Mid-infrared interferometric observations of four oxygen-rich Mira variables

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁴ National Science Foundation, 4201 Wilson Boulevard, Arlington, VA, 22230, USA
⁵ Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d'Azur, 06300 Nice, France
⁶ Zentrum für Astronomie der Universität Heidelberg (ZAH), Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney NSW 2006, Australia

Abstract

We present an investigation of the dust formation process in the atmospheres of the oxygen-rich AGB stars RR Aql, S Ori, GX Mon and R Cnc using spatially and spectrally resolved mid-infrared interferometric observations. We successfully compared multi epoch observations to a radiative transfer model of the dust shells, where the central stellar intensity profile is described by a series of dust-free dynamic model atmospheres based on self-excited pulsation models. We show that the Al₂O₃ shells have inner radii between 1.9 and 2.2 stellar photospheric radii, and that the silicate shells have inner radii between 4.1 and 4.6 stellar photospheric radii. The best-fit photospheric angular diameters are consistent with independent estimates. The model dust temperatures at the inner radii of 1.9–2.2 stellar radii and 4.1–4.6 stellar radii are consistent with dust condensation temperatures of Al₂O₃ and silicates, respectively.