Large dust grains in the wind of VY Canis Majoris

Scicluna, Peter; Siebenmorgen, R.; Wesson, R.; Blommaert, J. A. D. L.; Kasper, Markus; Вощинников, Н. В.; Wolf, S.

doi:10.1051/0004-6361/201527563

Cited by 61 publications

(59 citation statements)

References 29 publications

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“…In recent years, however, there is increasing observational evidence for the existence of such large particles in the close vicinity of AGB stars and supergiants (e.g. Norris et al 2012;Scicluna et al 2015;Ohnaka et al 2016). Furthermore, detailed atmosphere and wind models based on this mechanism show good agreement with observations regarding mass loss rates and wind velocities, as well as visual and near-IR colors, and their variation with pulsation phase (Bladh et al 2013(Bladh et al , 2015.…”

Section: Introductionmentioning

confidence: 68%

Dynamic atmospheres and winds of cool luminous giants

Höfner

Bladh

Aringer

et al. 2016

A&A

108

160

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Context. In recent years, high spatial resolution techniques have given valuable insights into the complex atmospheres of AGB stars and their wind-forming regions. They make it possible to trace the dynamics of molecular layers and shock waves, to estimate dust condensation distances, and to obtain information on the chemical composition and size of dust grains close to the star. These are essential constraints for understanding the mass loss mechanism, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust, forming in the cool upper layers of the atmospheres. Aims. Spectro-interferometric observations indicate that Al 2 O 3 condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al 2 O 3 grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. The purpose of this paper is to study the necessary conditions for the formation of Al 2 O 3 and the potential effects on mass loss, using detailed atmosphere and wind models. Methods. We have constructed a new generation of Dynamic Atmosphere and Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth and evaporation for both Al 2 O 3 and Fe-free silicates (Mg 2 SiO 4 ). The equations describing these dust species are solved in the framework of a frequency-dependent radiationhydrodynamical model for the atmosphere and wind structure, taking pulsation-induced shock waves and periodic luminosity variations into account. Results. Condensation of Al 2 O 3 at the close distances and in the high concentrations implied by observations requires high transparency of the grains in the visual and near-IR region to avoid destruction by radiative heating. We derive an upper limit for the imaginary part of the refractive index k around 10 −3 at these wavelengths. For solar abundances, radiation pressure due to Al 2 O 3 is too low to drive a wind. Nevertheless, this dust species may have indirect effects on mass loss. The formation of composite grains with an Al 2 O 3 core and a silicate mantle can give grain growth a head start, increasing both mass loss rates and wind velocities. Furthermore, our experimental core-mantle grain models lead to variations of visual and near-IR colors during a pulsation cycle which are in excellent agreement with observations. Conclusions. Al 2 O 3 grains are promising candidates for explaining the presence of gravitationally bound dust shells close to M-type AGB stars, as implied by both scattered light observations and mid-IR spectro-interferometry. The required level of transparency at near-IR wavelengths is compatible with impurities due to a few percent of transition metals (e.g., Cr), consistent with cosmic abundances. Grains consisting of an Al 2 O 3 core and an Fe-free silicate mantle with total grain radi...

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Section: Introductionmentioning

confidence: 68%

Dynamic atmospheres and winds of cool luminous giants

Höfner

Bladh

Aringer

et al. 2016

A&A

108

160

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“…In our analysis, we also include that observations of polarized visible light obtained with Hubble ) and SPHERE/VLT (Scicluna et al 2015) show that the polarization vectors seen towards clump C in visible wavelengths are roughly perpendicular to those observed at mm wavelength presented here.…”

Section: Dust Polarization Of Clump Cmentioning

confidence: 87%

Magnetically aligned dust and SiO maser polarisation in the envelope of the red supergiant VY Canis Majoris

Vlemmings

Khouri

Martí-Vidal

et al. 2017

A&A

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Aims. Polarization observations of circumstellar dust and molecular (thermal and maser) lines provide unique information about dust properties and magnetic fields in circumstellar envelopes of evolved stars. Methods. We use Atacama Large Millimeter/submillimeter Array Band 5 science verification observations of the red supergiant VY CMa to study the polarization of SiO thermal/masers lines and dust continuum at ∼ 1.7 mm wavelength. We analyse both linear and circular polarization and derive the magnetic field strength and structure, assuming the polarization of the lines originates from the Zeeman effect, and that of the dust originates from aligned dust grains. We also discuss other effects that could give rise to the observed polarization. Results. We detect, for the first time, significant polarization (∼ 3%) of the circumstellar dust emission at millimeter wavelengths. The polarization is uniform with an electric vector position angle of ∼ 8• . Varying levels of linear polarization are detected for the J = 4−3 28 SiO v = 0, 1, 2, and 29 SiO v = 0, 1 lines, with the strongest polarization fraction of ∼ 30% found for the 29 SiO v = 1 maser. The linear polarization vectors rotate with velocity, consistent with earlier observations. We also find significant (up to ∼ 1%) circular polarization in several lines, consistent with previous measurements. We conclude that the detection is robust against calibration and regular instrumental errors, although we cannot yet fully rule out non-standard instrumental effects. Conclusions. Emission from magnetically aligned grains is the most likely origin of the observed continuum polarization. This implies that the dust is embedded in a magnetic field > 13 mG. The maser line polarization traces the magnetic field structure. The magnetic field in the gas and dust is consistent with an approximately toroidal field configuration, but only higher angular resolution observations will be able to reveal more detailed field structure. If the circular polarization is due to Zeeman splitting, it indicates a magnetic field strength of ∼ 1 − 3 Gauss, consistent with previous maser observations.

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“…Examples include IRC +10 216 and OH 26.5, which were fitted with MoD code by Groenewegen et al (2012) and Groenewegen (2012), respectively. Recently, Norris et al (2012), Scicluna et al (2015), and Ohnaka et al (2016) found evidence for grains in the range 0.3-0.5 µm, and 0.1-1 µm grains are advocated to drive the outlow around oxygen-rich stars (Höfner 2008, Bladh & Höfner 2012). …”

Section: Dust Grain Propertiesmentioning

confidence: 99%

Luminosities and mass-loss rates of Local Group AGB stars and red supergiants

Groenewegen

Sloan

2018

A&A

102

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Context. Mass loss is one of the fundamental properties of asymptotic giant branch (AGB) stars, and through the enrichment of the interstellar medium, AGB stars are key players in the life cycle of dust and gas in the universe. However, a quantitative understanding of the mass-loss process is still largely lacking. Aims. We aim to investigate mass loss and luminosity in a large sample of evolved stars in several Local Group galaxies with a variety of metalliticies and star-formation histories: the Small and Large Magellanic Cloud, and the Fornax, Carina, and Sculptor dwarf spheroidal galaxies (dSphs). Methods. Dust radiative transfer models are presented for 225 carbon stars and 171 oxygen-rich evolved stars in several Local Group galaxies for which spectra from the Infrared Spectrograph on Spitzer are available. The spectra are complemented with available optical and infrared photometry to construct spectral energy distributions. A minimization procedure was used to determine luminosity and mass-loss rate (MLR). Pulsation periods were derived for a large fraction of the sample based on a re-analysis of existing data. Results. New deep K-band photometry from the VMC survey and multi-epoch data from IRAC (at 4.5 µm) and AllWISE and NEOWISE have allowed us to derive pulsation periods longer than 1000 days for some of the most heavily obscured and reddened objects. We derive (dust) MLRs and luminosities for the entire sample. The estimated MLRs can differ significantly from estimates for the same objects in the literature due to differences in adopted optical constants (up to factors of several) and details in the radiative transfer modelling. Updated parameters for the super-AGB candidate MSX SMC 055 (IRAS 00483−7347) are presented. Its current mass is estimated to be 8.5 ± 1.6 M ⊙ , suggesting an initial mass well above 8 M ⊙ in agreement with estimates based on its large Rubidium abundance. Using synthetic photometry, we present and discuss colour-colour and colour-magnitude diagrams which can be expected from the James Webb Space Telescope.

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Large dust grains in the wind of VY Canis Majoris

Cited by 61 publications

References 29 publications

Dynamic atmospheres and winds of cool luminous giants

Dynamic atmospheres and winds of cool luminous giants

Magnetically aligned dust and SiO maser polarisation in the envelope of the red supergiant VY Canis Majoris

Luminosities and mass-loss rates of Local Group AGB stars and red supergiants

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