2021ApJ...906....1S

I propose a scenario according to which the dense compact circumstellar matter (CSM) that the ejecta of many core-collapse supernovae (CCSNe) collide with within several days after explosion results from a dense zone where in addition to the stellar wind there is gas that does not reach the escape velocity. In this effervescent zone around red supergiant (RSG) stars, there are dense clumps that are ejected from the vicinity of the RSG surface, rise to radii of tens of astronomical units, and then fall back. I consider two simple velocity distributions of the ejected clumps. I find that the density of the bound mass can be tens of times that of the escaping wind, and therefore can mimic a very high mass-loss rate. The dense effervescent compact CSM zone can (1) explain the collision of the ejecta of many CCSNe with a dense compact CSM days after explosion, (2) facilitate very high mass-loss rate if the star experiences powerful pre-explosion activity, (3) form dust that obscures the progenitor in the visible band, and (4) lead to an efficient mass transfer to a stellar companion at separations of tens of astronomical units, if it exists. The effervescent zone might exist for thousands of years and more, and therefore the effervescent CSM model removes the requirement from many type II CCSN progenitors to experience a very strong outburst just years to months before explosion.