(cba:news) midwinter changes; the south shall rise again
jop at astro.columbia.edu
Sun Feb 17 07:05:15 EST 2013
Just back from the nova conference in South Africa. I had hoped to see
Berto there, but class commitments back home were too severe. It was a
good conference. I was surprised how much disagreement there is among
nova theorists. In large measure this has been sown by the continuing
provocation of new data - it's tough to survive collision with new
facts! Great motivation for us observers.
T Pyx is certainly a good example. The large and abrupt period increase
in outburst was a shock. We could explain a tiny period increase (mass
loss), or a period decrease of almost any size (angular momentum loss).
A big period increase requires hefty mass loss, which we don't expect
from a recurrent nova (since it has only had a few years to accrete).
We'll come up with some sort of excuse, of course... until the next
surprise comes along.
We have been going great guns on our two big southern targets: T Pyx and
CP Pup, with huge efforts from Arto, Berto, and Bob Rea - aided also by
Peter Nelson, Gordon Myers, Josch Hambsch, and Shawn Dvorak. Now it's
time to halt the campaigns, for two completely different reasons. For T
Pyx, the signal appears to be completely stable; a few runs in April
will tweak the value of Porb, but it's not a useful target until then
(unless the star blows up again!).
Time to quite also on CP Pup, for (sort of) the *opposite* reason. This
star astounds me. There is a fairly good - not beyond any doubt, but
pretty good - spectroscopic measure of Porb at 0.06143 d. And that
signal appears to be also weakly present in the photometry. But the
stronger photometric signal occurs at lower frequency, and some 1993
data - very sparse by our current standards - convinced me that was a
common superhump, about 2% longer than Porb. Now that we have long
observing campaigns in three recent years, I see that this is wrong.
Actually the signal is 10-100 times less stable than a common superhump,
and on average about 5% longer than Porb (and much larger in amplitude
than a common superhump). Anyway, the coverage has become nearly
perfect, and it's now clear that the signal - large though it is! - is
so unstable that long baseline is of little use in improving its study.
It's QUASIperiodic, not periodic. Quite fascinating, and susceptible
of interpretation, but not needing any more data.
Time to end coverage of V1159 Ori, too.
The best evening object for all hemispheres right now is definitely GR
Ori, a long-dormant eruptive star which now appears to be an extreme
dwarf nova (not fully confirmed yet, but very likely). Another in Rod
Stubbings's amazing gallery of finds. Some of you are already observing
it - nice move - and might want to send some useful info to this space.
AAVSO Special Notice 335 contains the information you need to observe
it (including the correct coordinates). This is probably a really
extreme WZ Sge-type dwarf nova, our favorite beast! It's 23rd magnitude
at quiescence, so savor it (and acquire time-series photometry) while ye
In the morning sky, if you can, I strongly recommend TCP
15375685-2440136, another new kid (dwarf nova) on the block who has
erupted off-season. I guess the odd ones can't be expected to
cooperate. Coords and finding chart in the last cba-news message.
At a similar RA, but at -52 deg and near magnitude 18, is IM Nor, which
jumps to my high priority list, now that T Pyx has done its dance. In
our group, only Berto has ever observed it. But it would be GREAT to
obtain time-series photometry around the globe, sufficient to define the
main (orbital) signal and search for others. Same comment for V382 Vel
(Nova 1999), although this one is more exploratory; how about one
lengthy time series to determine magnitude and assess likelihood of
periodic signals (present when we observed it 7 years ago).
A bonanza of southern stuff! I'll write again in the next 1-2 days re
our decidedly-northern targets, which I think are still good. But
Enrique keeps better track of these, and may write in the meantime.
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