Evidence of a Mira-like tail and bow shock about the semi-regular variable V CVn from four decades of polarization measurements

¹ Department of Physics & AstronomyEast Tennessee State University, Box 70652, Johnson City TN 37614, USA
e-mail: neilsonh@etsu.edu
² Department of Physics, Arizona State University, Tempe AZ 85287, USA

Received: 21 April 2014
Accepted: 18 July 2014

Abstract

Polarization is a powerful tool for understanding stellar atmospheres and circumstellar environments. Mira and semi-regular variable stars have been observed for decades and some are known to be polarimetrically variable, however, the semi-regular variable V Canes Venatici displays an unusually large, unexplained amount of polarization. We present ten years of optical polarization observations obtained with the HPOL instrument, supplemented by published observations spanning a total interval of about forty years for V CVn. We find that V CVn shows large polarization variations ranging from 1–6%. We also find that for the past forty years the position angle measured for V CVn has been virtually constant suggesting a long-term, stable, asymmetric structure about the star. We suggest that this asymmetry is caused by the presence of a stellar wind bow shock and tail, consistent with the star’s large space velocity.