Ic Photometry

["Thomas Droege" <tdroege2@earthlink.net>]

Looking at the attached plot, a big dip will be noticed in the Ic
photometry.  There is a much smaller dip in the V photometry.  This occurs
on a number of the plots.  All so far that I have looked at are from TOM1.

The dip always happens around day 2820 but there are several days in a row
where the dip is evident.

At this time, the weather was hazy to the South.  TOM2 which points mostly
up did not have a problem.  TOM3 which points to the North also does not
seem to have this effect.

The Question is:  Why the Ic dip?  

I have no doubt that the haze cut down the light received for stars near
the horizon.  But why do the V measurements come out pretty good while the
Ic measurements are a mag or so too faint.   Note that I have lots of
measurements, so I can find long period variables that show this problem
and which confirm that the V measurements are pretty good - they follow the
trend of the long period variable.

Tom Droege

J172857.2051937.png