The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA

Abstract

Our current understanding of the chemistry and mass-loss processes in solar-like stars at the end of their evolution depends critically on the description of convection, pulsations and shocks in the extended stellar atmosphere. Three-dimensional hydrodynamical stellar atmosphere models provide observational predictions, but so far the resolution to constrain the complex temperature and velocity structures seen in the models has been lacking. Here we present submillimeter continuum and line observations that resolve the atmosphere of the asymptotic giant branch star W Hya. We show that hot gas with chromospheric characteristics exists around the star. Its filling factor is shown to be small. The existence of such gas requires shocks with a cooling time larger than commonly assumed. A shocked hot layer will be an important ingredient in the models of stellar convection, pulsation and chemistry that underlie our current understanding of the late stages of stellar evolution.

30 pages, 9 figures, including Supplementary information. Author manuscript version before editorial/copyediting by Nature Astronomy. Journal version available via http://rdcu.be/xUWV

References in corpus (6)

• Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216
• 2D Models for Dust-driven AGB Star Winds
• Dynamical Opacity-Sampling Models of Mira Variables. I: Modelling Description and Analysis of Approximations
• Imaging the Radio Photospheres of Mira Variables
• A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars
• ALMA observations of the vibrationally-excited rotational CO transition $v=1,J=3-2$ towards five AGB stars

Cited by in corpus (23)

• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
• Global 3D radiation-hydrodynamical models of AGB stars with dust-driven winds
• Exploring the origin of clumpy dust clouds around cool giants. A global 3D RHD model of a dust-forming M-type AGB star
• Resolving the extended stellar atmospheres of Asymptotic Giant Branch stars at (sub-)millimetre wavelengths
• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
• A 3D radiation-hydrodynamic AGB binary model
• Inner dusty envelope of the AGB stars W~Hydrae, SW\,Virginis, and R~Crateris using SPHERE/ZIMPOL
• HD101584: Circumstellar characteristics and evolutionary status
• The morpho-kinematics of the circumstellar envelope around the AGB star EP Aqr
• Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars
• Detection of highly excited OH towards AGB stars: A new probe of shocked gas in the extended atmospheres
• Gas infall and possible circumstellar rotation in R Leo
• One month convection timescale on the surface of a giant evolved star
• Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn
• Maser emission from the CO envelope of the asymptotic giant branch star W Hydrae
• Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri
• Contemporaneous high-angular-resolution imaging of the AGB star W Hya in vibrationally excited H2O lines and visible polarized light with ALMA and VLT/SPHERE-ZIMPOL
• Overall variation of the $H_{2}O$ masers around W Hydrae in 28 years
• Evidence for episodic and patchy mass ejection in the circumstellar envelope of AGB star R Leonis
• High-angular-resolution ALMA imaging of the inhomogeneous dynamical atmosphere of the asymptotic giant branch star W Hya
• Millimetre observations of the S-type AGB star $\chi$ Cygni: variability of the emission of the inner envelope
• Effects of Metallicity on Graphite, TiC, and SiC Condensation in Carbon Stars
• X TrA through the eyes of MATISSE: More evidence of clumpy molecular layers around C-type asymptotic giant branch stars