[vsnet-alert 10142] Re: CH UMa in outburst again?

Taichi Kato tkato at kusastro.kyoto-u.ac.jp
Thu May 1 10:13:17 JST 2008

> AAVSO observers report the brightening of CH UMa:

> If the outburst is confirmed, this is only 116 days since the previous 
> one - exceptionally short interval compared to the average cycle of 370 
> days for this star.  But CH UMa has been "misbehaving" during last two 
> years: there were 543 days between Nov. 2005 and May 2007 outbursts 
> followed by the unusual slow outburst in Jan. 2008.  Looks like 
> something strange is going on with the accretion rate in this 
> (previously quite regular) system.  Definitely worth monitoring!

   Although long outbursts have been relatively frequent in recent
years, there were epochs with frequent similar smaller outbursts.

1990 Jan.-Feb. short outburst max at 13.0
     Mar. 26  13.7
     Apr. 23-24  13.2

   Obviously such behavior is very atypical for this object.
During this period of activity in 1990, the intervals of long
outbursts didn't vary very much, suggesting that short outbursts
are somehow suppressed most of the time rather than true mass-transfer

A similar phenomenon, but in an SU UMa-type dwarf nova:

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