Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL

Abstract

We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study the photosphere, the warm molecular layer, and the inner wind of the close-by oxygen-rich AGB star R Doradus. We present observations in filters V, cntH$\alpha$, and cnt820 and investigate the surface brightness distribution of the star and of the polarised light produced in the inner envelope. Thanks to second-epoch observations in cntH$\alpha$, we are able to see variability on the stellar photosphere. We find that in the first epoch the surface brightness of R Dor is asymmetric in V and cntH$\alpha$, the filters where molecular opacity is stronger, while in cnt820 the surface brightness is closer to being axisymmetric. The second-epoch observations in cntH$\alpha$ show that the morphology of R Dor changes completely in a timespan of 48 days to a more axisymmetric and compact configuration. The polarised intensity is asymmetric in all epochs and varies by between a factor of 2.3 and 3.7 with azimuth for the different images. We fit the radial profile of the polarised intensity using a spherically symmetric model and a parametric description of the dust density profile, $\rho (r)={\rho }_{\circ }{r}^{-n}$. On average, we find exponents of $-4.5\pm 0.5$ that correspond to a much steeper density profile than that of a wind expanding at constant velocity. The dust densities we derive imply an upper limit for the dust-to-gas ratio of $\sim 2\times 10^{-4}$ at 5.0 $R_{\star }$. Given the uncertainties in observations and models, this value is consistent with the minimum values required by wind-driving models for the onset of a wind, of $\sim 3.3\times 10^{-4}$. However, if the steep density profile we find extends to larger distances from the star, the dust-to-gas ratio will quickly become too small for the wind of R Dor to be driven by the grains that produce the scattered light.

10 pages, 8 figures, 4 tables

References in corpus (14)

• The chemical composition of the Sun
• Radiative transfer in very optically thick circumstellar disks
• 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
• Circumstellar water vapour in M-type AGB stars: Radiative transfer models, abundances and predictions for HIFI
• Exploring wind-driving dust species in cool luminous giants I. Basic criteria and dynamical models of M-type AGB stars
• Clumpy dust clouds and extended atmosphere of the AGB star W Hya revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER
• Mode switching in the nearby Mira-like variable R Doradus
• The wind of W Hya as seen by Herschel - I. The CO envelope
• Exploring wind-driving dust species in cool luminous giants III. Wind models for M-type AGB stars: dynamic and photometric properties
• Multi-wavelength Diameters of Nearby Miras and Semiregulars
• J, H, K spectro-interferometry of the Mira variable S Orionis
• Dust Scattering in Miras R Car and RR Sco resolved by optical interferometric polarimetry
• The Keck Aperture Masking Experiment: spectro-interferometry of 3 Mira Variables from 1.1 to 3.8 microns

Cited by in corpus (54)

• SPHERE: the exoplanet imager for the Very Large Telescope
• SPHERE / ZIMPOL high resolution polarimetric imager. I. System overview, PSF parameters, coronagraphy, and polarimetry
• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
• Tracing the phase transition of Al-bearing species from molecules to dust in AGB winds. Constraining the presence of gas-phase (Al2O3)n clusters
• 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
• 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
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• Exploring the origin of clumpy dust clouds around cool giants. A global 3D RHD model of a dust-forming M-type AGB star
• Global 3D radiation-hydrodynamical models of AGB stars with dust-driven winds
• Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow
• Wind morphology around cool evolved stars in binaries: the case of slowly accelerating oxygen-rich outflows
• The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA
• Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk
• 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
• Developing a self-consistent AGB wind model: II. Non-classical, non-equilibrium polymer nucleation in a chemical mixture
• Rotation of the asymptotic giant branch star R Doradus
• The impact of stellar companion UV photons on the chemistry of the circumstellar environments of AGB stars
• An unusual face-on spiral in the wind of the M-type AGB star EP Aquarii
• Atomium: A high-resolution view on the highly asymmetric wind of the AGB star Pi1 Gruis. I. First detection of a new companion and its effect on the inner wind
• ALMA detection of a tentative nearly edge-on rotating disk around the nearby AGB star R~Doradus
• 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
• The inner dust shell of Betelgeuse detected by polarimetric aperture-masking interferometry
• Properties of self-excited pulsations in 3D simulations of AGB stars and red supergiants
• Constraints on metal oxide and metal hydroxide abundances in the winds of AGB stars - Potential detection of FeO in R Dor
• Exploring the innermost dust formation region of the oxygen-rich AGB star IK~Tau with VLT/SPHERE-ZIMPOL and VLTI/AMBER
• Rotational spectra of vibrationally excited AlO and TiO in oxygen rich stars
• ALMA observations of the nearby AGB star L${}_2$ Puppis. II. Gas disk properties derived from ${}^{12}$CO and ${}^{13}$CO $J=$3$-$2 emission
• HD101584: Circumstellar characteristics and evolutionary status
• Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars
• The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview: Sample characterization through polarization analysis
• Infrared interferometric three-dimensional diagnosis of the atmospheric dynamics of the AGB star R Dor with VLTI/AMBER
• Dust in AGB wind-ISM interaction regions
• Chemical modelling of dust-gas chemistry within AGB outflows III. Photoprocessing of the ice and return to the ISM
• Morpho-kinematics of the circumstellar envelope of the AGB star R Dor: a global view
• Chemical modelling of dust-gas chemistry within AGB outflows -- II. Effect of the dust-grain size distribution
• Evidence for localized onset of episodic mass loss in Mira
• Radiation-pressure-driven sub-Keplerian rotation of the disc around the AGB star L2 Pup
• Properties of dust in the detached shells around U Ant, DR Ser, and V644 Sco
• Modelling polarized light from dust shells surrounding asymptotic giant branch stars
• A large bubble around the AGB star R Dor detected in the UV
• Vanadium oxide clusters in substellar atmospheres: A quantum chemical study
• 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
• Disentangling physics and chemistry in AGB outflows: revealing degeneracies when adding complexity
• Synthetic photometry for carbon-rich giants. V. Effects of grain-size-dependent dust opacities
• The nascent wind of AGB star R Doradus: evidence for a recent episode of enhanced mass loss
• Asymmetries in asymptotic giant branch stars and their winds. I. From 3D RHD models to synthetic observables
• On the optical properties of Resonant Drag Instabilities: Variability of Asymptotic Giant Branch and R Coronae Borealis stars
• Probing the Extended Atmospheres of AGB Stars: I. Synthetic imaging of 1D hydrodynamical models at radio and (sub-)millimeter wavelengths
• Infrared interferometric imaging of the compact dust disk around the AGB star HR3126 with the bipolar Toby Jug Nebula
• High-angular-resolution ALMA imaging of the inhomogeneous dynamical atmosphere of the asymptotic giant branch star W Hya