(cba:news) october observing
jop at astro.columbia.edu
Thu Oct 16 09:39:59 EDT 2008
Time to sweep most of the September stars off the stage. V466 And has
faded below the limit of our telescopes; on the best of dark nights, we
can faintly trace the hump - but not well enough to obtain good data.
So let's say goodbye till the next eruption (which is probably many years
The main center of activity recently has been BW Scl and AO Psc. Berto
and Bob Rea have been carrying the torch for the former. This is a very
nearby, low-luminosity CV, much like WZ Sge except that it has never
erupted. (Presumably it will, but the timescale is 20 years or longer.)
Its special interest is the rapid white-dwarf pulsations, and a large-
amplitude "superhump" at a period much longer than Porb. This year, it
showed the former, and indeed the new data specified their properties
better than ever before. But the superhump had vanished. It was worth a
few weeks of looking... but now should go into the proverbial cold-case
AO Psc has been monitored extensively by Bob Rea, Jerry Foote, and Tut
Campbell (through George Roberts). The 14 minute pulse and the 3.6 hour
orbital signal are well tracked; these basically never fail, and the fast
pulse continued its regular spin-up. The star failed to deliver its
4.0 hr superhump, or possible superhump. The latter would be essentially
unprecedented, a superhump in an intermediate pola. But we only saw it
once; it lasted for a full two weeks, but the frequency was *exactly*
6.00 cycles/day... and the numerical coincidence was just too much for me
to accept. So I've been trying to conform it. No help from the 2008
data... and time to move on.
While the Moon is bright, the best northern target is V592 Cas, a 12th
mag novalike which we have not substantially observed in years. It
flashed a nice normal (apsidal) superhump last time around, and a marginal
negative superhump. It's beautifully placed in the midnight sky these days,
and a great target for all-night observation. With long nightly coverage
in Europe and the USA, we should be able to explore the superhump "spectrum"
far better than anything to date.
The other priority northern target is V455 And (=HS2331+3905), also very
well placed in the sky and equipped with a fascinating set of periodic
signals - which we're tracking. This star is now around V=15.7, a tough
target for bright and/or marginal skies - but plenty bright enough for
In the south, there's a great opportunity provided by VY Scl's falling
down into a low state. The (very) bad news is that it's 18th magnitude...
but one theory for this star predicts a very strong orbital modulation
after the star dives into a low state. This would arise because the
white dwarf is very hot and can power a strong "reflection effect" off the
secondary. So it would be very desirable to detect, or set a limit on,
any orbital signal in this star. So if you can handle the brightness,
give it a shot!
Speaking of 18th mag stars in the southern sky, consider RX0232-37. This
newly discovered dwarf nova has long faded since outburst, and we don't
quite know how bright it is. Possibly as faint as 18, its normal quiescent
level. But it's an extremely important star, quite nearby and will
eventually teach us a lot about the rarest of dwarf-nova erupters. Can
you possibly observe it, and obtain time series?
Granted, that's a long shot! A more manageable, but still ambitious, target
is ES Cet - still the shortest-period (confirmed) CV in the sky. This is
the 9-minute AM CVn star, and we've been tracking its orbital period change
to constrain its emission of gravitational waves. Someone else might,
or might not, find those waves directly... but we can definitely measure
its effect, the change in orbital period. It's a pretty healthy signal,
about 10%, and the star is decently bright (16.5-17) if your skies are
good and the Moon isn't lurking too near. You probably won't be too
thrilled with your signal-to-noise... but pretty good timings can be
obtained from quite homely data, when the periodicity is as simple as in
this star (basically a sinusoid).
Still more manageable (vastly) in the south is FO Aqr, for which we still
need abiut a dozen timings to pin down the behavior for 2008.
As a reminder, many CBAers are planning to attend the AAVSO/IAPPP meeting
in Big Bear (California) in late May... and I'm planning on the Tucson
CV workshop in mid-March meeting as well. You might want to think about
these - esp. the former. I had been planning on the Hawaii New Years'
conference as well, but now it looks like family health issues will
keep me from travelling for quite a few months.
Enjoy that October observing - the best time of year for us in the
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