That Ol' Hemispheric Spirit

From: Joe Patterson <*jop_at_astro.columbia.edu*> Date: Thu, 17 Dec 1998 10:26:52 -0500 (EST) · jop_at_astro.columbia.edu

Dear CBAers (especially australites),                        12/17/98

     Time for the world to know about....... CP ERIDANI!

     Tim Abbott wrote a very nice and provocative paper about this faint
helium binary in 1992 (ApJ).  Finally we've gotten in some intensive 
observations, from Arizona.  Last year it superoutbursted for us, then
in September it stayed at magnitude 20 for about a week, giving a
nice baseline for period determination.  It seems that the orbital
period is 1701 s, and the superhump period is 1716 s (this star
superhumps at quiescence, like several other CVs, despite the well-
known legislation forbidding it).  Now the star is in its "cycling"
state, with little eruptions (rising to 17 from a lower level of 18)
once a day or thereabouts.  We've been following it, fascinated, every
night for 8 nights.

     But the 24 hr aliasing is severe!  The star's too faint for most
CBAers, so we have *never* tracked the star over multiple longitudes.
That's what it needs now, in order to ascertain what the cycling period
is.  Seems to be 2.2 d/N, where N=1,2,3, or 4 (my guess is 3, which
would break the record; but until we get another longitude humming,
quien sabe?).

     Who can help this dim and tantalizing little star?  Brian and Dave
B, spies tell me you may have some large-telescope time in the near
future.  But even the humbler scopes can probably snapshot the star and
get rough magnitudes.  It ramps up and down at 0.15 mag/hr, so puts
on a sparkling show!

             *          *          *          *

     Then there's... TV COLUMBAE (0526-33).

     This star is the world's first negative superhumper, with a period 
of 5.2 hr.  It also shows the "precession" period itself of 4.0 hr.  At
13.5 it's a tempting target, but a very close companion makes for some
difficulty in measurement.  It's somewhat ideal for us because it's
bright, multiperiodic, and probably has slightly unstable signals which
we can actually track as they wander.  I was hoping we could get round-
the-world coverage (AU/NZ, South Africa, Chile/Arizona) during December.
Let me know how yer doin' out there in CBAland!

     And rounding out the list is AH MENSAE or Men 1 (0616-82).  Strangely
enough, everything I just said goes for this far-southern superhumper
also! - where the periods are 3.0 hr and 3.6 d, the star is also 13.5,
and also has a close contaminant 4 arcsec away.  Spooky.  I'm quite on
the fence about whether to go primarily for TV Col or AH Men.  Both are 
very suitable as campaign targets in December.

     Some of you, for reasons of sky position, type of mounting, etc., can
just do one of these.  Great; go for whichever one.  But I vote for     
AH Men as the target for the bigger telescopes (30" SAAO, 36" CTIO, 
Meintjes and Kemp).  We'll observe in U light and try to see the (putative)
white dwarf rotation.  We'll also study how to transform to V and 
unfiltered ("pink") magnitudes, so we can use other data and especially
CCD data from small scopes.  Let's show those borealites how to conduct
a real round-the-world campaign!

     Nota bene, aussies and kiwis! 
     
     
                joe