The circumstellar environments of EP Aqr and Y CVn probed by the HI emission at 21 cm

Abstract

The HI line at 21 cm has been detected in the circumstellar shells of the two semi-regular variables, EPAqr and YCVn, with the Nançay Radio-Telescope (NRT). In both cases the line shape is composite and the emission is spatially extended compared to the NRT beam size (4′). The total HI masses of the two envelopes are respectively ∼0.047 M ⊙ and 0.044 M⊙. For EPAqr, we find three components: a narrow one centered on the star and spatially unresolved, and two broad, Gaussian components, offset w.r.t. the star and spatially extended. The narrow component traces the present wind from EP Aqr whereas the two others seem to trace one or several mass-loss episodes of long duration. For Y CVn, we find two components: a narrow, spatially very extended, feature, and a broad one, less extended. We argue that the second component traces the outflow and the first one, its interaction with the ISM. These observations show that the HI emission can be used not only to probe the mass loss history of long-period variables, but also to investigate the interaction between stellar outflows and the surrounding ISM.