From: Michael Koppelman <lolife
Date: Fri, 7 Apr 2006 09:44:07 -0500
To: "Chris Sauer" <chris

Try it both ways: do the photometry on the individual images and also  
try it on a sum of all the images. The average of the individual  
frames should roughly equal the value you get on a combined image.

It is shocking how many photons you lose through a V filter,  
especially if you don't have the "E" chip. You get used to it.

If I were you, I would do ensemble photometry, meaning more than one  
comp star, but many folks just use a single comp star, which is  
easier and virtually all software will do it for you (such as  
CCDSoft, which you used to acquire the images).

What software did you use to reduce the data? You didn't apply flat  
darks and flat bias to the data frames, right? The HISTORY headers  
are a little confusing in that regard.

Cheers,
Michael
http://www.lolife.com/astronomy/


On Apr 7, 2006, at 5:53 AM, Chris Sauer wrote:

> Hi,
>
> The skies cleared and I was able to get 30 minutes of data on RS  
> Leonis last
> evening.  First off, I was amazed at how much the V filter  
> attenuates the
> light.  In 1 X 1 binning, I needed three minute subs to get decent ADU
> counts on RS Leo itself.
>
> So my question now is what to do with the data?  I've calibrated  
> the sub
> frames separately via dark subtraction/flat division and I'm left  
> wondering
> what to do next.
>
> Do I combine all 10 images into one averaged final and perform the
> photometry or do I approach each image separately?
>
> Also, what's the best way to perform the photometry?
>
> I've placed one of my calibrated images on my website in case  
> someone would
> like to check my work.  North is up.
>
>
> Thanks for your help,
>
> Chris
>
> Sauer
> Sent: Thursday, March 30, 2006 5:39 AM
>
> Hi,
>
> As most of you already know, this winter has been horrific for  
> astronomical
> imaging here in the northeast.  As a result, I'm only now getting  
> to the
> stage where I need to ask these questions despite having completed an
> observatory back around Thanksgiving.
>
> Just this past week, I finally got a chance to finalize bringing the
> observatory into an online mode.  My primary scope is mounted and  
> working
> well, polar alignment has been refined so that 2 minute unguided  
> images are
> showing no noticeable drift and the mechanism I devised for flats  
> seems to
> be working well.  In other words, I think I'm ready to begin my  
> first "real"
> imaging session of a variable star.
>
> I'm looking for suggestions on a good first target in the eastern  
> part of
> the sky (west is light polluted) between the hours of 19:00 & 00:00  
> EST.
> Additionally, I could use a little tutelage on exactly what to do  
> with the
> data once my images are calibrated with darks/flats.
>
> Are there any takers out there willing to assist a fledgling  
> variable star
> observer in coming up to speed?
>
> Thank you,
>
> Chris
> _______________________________________________
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