(cba:news) cp puppis sets, hp lib and am cvn rise

[Joe Patterson]

Dear CBAers,

   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 
these respects:
(1) the amplitude ranges - even on consecutive days - from 0.30 mag to 
undetectable;
(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 
mentioned above.
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 
the season.

   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 
quite yet.

   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 
mighty nice!

   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.

joe


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