Data Files of "A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources"

The semi-regular variable star V Canum Venaticorum (V CVn) is well-known for its unusual linear polarization position angle (PA).<br> Decades of observing V CVn reveal a nearly constant PA spanning hundreds of pulsation cycles. This phenomenon has persisted<br> through variability that has ranged by 2 magnitudes in optical brightness and through variability in the polarization amplitude over<br> 0.3% and 6.9%. Additionally, the polarization fraction of V CVn varies inversely with brightness.<br> This paper presents polarization measurements obtained over three pulsation cycles. We find that the polarization maximum does<br> not always occur precisely at the same time as the brightness minimum. Instead, we observe a small lead or lag in relation to the<br> brightness minimum, spanning a period of a few days up to three weeks. Furthermore, the PA sometimes exhibits a non-negligible<br> rotation, especially at lower polarization levels.<br> To elucidate the unusual optical behavior of V CVn, we present a list of literature sources that also exhibit polarization variability<br> with a roughly fixed PA.We find this correlation occurs in stars with high tangential space velocities, i.e., “runaway” stars, suggesting<br> that the long-term constant PA is related to how the circumstellar gas is shaped by the star’s high-speed motion through the interstellar<br> medium.