Tracing the phase transition of Al-bearing species from molecules to dust in AGB winds. Constraining the presence of gas-phase (Al2O3)n clusters

Abstract

(abbreviated) We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. We have obtained ALMA observations with a spatial resolution of 120x150 mas tracing the dust formation region of a low mass-loss rate and a high mass-loss rate AGB star, R Dor and IK Tau. Emission line profiles of AlO, AlOH and AlCl are detected and are used to derive a lower limit of atomic aluminium incorporated in molecules. We show that the gas-phase aluminium chemistry is completely different in both stars, with a remarkable difference in the AlO and AlOH abundance stratification. The amount of aluminium locked up in these 3 molecules is small, <=1.1e-7, for both stars, i.e. only <=2% of the total aluminium budget. This leaves ample of room for aluminium to be incorporated in grains. A fundamental result is that AlO and AlOH, being the direct precursors of alumina grains, are detected well beyond the onset of the dust condensation proving that the aluminium oxide condensation cycle is not fully efficient. The ALMA observations allow us to quantitatively assess the current generation of theoretical dynamical-chemical models for AGB winds. We discuss how the current proposed scenario of aluminium dust condensation for low mass-loss rate AGB stars at a distance of ~1.5 Rstar, in particular for the stars R Dor and W Hya, poses a challenge if one wishes to explain both the dust spectral features in the spectral energy distribution (SED), in interferometric data, and in polarized light signal. In particular, the estimated grain temperature of Al2O3 is too high for the grains to retain their amorphous structure. We propose that large gas-phase (Al2O3)n-clusters (n>34) can be the potential agents of the broad 11 micron feature in the SED and in the interferometric data and we explain how these large clusters can be formed.

21 pages, submitted to Astronomy & Astrophysics (A&A), figures at reduced resolution in arxiv paper; full resolution in Astronomy & Astrophysics paper

References in corpus (14)

• A close halo of large transparent grains around extreme red giant stars
• Aluminum-, Calcium- And Titanium-Rich Oxide Stardust In Ordinary Chondrite Meteorites
• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• Global 3D radiation-hydrodynamics models of AGB stars. Effects of convection and radial pulsations on atmospheric structures
• Dynamic atmospheres and winds of cool luminous giants, I. Al${}_2$O${}_3$ and silicate dust in the close vicinity of M-type AGB stars
• Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL
• The Mira variable S Ori: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs
• The millimeter IRAM-30m line survey toward IK Tau
• Winds of M- and S-type AGB stars: an unorthodox suggestion for the driving mechanism
• The wind of W Hya as seen by Herschel - I. The CO envelope
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• An observational study of dust nucleation in Mira ($o$ Ceti): II. Titanium oxides are negligible for nucleation at high temperatures
• Search for aluminium monoxide in the winds of oxygen-rich AGB stars
• The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI

Cited by in corpus (38)

• Equilibrium chemistry down to 100 K - Impact of silicates and phyllosilicates on carbon/oxygen ratio
• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
• Exoplanet Clouds
• Evolution and Mass Loss of Cool Ageing Stars: a Daedalean Story
• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• The ASAS-SN Catalog of Variable Stars IX: The Spectroscopic Properties of Galactic Variable Stars
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• Bottom-up dust nucleation theory in oxygen-rich evolved stars I. Aluminium oxide clusters
• Mineral cloud and hydrocarbon haze particles in the atmosphere of the hot Jupiter JWST target WASP-43b
• High-resolution observations of gas and dust around Mira using ALMA and SPHERE/ZIMPOL
• Developing a self-consistent AGB wind model: II. Non-classical, non-equilibrium polymer nucleation in a chemical mixture
• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
• Aluminium oxide in the atmosphere of hot Jupiter WASP-43b
• Dust Formation in Astrophysical Environments: The Importance of Kinetics
• Circumstellar environment of the M-type AGB star R Dor. APEX spectral scan at $159.0-368.5$ GHz
• The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars
• Inner dusty envelope of the AGB stars W~Hydrae, SW\,Virginis, and R~Crateris using SPHERE/ZIMPOL
• An ALMA view of CS and SiS around oxygen-rich AGB stars
• Spectroscopy on the $A^1\Pi \leftarrow X^1{\Sigma }^{+}$ Transition of Buffer-Gas Cooled AlCl
• Constraints on metal oxide and metal hydroxide abundances in the winds of AGB stars - Potential detection of FeO in R Dor
• Dust-gas chemistry in AGB outflows: Chemical modelling of dust-gas chemistry within AGB outflows I. Effect on the gas-phase chemistry
• The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars
• Interplay between pulsation, mass loss, and third dredge-up: More about Miras with and without technetium
• ATOMIUM: Molecular inventory of 17 oxygen-rich evolved stars observed with ALMA
• Rotational spectra of vibrationally excited AlO and TiO in oxygen rich stars
• ATOMIUM: Halide molecules around the S-type AGB star W Aquilae
• A global optimisation study of the low-lying isomers of the alumina octomer (Al${}_2$O${}_3$)${}_8$
• Chemical modelling of dust-gas chemistry within AGB outflows -- II. Effect of the dust-grain size distribution
• Morpho-kinematics of the circumstellar envelope of the AGB star R Dor: a global view
• Bottom-up dust nucleation theory in oxygen-rich evolved stars II. Magnesium and calcium aluminate clusters
• The unusual 3D distribution of NaCl around the AGB star IK Tau
• Dust in brown dwarfs and extra-solar planets. VIII. TiO${}_2$ seed formation: 3D Monte Carlo versus kinetic approach
• Vanadium oxide clusters in substellar atmospheres: A quantum chemical study
• Hyperfine structure of the ${\mathbf{A}}^1\mathbf{\Pi }$ state of AlCl and its relevance to laser cooling and trapping
• The Ionization Energies of Dust-Forming Metal Oxide Clusters
• High-angular-resolution ALMA imaging of the inhomogeneous dynamical atmosphere of the asymptotic giant branch star W Hya
• Measurement of the Electric Dipole Moment of AlCl by Stark Level Spectroscopy
• Condensation sequence of circumstellar cluster seeds (CSCCS)