(cba:news) Fwd: DW UMa, SDSS 0902+38, CR Boo

Joe Patterson jop at astro.columbia.edu
Tue Mar 25 15:48:29 EDT 2014



Hi CBAers,

SDSS 0902+38 has been performing beautifully for us... or, from a more
practical viewpoint I guess, you've been performing beautifully for it.
Looks like it may go down as the best observed AM CVn superoutburst
ever.  Still bright, so keep it up!

In 1996 we (actually an earlier generation of CBAers, especially Dave
Skillman, who started the CBA) found some wonderful signals in DW UMa -
a powerful negative superhump and a very powerful nodal precession
signal (at the beat frequency of orbit and superhump).  But it was back
in the floppy-disk era... and with each passing year, that data got less 
and less accessible to me.  I published a brief summary in a 2002 paper, 
and resolved to mount a really wide campaign in a subsequent year.  We 
did, in several years - but the signal disappeared.  A positive 
superhump appeared, which was nice, but a powerful negative superhump, 
TOGETHER WITH THE DEEP ECLIPSE, is a much greater prize since it 
promises to give a diagnostic of how the shape varies with precession 
phase (by watching the eclipse shape change with precession phase).

Enrique tells me that the negative superhump is back!  The season and
declination are great, and it's decently bright too (about 14.7 out of
eclipse).  A great northern target for the next month.

Every few years we run a campaign on CR Boo, the second (or maybe third) 
brightest AM CVn star.  We published a pretty good paper (attached) on 
it back in 1997, but our coverage since then has been kinda fragmentary. 
    The equatorial location (1346+08) means that no one gets long 
runs... and although we have all-longitude coverage in principle, we 
never manage to accomplish it.  Bad weather, bad luck, reluctance of 
southerners to observe a technically-northern star, who knows.  CR Boo 
is especially demanding of almost-round-the-clock coverage, because of 
the rapid cycling (~19 hours).  On the other hand, its relatively short 
stays in the very-bright (13) and very-faint (17) states are much easier 
to analyze and decipher, because one doesn't have to figure out how to 
handle the rapid cycling.

So that all amounts to a fairly complicated story for CR Boo.  But the
time is ripe to start a 2014 campaign - and to sound the alarm if it's
in that very-bright or very-faint state.

And also to continue the HP Lib campaign - on a somewhat lower priority
basis, since it's sort of a April-May-June target, but to get the ball
rolling.

joe


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