(cba:news) crabber redux

Joe Patterson jop at astro.columbia.edu
Sun Mar 23 21:42:05 EST 1997

Dear CBAers,                                        March 23, 1997.

I know it's a broken record, but...

Our old friend EG Cancri is *still* pumping out large-amplitude
photometric waves at some period close to the old superhump period
(86 min).  But we are just not getting enough data to define the period
sufficiently (orbit? common superhump? negative superhump? some
combination?).  I know most of you are plenty averse to working so
faint (about 18.2), but dig deep in your heart for this one, folks.
The raw light curve may *look* ugly, but the scientific return is very
great.  If it's an orbital modulation, then it will give us Porb and
enable us to put EG Cnc in its proper place, whatever that may be, in
the family of CVs and superhumpers.  If it's the old superhump, why,
it's by far the most enduring signal of this type among the SU UMas.
Not knowing is agony.

The signal has a quite large amplitude, 0.3 mag.  But the star is
awfully faint and the runs are a little short these days (<0.2 d).  So
we have a daily alias problem.  The USA observers are usually our
strongest node, and I beg them to keep faith on this star when
conditions permit.  Longish integrations are fine, since the activity
we care about it is somewhere near 86 min.  Jonathan and I will make it
our top priority in the early evening from South Africa during March
27-31.  I believe that a single matched set of observations from such
different longitudes on the same night will decisively settle the alias
problem.  But it's a very tough observation from South Africa.  So I'm
really, REALLY begging our friends at Wise and Ouda observatories for
help with this!

Well that's the story.  My knees are getting bloodied.  Think "white
light" for such a faint star.

             *          *          *          *          *

On to the bread and butter...

For northerners, Lasse and Dave West have started the season's coverage
on AM CVn and LX Ser.  Both 14th mag and likely to be prime, excellent
CBA targets for a couple months to come.  AM CVn is a sure winner but
could bore you somewhat because all the action is in the 0.02 mag
signals at 9 and 17 min.  LX Ser is more speculative but more
entertaining, since it throws a deep eclipse at you.

For southerners, V803 Cen is the star of the month.  This seems to have
low states around 17, high states around 13, and "cycling states" where
it moves back and forth on a timescale <1 day.  Very much like CR Boo,
last year's prima ballerina.  It's top priority during our 21-night
observing run in South Africa (on the SAAO 0.75 m, starting March 25),
and our 10-night run in Chile (CTIO 0.9 m, starting April 9).  If the
star is not stuck in a low state, then our friends in Australia and New
Zealand can fill in that gap in our light curves and give us close to
24-hr coverage.  It's a dream but worth staying focussed on!  The star
also has a 27 minute periodic signal - plenty of photometric action in
all brightness states.

Finally there's EC1533-1403.  The major campaign still lies ahead, but
worth a get-acquainted visit some chilly morning.  Or an excellent
choice for out-and-out southerners right now.  Magnitude 13.6 and a
handsome 19 minute superhump at 0.05 mag.

             *          *          *          *          *

Some of you know that the NY Times ran a feature on the CBA March 18.
Kinda warm and fuzzy.  It was nice to see it, and augurs well for our
future prospects in backyard research.  Some of you also know that we
had some success with grant support, from the NSF and the Research
Corporation.  That was mighty nice to see too, and will keep the toys
flowing for a while.


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