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Register a new userInfrared interferometric three-dimensional diagnosis of the atmospheric dynamics of the AGB star R Dor with VLTI/AMBER
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The mechanism of mass loss in late evolutionary stages of low- and intermediate-mass stars is not yet well understood. Therefore, it is crucial to study the dynamics of the region within a few stellar radii, where the wind acceleration is considered to take place. We present three-dimensional diagnosis of the atmospheric dynamics of the closest asymptotic giant branch (AGB) star R Dor from the low photospheric layers to the extended outer atmosphere--for the first time for a star other than the Sun. The images reconstructed with a spatial resolution of 6.8 mas--seven times finer than the stars angular diameter of 51.2 mas in the continuum--using the AMBER instrument at the Very Large Telescope Interferometer show a large, bright region over the surface of the star and an extended atmosphere. The velocity-field maps over the stars surface and atmosphere obtained from the Mg and H2O lines near 2.3 micron forming at atmospheric heights below ~1.5 stellar radii show little systematic motion beyond the measurement uncertainty of 1.7 km/s. In marked contrast, the velocity-field map obtained from the CO first overtone lines reveals systematic outward motion at 7--15 km/s in the extended outer atmosphere at a height of ~1.8 stellar radii. Given the detection of dust formation at ~1.5 stellar radii, the strong acceleration of material between ~1.5 and 1.8 stellar radii may be caused by the radiation pressure on dust grains. However, we cannot yet exclude the possibility that the outward motion may be intermittent, caused by ballistic motion due to convection and/or pulsation.
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We present a near-infrared spectro-interferometric observation of the non-Mira-type, semiregular asymptotic giant branch star SW Vir. Our aim is to probe the physical properties of the outer atmosphere with spatially resolved data in individual molecular and atomic lines. We observed SW Vir in the spectral window between 2.28 and 2.31 micron with the near-infrared interferometric instrument AMBER at ESOs Very Large Telescope Interferometer (VLTI). Thanks to AMBERs high spatial resolution and high spectral resolution of 12000, the atmosphere of SW Vir has been spatially resolved not only in strong CO first overtone lines but also in weak molecular and atomic lines of H2O, CN, HF, Ti, Fe, Mg, and Ca. Comparison with the MARCS photospheric models reveals that the star appears larger than predicted by the hydrostatic models not only in the CO lines but also even in the weak molecular and atomic lines. We found that this is primarily due to the H2O lines (but also possibly due to the HF and Ti lines) originating in the extended outer atmosphere. Although the H2O lines manifest themselves very little in the spatially unresolved spectrum, the individual rovibrational H2O lines from the outer atmosphere can be identified in the spectro-interferometric data. Our modeling suggests an H2O column density of 10^{19}--10^{20} cm^{-2} in the outer atmosphere extending out to ~2 Rstar. Our study has revealed that the effects of the nonphotospheric outer atmosphere are present in the spectro-interferometric data not only in the strong CO first overtone lines but also in the weak molecular and atomic lines. Therefore, analyses of spatially unresolved spectra, such as for example analyses of the chemical composition, should be carried out with care even if the lines appear to be weak.
We analyse new ALMA observations of the $^{29}$SiO ($ u$=0, $J$=8$-$7) and SO$_2$($ u$=0, $34_{3,31}$$-$$34_{2,32}$) line emissions of the circumstellar envelope (CSE) of the oxygen-rich AGB star R Dor. With a spatial resolution of $sim$2.3 au, they cover distances below $sim$30 au from the star providing a link between earlier observations and clarifying some open issues. The main conclusions are: 1) Rotation is confined below $sim$15 au from the star, with velocity reaching a maximum below 10 au and morphology showing no significant disc-like flattening. 2) In the south-eastern quadrant, a large Doppler velocity gas stream is studied in more detail than previously possible and its possible association with an evaporating planetary companion is questioned. 3) A crude evaluation of the respective contributions of rotation, expansion and turbulence to the morpho-kinematics is presented. Significant line broadening occurs below $sim$12 au from the star and causes the presence of high Doppler velocity components near the line of sight pointing to the centre of the star. 4) Strong absorption of the continuum emission of the stellar disc and its immediate dusty environment is observed to extend beyond the disc in the form of self-absorption. The presence of a cold SiO layer extending up to some 60 au from the star is shown to be the cause. 5) Line emissions from SO, $^{28}$SiO, CO and HCN molecules are used to probe the CSE up to some 100 au from the star and reveal the presence of two broad back-to-back outflows, the morphology of which is studied in finer detail than in earlier work.
Aims. We study the enigmatic B[e] star MWC 300 to investigate its disk and binary with milli-arcsecond-scale angular resolution. Methods. We observed MWC 300 with the VLTI/AMBER instrument in the H and K bands and compared these observations with temperature-gradient models to derive model parameters. Results. The measured low visibility values, wavelength dependence of the visibilities, and wavelength dependence of the closure phase directly suggest that MWC 300 consists of a resolved disk and a close binary. We present a model consisting of a binary and a temperature-gradient disk that is able to reproduce the visibilities, closure phases, and spectral energy distribution. This model allows us to constrain the projected binary separation (~4.4 mas or ~7.9 AU), the flux ratio of the binary components (~2.2), the disk temperature power-law index, and other parameters.
We present visible polarimetric imaging observations of the well-studied AGB star W Hya taken with VLT/SPHERE-ZIMPOL as well as high spectral resolution long-baseline interferometric observations with the AMBER instrument of the Very Large Telescope Interferometer (VLTI). We observed W Hya with VLT/SPHERE-ZIMPOL at three wavelengths in the continuum (645, 748, and 820 nm), in the Halpha line at 656.3 nm, and in the TiO band at 717 nm. The VLTI/AMBER observations were carried out in the wavelength region of the CO first overtone lines near 2.3 micron with a spectral resolution of 12000. Taking advantage of the polarimetric imaging capability of SPHERE-ZIMPOL combined with the superb adaptive optics performance, we have succeeded in spatially resolving three clumpy dust clouds located at ~50 mas (~2 Rstar) from the central star, revealing dust formation very close to the star. The AMBER data in the individual CO lines suggest a molecular outer atmosphere extending to ~3 Rstar. Furthermore, the SPHERE-ZIMPOL image taken over the Halpha line shows emission with a radius of up to ~160 mas (~7 Rstar). We found that dust, molecular gas, and Halpha-emitting hot gas are coexisting within 2--3 Rstar. Our modeling suggests that the observed polarized intensity maps can reasonably be explained by large (0.4--0.5 micron) grains of Al2O3 or Mg2SiO4 or MgSiO3 in an optically thin shell with an inner boundary radius of 1.9--2.0 Rstar. The observed clumpy structure can be reproduced by a density enhancement by a factor of 4 +/- 1. The grain size derived from our polarimetric images is consistent with the prediction of the hydrodynamical models for the mass loss driven by the scattering due to micron-sized grains. The detection of the clumpy dust clouds close to the star lends support to the dust formation induced by pulsation and large convective cells as predicted by the 3-D simulations for AGB stars.
The rapidly rotating primary component of Regulus A system has been observed, for the first time, using the technique of differential interferometry at high spectral resolution. The observations have been performed across the Br$_gamma$ spectral line with the VLTI/AMBER focal instrument in high spectral resolution mode (R $approx$ 12000) at $approx$ 80-130m (projected on the sky) Auxiliary Telescopes triplet baseline configurations. We confirm, within the uncertainties, the results previously obtained using the techniques of classical long-baseline interferometry, although the question of anomalous gravity darkening remains open for the future study.
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