Oxygen-rich Mass Loss with a Pinch of Salt: NaCl in the Circumstellar Gas of IK Tauri and VY Canis Majoris

Milam, Stefanie N.; Apponi, A. J.; Woolf, N. J.; Ziurys, L. M.

doi:10.1086/522928

Cited by 48 publications

(59 citation statements)

References 22 publications

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“…This is in accord with thermochemical equilibrium predictions, not taking phase changes into account, predicting that the gaseous NaCl abundance peaks around 500 to 1200 K at densities n ∼ 10 11 cm −3 (see Fig. 3 in Milam et al 2007), with NaCl being the main sodium carrier in oxygen-rich environments 3 . For temperatures above 1500 K, the fractional abundance of gaseous NaCl is below 10 −12 .…”

Section: Discussionsupporting

confidence: 88%

“…The 22 GHz and 321 GHz H 2 O maser features at the greatest angular separations lie approximately east and west or to the southwest. Milam et al (2007) observed several rotational lines in the ground vibrational state of NaCl using single-dish telescopes with beam sizes between 29 -44 . The NaCl emission was spatially unresolved and modelling the observed spectra resulted in an abundance relative to H 2 of 5 × 10 −9 with a source size of 0.5 .…”

Section: Morphological Comparison To Other Tracers Of the Envelopementioning

confidence: 99%

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ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Decin

Richards

Millar

et al. 2016

A&A

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Context. At the end of their lives, most stars lose a significant amount of mass through a stellar wind. The specific physical and chemical circumstances that lead to the onset of the stellar wind for cool luminous stars are not yet understood. Complex geometrical morphologies in the circumstellar envelopes prove that various dynamical and chemical processes are interlocked and their relative contributions are not easy to disentangle. Aims. We aim to study the inner-wind structure (R < 250 R ) of the well-known red supergiant VY CMa, the archetype for the class of luminous red supergiant stars suffering high mass loss. Specifically, the objective is to unravel the density structure in the inner envelope and to examine the chemical interaction between some gas and dust species. Methods. We analyse high spatial resolution (∼ 0 . 24 × 0 . 13) ALMA Science Verification (SV) data in band 7 in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. Results. For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ∼50• measured from north to east. However, this picture can not capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profiles is significantly lower than the average wind terminal velocity, and much slower than some of the fastest mass ejections, signalling a wide range of characteristic speeds for the mass loss. Gaseous NaCl is detected far beyond the main dust condensation region. Realising the refractory nature of this metal halide, this hints at a chemical process preventing all NaCl from condensing onto dust grains. We show that in the case of the ratio of the surface binding temperature to the grain temperature being ∼50, only some 10% of NaCl remains in gaseous form, while for lower values of this ratio thermal desorption efficiently evaporates NaCl. Photodesorption by stellar photons seems not to be a viable explanation for the detection of gaseous NaCl at 220 R from the central star, and instead, we propose shock-induced sputtering driven by localized mass ejection events as alternative. Conclusions. The analysis of the NaCl lines demonstrate the capabilities of ALMA to decode the geometric morphologies and chemical pathways prevailing in the winds of evolved stars. These early ALMA results prove that the envelopes surrounding evolved stars are far from homogeneous, and that a variety of dynamical and chemical processes dictate the wind structure.

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Section: Discussionsupporting

confidence: 88%

Section: Morphological Comparison To Other Tracers Of the Envelopementioning

confidence: 99%

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Decin

Richards

Millar

et al. 2016

A&A

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“…The main Gaussianlike component of the TiO emission, however, is very likely formed in the inner outflow because it is centrally peaked and much narrower than 2V ∞ . Similar narrow molecular emission lines in VY CMa have been attributed to the accelerating wind (e.g., Milam et al 2007). Following Tenenbaum & Ziurys (2009) and Kamiński et al (2013), to better localize the TiO emission region we use the semi-empirical windacceleration model in VY CMa constrained from multi-epoch observations of H 2 O masers (Richards et al 1998).…”

Section: Localization and Abundances Of The Tio And Tio 2 Gasmentioning

confidence: 94%

Pure rotational spectra of TiO and TiO₂in VY Canis Majoris

Kamiński

Gottlieb

Menten

et al. 2013

A&A

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We report the first detection of pure rotational transitions of TiO and TiO 2 at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational temperature, T rot , of about 250 K was derived for TiO 2 . Although T rot was not well constrained for TiO, it is likely somewhat higher than that of TiO 2 . The detection of the Ti oxides confirms that they are formed in the circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of inorganic-dust formation, but alternative explanations for our observation of TiO and TiO 2 in the cooler regions of the envelope cannot be ruled out at this time. The observations suggest that a significant fraction of the oxides is not converted to dust, but instead remains in the gas phase throughout the outflow.

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“…The angular diameter is estimated around 20 mas (Decin et al 2010a). Currently, a dozen different molecules and some of their isotopologues have been discovered in IK Tau, including CO, HCN, SiO, SiS, SO, SO 2 , NaCl, NS, NO, HCO + , H 2 CO, PO, PN, and H 2 S (Milam et al 2007;Kim et al 2010;Decin et al 2010a,b;De Beck et al 2013Velilla Prieto et al 2017). Some molecules including SiO and SiS are depleted in the circumstellar envelope, possibly owing to condensation onto dust grains.…”

Section: Target Selectionmentioning

confidence: 99%

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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Oxygen-rich Mass Loss with a Pinch of Salt: NaCl in the Circumstellar Gas of IK Tauri and VY Canis Majoris

Cited by 48 publications

References 22 publications

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Pure rotational spectra of TiO and TiO₂in VY Canis Majoris

Study of the aluminium content in AGB winds using ALMA

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Oxygen-rich Mass Loss with a Pinch of Salt: NaCl in the Circumstellar Gas of IK Tauri and VY Canis Majoris

Cited by 48 publications

References 22 publications

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Pure rotational spectra of TiO and TiO2in VY Canis Majoris

Study of the aluminium content in AGB winds using ALMA

Contact Info

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Pure rotational spectra of TiO and TiO₂in VY Canis Majoris