High-angular-resolution ALMA imaging of the inhomogeneous dynamical atmosphere of the asymptotic giant branch star W Hya

Abstract

We present high-angular-resolution imaging of the asymptotic giant branch star W Hya with the Atacama Large Millimeter/submillimeter Array (ALMA) to probe the dynamics and chemistry in the atmosphere and inner wind. W Hya was observed with the longest baselines of ALMA at 250-268 GHz with an angular resolution of ~17x20 mas. ALMA's high angular resolution allowed us to resolve the stellar disk of W Hya, along with clumpy, irregularly shaped emission extending to ~100 mas: plume in the north-northwest, a tail in the south-southwest, and the extended atmosphere elongated in the east-northeast--west-southwest direction, with semimajor and semiminor axes of ~70 and 40 mas (~3.4 and 1.9 Rstar), respectively. We identified 57 lines, which include SiO, H2O, SO2, SO, HCN, AlO, AlOH, TiO, TiO2, OH, and some of their isotopologues. The molecular line images show spatially inhomogeneous molecular formation. Our ALMA data taken at phase 0.53 (minimum light) indicate global, accelerating infall within ~75 mas (3.6 Rstar) but also outflow at up to ~10 km/s in deeper layers. While 38 of the detected lines appear in absorption against the continuum stellar disk as expected, we detect nonthermal emission on top of the continuum over the stellar disk in 19 lines of SiO, H2O, SO2, and AlO. The emission of SiO, AlO, TiO, TiO2, SO, and SO2 coincides well with the clumpy dust cloud distribution obtained from contemporaneous visible polarimetric imaging in addition to H2O reported in our previous work. This lends support to the idea that SiO, H2O, and AlO are directly involved in grain nucleation. The overlap of SO/SO2 (possibly also TiO/TiO2) with the dust clouds suggests the formation of these molecules and dust behind shocks induced by pulsation and/or convection. We detect HCN emission close to the star, down to ~30 mas (~1.4 Rstar), which is consistent with shock-induced chemistry.

30 pages, 19 figures, published in Astronomy and Astrophysics

References in corpus (72)

• Validation of the new Hipparcos reduction
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual Atomic and Molecular Data Centre, VAMDC
• Multi-Scale CLEAN deconvolution of radio synthesis images
• Dust formation in the oxygen-rich AGB star IK Tau
• A close halo of large transparent grains around extreme red giant stars
• Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
• UVMULTIFIT: A versatile tool for fitting astronomical radio interferometric data
• Reprocessing the Hipparcos data for evolved stars III Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
• (Sub)stellar companions shape the winds of evolved stars
• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
• Line formation in AGB atmospheres including velocity effects. Molecular line profile variations of long period variables
• 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
• Numerical simulations of stellar SiO maser variability. Investigation of the effect of shocks
• Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL
• Tracing the phase transition of Al-bearing species from molecules to dust in AGB winds. Constraining the presence of gas-phase (Al2O3)n clusters
• The Physics of Water Masers observable with ALMA and SOFIA: Model Predictions for Evolved Stars
• Photochemistry in the inner layers of clumpy circumstellar envelopes: formation of water in C-rich objects and of C-bearing molecules in O-rich objects
• Distance estimates for AGB stars from parallax measurements
• Clumpy dust clouds and extended atmosphere of the AGB star W Hya revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER
• VLBI astrometry of circumstellar OH masers; proper motions and parallaxes of four AGB stars
• An observational study of dust nucleation in Mira ($o$ Ceti): I. Variable features of AlO and other Al-bearing species
• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• The wind of W Hya as seen by Herschel - I. The CO envelope
• Sulphur molecules in the circumstellar envelopes of M-type AGB stars
• An extensive grid of DARWIN models for M-type AGB stars I. Mass-loss rates and other properties of dust-driven winds
• The evolution of DARWIN: current status of wind models for AGB stars
• Dust Scattering in Miras R Car and RR Sco resolved by optical interferometric polarimetry
• Resolving the extended atmosphere and the inner wind of Mira ($o$ Ceti) with long ALMA baselines
• Imaging the Radio Photospheres of Mira Variables
• Clumpy dust clouds and extended atmosphere of the AGB star W Hya revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER II. Time variations between pre-maximum and minimum light
• Magnetic Fields in Evolved Stars: Imaging the Polarized Emission of High-Frequency SiO Masers
• Bottom-up dust nucleation theory in oxygen-rich evolved stars I. Aluminium oxide clusters
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• 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
• Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk
• The evolutionary state of Miras with changing pulsation periods
• The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA
• Resolving the extended stellar atmospheres of Asymptotic Giant Branch stars at (sub-)millimetre wavelengths
• High-resolution observations of gas and dust around Mira using ALMA and SPHERE/ZIMPOL
• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
• An observational study of dust nucleation in Mira ($o$ Ceti): II. Titanium oxides are negligible for nucleation at high temperatures
• Circumstellar environment of the M-type AGB star R Dor. APEX spectral scan at $159.0-368.5$ GHz
• The impact of stellar companion UV photons on the chemistry of the circumstellar environments of AGB stars
• Detection of HCN Direct l-Type Transitions Probing Hot Molecular Gas in the Proto-Planetary Nebula CRL 618
• The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars
• The mid-infrared diameter of W Hydrae
• Continuum emission around AGB stars at 1.2 mm
• ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H${}_2$O and OH lines
• Dynamic atmospheres and winds of cool luminous giants, II. Gradual Fe enrichment of wind-driving silicate grains
• ATOMIUM: Molecular inventory of 17 oxygen-rich evolved stars observed with ALMA
• Exploring the innermost dust formation region of the oxygen-rich AGB star IK~Tau with VLT/SPHERE-ZIMPOL and VLTI/AMBER
• An ALMA view of SO and SO${}_2$ around oxygen-rich AGB stars
• New Measurements of the Radio Photosphere of Mira based on Data from the JVLA and ALMA
• Water isotopologues in the circumstellar envelopes of M-type AGB stars
• Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through Interferometric Observations of HC${}_3$N
• Silicon isotopic abundance toward evolved stars and its application for presolar grains
• Pulsation-induced atmospheric dynamics in M-type AGB stars. Effects on wind properties, photometric variations and near-IR CO line profiles
• Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars
• Distribution and kinematics of the HCN(3-2) emission down to the innermost region in the envelope of the O-rich star W Hya
• Mechanisms of SiO oxidation: Implications for dust formation
• Infrared interferometric three-dimensional diagnosis of the atmospheric dynamics of the AGB star R Dor with VLTI/AMBER
• Detection of highly excited OH towards AGB stars: A new probe of shocked gas in the extended atmospheres
• 4mu spectra of AGB stars I: Observations
• One month convection timescale on the surface of a giant evolved star
• The solar photospheric silicon abundance according to CO5BOLD: Investigating line broadening, magnetic fields, and model effects
• Maser emission from the CO envelope of the asymptotic giant branch star W Hydrae
• An impressionist view of V Hydrae. When MATISSE paints Asymmetric Giant Blobs
• 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
• Locating dust and molecules in the inner circumstellar environment of R~Sculptoris with MATISSE
• Probing the Extended Atmospheres of AGB Stars: I. Synthetic imaging of 1D hydrodynamical models at radio and (sub-)millimeter wavelengths