(cba:news) April's Battle Plan

Joe Patterson jop at astro.columbia.edu
Fri Apr 6 15:40:23 EDT 2001

Dear CBAers,                                            April 6, 2001.

     OK, the flowers are in bloom, the baseball season has started, so
has the Masters, and the first-round leader of the Masters is (sort of)
a baseball player!  How wonderfully fitting is that.  What could be

     The answer is, a very exciting photometry campaign on catclysmic
variables with the CBA.  So let's think on that subject...


     During April 9-24 Jonathan will be at SAAO, so we'll have much
improved coverage of the Earth's longitudes and latitudes.  (We still
have a terribly regrettable lack of representation in South America and
Asia, but we press on with what we have!)  This is therefore a very
timely moment to work hard on CV light curves.

     For reasons known to no human, practically all the known helium
CVs are clustered in a narrow RA range available during March-April-
May.  These are the binaries of shortest period, with Porb between 17
and 46 minutes, and with an impressive arsenal of machinery for
producing periods.  These are our prime targets, and April is the
"soft underbelly" of the stars for yielding those precious periods.
Here's the roster:

STAR            COORDINATES         V MAG    PERIODS

V803 Cen 13 23 44.51  -41 44 30.4   13-17    1610 s and 23 hrs
CR Boo   13 48 55.29  +07 57 34.8   13-17    1490 s and 20 hrs
CE-315   13 12 46.93  -23 21 31.3   17.5     ~4000 s
HP Lib   15 35 53.08  -14 13 12.3   13.6     1119 s
GP Com   13 05 42.85  +18 01 02.6   15.5-16  2800 s, but not known to
                                             be periodic in photometry

We do not plan a campaign on GP Com - last year's gave poor results -
but I include it as a target for a "fishing expedition", since the star
may one day awaken and flash some periodic signals at us.

We have ongoing campaigns for 3 other stars, which may possibly suit
your tastes in terms of sky position, magnitude, dislike for helium,

AH Men   06 11 44.07  -81 49 24.1   12.5-13    complex near 3.0 hrs
RZ LMi   09 51 49.02  +34 07 24.6   14.5-17.3  near 1.4 hrs
DW UMa   10 33 52.95  +58 46 54.9   14.5-18    3.3 hrs and 4 days

As usual, it's best to select one (or two) of these stars, and
concentrate on amassing many-hour light curves of that one star.
Charts and suggested comparison stars are at the CBA website.  As
usual, you may prefer a different comp, and that's OK as long as you
identify it.

     Barring surprises, the first three objects named are the prime
goals of the campaign.  I want to especially talk up CR Boo and HP Lib,
which in principle we can track around the Earth since they are
roughly equatorial and we do have good longitude distribution.
Whole-earth runs of very high quality are likely to reveal the
intricate period structure, and thus the underlying orbital and
precession periods.

     You should start observing as soon as possible, and note any
surprises in terms of brightness.  For example, V803 Cen or CR Boo
jumping to magnitude 13.0 would indicate a "superoutburst", which we
have never properly observed in any helium CV with time-series
photometry.  Yum, yum, that would be great.  And if HP Lib sank to
fainter than 14, that's never been observed either... so would merit
very high priority.  For the next 7-9 days, shade your choices on the
bright side, and watch out for that rampaging Moon, which we really 
need to respect in our biz.

     It would be helpful if you let me know what observations you
managed to get, even if the time-series is not yet analyzed. That would
allow me to see the overall picture, and also communicate more
precisely with the actual front-line troops... rather than send out a
lot of detailed emails to people who plan to do mostly heavy-duty
gardening during April.

     Good luck!


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