(cba:news) comparisons 'n stuff

Joe Patterson jop at astro.columbia.edu
Thu Feb 14 15:59:53 EST 2002

Thanks Arne, Dave, Berto -

Interesting issues.  I don't have anything really *factual* to add to what
these 3 have said - but I favor the traditional V-C, K-C approach for a
systematic program like ours which will blend observations from different
telescopes.  If we all use the same comp and the same detector (those
Kodak chips were great because there were so many around, and they were
sufficiently blue-blind that the blue excess of the CV wasn't too bad),
then V-C means something straightforward.  With ensemble photometry it's
harder to say - everyone uses a different ensemble, etc.  Also, I
sometimes apply corrections for differential extinction - this will
become more important as the enhanced-blue detectors get out into the
world, because there will then be a *large* difference in the effective
color of CV and comp.  With ensemble photometry it's too vague, because
the "supercomp" doesn't have any definable color.

Perils of white light.  Filters help with many of these problems.  But
then our little faint stars go away... and we get nothing at all.  We
need all those tainted pink photons!

I think a few CBAers do ensemble photometry, and that's OK, but the
traditional V, V-C, C-K is just fine.  Makes me feel warm all over.

By the way, if you want to add another column, consider *airmass*.
That would help me for the very bluest of CVs - the AM CVn stars, who
clock in about B-V=-0.2 - which show differential extinction effects
that can be pretty annoying.  (They tend to insert artificial periods of
1, 2, 3, and 4 cycles/day into the time-series).

Oh.......... and let's take BH Lyn off the menu!  Time to get going
BIG-TIME on DW UMa.  Nearer the equator, and in the evening, there's BG
CMi and PQ Gem.  More details tomorrow.


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