(cba:news) AM CVn mostly

[Joe Patterson]

Dear CBAers,

Reports from Tut Campbell, George Roberts, and Jeremy Shears indicate 
that SDSS 1055+09 faded fast... which usually means a normal outburst. 
There's some chance it'll trigger a super, so 2-3 more days of snapshots 
would be good.  Unless it jumps back into a super within 3 days, forget 
about it.

Thanks in part to a long season-opening baseball game, I've finished 
analyzing the month's data on AM CVn.  The perpetrators were Bob Koff, 
Tut Campbell/George Roberts, Russ Garrett, Arto Oksanen, Bart Staels, 
and Gordon Myers.  A great team, and a great month of data!  As some of 
you know, we don't particularly track the main superhump (at 525.6 sec) 
nowadays.  It's always present with the same amplitude, and its phase 
wanders on a timescale of weeks - as we've shown in many papers 
stretching over 30 years (although for 22 of them, this was considered 
"controversial").  Now my main interest is tracking the orbital wave, 
which is significantly weaker and therefore requires many long time 
series to specify with the needed precision. That wave occurs at 
1028.7322 s.  It's particularly interesting because AM CVn is a likely 
target for the upcoming gravitational-wave detectors (2 WDs orbiting in 
17.5 minutes, that's a pretty potent radiator of GR).  And also because 
when we see the Porb *change*, it signifies the direction and rate of 
binary evolution - which we'd dearly like to know for these ancient 
binaries!

I have 3 good orbital timings for the month, which is normally a good 
haul for a whole observing season.  However, I noticed that the NODAL 
SUPERHUMP - the 1011 second signal which probably comes from the 
retrograde wobble of the disk - was strong throughout March.  I've never 
seen it so consistently strong.  We've *never* done (nor has anyone else 
of course) a thorough study of that signal - for stability, harmonics, 
and correlations with the wandering of the 525 s signal.  Since we've 
already got a good baseline and the observing season has plenty of life 
left in it, let's KEEP THE CAMPAIGN GOING.  It's particularly a good 
choice for smaller scopes (not suitable for the deep-sea targets) or for 
mediocre nights (since our interest is *periodic signals*, mere loss of 
signal-to-noise is not that important).  But of course, best of all are 
long time series on excellent nights with large telescopes!

This doesn't cancel or modify my earlier target suggestions.  But they 
did run a touch on the *faint* side... and I was delighted to see such 
interesting and new things come once again from our old friend AM CVn!

joe