ALMA observations of the vibrationally excited rotational CO transition <i>v</i> = 1, <i>J</i> = 3 − 2 towards five AGB stars

Khouri, T.; Vlemmings, Wouter; Ramstedt, S.; Lombaert, R.; Maercker, M.; Beck, E. De

doi:10.1093/mnrasl/slw161

Cited by 21 publications

(20 citation statements)

References 21 publications

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“…To determine the robustness of this detection we perform similar calculations for other features in the spectra that span more than four channels, but none of these exceed a 2σ detection threshold. As noted above, the temperature of our best fit warm layer is also consistent with similar warm layers found from infrared CO observations (27) and…”

Section: ) Co J=3-2 V=1 Modelingsupporting

confidence: 90%

“…In addition to the stellar continuum emission, the observations also covered the pure-rotational CO transition, J=3-2, in the first vibrationally excited state, v=1, at 342.647 GHz. This transition, with an upper level at ~3120 K, is a unique probe of the warm gas in the extended AGB atmosphere (27). The line was detected both in absorption towards the star and in emission around the star, as indicated in the velocity channel maps shown in Supplementary Figure 1.…”

Section: Kmentioning

confidence: 77%

“…GHz (v=1, J=3-2) (35), we calculated radiative-transfer models consisting of a spherical symmetric circumstellar envelope extending radially from the measured R *,338 out to the outer radius of the line emission region, R out , at 2.4 R★ (4.8 au). The model is based on the one presented in (27), but was modified to include three different layers, the outflowing gas, the inflowing gas, and the warm gas (T > 2400 K). The density and excitation temperature of CO in a given layer are assumed to be constant for simplicity.…”

Section: ) Co J=3-2 V=1 Modelingmentioning

confidence: 99%

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The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA

et al. 2017

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Our current understanding of the chemistry and mass-loss processes in solar-like stars at the end of their evolution depends critically on the description of convection, pulsations and shocks in the extended stellar atmosphere (1). Threedimensional hydrodynamical stellar atmosphere models provide observational predictions (2), but so far the resolution to constrain the complex temperature and velocity structures seen in the models has been lacking. Here we present submillimeter continuum and line observations that resolve the atmosphere of the asymptotic giant branch star W Hya. We show that hot gas with chromospheric characteristics exists around the star. Its filling factor is shown to be small. The existence of such gas requires shocks with a cooling time larger than commonly assumed. A shocked hot layer will be an important ingredient in the models of stellar convection, pulsation and chemistry that underlie our current understanding of the late stages of stellar evolution.Asymptotic giant branch (AGB) stars are among the most important sources of enrichment of the Galactic interstellar medium (ISM). Molecules and dust formed in the warm extended atmospheres and the cool and dense circumstellar envelopes (CSEs) around AGB stars are injected into the ISM by a stellar wind that has overcome stellar gravity (1). It is generally assumed that the stellar wind is driven by radiation pressure on dust that forms at a few stellar radii, where the temperature in the CSE has dropped so that dust condensation can occur (3). In order for the gas in the extended stellar atmosphere to reach the dust formation region, the most recent AGB mass-loss models typically invoke stellar pulsations and convective motions (2,(4)(5)(6).Both convective motions and pulsations induce outward moving shocks that critically affect the upper layers of the AGB atmosphere where the stellar mass loss is determined. The propagation of shocks also strongly affects the chemistry in the stellar atmosphere (7-9). In early AGB atmosphere models, the outward propagation of strong shocks is responsible for the creation of a chromosphere (6, 10), from which ultraviolet line and continuum emissions originate. Such emissions have been observed from AGB stars (11,12). However, the observations of molecules and dust close to the star are not consistent with the extended chromosphere produced by the models. Observations have so far not been able to resolve this ambiguity. High angular resolution images of the stellar disks of AGB stars have revealed asymmetries of which the source is not yet clear, but convective motions are believed to play a role (13)(14)(15)(16). Since at most wavelengths, the observations are probing distinct molecular opacity sources (16), or averages over the stellar disk (17), the dynamics and temperature structures in the atmosphere closest to the stellar photosphere have not yet been observed in detail.We present observations of the AGB star W Hya that reveal evidence for the presence of shocks and map the distribution of molecular g...

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Section: ) Co J=3-2 V=1 Modelingsupporting

confidence: 90%

Section: Kmentioning

confidence: 77%

Section: ) Co J=3-2 V=1 Modelingmentioning

confidence: 99%

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The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA

et al. 2017

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“…Historically, vibrationally excited rotational transitions of SiO [27,28] and HCN [29][30][31] have been frequently detected, often thanks to maser activity. These are now joined by a plethora of other molecules in vibrationally excited states such as CO [32], H 2 O [33,34], SiS, SO, SO 2 [35], and others. Of course, the identification of these vibrationally excited lines requires their presence in line lists, which is true of the molecules listed above.…”

Section: Radiative Ratesmentioning

confidence: 99%

Molecular Data Needs for Modelling AGB Stellar Winds and Other Molecular Environments

2018

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Abstract:The modern era of highly sensitive telescopes is enabling the detection of more and more molecular species in various astronomical environments. Many of these are now being carefully examined for the first time. However, to move beyond detection to more detailed analysis such as radiative transfer modelling, certain molecular properties need to be properly measured and calculated. The importance of contributions from vibrationally excited states or collisional (de-)excitations can vary greatly, depending on the specific molecule and the environment being studied. Here, we discuss the present molecular data needs for detailed radiative transfer modelling of observations of molecular rotational transitions, primarily in the (sub-)millimetre and adjacent regimes, and with a focus on the stellar winds of AGB stars.

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“…High-resolution spectroscopy, on the other hand, is limited to 96 S. Höfner smaller samples, but provides critical quantitative information on atmospheric and wind dynamics via line profiles. In particular, CO vibration-rotation lines at near-IR wavelengths have been used successfully in that context, e.g., Hinkle et al (1982), Scholz & Wood (2000), Nowotny et al (2010); however, profile variability of rotational CO lines in the radio regime have also been detected recently with ALMA by Khouri et al (2016a). The recent progress in high-angular-resolution imaging and spectro-interferometry, spanning wavelengths from the visual to the radio regime, has made it possible to observe evolving dynamical structures directly on the surfaces and in the dusty atmospheres of a few nearby cool giants, and in real time, e.g., Haubois et al (2015), Khouri et al (2016b), Ohnaka et al (2017).…”

Section: Variability Of Agb Stars: Observations and Modelsmentioning

confidence: 99%

Variability, Pulsations and Mass Loss of Evolved Stars

Höfner

2017

Proc. IAU

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Evolved low- and intermediate-mass stars that have reached the Asymptotic Giant Branch (AGB) phase tend to show pronounced long-period variability due to large-amplitude pulsations. Those pulsations are considered to play a key role in triggering mass loss through massive dusty winds. The winds enrich the surrounding interstellar medium with newly-produced chemical elements and dust grains, providing building blocks for new generations of stars and planets. Considerable efforts are being made to understand the physics of AGB stars, and to develop quantitative models. This talk gave a brief summary of recent developments, with references to the literature.

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ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars

Cited by 21 publications

References 21 publications

The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA

The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA

Molecular Data Needs for Modelling AGB Stellar Winds and Other Molecular Environments

Variability, Pulsations and Mass Loss of Evolved Stars

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