(cba:news) shout-out to UX UMa
jop at astro.columbia.edu
Sat Apr 4 21:40:45 EDT 2015
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!
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