From jop at astro.columbia.edu Fri Apr 9 08:49:40 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Fri, 9 Apr 2004 08:49:40 -0400 (EDT) Subject: (cba:news) Stars for mid-april Message-ID: Dear CBAers, The DW UMa and V803 Cen campaigns did very well - each of these stars tempting us by flashing a quick look at some of their most closely guarded secrets. Greg Bolt, Tom Richards, Bob Rea, Jennie McCormick, and Berto Monard got beautiful long runs... and to my amazement the photometric period was not the usual 1618 s, but rather the 1612 s that is historically characteristic of quiescence (or anyway a luminosity state close to quiescence). The latter is normally interpreted as the orbital period. But this hyperactive star may well flaunt normality - and it's for us to track how the period evolves over the next few weeks. A wonderful southern target crossing local meridians near midnight! DW UMa is tougher to decipher. We wrote a paper last year (with Harvey, Skillman, Fried, Monard, Beshore, Martin, Niarchos, Vanmunster, Foote, Bolt, Rea, Cook, Butterworth - PASP 114, 1364) which reported quite good campaigns in 1996 and 2002. Roughly speaking, the 2004 campaign (which will be accompanied by long HST coverage, when the latter chugs down the pipeline) is consistent with 2002 - basically an apsidal superhump at 6.86 c/day. However, there are also many significant peaks near (but displaced from) the harmonics... and they tantalize with the prospect of understanding the systematics of their structure. This has only been done for one CV, AM CVn - and being a helium star, it can't be relied on for extrapolatuion to the whole class. Anyway, the star is well worth continuing coverage! SDSS 0809+38 should be abandoned. It's just too late. Lew Cook was our stalwart on this star - and (nearly) single-handedly managed to pull it off. It seems to be one of these weird CVs with vastly discrepant photometric and spectroscopic periods. Gonna have to wait till next year. Then we'll figure out what this year's oddities are all about! Two other good northern targets. AM CVn itself. The 1011 s signal (negative superhump) is back in spades. Positive (apsidal) superhumps have a well-known pattern of period evolution, but nothing like this is known for negative superhumps. This is the chance to remedy that unhappy state of affairs. For new AM CVn observers: the star hardly flickers at all, and with mediocre data you might wonder if it's even varying... but rest assured there's a small-amplitude 9/18 minute clock beating within - and the periodic signal *jumps* out of the power spectrum, even when the light curve looks worthless. And the other is ES Dra. Sort of terra incognita. Reasonably well-behaved radial-velocity period, thought to signify the orbit. But a photometric signal that may be at a very different period (about 70% of Pspec). A rare and altogether mysterious property of these beasties! More on southern targets in a few days. Happy observing! joe From jop at astro.columbia.edu Wed Apr 21 13:05:55 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 21 Apr 2004 13:05:55 -0400 (EDT) Subject: (cba:news) stars for late april Message-ID: Dear CBAers, Bill Allen's coverage of V803 Cen last night showed a most remarkable thing - the apparent beginning of another superoutburst, after just a 20 day wait (compared to the usual 80-90). Big superhumps popped up once again. Our coverage over the last 20 days has been just sensational, with long and excellent runs by Berto, Jennie, Bob Rea, Bill Allen, Greg Bolt, and Tom Richards. So it's a complete accounting of SO->SO, something we've never really had before. But why stop now? The star is still beautifully placed and plenty bright. Fire all available (Southern) weaponry! In the north, DW UMa should retire (too late in season), and AM CVn should get all-night coverage. The 1011 s signal (negative superhump) is now as strong as it has ever been, and this offers the best opportunity to study it throughly over a long time baseline (couple of months). Those are the big ones. I'll write again next week after I return from a spot of travelling. joe