[Aavso-photometry] Questions about Z And Photometry

[Barbara G. Harris]

I submitted a CCDV observation of Z And taken on 12/30/2007 @ 01:52 UT.  I
use MaximDL for photometry.  I used the 9.2 star as my reference star (9.165
from field photometry).  Using that as a reference, I go a Mag of 9.25 for Z
And.  I submitted this to AAVSO.   Later after looking at other observations
around that time I noticed that the 9.25 was not consistent with the other
observations around that time (9.7226 CCDV, 9.6 Vis).  I then went back to
my image and used the 11.2 star as a reference (11.194 field photometry).
With that star as a reference I got a mag of 9.56 for Z And which is more in
line with the other observations at that time.  When I selected the 11.2
star as my reference and then selected the 9.2 star as a check star, the mag
that I got as a check for the 9.2  star was 9.49.   If I use them both as
reference then I get a mag of 9.40 for Z And.  I have gone back and modified
my observation in AAVSO.

 

So that teaches me that I should always use a check star.  My question is:
Why was there such a disparity in my 9.2 star?  I consider myself still new
at CCD photometry so any other advice or recommendations would be
appreciated.

 

Barbara G. Harris

HBB


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