(cba:news) OV Boo and eclipsers

Joe Patterson jop at astro.columbia.edu
Sun Apr 30 05:18:00 EDT 2017

  Hi CBAers,

Due to the deadline for submitting papers for the SAS/AAVSO meeting 
(mid-June in Ontario, California), Enrique and I have had to rush 
something for publication re the still-ongoing outburst of OV Boo. I'm 
attaching the abstract and author list, and will send the paper within 3 
days (to be followed a few months later by a regular-journal submission. 
  If you're an author, send me, and also Enrique: your postal address, 
telescope aperture, and how many nights/hours you have observed this 
star.  These things are sometimes needed for the eventual paper in a 
regular journal.

But I wanted to mention now a discovery that really amazed me, in the 
course of analyzing the data so far.  And that is: how accurately we can 
measure the moments of mid-eclipse.  In superoutburst, there is a large 
elliptical accretion disk which precesses around and modulates the 
mid-eclipse timing with a 3.9 day period.  If it weren't for that, we 
could do even better. But from the several hundred timings obtained to 
date, that simple O-C curve, manifesting the 3.9 day period, shows an 
internal dispersion of just 3.1 seconds.  This despite some seemingly 
formidable problems:  integration times are in the range 40-60 
seconds... S/N ratio at mid-eclipse is around 5... the white-dwarf 
eclipse is convolved with the disk eclipse... I only calculate 
heliocentric corrections accurate to 1-1.5 s.  From this I learn:
* CBA observers are very diligent with their time reports
* the benefits of "crowd-sourced" data
* the benefits of sharp eclipses
* CBA observers are intrepid when it comes to faint stars
* I should be more careful about heliocentric corrections.

We should definitely pay more attention to eclipsers in general, and 
especially to sharp eclipsers.  Accuracy of a few seconds brings into 
range long-term evolution issues, for which actual observational 
constraints in CVs have been meager.  Gravitational radiation?  Magnetic 
braking (quantitatively)?  It requires a lot of persistence, which we 
definitely have... but not necessarily a lot of aperture, which we don't 

I'll soon send a list of seasonally-appropriate stars which could be 
quite good targets.  But here's a few which come to mind right away:
Z Cha, OY Car, DV UMa, IY UMa, V1432 Aql, DQ Her, LX Ser.

Some degree of fearlessness is an asset here.  Who woulda thunk that our 
little telescopes could get such good data on a mag 18.5 eclipse that 
lasts 2 minutes?  But they can.  Best strategy here is to adopt a star 
and pound it.  The dispersion in the timings, as well as the timings 
themselves, carries critical information.

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