(cba:news) humpers 'n pitchers

Joe Patterson jop at astro.columbia.edu
Sat Jan 17 19:11:23 EST 1998

Dear CBAers,                                        Jan. 17, 1998.

Back in town for good now.  Sorry for my lax correspondence, I'll be
rapidly catching up over the next week.  Been emailblind for 12 days.

Campaigns.  Southern first, for a change.  Marc Bos and Paul Warhurst
from Auckland have selected bright stars (AH Men = Men 1 = Tafelberg,
and RR Pic) for relentless coverage.  The data have been excellent,
and really underscore the advantages of piling up many long time
series, maximally dense (i.e. night after night on the same star).
There are basically three big advantages.

One, the random flickering in most CVs (which we don't understand and
therefore consider as "noise", although no doubt some clever and
courageous soul in the distant future will consider it "signal") is
usually bigger than the periodic signals we wish to measure, so we must
average over many cycles to beat down the noise.

Two, all long light curves are punctuated by inevitable gaps due to
daylight and bad weather, and these gaps create alias structures for
periodic signals.  With maximum density of coverage the aliases are
small and can be overcome.

Three, we have special problems calibrating our data because we have so
many telescopes, mostly without filters.  Each telescope has a slightly
different "zero-point", and ideally we use overlapped data to measure
these zero-points.  More commonly, we cannot measure them and must
settle for removal of the "DC" component of each nightly light curve.
Only *long* observations define the DC level with good precision.

So: observe 'em long, observe 'em dense, and never (or hardly ever) say
die.  This is surgery, not surveys.

Now the north or semi-north.  Two bright and friendly stars slinking
low in the west: V592 Cas and TT Ari.  For both, it's now time to
accumulate a couple weeks of coverage to define the "late-season" phase
with high accuracy.  We'll then do the same in June/July, and that will
enable us to count cycles across the yearly gap.  Go for it.

Taus 1 and 2 were not winners this year, so we'll roll them over
till next year and ponder them so more.  Cease fire.

The largest telescopes in our network (>20 inch) might consider CP Eri.
It's annoyingly faint and not really well-placed for anybody (16.5-19.5
and at 0310-10), but in early January we got a brief episode of good
coverage (Jonathan in Arizona, Brian Warner/Liza van Zyl in South
Africa, Alon Retter in Israel) and found beautiful 29-minute
superhumps.  This is a star that only Tim Abbott has ever known
anything about - so move over, Tim!  It's too late in the season to do
anything really thorough, but two more weeks of coverage would be nice.

     A perfectly timed target now is BG CMi (0729+10), which has
photometric periods at 15 minutes and 3.2 hours.  We'd like to organize
an intensive 7-day campaign on it (all longitudes and latitudes)
somewhere in the window January 27-February 20.  So get your chart
ready (at website).  Time series outside that window are plenty useful
too, by the way.

     There's a huge collection of northern stars around RA=9 or 10 hr
now coming into view.  DW UMa is basically the brightest of these.
Some of you with slightly bigger telescopes should do "UMa 6" (name in
original Downes & Shara).  And AM CVn is back in that ol' morning sky -
as usual we are richly desirous of coverage on that star.

     By the way our papers on V Sge/T Pyx and FO Aqr are scheduled for
the April PASP.  And the Harvey et al. paper on AM CVn will I think
appear in the Feb 1 ApJLetters.

     Oh, and we're preparing a feature article for Sky and Telescope,
and could use some *pictures* of the CBA gang.  You know, crude-looking
telescopes with happy observers.  Maybe with a dog and a swing set and 
a knocked-over tricycle?  Anything for that backyard feeling.  Where 
is Norman Rockwell now that we need him?


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