Preliminary Mark III Data Reprocessing Results

[Glenn Gombert <gleng@infinet.com>]

Hello,

        I have been experimenting with using Mike G's new "FlatComp" program
to reprocess 14 nights of Mark III data taken last year in Dayton and the
initial results appear _very_ encouraging. The FlatComp program is used to
correct background variation in Mark III starlists due to flatfielding
errors, sky backgound gradients, etc that limit the accuracy of the
photometry that we have been able to achieve in Mark III data collection,
reduction and processing.

        I used a modified version of Arne's suite of programs to create a
new Master Photometry File from 14 nights worth of data taken last year. The
new file contains ~57,000 stars. The FlatComp program was used to correct
the background variation in each nights worth of data to 0.02 magnitude
using 8 "zones" in Mike program. The histogrammed output fromArne's "Master"
is shown below:

 6.50    0  0.000
 7.00    0  0.000
 7.50    86   .027
 8.00   281   .025
 8.50   449   .020
 9.00   720   .022
 9.50  1085   .023
10.00  1685   .024
10.50  2623   .029
11.00  3934   .035
11.50  5814   .043
12.00  8006   .056
12.50 10851   .080
13.00 13836   .116
13.50 15666   .170
14.00 10633   .209
14.50     0  0.000


        As can be seen the "average scatter" for 8.5 magnitude stars is
indeed 0.02 magnitude and gradually increases with decreasing magnitude as
might be expected. These results are without differential magnitudes
corrections that are applied by Arne's "diffcal" program. 

        The results are encouraging enough that I am going to try to process
some night of data with a 0.01 backgound variation seeting in FlatComp and
see what type of reults can be achived. These prelimiary results are *very*
encouraging which should enable use to greatly improve the kind of
photomertic results that can be achived from light polluted suburban backyards!

        I will post more results in the next week or so after a new set of
corrected data has been generated.

Glenn G.

PS: IBVS #4609 has been published on the IBVS Web Page, Michael has created
a link to this under the publications section of the TASS Home Page...
Glenn Gombert <gleng@infinet.com>