[vsnet-alert 12886] ER UMa : negative superhumps variation in the middle-term

[Ohshima]

ER UMa : negative superhumps variation in the middle-term

 We have received further observations from Akazawa-san, de Miguel, Krajci,
and Stein. These obsevrations shows clearly negative superhumps with ~ 
0.8mag at minimum during Feb 20-22.

 We also investigate the period variation from the superoutburst with
O-C curve. Interestingly,  there were 2 period changes at least. First
stage is until Jan. 28, which is the last stage of the superoutburst. 
Abrupt period change (suich as stage A-B or B-C transition) occurred.
Second stage is from the end of first stage until. Feb 15. In this stage,
negative Pdot seems to present (Pdot = -7.4(8)*10^(-7)). Third stage is
after that, it is uncertain whether the variation of negative superhump
period. With linear regression, negative superhump periods are calclated
as 0.062375(3) d (first stage) ,0.062398(4) d (second stage), 
0.062307(12) d (third stage). The period change of second stage might be 
a result of a combination of two stages and thus this stage might be 
devided two stages furthermore, however. 

 The timings of these period change are puzzling. The timing of the 
first period change is similar to the B-C transition in ordinary dwarf
novae. However, as to the second one, we have no idea.

 Further observations are strongly required!