Speaker: Boris Safonov (Sternberg Astronomical Institute, MSU, Moscow)
Title: Differential speckle polarimetry of evolved stars including Betelgeuse
Differential speckle polarimetry (DSP) is a method aimed at study of distribution of polarized flux in astrophysical objects at diffraction limited resolution. Using DSP at SAI 2.5 m, telescope we detected in visual wavelength range dusty envelopes with an angular size of 0.05-0.15 arcsec around a number of evolved stars, e.g. mu Cep (Safonov et al, MNRAS, 484, 5129). Quite frequently these envelopes exhibit variability of morphology associated with the photometric variability. For example, in the circumstellar envelope of semiregular variable star V CVn we detected two regions changing their brightness with the same period as the star, but with significant phase delays, up to a half of the period. On the basis of these data we suggest that the pulsations of V CVn are non-radial (Safonov et al, AstL, 45, 453). In case of Betelgeuse we confirm that the brightness minimum of 2019-2020 is due to the formation of a dust cloud at the line of sight. Apart from this, during recovery from minimum the amount of scattering dust in the envelope increased (arXiv:2005.05215). DSP provides new interesting opportunities to study the mass loss of evolved stars.
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