ИСТИНА

It is an open question whether variability of high amplitude semiregular stars are induced by solar-like acoustic oscillations or by Mira mechanism. V CVn is a semiregular variable star with the period of 196 days and amplitude of 2 magnitudes in V band. We report the discovery of a circumstellar reflection nebula around V CVn with characteristic size of 0.1" using Differential Speckle Polarimetry. 42 observational epochs distributed over 6 pulsation cycles demonstrate that different parts of the nebula change their brightness with the same period as the star, but significant phase delays. Thus, a northern feature of the nebula reaches maximum brightness when the whole object is at minimum. The only hypothesis explaining such behaviour is significantly non-radial pulsation. Such mode of pulsation is typical for acoustic oscillations. However the V band amplitude of the star is very large and precludes the stability of star if pulsations are acoustic oscillations.