Evidence for localized onset of episodic mass loss in Mira

Abstract

We report Multi-telescope interferometric measurements taken with the Interferometric Optical Telescope Array (IOTA) to provide imagery of the LPV Mira in the H-band. This wavelength region is well suited to studying mass loss given the low continuum opacity, which allows for emission to be observed over a very long path in the stellar atmosphere and envelope. The observed visibilities are consistent with a simple core-halo model to represent the central object and the extended molecular layers but, in addition, they demonstrate a substantial asymmetry. An analysis with image reconstruction software shows that the asymmetry is consistent with a localized absorbing patch. The observed opacity is tentatively associated with small dust grains, which will grow substantially during a multi-year ejection process. Spatial information along with a deduced dust content of the cloud, known mass loss rates, and ejection velocities provide evidence for the pulsational pumping of the extended molecular layers. The cloud may be understood as a spatially local zone of enhanced dust formation, very near to the pulsating halo. The observed mass loss could be provided by several such active regions around the star. This result provides an additional clue for better understanding the clumpiness of dust production in the atmosphere of AGB stars. It is compatible with scenarios where the combination of pulsation and convection play a key role in the process of mass loss.

Accepted by A&A, 12 pages, 9 figures

References in corpus (16)

• A close halo of large transparent grains around extreme red giant stars
• Few Skewed Disks Found in First Closure-Phase Survey of Herbig Ae/Be stars
• The Mira variable S Ori: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs
• Exploring wind-driving dust species in cool luminous giants I. Basic criteria and dynamical models of M-type AGB stars
• Exploring wind-driving dust species in cool luminous giants III. Wind models for M-type AGB stars: dynamic and photometric properties
• Principles of image reconstruction in optical interferometry: tutorial
• Clumpy dust clouds and extended atmosphere of the AGB star W Hya revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER II. Time variations between pre-maximum and minimum light
• The limb-darkened Arcturus; Imaging with the IOTA/IONIC interferometer
• Pre-maximum spectro-imaging of the Mira star T Lep with AMBER/VLTI
• The Keck Aperture Masking Experiment: Multi-Wavelength Observations of 6 Mira Variables
• Inhomogeneities in molecular layers of Mira atmospheres
• Exploring the origin of clumpy dust clouds around cool giants. A global 3D RHD model of a dust-forming M-type AGB star
• An observational study of dust nucleation in Mira ($o$ Ceti): II. Titanium oxides are negligible for nucleation at high temperatures
• An original interferometric study of NGC 1068 with VISIR BURST mode images
• Pulsation-induced atmospheric dynamics in M-type AGB stars. Effects on wind properties, photometric variations and near-IR CO line profiles
• Modelling polarized light from dust shells surrounding asymptotic giant branch stars

Cited by in corpus (9)

• The OGLE Collection of Variable Stars. Nearly 66,000 Mira stars in the Milky Way
• Mid-Infrared Period$-$Luminosity Relations for Miras in the Large Magellanic Cloud
• Multiwavelength properties of Miras
• The Symbiotic X-ray binaries Sct X-1, 4U 1700+24 and IGR J17329-2731
• A new dimension in the variability of AGB stars: convection patterns size changes with pulsation
• Mira Ceti, atypical archetype
• The K-band highest-resolution images of the Mira star R Car with GRAVITY-VLTI
• A New Period Determination Method for Periodic Variable Stars
• Water vapour masers in long-period variable stars II. The semi-regular variables R Crt and RT Vir