Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Marigo, Paola; Ripamonti, E.; Nanni, Ambra; Bressan, A.; Girardi, L.

doi:10.1093/mnras/stv2547

Cited by 15 publications

(17 citation statements)

References 92 publications

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“…From Table 1 Marigo et al 2016), the similarly scaled line brightness temperatures become 6700 − 1 × 10 5 K. This is too high for thermal line emission. Thus, the observed line variations can not solely come from the small shock region, unless some of them are masers.…”

Section: Interpretation Of the Line Strength Variationmentioning

confidence: 91%

Monitor Variability of Millimeter Lines in IRC+10216

Dinh-V-Trung

Hasegawa

2017

ApJ

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A single dish monitoring of millimeter maser lines SiS J=14-13 and HCN ν 2 = 1 f J=3-2 and several other rotational lines is reported for the archetypal carbon star IRC +10216. Relative line strength variations of 5%∼30% are found for eight molecular line features with respect to selected reference lines. Definite line-shape variation is found in limited velocity intervals of the SiS and HCN line profiles. The asymmetrical line profiles of the two lines are mainly due to the varying components. Their dominant varying components of the line profiles have similar periods and phases as the IR light variation, although both quantities show some degree of velocity dependence; there is also variability asymmetry between the blue and red line wings of both lines. Combining the velocities and amplitudes with a wind velocity model, we suggest that the line profile variations are due to SiS and HCN masing lines emanating from the wind acceleration zone. The possible link of the variabilities to thermal, dynamical and/or chemical processes within or under this region is also discussed.

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Section: Interpretation Of the Line Strength Variationmentioning

confidence: 91%

Monitor Variability of Millimeter Lines in IRC+10216

Dinh-V-Trung

Hasegawa

2017

ApJ

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“…Mass-loss rates,Ṁ, on the AGB are found to range from ∼10 −8 -10 −4 M yr −1 (e.g., Höfner & Olofsson 2018, and references therein). It is challenging to find reliable observational methods to measure mass-loss rates covering this wide range (Ramstedt et al 2008), but it is crucial since the measurements will provide key constraints for theoretical models (e.g., Eriksson et al 2014;Marigo et al 2016;Bladh et al 2019). Wind formation is studied using dynamical wind models (e.g., Höfner 2008;Eriksson et al 2014;Bladh et al 2015;Höfner et al 2016) with the ultimate goal of developing a predictive theory of AGB mass loss.…”

Section: Introductionmentioning

confidence: 99%

DEATHSTAR: Nearby AGB stars with the Atacama Compact Array

Ramstedt

Vlemmings

Doan

et al. 2020

A&A

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Context. This is the first publication from the DEATHSTAR project. The overall goal of the project is to reduce the uncertainties of the observational estimates of mass-loss rates from evolved stars on the Asymptotic Giant Branch (AGB). Aim. The aim in this first publication is to constrain the sizes of the 12CO emitting region from the circumstellar envelopes around 42 mostly southern AGB stars, of which 21 are M-type and 21 are C-type, using the Atacama Compact Array (ACA) at the Atacama Large Millimeter/submillimeter Array. The symmetry of the outflows is also investigated. Methods. Line emission from 12CO J = 2→1 and 3→2 from all of the sources were mapped using the ACA. In this initial analysis, the emission distribution was fit to a Gaussian distribution in the uv-plane. A detailed radiative transfer analysis will be presented in a future publication. The major and minor axis of the best-fit Gaussian at the line center velocity of the 12CO J = 2→1 emission gives a first indication of the size of the emitting region. Furthermore, the fitting results, such as the Gaussian major and minor axis, center position, and the goodness of fit across both lines, constrain the symmetry of the emission distribution. For a subsample of sources, the measured emission distribution is compared to predictions from previous best-fit radiative transfer modeling results. Results. We find that the CO envelope sizes are, in general, larger for C-type than for M-type AGB stars, which is as expected if the CO/H2 ratio is larger in C-type stars. Furthermore, the measurements show a relation between the measured (Gaussian) 12CO J = 2→1 size and circumstellar density that, while in broad agreement with photodissociation calculations, reveals large scatter and some systematic differences between the different stellar types. For lower mass-loss-rate irregular and semi-regular variables of both M- and C-type AGB stars, the 12CO J = 2→1 size appears to be independent of the ratio of the mass-loss rate to outflow velocity, which is a measure of circumstellar density. For the higher mass-loss-rate Mira stars, the 12CO J = 2→1 size clearly increases with circumstellar density, with larger sizes for the higher CO-abundance C-type stars. The M-type stars appear to be consistently smaller than predicted from photodissociation theory. The majority of the sources have CO envelope sizes that are consistent with a spherically symmetric, smooth outflow, at least on larger scales. For about a third of the sources, indications of strong asymmetries are detected. This is consistent with what was found in previous interferometric investigations of northern sources. Smaller scale asymmetries are found in a larger fraction of sources. Conclusions. These results for CO envelope radii and shapes can be used to constrain detailed radiative transfer modeling of the same stars so as to determine mass-loss rates that are independent of photodissociation models. For a large fraction of the sources, observations at higher spatial resolution will be necessary to deduce the nature and origin of the complex circumstellar dynamics revealed by our ACA observations.

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“…They include the presence of shocks that substantially change our view of the chemistry in the envelopes of pulsating giants (e.g. Willacy & Cherchneff 1998;Cherchneff 2006;Marigo et al 2016;Millar 2016). Recent models highlight the chief role of Al oxides as a separate form of warm dust in AGB stars (Gobrecht et al 2016).…”

Section: Introductionmentioning

confidence: 99%

An observational study of dust nucleation in Mira (o Ceti)

Kamiński

Wong

Schmidt

et al. 2016

A&A

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Context. Dust is efficiently produced by cool giant stars, but the condensation of inorganic dust is poorly understood. Observations of key aluminum bearing molecules around evolved stars has enabled us to investigate the nucleation of alumina (Al 2 O 3 ) dust in the gas. Aims. We aim to identify and characterize aluminum bearing species in the circumstellar gas of Mira (o Ceti) in order to elucidate their role in the production of Al 2 O 3 dust. Methods. We used multiepoch spectral line observations at (sub-)millimeter, far-infrared, and optical wavelengths including: maps with ALMA that probe the gas distribution in the immediate vicinity of the star at ∼30 mas; observations with ALMA, APEX, and Herschel in 2013−2015 for studying cycle and inter-cycle variability of the rotational lines of Al-bearing molecules; optical records as far back as 1965 to examine variations in electronic transitions over time spans of days to decades; and velocity measurements and excitation analysis of the spectral features that constrain the physical parameters of the gas.Results. Three diatomic molecules AlO, AlOH, and AlH, and atomic Al i are the main observable aluminum species in Mira, although a significant fraction of aluminum might reside in other species that have not yet been identified. Strong irregular variability in the (sub-)millimeter and optical features of AlO (possibly the direct precursor of Al 2 O 3 ) indicates substantial changes in the excitation conditions, or varying abundance that is likely related to shocks in the star. The inhomogeneous distribution of AlO might influence the spatial and temporal characteristics of dust production. Conclusions. We are unable to quantitatively trace aluminum depletion from the gas, but the rich observational material constrains time-dependent chemical networks. Future improvements should include spectroscopic characterization of higher aluminum oxides, coordinated observations of dust and gas species at different variability phases, and tools to derive abundances in shock-excited gas.

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Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Cited by 15 publications

References 92 publications

Monitor Variability of Millimeter Lines in IRC+10216

Monitor Variability of Millimeter Lines in IRC+10216

DEATHSTAR: Nearby AGB stars with the Atacama Compact Array

An observational study of dust nucleation in Mira (o Ceti)

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