Are dust shell models well-suited to explain interferometric data of late-type stars in the near-infrared?

Abstract

Recently available near-infrared interferometric data on late-type stars show a strong increase of diameter for asymptotic giant branch (AGB) stars between the K (2.0 - 2.4 μm) and L (3.4 - 4.1 μm) bands. Aiming at an explanation of these findings, we chose the objects αOrionis (Betelgeuse), SW Virginis, and R Leonis, which are of different spectral types and stages of evolution, and which are surrounded by circumstellar envelopes with different optical thicknesses. For these stars, we compared observations with spherically symmetric dust shell models. Photometric and 11 μm interferometric data were also taken into account to further constrain the models. -- [...] -- We conclude that AGB models comprising a photosphere and dust shell, although consistent with SED data and also interferometric data in K and at 11 μm, cannot explain the visibility data in L; an additional source of model opacity, possibly related to a gas component, is needed in L to be consistent with the visibility data.

12 pages, 4 figures, to be published in A&A; Latex aa class, uses packages graphicx, hyperref, natbib, and txfonts; keywords: Techniques: interferometric -- Radiative transfer -- Circumstellar matter -- Infrared: stars -- Stars: late-type -- Stars: individual: αOrionis, SW Virginis, R Leonis

References in corpus (3)

• Multiple Molecular Winds in Evolved Stars I. A Survey of CO(2-1) and CO(3-2) Emission from 45 Nearby AGB Stars
• Temporal Variations of Mid-IR Spectra in Late-Type Stars
• The calibration of interferometric visibilities obtained with single-mode optical interferometers. Computation of error bars and correlations

Cited by in corpus (9)

• Interferometric observations of the supergiant stars alpha Orionis and alpha Herculis with FLUOR at IOTA
• The close circumstellar environment of Betelgeuse - II. Diffraction-limited spectro-imaging from 7.76 to 19.50 microns with VLT/VISIR
• Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared
• Pulsation of M-type Mira variables with moderately different mass: search for observable mass effects
• The Mid-IR spatially resolved environment of OH26.5+0.6 at maximum luminosity
• Water Vapor on Betelgeuse as Revealed by TEXES High-Resolution 12 Micron Spectra
• The VLTI/MIDI view on the inner mass loss of evolved stars from the Herschel MESS sample
• Comparison of dynamical model atmospheres of Mira variables with mid-infrared interferometric and spectroscopic observations
• Angular diameter measurements of evolved variables by lunar occultations at 2.2 and 3.8 micron