(cba:news) spring 06 stars

Joe Patterson jop at astro.columbia.edu
Thu Apr 13 05:35:13 EDT 2006

Dear CBAers,

The flowers and leaves are emerging from the long freeze... and it's
time for the new season of stars to emerge, too.  Quite a few need to
retire for the season, mainly because solar glare is getting just too
bothersome.  These are: Swif0732-16, WX Cen, DW Cnc, UMa 6, BG CMi,
and V405 Aur.  We had good campaigns on the first four, and will be
writing up the results later this year.  The latter two were somewhat
sparsely observed - probably enough to maintain cycle count and thereby
improve knowledge of their periods, but we'll see for sure when we do
the complete study of the year's data (always in the summer!).

It's also too late for WX Pyx.  This is an unpopular target among CBAers,
to my chagrin.  Definitely a touch faint, but with quite a big periodic
signal.  Anyway, I think it's gone... so I'll cheerlead for it next year.

I still like RX1039-05 = Sex. This star is 18th mag, but the periodic
signal is huge (>1 mag) and especially big in the infrared.  Several
CBAers have gotten good data, especially Bob Rea; a few more nights of
coverage would finish up a good season and - I think - clinch a long-term
ephemeris with certainty.

Alas for me, the same is not true for RX1050-14 = Hya.  This star is of
huge interest as a candidate period-bouncer - the most ancient of the CVs
(assuming they exist at all).  Two years ago we had a decent indication
of a photometric signal at a period close to the period suggested by
spectroscopy.  The latter was not firm, and certainly not accurate; we
could have done much better with photometry.  But as the poet sayeth,
coulda woulda shoulda.  Tom Krajci's diligent coverage showed that at our
level of sensitivity (0.03 mag), there's no significant periodic signal.
That generally gets you demoted from CBA lists.

Soooo... here come the spring stars.

I'm gonna take a pass on IY UMa, which some of you are observing now.
It did jump into supermax, and this eclipsing dwarf nova has truly great
supermaxima.  But we published a very extensive study back in 2000 (I
think)... and there's a good chance that our conclusion now would be "yep,
it's pretty much the same."  Of course we can't know this without looking,
but it's pattern among dwarf novae.  Light curves obtained so far do help
tighten the ephemeris... but I don't think it warrants a big effort now.

April is the big month for the AM CVn stars.  The brightest of these are
AM CVn (V=14.2 at 1237+38) and HP Lib (V=13.6 at 1535-14).  Both have
very intricate superhumps and a detectable signal at Porb - and very low
flickering, which is a delight since it allows much greater sensitivity
to periodic signals.  They're also prime targets for the gravitational-
wave experiments of the next decade.  Since we seem to be the only
people who can measure these periods with any precision, it's incumbent
on us to establish long-term ephemerides (for Porb, that is).  The stars
are bright enough to overcome moonlight, so I strongly recommend that
these be prime targets for the next couple of weeks.

In the south, I also recommend EX Hya in the next week or two.  The
ephemeris is getting a bit rusty - time to tune it up!  It takes a couple
of weeks, because there are TWO periods that have to be adequately
decoupled: the 98 min orbital period and the 67 minute spin period.

That's a pow'f'l short list.  But that gives us a better chance for very
concentrated coverage... and I think it's proper till dark skies give us
access to the fainter among our stars.

For those of you planning to come to Big Bear, let me remind you about
dates.  The conference proper is Wednesday and Thursday, May 24 and 25.
Information about logistics is on the "socastrosci" website.  It's
preceded by a day of workshops on May 23.  Since Tonny and Jerry are
presenting workshops, I imagine that some/most of the CBAers will be
present on the 23rd as well.  A few of us will be driving in from
Tucson on the night of the 22nd - but most people are making their own
travel arrangements.  You need to register on the SAS website, but
there's no CBA registration or anything of that ilk.  Since we're all
likely to be in the Northwoods resort, it should be a simple matter to
arrange to meet together and discuss items of mutual interest.  Any
questions, please write.

Happy observing!


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