HST Observations of Heliospheric and Astrospheric Lyα Absorption Toward the α Cen System

Abstract

We use HST observations of the nearest star system (the α Cen system) to search for Lyα absorption from both heliospheric material around the Sun and analogous astrospheric material around the stars which has been heated by the collision between the solar/stellar winds and the interstellar medium. For α Cen A and B, both heliospheric and astrospheric absorption are detected, whereas for α Cen's distant companion star Proxima Cen only heliospheric absorption is detected, suggesting that Proxima Cen's astrosphere must be smaller and its wind therefore weaker than that of α Cen. Based on observations of these stars taken many years apart, we find that neither the heliospheric absorption nor the astrospheric absorption detected toward α Cen AB varies significantly.