From jop at astro.columbia.edu  Thu Apr 12 09:55:31 2007
From: jop at astro.columbia.edu (Joe Patterson)
Date: Thu, 12 Apr 2007 09:55:31 -0400
Subject: (cba:news) GW Lib at last...
Message-ID: <461E3A53.4080907@astro.columbia.edu>


Dear CBAers,

Rod Stubbings just reported that GW Lib, practically dormant since 1983, 
is in outburst at 13.8.  GW Lib had at least one previous short 
outburst, and that's probably what this is.  But it may also be the 
beginning of a superoutburst... and if so, it's tremendously important.
And well placed in the sky too!  At -25 degrees, it's even marginally 
available for southern USA observers.

So it's absolute top priority now for (nearly) all observers, and worth 
staying on until it arrives back at minimum (V=16.6, although catalogues 
tend to assign it an incorrect V=18.5).  That might come in just a few 
days; or it could well be a few months!  Even if it's just a short 
outburst, it's still quite interesting: the only previous coverage of 
short outbursts is a single image.

Here's Rod's message...

________________________________

Gw Lib is in outburst.

LIBGW          070411.509  <157  Stu.RASNZ
LIBGW          070412.494   138  Stu.RASNZ

Regards,
Rod Stubbings
_________________________________

Re other objects, it's time to DROP DT Oct.  YY Sex, AM CVn, and CR Boo 
remain good targets.  BZ UMa went into outburst a few days ago, and 
CBAers jumped to attention pretty fast.  I'm kinda torn about it.  It's 
true that BZ UMa is a strange star that stands well apart from other CVs 
of short Porb; that makes it a very tempting target, very desirable for 
study.  On the other hand, we've gotten good coverage of a previous 
outburst, and the star exhibited mainly erratic variability.  So that's 
one excellent reason to study it, and one fair reason not to.  Excellent 
trumps fair, so I guess it's a good evening target for you borealites.
I'll study the data and comment again soon.

Actually, I don't think I've received any yet.  Can you send me the BZ 
UMa data?

Happy observing!  We're in a major extension of winter here in the 
Northeast USA.  Decently clear nights... but I didn't think I signed up 
for all this springtime cold.

joe




From jop at astro.columbia.edu  Thu Apr 12 17:39:57 2007
From: jop at astro.columbia.edu (Joe Patterson)
Date: Thu, 12 Apr 2007 17:39:57 -0400
Subject: (cba:news) GW Lib Rapid Brightening
Message-ID: <461EA72D.2060809@astro.columbia.edu>


Well, CBAers, at that rate of brightening, it's pretty likely to be a 
super.  Let the madness begin!

joe




-------- Original Message --------
Subject: [vsnet-alert 9293] GW Lib Rapid Brightening
Date: Fri, 13 Apr 2007 04:30:21 +0800
From: Andrew & Tracey Pearce <a.tpearce at bigpond.com>
To: vsnet-alert <vsnet-alert at ooruri.kusastro.kyoto-u.ac.jp>
CC: observations at aavso.org,	vsnet-obs <vsnet-obs at kusastro.kyoto-u.ac.jp>

GW Lib continues to brighten rapidly as detailed below:

LIBGW          070412.568   140  Pea.RASNZ
LIBGW          070412.617   132  Pea.RASNZ
LIBGW          070412.658   120  Pea.RASNZ
LIBGW          070412.853   99  Pea.RASNZ


Regards
Andrew Pearce
Western Australia




From jop at astro.columbia.edu  Sat Apr 14 21:57:17 2007
From: jop at astro.columbia.edu (Joe Patterson)
Date: Sat, 14 Apr 2007 21:57:17 -0400
Subject: (cba:news) what a week...
Message-ID: <4621867D.3010304@astro.columbia.edu>


and what a weekend to be (almost) away from email.  So BZ UMa and GW Lib 
have finally emerged from the shadows.  Keep the faith on 'em!

joe


From jop at astro.columbia.edu  Mon Apr 16 11:16:01 2007
From: jop at astro.columbia.edu (Joe Patterson)
Date: Mon, 16 Apr 2007 11:16:01 -0400
Subject: (cba:news) data-taking issues
Message-ID: <46239331.3080806@astro.columbia.edu>

Dear CBAers,

Back in NYC now, anxious to look at that great data for BZ UMa and GW 
Lib. Best targets in a couple years, except maybe for the Halloween 
transient.

Both stars are pretty bright, and you'll need to think about saturation.
Some people are fighting this with filters (generally, V filter 
recommended)... some with short exposures... and some with stopped-down 
telescopes.  One of these should work for you.

In general, superhumps and orbital humps have a color similar to the 
star's mean color - hence the amplitude in near-optical passbands (BVRI) 
tends to be similar.  This is one of the reasons we've tended to 
recommend unfiltered photometry: the extra information from filtering 
isn't worth the lowered signal-to-noise.  But this isn't true for all 
stars, and for most stars it has not been studied and hence isn't known 
one way or the other.  I'd find it very interesting if ANY superhumper 
showed a large color effect; superhumps come from heating effects, and 
thermal processes at the relevant temperatures (c. 15000 K) are pretty 
white.  But that's just theory; it is well worth a filtered study if you 
have the filters and can still get good signal-to-noise.  V-I or B-I are 
good choices (we want a good range in central wavelength, but can't 
afford the variable atmospheric transmission typical of U).

BTW these pooh-poohs of filtered photometry don't apply to the DQ Her 
stars (intermediate polars).  There the origin of the pulsed light is
an open question: it could well be a magnetic process (cyclotron 
radiation), which can be a very strange color, and is somewhat commonly 
very red.  PQ Gem is an example of this.  Not much is known about this, 
because extensive multicolor photometry isn't obtained for most DQ Hers. 
An interesting project, perhaps.

Have a wonderful time with these two grand new superhumpers!

joe


From jop at astro.columbia.edu  Thu Apr 26 08:43:05 2007
From: jop at astro.columbia.edu (Joe Patterson)
Date: Thu, 26 Apr 2007 08:43:05 -0400
Subject: (cba:news) april-may stars
Message-ID: <46309E59.7020806@astro.columbia.edu>

Dear CBAers,

As most of you know, the sky has recently furnished us with beautiful 
new bookended superhumpers: BZ UMa and GW Lib.  Great rewards for these 
long nights!  GW Lib will likely keep going for a long time - a few more 
weeks at least - and will get even better placed in the sky.  So that 
will remain the prime choice in the southern sky.  Superhumps in these 
"WZ Sge stars" (SU UMas of very long recurrence time) are little known - 
practically all our knowledge is based on WZ Sge itself, and it remains 
unknown whether those lessons are general to the class.  So keeping the 
faith on GW Lib is nighty desirable - it's sure to pay off.

The BZ UMa outburst may be about to end - or maybe not.  In any case, it 
too is an excellent star for a lot more vigilance.  It may have echoes, 
and it only falls to about 15.5 anyway, so you're likely to be able to 
track it pretty well all the way to quiescence.  Except maybe for the 
increasingly difficult position, which will get awkward in a few weeks.

So, let's keep going on both.  No deadlines for BZ UMa or GW Lib.  Just 
for IR Aq.

YY Sex we can say goodbye to.  Bob Rea has been observing up a storm, 
and his observations show that the period has been stable for 5 years. 
That plus the extremely red color of the signal establishes that it is 
an AM Her star, not a DQ as generally catalogued.  Point proved; time to 
move on.

Moonlight is getting bright now, and a good northern target is AM CVn. 
The goal is the tracking of the 1028 s signal.  We now have enough to 
establish cycle count over a 15-year (and likely 29-year) interval, and 
this is our main objective.  But the 2007 timings, though establishing a 
secure cycle count, don't specify the absolute phase as accurately as 
we'd like.  The last really good year was 2004, so there's about a 50 s 
uncertainty (about 0.05 in phase) now.  Kind of annoying.  If we could 
narrow this to about 20 s, no one would have to do this period study for 
another 5-10 years.  Let's tune it up!  However, since there are more 
powerful signals at 525 and 1011 s, you really have to get long 
observations (4 hrs or more) to separate the various signals.  A good 
target, but only if you can get long runs.

A good equatorial target is CR Boo.  Hardly anyone responded to my last 
plea for it - those flashy superhumpers bumped it off, I think.  But 
it's in good sky position, available to all observers, and its 
superhumps are still not much studied - really nothing of consequence 
since 1996.  Pretty strange for a bright AM CVn star with a very short 
period.  I dunno, maybe we have to wait till GW Lib fades... but I urge 
you to consider CR Boo.  The usual guidelines apply: long runs very very 
desirable, unfiltered data best unless you have >20" of aperture (in 
which case I recommend V).

Finally there's EX Hya.  Good for bright skies.  We're putting the 
finishing touches on a long-term ephemeris, and it's well-placed as an 
evening southern target.

Happy observing!  My life has gotten a little complicated lately, so I 
won't be seeing any of you in Big Bear.  We may very well organize 
something for 2008, quite possibly at the Hawaii meeting Russ Genet is 
organizing at the end of the year.  Or maybe earlier and cheaper - 
anyone want to make a proposal?

joe