[Aavso-photometry] Short-Exposure Photometry

[Arne Henden]

Dan Kaiser wrote:
>>I don't think you need to worry about guide stars.  If the image wanders
>>a bit on the CCD, that won't hurt, but guiding a 10-second exposure should
>>not be necessary.
> 
> It has been my experience that my best photometry is when the stars stay
> on the same pixels.  Thus my desire to guide.  However I may not have a
> bright enough guide star in B, time will tell.  If not I will have to
> deal with it.
> 
We do the same thing here for precision astrometry.  However, letting the
image wander is a way to reduce the systematic effects of remaining on
a fixed set of pixels.

> 
>>This is a good event for the USA.  It is difficult (total depth is 0.02mag),
>>but if you can't do this one, you need to improve your techniques as all
>>other potential eclipse systems are predicted to be even shallower. 
> 
> I'm sure Arne meant transit systems rather than eclipsing.
> 
Hey, hey, no snide remarks, please!  I just finished my first cup of coffee
this morning and the caffeine hasn't kicked in yet. :-)
Seriously, if anyone is at all interested in testing their limits of
precision, or in planetary transits, I recommend visiting
http://www.transitsearch.org
as there are plenty of targets to investigate.  For HD209458, the
parameters of the upcoming transit are:

Position:   22:03:10.8  +18:53:04  J2000
approx mags:   B = 8.3  V= 7.7
start of transit:  July 17 UT at 0500
mid transit:                     0640
end transit:                     0819

transit depth is 0.02mag at V.  There are fairly fast transitions
and a flat-bottomed "eclipse".
Arne