The Circumstellar Envelope of the Semiregular Variable Star V CVn

Abstract

V CVn is a red semiregular variable star with an amplitude of its V-band brightness variations of ≈2^m. An unusually high amplitude of its polarization variability, up to 6%, a noticeable inverse correlation between polarization and total flux, and relative constancy of the angle of polarization distinguish this star from other semiregular variables. To clarify the nature of these peculiarities, we have observed the object with the 2.5-m telescope at the Caucasian Observatory of the Sternberg Astronomical Institute of the Moscow State University using differential speckle polarimetry at wavelengths of 550, 625, and 880 nm. The observations were performed on 20 dates distributed over three pulsation periods. We have detected an asymmetric reflection nebula around the star at a distance of ≈35 mas. Three regions that change their brightness with the same characteristic time scale as the star, but with different phase shifts are identified in the nebula. We consider several hypotheses that could explain this behavior.