Dusty wind of W Hya. Multi-wavelength modelling of the present-day and recent mass-loss

Abstract

Low- and intermediate-mass stars go through a period of intense mass-loss at the end of their lives in a phase known as the asymptotic giant branch (AGB). During the AGB a significant fraction of their initial mass is expelled in a stellar wind. This process controls the final stages of their evolution and contributes to the chemical evolution of galaxies. However, the wind-driving mechanism of AGB stars is not yet well understood, especially so for oxygen-rich sources. Characterizing both the present-day mass-loss and wind structure and the evolution of the mass-loss rate of such stars is paramount to advancing our understanding of this processes. We modelled the dust envelope of W Hya using an advanced radiative transfer code. The dust model was analysed in the light of a previously calculated gas-phase wind model and compared to measurements available in the literature, such as infrared spectra, infrared images, and optical scattered light fractions. We find that the dust spectrum of W Hya can partly be explained by a gravitationally bound dust shell that probably is responsible for most of the amorphous Al${}_2$O${}_3$ emission. The composition of the large ($\sim$\,0.3\,$\mu$m) grains needed to explain the scattered light cannot be constrained, but probably is dominated by silicates. Silicate emission in the thermal infrared was found to originate from beyond 40 AU from the star and we find that they need to have substantial near-infrared opacities to be visible at such large distances. The increase in near-infrared opacity of the dust at these distances roughly coincides with a sudden increase in expansion velocity as deduced from the gas-phase CO lines. Finally, the recent mass loss of W Hya is confirmed to be highly variable and we identify a strong peak in the mass-loss rate that occurred about 3500 years ago and lasted for a few hundred years.

arXiv comment15 pages, 13 figures

References in corpus (16)

• The chemical composition of the Sun
• The Herschel-SPIRE instrument and its in-flight performance
• Radiative transfer in very optically thick circumstellar disks
• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• A close halo of large transparent grains around extreme red giant stars
• Mass loss rates of a sample of irregular and semiregular M-type AGB-variables
• Dust and the spectral energy distribution of the OH/IR star OH 127.8+0.0: Evidence for circumstellar metallic iron
• Optical constants of refractory oxides at high temperatures
• The wind of W Hya as seen by Herschel - I. The CO envelope
• Amorphous alumina in the extended atmosphere of Alpha Orionis
• Multi-wavelength Diameters of Nearby Miras and Semiregulars
• Disordered Silicates in Space: a Study of Laboratory Spectra of "Amorphous" Silicates
• Mass Loss Evolution and the Formation of Detached Shells around TP-AGB Stars
• On the alumina dust production in the winds of O-rich Asymptotic Giant Branch stars
• The wind of W Hya as seen by Herschel. II. The molecular envelope of W Hya
• Distribution and kinematics of the HCN(3-2) emission down to the innermost region in the envelope of the O-rich star W Hya

Cited by in corpus (10)

• 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
• High-resolution observations of gas and dust around Mira using ALMA and SPHERE/ZIMPOL
• Search for aluminium monoxide in the winds of oxygen-rich AGB stars
• Inner dusty envelope of the AGB stars W~Hydrae, SW\,Virginis, and R~Crateris using SPHERE/ZIMPOL
• Rotational spectra of vibrationally excited AlO and TiO in oxygen rich stars
• Modelling polarized light from dust shells surrounding asymptotic giant branch stars
• Circumstellar CO J = 3-2 detected around the evolving metal-poor ([Fe/H] ~ -1.15 dex) AGB star RU Vulpeculae
• ALMA Observations of W Hya: Impact of missing baselines