(cba:news) echo outbursts, and missed outbursts
jop at astro.columbia.edu
Tue Oct 13 07:48:52 EDT 2009
Just a few musings/speculations this time.
Some of you know that EG Cnc jumped into outburst a few days ago, and is
now (or was yesterday) declining rapidly. Definitely one of our
favorite stars! It's pretty early in the Cancer observing season, so we
have only a weak constraint on when that outburst started. It could be
the very beginning of a super, or the end (one of the infamous "echo
outbursts"). Or it could be merely a normal outburst; I believe two
such events have been seen in EG Cnc, and they are generally documented
in WZ Sge stars, other than grand old WZ itself. The next week will
probably tell us which of these is true, or perhaps yet another
possibility. The most interesting would be the beginning of a super...
although the poor seasonal timing (Cancer in mid-October) probably means
that we can't expect to get as much coverage as we did in the 1996
outburst. The latter was one of the best-observed DN eruptions in history.
VX For is likely a similar binary, a very old guy with a puny secondary.
Accordingly the star is busily executing echo outbursts now - a poorly
understood phenomenon but one that appears to characterize the WZ Sge
stars. Superhumps have become very weak and hard to follow, maybe even
gone altogether. The smart money says they're not likely to come back.
But the echoes might go on for a while, and documenting those is
mighty important, since this is essentially the first observed outburst
in history (that of 1990 really didn't produce anything, aside from many
puzzled conversations in Chile). The era of handsome light curves is
probably over, but the star's behavior over the next two weeks is likely
to be scientifically rewarding. In case it's not obvious, I'm really
excited by this return of a mysterious old friend!
A big and very uncertain question for all these normally faint stars
which rarely erupt is: just how common are non-supers? (Often called
"normal" outbursts, but it's an odd term, since they are presumed to
happen very rarely or even never.) Of course we can simply count the
ones in the documentary record... but how many do we miss? I don't have
any suggestions about this, but thought I'd raise it in case anyone else
V368 Peg is probably an "ordinary" SU UMa star, with supers roughly once
a year. As Arto remarked and as his light curve proved, the star has
declined from plateau, yet kept its superhumps going strong. This could
be interesting to track; we know that generally speaking, superhumps
tend to outlast the superoutbursts which create them... but there has
never been a star (or at least not a hydrogen-rich star) which
illustrated this in sufficient detail to yield some nice numerical
estimates of this.
Olde Whiteface is finally falling out of the sky, so you might be able
to get some good data on these stars, now pretty faint.
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