(cba:news) stars for june

Joe Patterson jop at astro.columbia.edu
Thu Jun 7 15:19:20 EDT 2001

Dear CBAers,                                             June 7, 2001.

Time for a report on those helium stars!

We've ended the V803 Cen campaign, as most of you know.  It was entirely
successful, yielding a definite orbital period and thus a precise value
for the fractional superhump period excess (0.0040, implying a
secondary-star mass of 0.013 Mo).  This was suggested by the 1999
campaign, and proved by this year's.

The HP Lib campaign has only been going 24 days, yet it too should be
declared about over.  I've been trying to measure HP Lib's Porb for years,
but always failing - the strong superhump really veils the weaker orbital
signal.  But this year the New Zealanders went hard after it (especially
Bob Rea, but also Fred Velthius, Jennie McCormick, Bill Allen), and the
regularity of the coverage brought out that little orbital signal at
1103.3 sec (compared with the superhump at 1119.2 s).  It's very small,
just 0.002 mag in amplitude, but quite established nevertheless.  I'm
really thrilled about that - the amateurs did what we couldn't do with
40-inch and 52-inch telescopes 2 years earlier!

We need to keep going on CR Boo.  We're getting some coverage from many
people, though no one has managed to string together a long series of long
nights.  There appear to be three characteristic periods in the star, at
~1491 s, 1487.3 s, and 1471.0 s.  This makes for quite complicated power
spectra, and because our sampling is complex too (many short observations
from different longitudes), it's quite hard to disentangle.  Let's try for
2 more weeks on CR Boo!

    That's the helium stars.  Now for other stuff.

    The best southern target right now is V551 Sgr, if indeed it is
staging a superoutburst - is it? look for the telltale superhumps!
2000 coords 18 00 56.2  -34 35 42  Obvious for NZ/AU.  But it would be
nice if others would try it, as that would break aliases and permit easy
period-finding.  Even if it doesn't immediately show superhumps, it still
probably will within a few days, assuming it stays bright.  Helluva field,
as usual in that unhappy constellation.

    The other southern is V2400 Oph = J1712-2414, which at 14.4 is a
bright and interesting - and little-studied DQ Her star.  Complex period
structure, which we want to master.

    And for the north, it's CR Boo and V795 Her.  Finally, it's time for a
long campaign on this bright northern CV - V795 Her - which we have not
managed to effectively study since we spread out in longitude.
17 12 56.09  +33 31 21.4

Plus some help for the wintry south on V2400 Oph.


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