(cba:news) echo outbursts, and missed outbursts

Joe Patterson jop at astro.columbia.edu
Tue Oct 13 07:48:52 EDT 2009

Dear CBAers,

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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