Optical flickering from the symbiotic star CH Cygni is still missing

ATel #4316; K. Stoyanov, R. Zamanov (Bulgaria), J. L. Sokoloski (Columbia, USA)
on 20 Aug 2012; 05:38 UT
Credential Certification: R. K. Zamanov (rkz@astro.bas.bg)

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CCD observations of the symbiotic star CH Cyg with the 60cm telescope of the Rozhen National Astronomical Observatory (Bulgaria) from 17 August 2010, 7 September 2010, 30 October 2010, 18 September 2011 and 18 June 2012 show an absence of flickering with amplitude greater than 0.1 mag.

On the night of 30 October 2010, however, we detected smooth variability resembling that of RS Oph after the 2006 outburst (see IBVS 5733) in both V and B bands.

The Table below lists the date of each observation, the band, the UT-start and UT-end of each run, the number of data points, the exposure time in seconds, the minimum and maximum brightness during the run (in magnitudes), the standard deviation of the brightness during the run, and the typical observational error.

DATE - BAND	UTstart - UTend	Npts / exp-time	MIN - MAX	Sigma / merr
	hh:mm hh:mm	/ [s]	[mag] - [mag]	[mag] / [mag]
17.08.2010 B	19:16 - 20:53	139 / 20	10.744 - 10.793	0.009 / 0.007
17.08.2010 V	19:16 - 20:53	139 / 10	9.179 - 9.234	0.009 / 0.005
07.09.2010 B	21:25 - 22:40	107 / 20	10.937 - 10.989	0.010 / 0.008
30.10.2010 B	18:07 - 19:59	250 / 10	11.102 - 11.203	0.020 / 0.012
30.10.2010 V	18:07 - 19:59	250 / 5	9.753 - 9.822	0.013 / 0.008
18.09.2011 B	21:31 - 22:58	450 / 10	9.652 - 9.703	0.010 / 0.010
18.06.2012 B	21:58 - 23:59	1100 / 5	8.531 - 8.585	0.008 / 0.008

It appears that the usual large-amplitude flickering has been missing since January 2010 (see also ATel #2707 and Shugarov et al. 2012, BaltA 21, 184). Most probably, the accretion disk is in an unusual state -- exhausted or destroyed by the 2009 outburst and/or accumulating matter.