(cba:news) cp puppis sets, hp lib and am cvn rise
jop at astro.columbia.edu
Sat Mar 26 07:53:20 EDT 2011
We've done some LONG campaigns this year, and I'm scrambling to keep
up. I did, however, finish the analysis of CP Puppis, and that star can
be retired. I didn't really believe my findings at first - they seemed
quite inconsistent with earlier results - but now I see that this is the
result of the global campaign, not any actual change in the star.
Earlier it seemed that CP Pup had two periods: one consistent with
Pspec at 0.06128 d (presumed to be Porb, and I think that interpretation
still holds up, although don't bet your life on it) and one 2% longer.
That's a pretty familiar pattern, hey? But behold the power of
longitude. We have observations from South Africa (Berto, Deanne de
Bude), Florida (Shawn Dvorak), New Mexico (Tom), New Zealand (Bob Rea,
Si Lowther) and Perth (Greg Bolt). That's the whole Earth, and it's now
obvious that the main photometric signal occurs at a much longer period,
0.0660+-0.0003 d. It differs from the more familiar superhump wave in
(1) the amplitude ranges - even on consecutive days - from 0.30 mag to
(2) the power in long (say 1 week) stretches of data is weak and
complex, even when the signal is strong throughout; and
(3) the period seems to be ~8% longer than the alleged Porb, as
Attached is an average power spectrum from 12 1-2 day stretches of good
and densely distributed data. Ugly but telltale. A coherent signal
would be a very narrow spike here.
Each of these properties is basically inconsistent with the
common-superhump family. A few other stars do it - BW Scl and CP Eri do
it in spades - but I've never seen it appear in a high luminosity state
(of any star). CP Pup is an intrinsically bright star... so this little
oddball family will have to make room for another member that is odd
even by its standards.
I've occasionally in print speculated that this phenomenon results
from a superhump at the 2:1 (rather than 3:1) orbital resonance in the
disk. Who knows if *that* interpretation can be massaged to accommodate
CP Pup! Anyway, the Puppis nights are getting short, and we're done for
I hope to write in the next few days of our other large campaigns: ER
UMa, SDSS1339+48, and YZ Cnc. Each will end soon... but probably not
It's definitely time to resume coverage of AM CVn, which took a break
after SDSS1339 erupted. And to start up on HP Lib, a nice bright AM CVn
star which can be attacked from all hemispheres. Long runs would be
Although there is no "CBA meeting" this year, clusters of CBAers will
be at the May AAVSO/AAS Boston meeting and the May SAS Big Bear meeting.
I'll only be at the former (along with Enrique, Helena, and possibly
Jonathan), but the Big Bear meeting is always a good one too.
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