(cba:news) jan-feb stars

[Joe Patterson]

Dear CBAers,                                                 1/27/97

Well, the declared "campaign" on BH Lyn and EG Cnc largely fizzled.
Bad weather and instrument down time struck many nodes of the CBA at
once, and this particular interval (Jan 19-26) actually was a time of
sparse observation.  Sometimes you get the bear...

But actually as data dribbled in from the preceding 10 days, I see that
we did quite well on both stars during this earlier interval.  Here's a
summary of what we learned.

BH Lyn.  As with PX And (and about 10 other stars in the sky), this
star too has simultaneous positive and negative superhumps.  The
positive guys are slightly stronger (0.12 versus 0.08 mag full
amplitude), reversed from PX And.  The eclipses are much deeper, giving
a better opportunity for using the changing eclipse shape to diagnose
the changing shape of the disk -- if our data are of sufficient
quality.

EG Cnc has continued to do its rather amazing thing.  It is certainly
the king of echo outbursts, whatever they are.  It also flashes the
most confusing superhumps I've seen.  On two occasions it seemed to
break off and start waving at a much different period, then return to
its familiar 0.0604 d period.  Will we understand this behavior?  I
dunno.  Certainly we'll have a better chance if we can increase our
vigilance.  So keep after this star with relentless time series, the
longer the better.  It's now spending most of its time around magnitude
16-16.5; most of you will find this tough, but the wave does have a 0.2
mag amplitude at this brightness level, so it may well be feasible.
Bob Fried has gotten excellent light curves at this magnitude with his
16-inch.

What of the future on these guys?  Well, I'd rate EG Cnc the highest
priority target.  I'm not sure we'll be able to decipher those strange
waves, but we might, if you can mount a big effort now.  The star is
just as attractive (if not more so) at 16th mag as at 13th!  BH Lyn is
also a good target, we should keep after it through Feb 22, when a
second Wise Observatory run ends.

But it's time to make friends with new stars also.  The other SW Sex
stars available now are DW UMa (1030+59) and SW Sex (1012-03).  Dave
Skillman saw very strong negative superhumps in the former last spring,
and Lasse Jensen has started the 1997 coverage which shows them still
present.  (With a 10-inch, by the way.)  A very good time to start your
coverage of DW UMa, really a pretty easy star to do because of the sky
position, large-amplitude wave, eclipses, and lack of flickering.
We'll concentrate on SW Sex in March when we have scheduled time in
South Africa (also, I think southerners might start the coverage
earlier).

Now let's talk about...  SNAPSHOTS.

We don't usually mess with these much, but they prove awfully useful
for stars where we really don't know the basic eruption timescales yet.
Here are the stars where we want an ongoing program of snapshot
magnitudes: CR Boo, HS Vir, PG1510+234 = Ser 1, V803 Cen, and EG Cnc.
Each of these stars shows very rapid photometric activity, so a high
density of observation (e.g. more than one/night) is highly warranted.

Good luck, and keep me informed as to what coverage you manage to get.
Lemme know if you'd like light curves of any of these stars.


                            joe


P.S.  By the way, despite Brian Skiff's recent fire-and-brimstone
denunciation in the VS-NET of unfiltered photometry, unfiltered is
definitely the best way to go for studies of periodic effects in stars
of this magnitude (13-16).  Even the Johnson and Cousins VRI filters,
usually called "broadband", transmit only ~10% of the total unfiltered
light available to the CCD.  That's not good enough.  Most of us have
small telescopes and cannot afford such a severe loss of light.  Longer
exposures can partially compensate, but are limited by the quality of
the telescope drive and by the (frequent) desire to maintain good time
resolution.  I'll write more completely on this subject later; but for
the present I just wanted to chip in with this *emphatic* endorsement
of unfiltered light for our programs.