VLBA SiO observations of bright O-rich AGB stars

William D. Cotton (1) , Guy Perrin (2, 3) , Bruno Lopez (4)

1 NRAO - National Radio Astronomy Observatory [Charlottesville]
2 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
3 Pôle Astronomie du LESIA
4 Observatoire de la Côte d'Azur

We present the results of observations of the SiO masers at 7 mm wavelength in several oxygen rich Asymptotic Giant Branch (AGB) stars. These observations were coordinated with observations using the ESO VLTI/MIDI interferometer at 10 mum wavelength. These stars are o Ceti (Mira), U Herculis (U Her), OH26.5+0.6, R Leonis (R Leo), and W Hydrae (W Hya). Both total intensity and linear polarizations are imaged. Linear radial features seen in o Ceti may be associated with an X-ray flare seen a year earlier by [CITE]. Similar linear features are also seen in R Leo, U Her and OH26.5+0.6. These features typically show systematic radial velocity variations and a tendency for the linear polarization to be perpendicular to the direction of elongation, suggesting that magnetic fields are dynamically important. A wide radial extent of the maser rings observed in U Herculis and OH26.5+0.6 is interpreted as meaning that the outer boundaries of the masing regions in these stars are not truncated by the condensation of SiO onto dust grains.

Domaines: Astrophysique [astro-ph]; Planète et Univers [physics]

William D. Cotton, Guy Perrin, Bruno Lopez. VLBA SiO observations of bright O-rich AGB stars. Astronomy and Astrophysics - A&A, 2008, 477, pp.853-863. ⟨10.1051/0004-6361:20077817⟩. ⟨hal-03785615⟩