[Aavso-photometry] Short-Exposure Photometry

[Tonny Vanmunster]

Hi Michael,

This is very likely a combination of scintillation and (maybe) saturation /
non-linearity of your CCD. I experienced similar things when I first
attempted to make CCD photometry observations of exoplanet HD 209458b. I
have written some "leasons learned" about this in an online article on my HD
209458b observations (you may read it at my website www.cbabelgium.com -
section "New at CBA Belgium").

Best regards,
Tonny

Tonny Vanmunster
CBA Belgium Observatory
http://www.cbabelgium.com
________________________________________________________
PERANSO : The Final Frontier of Period Analysis Software
http://www.peranso.com
________________________________________________________


-----Original Message-----
From: aavso-photometry-bounces at mira.aavso.org
[mailto:aavso-photometry-bounces at mira.aavso.org]On Behalf Of Michael
Koppelman
Sent: Tuesday, July 13, 2004 4:31 PM
To: aavso-photometry at aavso.org
Subject: [Aavso-photometry] Short-Exposure Photometry


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.

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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