[Aavso-photometry] Short-Exposure Photometry

[Radu Corlan]

On Tue, 13 Jul 2004, Michael Koppelman wrote:

> So I'm taking a look at V972 Her. It's bright, at V=6.7 or so. I did 
> BRVI photometry with the following exposures times:
> 
> I  10 sec.
> R   5 sec.
> V   9 sec.
> B  20 sec.
> 
> The signal-to-noise ratio is really good 'cause I got lots of counts, 
> so the random error is like 0.002. What's weird is the comp star 
> standard deviation is really high, upwards of 0.03 in V. (This is a 
> variable that, as far as I can tell, varies less than 0.1 magnitude.) 
> This is usually more like 0.008 or something for me.

could it be scintillation? With a short exposure, you could have 
scintillation effects if the star is not too high in the sky or the 
telescope aperture is small.

Radu

> 
> Is there some reason why short exposures would cause higher errors?
> 
> I do not believe I am saturated. Most images have a max pixel value 
> between 30,000 and 55,000 or so (on an SBIG ST-7XE). I don't think I 
> should have shutter effects at exposures at 5 seconds or greater (see: 
> http://www.lolife.com/astronomy/lintest/lin5.jpg ), at least not more 
> than 1%.
> 
> I have a little page about this star here:
> 
> http://www.lolife.com/astronomy/V972Her/
> 
> Cheers,
> Michael
> 
> PS - Resending this because of the discussion area downtime...
> 
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> 

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-------------
Radu Corlan       Snail Mail: Bucuresti sect. 1, 
rcorlan at pcnet.ro  str. Argentina nr. 28, Romania

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