(cba:news) stars for early May (Joe Patterson) [2010-05-03T02:12:08Z]

                                                         May 2, 2010.
Dear CBAers,

    Olde Whiteface is receding from the sky, and it's time to install
a new set of program stars.

    The AM CVn campaign has been the best ever.  During this season the
star has flashed periodic signals at 525 s, 1051 s, 1011 s... and, most
importantly, 1028.7 s, the orbital period.  The weakest of these is the
orbital signal, so to study it you have to subtract off all the other guys.
This is possible with or long multi-site observations, and in 2010 we
accumulated six precise timings of the orbital signal (each requires about
a week of data).  Combined with timings over the last 16 years, they show
that AM CVn is slowly decreasing its orbital period.  This implies that
the secondary is probably a *non*degenerate helium star, contrary to
the usual assumption.  This definitely brings to an end our 2010 campaign...
and maybe will take the star off our lists for a few years to come.

   I'm also going to scrub CR Boo.  This star is maximally rewarding when
it is at absolute maximum light (13.0) or minimum (17.3).  In fact, there's
very little recorded data at either extreme, because CR Boo spends so
little time there: ususally it is ramping speedily up and down between
13.6 and 14.5 - the "cycling state".  When it is, the high-speed activity
becomes subtle and complex - just what we don't like!  Out it goes.

   The third of the bright May-June helium CVs is HP Lib - and this should
now be a featured target of the CBA for at least the next month,  We have
done only one campaign on it - worked pretty well, and it's perfectly
placed now for both hemisiphere.  Very bright at 13.7!

   Dwarf novae have taken a rest.  Here are some more ambitious targets.

ASAS 1536-08 (Lib in Downes catalog) is a star alleged to be at 17.5 in
quiescence.  Is it really that bright?  If so, it is definitely worth
time-series photometry on good nights.  Probably this is a very old CV,
and may show some photometric periods in quiescence.

WX Cen.  Good southern target for *bright moon* conditions, or for cirrus.
We mainly are tracking the eclipse.  13th mag.

V1084 Her = RX1643+34 = "Her".  Mag 12.7, great target for bright moon,
or cirrus.

Finally, there's GW Lib.  It's high time to do an extensive study of the
post-outburst state (since 2006).  At 16.6 and at dec=-25, it's bright
enough and suitably located to be a target for practically all of us.

That's a good list.  Happy observing!  I hope to see as many as possible
of you at the SAS conference in Big Bear next week.

joe