(cba:news) TT Ari, take 1... and filter selection

Joe Patterson jop at astro.columbia.edu
Fri Oct 23 17:39:17 EDT 2009

Or at least publicly take one.  We decided to jump out with a quick 
"what we learned on the first day" note, and here it is:


I limited the author list to those with light curves coincident with the 
X-ray observation.  However, there are some really beautiful light 
curves rolling in now, and such beauties are hard to keep cooped up in a 
computer for long.  We'll figure out some way to get 'em out in the 
light of day pretty soon.

At this early stage, the ~0.38 day waves are the most interesting aspect 
of the light curve, and this timescale forces us to worry about how we 
take our data.  In particular, our longest/best light curves last 8-9 
hours, and this is practically the same as the signals we wish to 
measure.  Thus uncorrected extinction effects will certainly contaminate 
our data.  It's *differential* extinction that matters, and this can be 
pretty large for clear-filter data, since the effective wavelength for 
TT Ari will be much bluer than that for an average field star (about 
0.10 mag/airmass).  I can satisfactorily correct your data if you supply 
the airmass - and the need is minimal if you observe in a decently 
narrow band (like V).  So one of those strategies would be helpful.  But 
if software/hardware limitations mean that you're a clear-filter guy, 
that's all right.  I learn a lot about how to make these corrections 
from experience.

It remains desirable, IN PRINCIPLE, to get B and I - or some similar 
well-spaced blue and infrared - light curves.  But we already know 
roughly that the light curves are similar - as is true for practically 
every CV.  So no quick riches for this approach.  Nevertheless, really 
extensive coverage like this would probably teach us a lot; I don't 
recommend it, but a very extensive set of B/I light curves would make a 
liar out of me.

Whew, tomorrow I promise to cover the rest of the CV goodies in the 
October sky.



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