The molecular and dusty composition of Betelgeuse's inner circumstellar environment

Abstract

The study of the atmosphere of red supergiant stars in general and of Betelgeuse (alpha Orionis) in particular is of prime importance to understand dust formation and how mass is lost to the interstellar medium in evolved massive stars. A molecular shell, the MOLsphere (Tsuji, 2000a), in the atmosphere of Betelgeuse has been proposed to account for the near- and mid-infrared spectroscopic observations of Betelgeuse. The goal is to further test this hypothesis and to identify some of the molecules in this MOLsphere. We report on measurements taken with the mid-infrared two-telescope beam combiner of the VLTI, MIDI, operated between 7.5 and 13.5 $\mu$m. The data are compared to a simple geometric model of a photosphere surrounded by a warm absorbing and emitting shell. Physical characteristics of the shell are derived: size, temperature and optical depth. The chemical constituents are determined with an analysis consistent with available infrared spectra and interferometric data. We are able to account for the measured optical depth of the shell in the N band, the ISO-SWS spectrum and K and L band interferometric data with a shell whose inner and outer radii are given by the above range and with the following species: H2O, SiO and Al2O3. These results confirm the MOLsphere model. We bring evidence for more constituents and for the presence of species participating in the formation of dust grains in the atmosphere of the star, i.e. well below the distance at which the dust shell is detected. We believe these results bring key elements to the understanding of mass loss in Betelgeuse and red supergiants in general and bring support to the dust-driven scenario.

arXiv comment11 pages, 10 figures, accepted for publication in A&A

References in corpus (13)

• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• Interferometric observations of the supergiant stars alpha Orionis and alpha Herculis with FLUOR at IOTA
• Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei
• Mid-infrared interferometry on spectral lines: III. Ammonia and Silane around IRC+10216 and VY CMa
• Amorphous alumina in the extended atmosphere of Alpha Orionis
• ISO-SWS calibration and the accurate modelling of cool-star atmospheres - IV. G9 to M2 stars
• Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared
• Warm water vapor envelope in the supergiants alf Ori and alf Her and its effects on the apparent size from the near-infrared to the mid-infrared
• Study of molecular layers in the atmosphere of the supergiant star mu Cep by interferometry in the K band
• Water Vapor on Betelgeuse as Revealed by TEXES High-Resolution 12 Micron Spectra
• Infrared Spectra and Visibilities as Probes of the Outer Atmospheres of Red Supergiant Stars
• The structure of H2O shells in Mira atmospheres: Correlation with disk brightness distributions and a spectrophotometric signature
• Subtracting the photon noise bias from single-mode optical interferometer visibilities

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