The linear polarization of nearby bright stars measured at the parts per million level

TL;DR

This study measures the linear polarization of 49 nearby bright stars at very high sensitivity, revealing mostly small interstellar polarization and providing insights into local dust and stellar atmospheres.

Contribution

It provides the first high-precision polarization measurements of nearby stars, showing minimal interstellar polarization and exploring stellar and circumstellar polarization sources.

Findings

Most stars have polarization below 2 x 10^-5.

Interstellar polarization is less than expected for the local environment.

Stars like Regulus and Vega show polarization likely due to stellar atmospheres or disks.

Abstract

We report observations of the linear polarization of a sample of 49 nearby bright stars measured to sensitivities of between ~1 and 4 x 10^-6. The majority of stars in the sample show measurable polarization, but most polarizations are small with 75% of the stars having P < 2 x 10^-5. Correlations of the polarization with distance and position, indicate that most of the polarization is of interstellar origin. Polarizations are small near the galactic pole and larger at low galactic latitudes, and the polarization increases with distance. However, the interstellar polarization is very much less than would be expected based on polarization-distance relations for distant stars showing that the solar neighbourhood has little interstellar dust. BS 3982 (Regulus) has a polarization of ~ 37 x 10^-6, which is most likely due to electron scattering in its rotationally flattened atmosphere. BS 7001 (Vega) has polarization at a level of ~ 17 x 10^-6 which could be due to scattering in its dust disk, but is also consistent with interstellar polarization in this direction. The highest polarization observed is that of BS 7405 (alpha Vul) with a polarization of 0.13%