The abundance of HCN in circumstellar envelopes of AGB stars of different chemical type

Schöier, F. L.; Ramstedt, S.; Olofsson, H.; Lindqvist, Michael; Bieging, John H.; Marvel, Kevin B.

doi:10.1051/0004-6361/201220400

Cited by 88 publications

(146 citation statements)

References 64 publications

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“…The SO (1 × 10 −6 ), SiO (5 × 10 −6 ), and CS (1 × 10 −6 ; after correcting the 13 CS abundance by the estimated 12 C/ 13 C ≈ 10) abundances all lie in the range reported for AGB CSEs (Danilovich et al 2016;Schöier et al 2013;Velilla Prieto et al 2017), while the H 2 CO abundance (2 × 10 −6 ; assuming an orthoto-para ratio of 3) is about an order of magnitude higher than in IK Tau (Velilla Prieto et al 2017). CH 3 OH has an estimated abundance of 3 × 10 −6 (assuming an E-to-A ratio of 1), almost two orders of magnitude higher than towards the supergiant IRC+10420 (Quintana-Lacaci et al 2016).…”

Section: Chemistrymentioning

confidence: 61%

First detection of methanol towards a post-AGB object, HD 101584

Olofsson

Vlemmings

Bergman

et al. 2017

A&A

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The circumstellar environments of objects on the asymptotic giant branch and beyond are rich in molecular species. Nevertheless, methanol has never been detected in such an object, and is therefore often taken as a clear signpost for a young stellar object. However, we report the first detection of CH 3 OH in a post-AGB object, HD 101584, using ALMA. Its emission, together with emissions from CO, SiO, SO, CS, and H 2 CO, comes from two extreme velocity spots on either side of the object where a high-velocity outflow appears to interact with the surrounding medium. We have derived molecular abundances, and propose that the detected molecular species are the effect of a post-shock chemistry where circumstellar grains play a role. We further provide evidence that HD 101584 was a low-mass, M-type AGB star.

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Section: Chemistrymentioning

confidence: 61%

First detection of methanol towards a post-AGB object, HD 101584

Olofsson

Vlemmings

Bergman

et al. 2017

A&A

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“…The radius of the CO envelope is determined by models of photodissociation of CO (Mamon et al 1988). The code and modelling method has been used extensively to model the emission lines from various molecules, including CO (e.g., Olofsson et al 2002), SiO (Ramstedt et al 2009), and HCN (Schöier et al 2013).…”

Section: The Basic Co Modelmentioning

confidence: 99%

A HIFI view on circumstellar H₂O in M-type AGB stars: radiative transfer, velocity profiles, and H₂O line cooling

Maercker

Danilovich

Olofsson

et al. 2016

A&A

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Aims. We aim to constrain the temperature and velocity structures, and H 2 O abundances in the winds of a sample of M-type asymptotic giant branch (AGB) stars. We further aim to determine the effect of H 2 O line cooling on the energy balance in the inner circumstellar envelope. Methods. We use two radiative-transfer codes to model molecular emission lines of CO and H 2 O towards four M-type AGB stars. We focus on spectrally resolved observations of CO and H 2 O from HIFI aboard the Herschel Space Observatory. The observations are complemented by ground-based CO observations, and spectrally unresolved CO and H 2 O observations with PACS aboard Herschel. The observed line profiles constrain the velocity structure throughout the circumstellar envelopes (CSEs), while the CO intensities constrain the temperature structure in the CSEs. The H 2 O observations constrain the o-H 2 O and p-H 2 O abundances relative to H 2 . Finally, the radiative-transfer modelling allows to solve the energy balance in the CSE, in principle including also H 2 O line cooling. Results. The fits to the line profiles only set moderate constraints on the velocity profile, indicating shallower acceleration profiles in the winds of M-type AGB stars than predicted by dynamical models, while the CO observations effectively constrain the temperature structure. Including H 2 O line cooling in the energy balance was only possible for the low-mass-loss-rate objects in the sample, and required an ad hoc adjustment of the dust velocity profile in order to counteract extreme cooling in the inner CSE. H 2 O line cooling was therefore excluded from the models. The constraints set on the temperature profile by the CO lines nevertheless allowed us to derive H 2 O abundances. The derived H 2 O abundances confirm previous estimates and are consistent with chemical models. However, the uncertainties in the derived abundances are relatively large, in particular for p-H 2 O, and consequently the derived o/p-H 2 O ratios are not well constrained.

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“…In this initial study we do not consider any process of dust condensation and growth, which we postpone to followup works, and we focus on the hydrogen cyanide molecule, for which observational evidence suggests that the formation is not affected by dust grain formation (Schöier et al 2013).…”

Section: Chemo-dynamic Integrationsmentioning

confidence: 99%

“…Indeed, the HCN molecule has been detected in AGB circumstellar envelopes of all chemical types (Schöier et al 2013;Muller et al 2008;Marvel 2005;Bieging, Shaked, & Gensheimer 2000). Using a detailed radiative transfer model Schöier et al (2013) have recently derived the circumstellar HCN abundances for a large sample of AGB stars, spanning a wide range of properties, mainly in terms of chemical types, mass-loss rates, and expansion velocities.…”

Section: Cse Abundances Of Hydrogen Cyanidementioning

confidence: 99%

“…Thanks to these works the available statistics are being importantly increased, allowing us to get the first insights on the dependence of the CSE chemistry on relevant stellar parameters, such as the spectral type (M, S, C), the pulsation period, and the rate of mass loss. Information of this kind is now available for the circumstellar abundances of SiO (Ramstedt, Schöier, & Olofsson 2009;Schöier, Olofsson, & Lundgren 2006;González Delgado et al 2003), SiS (Schöier et al 2007), and HCN (Schöier et al 2013). As for H2O, we have measures for few M-type stars (Maercker et al 2009); for carbon stars precise estimates are in most cases still missing, though the presence of H2O in significant concentrations is confirmed to be a widespread feature (Neufeld et al 2011a,b).…”

Section: Introductionmentioning

confidence: 96%

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

Marigo

Ripamonti

Nanni

et al. 2015

Mon. Not. R. Astron. Soc.

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We investigate the formation of hydrogen cyanide (HCN) in the inner circumstellar envelopes of thermally pulsing asymptotic giant branch (TP-AGB) stars. A dynamic model for periodically shocked atmospheres, which includes an extended chemo-kinetic network, is for the first time coupled to detailed evolutionary tracks for the TP-AGB phase computed with the COLIBRI code. We carried out a calibration of the main shock parameters (the shock formation radius r s,0 , and the effective adiabatic index γ eff ad ) using the circumstellar HCN abundances recently measured for a populous sample of pulsating TP-AGB stars. Our models recover the range of the observed HCN concentrations as a function of the mass-loss rates, and successfully reproduce the systematic increase of HCN moving along the M-S-C chemical sequence of TP-AGB stars, that traces the increase of the surface C/O ratio. The chemical calibration brings along two important implications for the physical properties of the pulsation-induced shocks: i) the first shock should emerge very close to the photosphere (r s,0 ≃ 1 R), and ii) shocks are expected to have a dominant isothermal character (γ eff ad ≃ 1) in the denser region close to the star (within ∼ 3 − 4 R), implying that radiative processes should be quite efficient. Our analysis also suggests that the HCN concentrations in the inner circumstellar envelopes are critically affected by the H-H 2 chemistry during the post-shock relaxation stages. Given the notable sensitiveness of the results to stellar parameters, this paper shows that such chemo-dynamic analyses may indeed provide a significant contribution to the broader goal of attaining a comprehensive calibration of the TP-AGB evolutionary phase.

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The abundance of HCN in circumstellar envelopes of AGB stars of different chemical type

Cited by 88 publications

References 64 publications

First detection of methanol towards a post-AGB object, HD 101584

First detection of methanol towards a post-AGB object, HD 101584

A HIFI view on circumstellar H₂O in M-type AGB stars: radiative transfer, velocity profiles, and H₂O line cooling

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

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The abundance of HCN in circumstellar envelopes of AGB stars of different chemical type

Cited by 88 publications

References 64 publications

First detection of methanol towards a post-AGB object, HD 101584

First detection of methanol towards a post-AGB object, HD 101584

A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling

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

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A HIFI view on circumstellar H₂O in M-type AGB stars: radiative transfer, velocity profiles, and H₂O line cooling