Wide Field Results

[Thomas Droege <tdroege2@earthlink.net>]

Does anyone know of any recent papers on the wide field surveys that show
error analysis of the results?

The last thing I have from ASAS that discusses error is their 13 Oct 2002
paper  Acta Astronomica 2002,52,397   Figure 1 shows a sigma v vs V curve
where the noise floor is unreadable but might be around 0.02.  The curve
indicates about 0.05 mag sigma at mag 12.  This compares to about 0.08
sigma at mag 12 for the whole tass data set.  The curves of figure 3
indicate that they have similar problems as tass The tass data is whole
field data and so compares to some combination of the three figures of
figure 3.  Hmmm!  This suggests that taking the center out of each image
might produce data of lower sigma.  Anyone want to try this?

From the HAT paper at http://cfa-www.harvard.edu/~gbakos/HAT/index.html  we
read on p-13 of the preprint:  "Our crude estimate for the latter from
Hipparcos I-band stars, standard star observations and the problematic
flatfielding is that absolute calibration errors can be as high 0.1m in the
field corners, but less than 0.05m in the center."

The Princeton Variability Survey at  http://arxiv.org/abs/astro-ph/0201394 
does not really say how well they did for a test run at Peyton Hall on the
Princeton University campus.  A pity since their conditions more nearly
match mine.  Having lived in Princeton, they roll up the streets at night
so they are probably darker than Batavia where everyone seems to want to
illuminate the underside of bats.  OK, the only thing they say is "The
total number of stars observed was approximately 3,000 over the five
fields, with approximately 1000 of these stars being bright enough to have
S/N such that the photometric errors are < 10%"  I am not sure what this
means but it sounds like roughly 0.1 mag for the brightest stars?

This is all that I have in my stack of papers.  There are other papers with
somewhat better results using large telescopes and smaller fields.  I don't
think these results are comparable.

OK my conclusion from reading what I have been able to find is that no one
else running a wide field telescope is doing a lot better than tass.  ASAS
has a better error number but they do not present their data in the same
way.  The data they do show computed in a similar way is comparable.  They
are obviously at a much better location -if that really is important.  Some
of you that are good at this might find a few more papers for study.

I would really like to hear from someone who has done better with a wide
field survey to tell us the secret of how they did it.  I suspect that the
things that everyone has learned to do to get good results from long focal
length instruments do not work in the same way for short focal length wide
field work. 

My suspicion is that we are doing pretty close to what can be done in
Batavia, IL.  So before making any drastic change in the proceedure I want
to see that someone else has done better.  I think there might be another
factor of two reduction in the noise to be found but not much more. 
Further it is going to take a lot of computation to derive any improvement.
I could keep refining the scheme and die before taking any final data.  I
am a cancer surviver and live from test to test.  I am also 74 years old.  

The survey is good enough to find a lot of variable stars.  We will easily
find lots of slowly varying red stars.  I like Michaels Chainsaw analogy. 
We can rough out a bunch of variables.  Later someone with a fine chisel
can turn the rough work into a polished piece of art.    

Tom Droege