attached is a .jpg of the filters.  They aren't pretty, but
> they work fine and are cheap, and don't shift the color...they can be used
> with Bessel and Johnson filters.
> 
> Best Regards,
> Ron Bissinger
> Pleasanton, CA
> 
> 
> In a message dated 12/3/2004 6:44:12 PM Eastern Standard Time, "Tonny
> Vanmunster" <Tonny.Vanmunster at cbabelgium.com> writes:
> >
> >Due to the
> >brightness of HD 74156 (V = 7.61), I had to keep exposure times extremely
> >short (3 to 4 seconds), to avoid pixel saturation. Clearly, this had a
> >negative impact on the final precision of my photometric results (see
> >further).