Dust formation and wind acceleration around the aluminum oxide–rich AGB star W Hydrae

Takigawa, Aki; Kamizuka, Takafumi; Tachibana, Shogo; Yamamura, I.

doi:10.1126/sciadv.aao2149

Cited by 48 publications

(58 citation statements)

References 28 publications

(46 reference statements)

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“…A. Takigawa) with a spatial resolution of ∼40 mas at three selected frequency bands GHz, and 344.03-345.91 GHz) encompassing the AlO N = 9-8 and AlOH J = 11-10 transition. AlO is detected in their data (Takigawa et al 2016). …”

Section: Target Selectionmentioning

confidence: 93%

“…The molecule AlOH was also potentially detected in Herschel and APEX data, while AlH and atomic Al I lines were detected in optical spectra. Takigawa et al (2016) have reported on ALMA long-baseline observations of several molecules, including AlO, in W Hya. Finally, De Beck et al (2017) has studied eight oxygen-rich AGB stars; AlO could clearly be identified in two of these stars and for four other targets tentative detections were shown.…”

Section: Introductionmentioning

confidence: 99%

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Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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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.

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Section: Target Selectionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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“…AlO has been detected in oxygen-rich stars (e.g. De Beck et al 2017;Takigawa et al 2017). There has, however, only been one previous observed indication of AlO in an exoplanet atmosphere, by von Essen et al (2019) in the atmosphere of the highly irradiated "super-hot Jupiter" WASP-33b.…”

Section: Introductionmentioning

confidence: 99%

Aluminium oxide in the atmosphere of hot Jupiter WASP-43b

Chubb

Min

Kawashima

et al. 2020

A&A

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We have conducted a re-analysis of publicly available Hubble Space Telescope Wide Field Camera 3 (HST WFC3) transmission data for the hot-Jupiter exoplanet WASP-43b, using the Bayesian retrieval package Tau-REx. We report evidence of AlO in transmission to a high level of statistical significance (>5σ in comparison to a flat model, and 3.4σ in comparison to a model with H2O only). We find no evidence of the presence of CO, CO2, or CH4 based on the available HST WFC3 data or on Spitzer IRAC data. We demonstrate that AlO is the molecule that fits the data to the highest level of confidence out of all molecules for which high-temperature opacity data currently exists in the infrared region covered by the HST WFC3 instrument, and that the subsequent inclusion of Spitzer IRAC data points in our retrieval further supports the presence of AlO. H2O is the only other molecule we find to be statistically significant in this region. AlO is not expected from the equilibrium chemistry at the temperatures and pressures of the atmospheric layer that is being probed by the observed data. Its presence therefore implies direct evidence of some disequilibrium processes with links to atmospheric dynamics. Implications for future study using instruments such as the James Webb Space Telescope are discussed, along with future opacity needs. Comparisons are made with previous studies into WASP-43b.

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“…Objects other than Mira were studied in this context as well. The AGB star W Hya was imaged at a high resolution with ALMA and its AlO emission shows similar features as these seen in Mira: it extends only out to ∼3 R and shows strong inhomogenities with the azimuthal angle (Takigawa et al (2017)). Fortunately, within 150 days of the ALMA observations, W Hya was observed with VLT/SPHERE in scat-8 Tomek Kamiński Figure 6.…”

Section: Alo and Aloh As The Alumina-dust Precursors In Agb Starsmentioning

confidence: 77%

Molecular dust precursors in envelopes of oxygen-rich AGB stars and red supergiants

Kamiński

2018

Proc. IAU

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Condensation of circumstellar dust begins with formation of molecular clusters close to the stellar photosphere. These clusters are predicted to act as condensation cores at lower temperatures and allow efficient dust formation farther away from the star. Recent observations of metal oxides, such as AlO, AlOH, TiO, and TiO2, whose emission can be traced at high angular resolutions with ALMA, have allowed first observational studies of the condensation process in oxygen-rich stars. We are now in the era when depletion of gas-phase species into dust can be observed directly. I review the most recent observations that allow us to identify gas species involved in the formation of inorganic dust of AGB stars and red supergiants. I also discuss challenges we face in interpreting the observations, especially those related to nonequilibrium gas excitation and the high complexity of stellar atmospheres in the dust-formation zone.

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Dust formation and wind acceleration around the aluminum oxide–rich AGB star W Hydrae

Abstract: AlO and 29SiO distributions around W Hya showed that AlO efficiently forms dust and contributes to the wind acceleration.

Cited by 48 publications

References 28 publications

Study of the aluminium content in AGB winds using ALMA

Study of the aluminium content in AGB winds using ALMA

Aluminium oxide in the atmosphere of hot Jupiter WASP-43b

Molecular dust precursors in envelopes of oxygen-rich AGB stars and red supergiants

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