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What's Happened to....

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BRJ's picture
What's Happened to....

With the matter of 1848-19 FN SGR now put to rest I'd like to point out another favorite object of mine whose recent behavior is most puzzling. This would be the bright dwarf nova 0959+68 CH UMA.

For a couple of decades this star, one of the brightest dwarf novae in the sky, exhibited textbook-like cyclic behavior with perhaps a couple of dozen 10th magnitude outbursts being recorded in the AAVSO's records. I don't believe that more than one, or two, of its roughly annual maxima was ever missed from the time the star was added to the AAVSO's program...that is up until 2011. Since February of 2011 not a single outburst (or even the suggestion of one occurring) appears in the database.

Now CH UMA is circumpolar from just about anywhere in North America and Europe, so coverage of the star's behavior doesn't really suffer much from any seasonal gaps. Nevertheless, no one has reported seeing this star much above minimum light (~14.5) in nearly three and one-half years! I would also point out that the duration CH UMA's usual outbursts would tend to preclude consecutive outburst events from being totally missed repeatedly. So what is happening here? 

I've witnessed this odd sort of behavior is several other dwarf novae down through the years. Taking the available data at face value has long suggested to me that some of these stars may essentially "turn off" for a time, often resuming their activity at a significantly later date. Such spells of seeming inactivity often appear to be preceded by some odd event, like a double or closely spaced, maxima abnormal to the star, soon after which the variable becomes silent. I note that CH UMA experienced two closely spaced and weaker than usual outbursts just one cycle before its current lull.   

Now I appreciate that none of these stars follows any sort of tight schedule with their outbursts, but when quiescence seems to last 3-4 complete cycles, that signals to me that something unique may be going on with the star.

J.Bortle   (BRJ)





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