Resolving asymmetries along the pulsation cycle of the Mira star X Hydrae^⋆,⋆⋆

¹ European Southern Observatory (ESO), Alonso de Cordova 3107, Vitacura, Casilla 19001, 19 Santiago Chile
e-mail: xhaubois@eso.org
² LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, PSL Research University, 5 place Jules Janssen, 92195 Meudon, France
³ Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia
⁴ European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁵ Unidad Mixta Internacional Franco-Chilena de Astronomía (UMI 3386), CNRS/INSU, France & Departamento de Astronomía, Universidad de Chile, 1515 Camino El Observatorio, Las Condes, Santiago, Chile
⁶ Centre de Recherche Astrophysique de Lyon, CNRS/UMR 5574, 69561 Saint Genis Laval, France
⁷ Kitt Peak National Observatory, National Optical Astronomy Observatories, PO Box 26732, Tucson, AZ 85726-6732, USA
⁸ Research School of Astronomy & Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁹ Zentrum für Astronomie der Universität Heidelberg (ZAH), Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany

Received: 7 May 2015
Accepted: 3 August 2015

Abstract

Context. The mass-loss process in Mira stars probably occurs in an asymmetric way where dust can form in inhomogeneous circumstellar molecular clumps. Following asymmetries along the pulsation cycle can give us clues about these mass-loss processes.

Aims. We imaged the Mira star X Hya and its environnement at different epochs to follow the evolution of the morphology in the continuum and in the molecular bands.

Methods. We observed X Hya with AMBER in J-H-K at low resolution at two epochs. We modelled squared visibilities with geometrical and physical models. We also present imaging reconstruction results obtained with MiRA and based on the physical a priori images.

Results. We report on the angular scale change of X Hya between the two epochs. 1D CODEX profiles allowed us to understand and model the spectral variation of squared visibilities and constrain the stellar parameters. Reconstructed model-dependent images enabled us to reproduce closure phase signals and the azimuthal dependence of squared visibilities. They show evidence for material inhomogeneities located in the immediate environment of the star.