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(cba:news) shout-out to UX UMa (Joe Patterson) [2015-04-05T01:41:57Z]


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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