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(cba:news) AM CVn mostly (Joe Patterson) [2010-04-05T12:40:11Z]


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