The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI

Sacuto, Stéphane; Ramstedt, S.; Höfner, Susanne; Olofsson, H.; Bladh, Sara; Eriksson, K.; Aringer, B.; Klotz, Daniela; Maercker, M.

doi:10.1051/0004-6361/201220524

Cited by 29 publications

(55 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…After its postulation in 2008 by Höfner et al, the latter scenario got more and more support from observations; the first such observations were reported by Norris et al (2012) using VLT/NACO data of three low mass-loss rate AGB stars (R Dor, W Hya, and R Leo). The mid-infrared interferometric observations of the semi-regular AGB star RT Vir with the MIDI instrument at VLTI also lent support to the presence of iron-free silicates between 2 and 3 stellar radii (Sacuto et al 2013). Recent polarized light data obtained with the VLT/SPHERE instrument offer us another way to look at the inner wind chemical and morphological structure.…”

Section: Introductionmentioning

confidence: 81%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

View full text Add to dashboard Cite

Context. The condensation of inorganic dust grains in the winds of evolved stars is poorly understood. As of today, it is not yet known which molecular clusters form the first dust grains in oxygen-rich (C/O < 1) asymptotic giant branch (AGB) winds. Aluminium oxides and iron-free silicates are often put forward as promising candidates for the first dust seeds. Aims. We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. Methods. We obtained Atacama Large Millimeter/sub-millimeter array (ALMA) observations with a spatial resolution of 120 × 150 mas tracing the dust formation region of the low mass-loss rate AGB star, R Dor, and the high mass-loss rate AGB star, IK Tau. We detected emission line profiles of AlO, AlOH, and AlCl in the ALMA data and used these line profiles to derive a lower limit of atomic aluminium incorporated in molecules. This constrains the aluminium budget that can condense into grains. Results. Radiative transfer models constrain the fractional abundances of AlO, AlOH, and AlCl in IK Tau and R Dor. We show that the gas-phase aluminium chemistry is completely different in both stars with a remarkable difference in the AlO and AlOH abundance stratification. The amount of aluminium locked up in these three molecules is small, ≤1.1 × 10 −7 w.r.t. H 2 , for both stars, i.e. only ≤2% of the total aluminium budget. An important result is that AlO and AlOH, which are the direct precursors of alumina (Al 2 O 3 ) grains, are detected well beyond the onset of the dust condensation, which proves that the aluminium oxide condensation cycle is not fully efficient. The ALMA observations allow us to quantitatively assess the current generation of theoretical dynamical-chemical models for AGB winds. We discuss how the current proposed scenario of aluminium dust condensation for low mass-loss rate AGB stars within a few stellar radii from the star, in particular for R Dor and W Hya, poses a challenge if one wishes to explain both the dust spectral features in the spectral energy distribution (SED) in interferometric data and in the polarized light signal. In particular, the estimated grain temperature of Al 2 O 3 is too high for the grains to retain their amorphous structure. We advocate that large gas-phase (Al 2 O 3 ) n clusters (n > 34) can be the potential agents of the broad 11 µm feature in the SED and in the interferometric data and we propose potential formation mechanisms for these large clusters.

show abstract

Section: Introductionmentioning

confidence: 81%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

View full text Add to dashboard Cite

show abstract

“…A possible interpretation is that the observed spatial gap between the Al 2 O 3 condensation zone (at about 2 stellar radii) and the region where pronounced mid-IR silicate emission originates (at 4 or more stellar radii) corresponds to a region dominated by Fe-free silicate dust. Spectro-interferometric observations of RT Vir by Sacuto et al (2013) show indeed signs of a weak silicate feature at about 2 stellar radii, implying the presence of Fe-free silicate grains.…”

Section: The Interplay Of Al 2 O 3 and Silicate Dustmentioning

confidence: 88%

“…In addition to general insights on photospheric and circumstellar structures, high spatial resolution techniques can provide specific measurements which are essential for our understanding of wind mechanisms, in particular condensation distances of various dust species (e.g. Ireland et al 2005;Wittkowski et al 2007;Zhao-Geisler et al 2011Karovicova et al 2013;Sacuto et al 2013) and grain sizes in the wind acceleration zone (e.g. Norris et al 2012;Ohnaka et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Dynamic atmospheres and winds of cool luminous giants

Höfner

Bladh

Aringer

et al. 2016

A&A

Self Cite

101

160

View full text Add to dashboard Cite

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...

show abstract

“…We combined spectroscopic photometric and interferometric observations and hydrostatic and dynamic model atmospheres, as well as simple geometrical models. Until now, the only studies with a similar approach to the one in the present study are those by Sacuto et al (2011) on R Scl and RT Vir Sacuto et al (2013) on RT Vir. While R Scl is a semi-regular pulsating star and RT Vir an M-type star, RU Vir is the first carbon-rich Mira variable for which photometry, spectroscopy, and interferometry are compared to DMAs.…”

Section: Discussionmentioning

confidence: 99%

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Rau

Paladini

Hron

et al. 2015

A&A

Self Cite

View full text Add to dashboard Cite

Context. We study the atmosphere of the carbon-rich Mira RU Vir using the mid-infrared high spatial resolution interferometric observations from VLTI/MIDI. Aims. The aim of this work is to analyse the atmosphere of the carbon-rich Mira RU Vir with hydrostatic and dynamic models, in this way deepening the knowledge of the dynamic processes at work in carbon-rich Miras. Methods. We compare spectro-photometric and interferometric measurements of this carbon-rich Mira AGB star with the predictions of different kinds of modelling approaches (hydrostatic model atmospheres plus MOD-More Of Dusty, self-consistent dynamic model atmospheres). A geometric model fitting tool is used for a first interpretation of the interferometric data. Results. The results show that a joint use of different kinds of observations (photometry, spectroscopy, interferometry) is essential for shedding light on the structure of the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit the ISO spectrum well in the wavelength range λ = [2.9, 25.0] µm. Nevertheless, a discrepancy is noticeable both in the SED (visible) and in the interferometric visibilities (shape and level), which is a possible explanation are intra-/inter-cycle variations in the dynamic model atmospheres, as well as in the observations. The presence of a companion star and/or a disk or a decrease in mass loss within the past few hundred years cannot be excluded, but these explanations are considered unlikely.

show abstract

The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI

Cited by 29 publications

References 50 publications

Study of the aluminium content in AGB winds using ALMA

Study of the aluminium content in AGB winds using ALMA

Dynamic atmospheres and winds of cool luminous giants

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Contact Info

Product

Resources

About