(cba:news) shout-out to UX UMa

Joe Patterson jop at astro.columbia.edu
Sat Apr 4 21:40:45 EDT 2015

Hi CBAers,

Permit me a short exultation about UX UMa.  I dunno exactly why I put 
this guy on the program.  Bright star, well-formed eclipses, a vast 
previous literature on the star (so that whatever we find, it has extra 
potential for probative value by comparing with other results).  There 
were no grounds for suspecting superhumps: it was neither a dwarf nova 
nor a SW Sex star, the period was too long, and besides, how could the 
previous ~80 papers on UX UMa have missed them?

And yet UX UMa is showing up with *great* superhumps, plus the "nodal" 
signal at nu = 0.27 c/d that is often a concomitant of negative 
superhumps.  If our physical picture of these things is correct, then it 
means the accretion-disk wobbles retrograde with a period of 3.7 days. 
(Precisely why is unknown, for this and all the other ~30 
negative-superhumpers.)  But UX UMa, whose basic properties are pretty 
well known, flunks all the supposed rules for having superhumps.  If it 
superhumps, then maybe all the other rule-flunking stars also do, and 
have just concealed them because no one bothered to look with an 
appropriate research tool.  Could it be that disk wobble occurs in *all* 
CVs who linger in a high-accretion state for at least a few hundred orbits?

That appropriate tool is time-series photometry over a range of 
longitudes.  We'll try now to target other bright novalikes of even 
longer orbital period.  This will be trickier, because with our 
observing/analysis methods, we run some risk of seeing waves in the 
light curve arising purely from differential extinction.  A V filter may 
well be a superior choice for the brighter stars.  However, unfiltered 
has worked well for UX UMa; its far-northern declination enables 
observers to get long runs with no great change in airmass, and the 
increased signal-to-noise will help in the analysis of the eclipses.

Anyway, UX UMa will remain a great target for another 10 days at least.
Keep up the great work.  Every new UX UMa run popping up in my inbox 
quickens the pulse!

joe p
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