Data Possibilities

[Tom Droege <tdroege2@earthlink.net>]

I keep looking at the ASAS[1,2,3] and HAT[4] and similar papers.  ASAS is 
the most useful and I keep looking at the mag vs mag sigma plots.  These 
seem to be about a factor of two better than the data that I have been able 
to analyze.

Possibly this even makes sense.  Here is why.

The ASAS data is most directly comparable.  They are running at a pixel 
scale of 14.2 arc sec which is not so far from our 7 arc sec.  Their later 
data[3] has a floor of ???? possibly 0.01 mag to 0.02 mag compared to our 
0.025 (my estimate of later data).  I think these plots should be made with 
a log sigma axis.  I think the only reason to plot otherwise is to obscure 
the real noise level.  However one can get a better estimate from their 
figure 1 at mag 12 where they have a sigma of about 0.06.  this compares to 
a sigma of  0.1 for my data.

They are running at Los Campanas where one might expect the night sky to be 
mag 20.  PVS[5] quotes 19.9 for CTIO which I would compare to Los Campanas 
and 18 for Princeton NJ, which I would compare to Batavia.  So the Batavia 
sky brightness is 6 x that of Los Campanas.  Their pixel has 4x the area of 
ours, so their noise should be a factor of two higher than my 
measurements.  since their sky is a factor of 6 darker, this leaves them 
with a factor of 4/6 in electron fiil.  Thus we should be noisier by a 
factor of sqrt 1.5 or 1.22.  Multiplying their mag 10 noise level of 0.06 
by 1.22 gives a noise of 0.07.  This compares to my estimate of our noise 
level of 0.1 at mag 12.  Everything is well within the error of reading the 
plots.

In other words, by the probably defective logic above, our noise level 
compares to the ASAS data taken at a good site if we take the sky noise 
into account.  Assuming that they are good guys and are doing as well as 
they can, then we are doing nearly equally well.

I think that is the case.  We are doing as well as possible at this site in 
Batavia.  I think there is little need to fuss too much more with the data 
analysis.  OK, we study the darks and light box flats over time and 
probably try the flocked paper, but I don't expect any improvement.  (I 
want to try the flocked paper for another reason.  I suspect it will help 
the data taking when I have a bright moon.)

I think we are up against the limit of the sky at our location.  Perhaps 
ARNE or ROB can take lower noise data.

BTW.  We had a nice advantage over others doing this work.  The Elliot 
Burke lenses are down possibly 8% at the edges.  HAT quotes 40% down at the 
edges for their Nikon lens.  So we require only 1/5 the flat field 
correction of a typical competitor.

Tom Droege

[1] Pojmanski, G. Acta Astron., 47, 467
[2] Pojmanski, G. Acta Astron., 48, 35
[3] Pojmanski, G. astro-ph/0005326 11 May 2000
[4] Bakos, G. PASP 114:9740987 2002 September
[5] Blake, C astro-ph/0201394v1 23 Jan 2002