(cba:news) getting greedy on TT Ari

Joe Patterson jop at astro.columbia.edu
Thu Oct 15 06:08:02 EDT 2009

Dear CBAers,

TT Ari is continuing to decline towards its historical V=15.5 low state, 
and in fact might be already there.  Some data has trickled in - just a 
little, but enough to make me awfully greedy for more.  As usual, being 
a CBAer deep in my heart, I'm most desirous of long nightly time series 
- which, after being spliced together around the globe, will yield a
superb record of periodic signals in the light curve.

Naturally that'll take a while to assemble. But I'm already surprised to 
see the very strong flickering/QPOs that continues in the light curve. 
It's not obvious where this flickering arises.  The accretion rate must 
be much lower now, but the hot WD should still be plenty luminous - 
it'll take months/years/decades for the WD, heated by centuries (at 
least) of accretion, to cool off.  So why doesn't the WD now (presumably 
a more or less constant source) dominate the faded disk?  This question 
will perhaps be best addressed by spectrophotometry, which can parse the 
secondary+disk+WD components.  However, multicolor photometry can probe 
it also.  It would be very nice to know the color of the flickering 
light.  Very few (or perhaps none) of you are equipped to obtain rapid
multicolor photometry - spinning the filter wheel fast enough to 
time-resolve the ten-minute flickering - but many of you have blue or 
infrared filters, and long time series in one filter (say B or I, 
something like that) could convey a lot of information.

But don't neglect the white-light ("pink") that we usually revere!  It's 
just that in this particular case, since the competing light sources are 
  very red (secondary) and very blue (hot WD), filtered data has a good 
chance of supplying important extra information.  You always have to 
balance that against the statistical quality of your data, though - and 
I fear that at V=15.5, the star might be a touch too faint for the 
filtered time series (which must have good time resolution, remember).

So think about that.  We (actually Koji Mukai) will be getting a Swift 
observation in X-rays and ultraviolet in the next few days.  So this is 
REALLY a good time to get thee to a telescope... and squeeze off some
beautiful time-series of the star!


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