2016A&A...589A..91O


Query : 2016A&A...589A..91O

2016A&A...589A..91O - Astronomy and Astrophysics, volume 589A, 91-91 (2016/5-1)

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER.

OHNAKA K., WEIGELT G. and HOFMANN K.-H.

Abstract (from CDS):

Context. Dust formation is thought to play an important role in the mass loss from stars at the asymptotic giant branch (AGB); however, where and how dust forms is still open to debate.
Aims. 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 taken with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Our goal is to spatially resolve the dust and molecule formation region within a few stellar radii.
Methods. We observed W Hya with VLT/SPHERE-ZIMPOL at three wavelengths in the continuum (645, 748, and 820nm), in the Hα line at 656.3nm, and in the TiO band at 717nm. The VLTI/AMBER observations were carried out in the wavelength region of the CO first overtone lines near 2.3 µm with a spectral resolution of 12000.
Results. Taking advantage of the polarimetric imaging capability of SPHERE-ZIMPOL combined with the superb adaptive optics performance, we succeeded in spatially resolving three clumpy dust clouds located at ∼50mas (∼2R*) 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 ∼3R*. Furthermore, the SPHERE-ZIMPOL image taken over the Hα line shows emission with a radius of up to ∼160 mas (∼7R*). We found that dust, molecular gas, and Hα-emitting hot gas coexist within 2-3R*. Our modeling suggests that the observed polarized intensity maps can reasonably be explained by large (0.4-0.5µm) grains of Al2O3, Mg2SiO4, or MgSiO3 in an optically thin shell (τ550nm=0.1±0.02) with an inner and outer boundary radius of 1.9-2.0R* and 3±0.5R*, respectively. The observed clumpy structure can be reproduced by a density enhancement of a factor of 4±1.
Conclusions. The grain size derived from our modeling of the SPHERE-ZIMPOL 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 3D simulations for AGB stars.

Abstract Copyright: © ESO, 2016

Journal keyword(s): techniques: polarimetric - techniques: interferometric - stars: AGB and post-AGB - circumstellar matter - stars: individual: W Hya - stars: imaging

Simbad objects: 11

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Number of rows : 11
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 V* IK Tau Mi* 03 53 28.8884898148 +11 24 21.865959095 16.99 17.03 13.39 7.29 3.20 M7-11 590 0
2 * alf Ori s*r 05 55 10.30536 +07 24 25.4304 4.38 2.27 0.42 -1.17 -2.45 M1-M2Ia-Iab 1525 0
3 * alf Car * 06 23 57.10988 -52 41 44.3810 -0.49 -0.59 -0.74 -0.96 -1.13 A9II 426 0
4 V* R Car Mi* 09 32 14.5996404553 -62 47 20.045197073 8.51 7.40 6.10 5.44 2.90 M5-8 164 1
5 IRC +10216 C* 09 47 57.40632 +13 16 43.5648     10.96     C9,5e 2201 0
6 V* RW LMi C* 10 16 02.2834693816 +30 34 18.977096332       15.27   C4,3e 384 0
7 V* RT Vir AB* 13 02 37.9836301550 +05 11 08.360733054 10.07 9.07 7.41     M8III 302 0
8 NAME Centaurus A Sy2 13 25 27.61509104 -43 01 08.8056025   8.18 6.84 6.66   ~ 4110 3
9 V* W Hya Mi* 13 49 02.0018313132 -28 22 03.532006894   8.97 7.70     M7.5-9e 614 0
10 HD 121653 * 13 57 17.1297856039 -28 38 06.765193785   8.62 7.18     K3III 9 0
11 V* RR Sco Mi* 16 56 37.8414071798 -30 34 48.189816056 8.46 7.64 6.10     M6+e 149 0

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2021.08.01-07:57:24

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