Multi-epoch spectropolarimetry of 6 symbiotic and 18 red giant stars shows frequent continuum polarization variability, with Hα line polarization detected in only one symbiotic star, UV Aur.
VLBI Astrometry of AGB Variables with VERA -- A Semiregular Variable S Crateris --
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abstract
We present a distance measurement for the semiregular variable S Crateris (S Crt) based on its annual parallax. With the unique dual beam system of the VLBI Exploration for Radio Astrometry (VERA) telescopes, we measured the absolute proper motion of a water maser spot associated with S Crt, referred to the quasar J1147-0724 located at an angular separation of 1.23$^{\circ}$. In observations spanning nearly two years, we have detected the maser spot at the LSR velocity of 34.7 km s$^{-1}$, for which we measured the annual parallax of 2.33$\pm$0.13 mas corresponding to a distance of 430$^{+25}_{-23}$ pc. This measurement has an accuracy one order of magnitude better than the parallax measurements of HIPPARCOS. The angular distribution and three-dimensional velocity field of maser spots indicate a bipolar outflow with the flow axis along northeast-southwest direction. Using the distance and photospheric temperature, we estimate the stellar radius of S Crt and compare it with those of Mira variables.
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Exploring the long-term temporal variability in polarization through multi-epoch optical spectro-polarimetry - Part II: A sample of symbiotic and red-giant stars
Multi-epoch spectropolarimetry of 6 symbiotic and 18 red giant stars shows frequent continuum polarization variability, with Hα line polarization detected in only one symbiotic star, UV Aur.