(cba:news) dissing the serpent, praising the bear

Joe Patterson jop at astro.columbia.edu
Sat Apr 26 03:27:22 EDT 1997

Dear CBAers,                                          April 25, 1997

Back in Vermont now.  Quick update on present campaigns...

V803 Cen brightened to V<13 3 nights ago, and broke into a 26 minute
oscillation (ooo!).  But now Stan Walker tells me it's flopping down
faint again (15.5).  I dunno if this was its version of a supermax, but
it sure would be great if we could observe this sucker more!

The DV UMa campaign is going very well.  This star is flashing the most
complicated superhump spectrum yet observed in a dwarf nova.  In this
unusual case, praised be the complexities!  The reason is that we have
found many stars (perhaps BZ Cam most notably) with photometric waves
suggestive of superhumps, but we've not been able to clinch that
identification because they do not *closely* resemble the humps in SU
UMa stars (the common defining standard for "true" superhumps).  I've
always wanted an obvious SU UMa superhumper to show such effects, which
would make more palatable the leap to the rather unstable, non-SU UMas.
I think I got my wish.  The star is remaining around mag 15, by the

LX Ser is getting fair coverage now, but the light curves do not look
promising.  Good orbital waveforms, good upper limits to superhumps,
but not worth tracking further.  I think we should end this campaign

                   *          *          *          *

DV UMa remains the best object for northerners.  In a few days the
Moon will clear out and we should be able to manage good data for the
rest of the outburst.  We definitely want to follow it a long time (at
least till the next lunar white-out in ~3.5 weeks), watching for any

The other objects we're tracking steadily are AM CVn and EC1533.
Please don't forget them!  (The data flow has been kinda sparse
lately.)  They're damn interesting objects both astrophysically and
to test your system sensitivity, because they have known short periods
and amplitudes (the arrival time of the pulses is unknown, and is
what we're mainly studying).  I recommend taking one of these stars and
observing it repeatedly (few hour time series) for the rest of the
season.  We have a strong data base from previous seasons, so there
is no doubt your data will be highly reinforced.

Tonny and Dave Skillman and Stan Walker have suggested several times
that it would be good to have bright targets for people new to our
network (or new to small-scope CV photometry).  Well, the time has
come.  V795 Her (1711+34, mag 12.6) has rolled back into the morning
sky.  We wrote something on this star in a 1994 PASP paper, but with
better global coverage we can do much better now.  And it's a damn
good target for new observers, or all observers during bright-moon
episodes (including now).  Sergei Shugarov has joined our network
and has been observing the star over the past few years; so we'll
basically funnel the data to him for analysis.  I'm happy about
that, it should work out well.  I believe we don't yet have an official
CBA chart, but it's in Downes and Shara (and also the Palomar-Green
catalogue as PG1711+336).  The best comparison star is the one
labelled "V795 Her-02" in Henden & Honeycutt (Apr 1995 PASP);  this has
V=13.77, B-V=0.63, and is 2.6' NE of the variable.  Another possibility
is the V=14.56 star just 40" W of the variable.  When we prepare an
official CBA chart we'll scout for slightly brighter stars farther
away, but Mister V795 Her-02 looks like a pretty good comp star.

As many of you know, we're not very religious about choice of
comparison stars.  What's ideal for one observer is sometimes
impossible for another, because of details of chip size, saturation
levels, telescope tracking errors, etc.  We find that over the course
of a season's campaign there is almost always enough overlap in
observations to calibrate each observer's data to the others - within
the error of ~0.1 mag that is intrinsic to virtually any multi-
observatory campaign.  So fire away with the comp star of your choice
(but tell me which one you chose).

And for any southerners still reading, try, try hard for V803 Centauri,
which I think we are still just scratching the surface of!  Everything
welcome: time series, snapshots, wild speculations.  Comp star 2 arcmin

Vermont is nonstop cloudy as usual, but wow have the birds ever come


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