Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 05/14/2015 - 13:03
For the first time in over 4 years this dwarf nova is finally experiencing an outburst! Last evening I recorded the star at 10.7 magnitude, likely near the peak of a normal maximum. The last definitely recorded outburst according to the AAVSO's database occurred in early 2011. Prior to that time outbursts had been recorded very regularly at about yearly intervals with only one or two missed since this star was added to the AAVSO's program many years ago. Being circumpolar from mid northern latitude it seems improbable that as many as 3 or 4 recent maxima might have been missed. I had previously called attention to this peculiar situation some time ago within these web pages.
J.Bortle (BRJ)
[quote=BRJ]
For the first time in over 4 years this dwarf nova is finally experiencing an outburst! ... The last definitely recorded outburst according to the AAVSO's database occurred in early 2011. Prior to that time outbursts had been recorded very regularly at about yearly intervals with only one or two missed since this star was added to the AAVSO's program many years ago.
[/quote]
Nice catch John! This long period of time in quiescence is indeed odd. It looks almost like a "reverse UGZ" where it stays near minimum for several cycles before resuming outbursts! However, a close look at the light curve:
http://www.aavso.org/lcg/plot?auid=000-BBR-176&starname=CH+UMA&lastdays…
Shows there may have been an outburst in early 2012 and several smaller brightenings in the more recent years. Coverage looks pretty thorough, but it might not be possible to absolutley rule out brief outbursts since 2012, may have been missed?
Mike
While I can not immediately discount the possibiliy of minor activity in CH UMA over the recent protracted interval of apparent total quiescence, I would like to more carefully check the source of the elevated datapoints to ascertain the individual observer's experience level and comp stars employed. Over my years of compiling the AAVSO Circular I saw more than a few mistaken positive observations of this star when it was simultaneous reported as at minimum by those more familiar with the field. Maybe I'll have the opportunity to look carefully into the old reported "active" datapoints tomorrow.
On a different front I can report that CH UMA would certainly not be the first well covered dwarf nova to totally cease outbursts for a number of cycles, only to return to the normal outburst pattern after a number of years. There aren't a great many such stars, at least as far as ones I've personally followed, but there certainly are at least a handful.
J.Bortle (BRJ)