Modelling the atmosphere of the carbon-rich Mira RU Virginis^⋆,⋆⋆

¹ University of ViennaDepartment of Astrophysics, Türkenschanzstrasse 17, 180 Vienna, Austria
e-mail: gioia.rau@univie.ac.at
² Institut d’Astronomie et d’Astrophysique, Université libre de Bruxelles, Boulevard du Triomphe CP 226, , 1050 Bruxelles, Belgium
³ Department of Physics and Astronomy G. Galilei, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁴ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium

Received: 27 April 2015
Accepted: 29 August 2015

Abstract

Context. We study the atmosphere of the carbon-rich Mira RU Vir using the mid-infrared high spatial resolution interferometric observations from VLTI/MIDI.

Aims. The aim of this work is to analyse the atmosphere of the carbon-rich Mira RU Vir with hydrostatic and dynamic models, in this way deepening the knowledge of the dynamic processes at work in carbon-rich Miras.

Methods. We compare spectro-photometric and interferometric measurements of this carbon-rich Mira AGB star with the predictions of different kinds of modelling approaches (hydrostatic model atmospheres plus MOD-More Of Dusty, self-consistent dynamic model atmospheres). A geometric model fitting tool is used for a first interpretation of the interferometric data.

Results. The results show that a joint use of different kinds of observations (photometry, spectroscopy, interferometry) is essential for shedding light on the structure of the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit the ISO spectrum well in the wavelength range λ = [2.9,25.0] μm. Nevertheless, a discrepancy is noticeable both in the SED (visible) and in the interferometric visibilities (shape and level), which is a possible explanation are intra-/inter-cycle variations in the dynamic model atmospheres, as well as in the observations. The presence of a companion star and/or a disk or a decrease in mass loss within the past few hundred years cannot be excluded, but these explanations are considered unlikely.