Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity

TL;DR

This study monitors Achernar's polarization with high precision, revealing rapid variability linked to mass ejection events and disk formation, indicating active circumstellar dynamics.

Contribution

It provides detailed polarization observations of Achernar, demonstrating the connection between polarization variability and circumstellar activity, including disk formation and mass ejections.

Findings

Detected polarization variations on timescales from hours to weeks.

Identified short-term variations as due to mass ejection events.

Long-term variations linked to inner disk ring formation.

Abstract

We present the results of a high accuracy ($\sigma \approx 0.005%$) polarization monitoring of the Be Star Achernar that was carried out between July 7th and November 5th, 2006. Our results indicate that, after a near quiescent phase from 1998 to 2002, Achernar is presently in an active phase and has built a circumstellar disk. We detect variations both in the polarization level and position angle in timescales as short as one hour and as long as several weeks. Detailed modeling of the observed polarization strongly suggests that the short-term variations originate from discrete mass ejection events which produce transient inhomogeneities in the inner disk. Long-term variations, on the other hand, can be explained by the formation of an inner ring following one or several mass ejection events.