[vsnet-chat 4341] Re: Apogee AP-7p

[aah@nofs.navy.mil]

The M67 paper does cover the AP-7, which lists
a canonical "SITe back-illuminated CCD,"
in this case the SI502AB.  The coefficients I
determined were b(v) = 0.2600  and b(r) = -0.2716
(that is, the SI502AB peaks between V and R).
These don't match Seiichi's values, and like Brian,
I wonder how he measured the slope since his slope varies
so dramatically during a night.  I presume Seiichi's
"k" is the same as my "b(v)".  I prefer to use a
letter besides "k" since this is traditionally used
for the extinction coefficient.
  The natural systems of reflectors and refractors
are quite different; not only do lenses have different
absorption at different wavelengths, but they are
not achromatic at all wavelengths.
  As I mentioned in the paper, unfiltered measures
are like extremely wide filters; very difficult to
transform accurately into the standard system.  The
traditional method of reporting unfiltered magnitudes
has been CCD or CCD(C), but that doesn't adequately
describe the results, since it depends highly on
the comparison star magnitudes used in your differential
photometry.  Were they V-band or R-band, or (groan) GSC?
Did you attempt to transform onto the standard system,
or just use the comp stars to zero-point your results?
I don't like unfiltered measures, and use them only rarely
in my research.  Vsnet-chat sounds like a good list to discuss
how such measures should be reported to make it as clear
as possible what methods were used in the reduction.
Arne

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