[Aavso-photometry] Short-Exposure Photometry

[Arto.Oksanen at tietoenator.com]

Hello Michael,

Been there and seen the same. It is scintillation or twinking of the star by atmospheric turbulence. The shorter the exposure the more the star brighness seem to vary. 

best regards,

arto

--
Arto Oksanen                         arto.oksanen at jklsirius.fi
Jyvaskylan Sirius ry, Kyllikinkatu 1, FI-40100 Jyväskylä, Finland 
Tel: +358-40-5659438                         Fax: +358-14-4157803
Nyrola Observatory  http://www.ursa.fi/sirius/nytt/nytt_info.html 

-----Original Message-----
From: aavso-photometry-bounces at mira.aavso.org [mailto:aavso-photometry-bounces at mira.aavso.org] On Behalf Of Michael Koppelman
Sent: 13. heinäkuuta 2004 17:31
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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