Re: [APML] Help Needed -- ST-4 and Sky Background

[Aplanatic@aol.com]

Hi Ron,

> I have been considering using the STV to get background readings by taking a
>  wide field picture with a know star in the field as a reference.  Then 
using
>  some area with no stars for the background, but I like your technique.
>  
>  What I don't know, (and would like), is the reference for your formulas.
>
>  I understand everything except the constant.  How did you come up with it?
>  (calculated, experiment, reference?  Can you elaborate? )

The constant is based upon three things:

SBIGs calibration factor for a 0 mag star as given in their manual.
The amount of sky in view by the TC211 chip in square arc seconds.
The area of a TC211 pixel in square inches.

If you are interested, the details are given here:

http://members.aol.com/aplanatic/ST4.htm

You can do calibrated photometry using the STV by taking an image and then 
making a stellar calibration sequence from the known brightness of stars in 
your image.  You then measure the average background in the image, normalize 
it to square arcseconds and then extrapolate the stellar sequence to the 
background level.  I have done this here in LA with my ST4 and the calibrated 
background was 0.3 magnitudes different from the background as measured with 
the wide open ST4.  

A great way to find measured star brightnesses is here:
http://www.nofs.navy.mil/data/FchPix/cfra2.html

If you would like more information on this stellar sequence method contact me 
off-list.

Dave

--  APML Archives at <http://www.system.missouri.edu/apml/>  ---
                Unsubscribe at <majordomo@seds.org>