Warm water vapour in the sooty outflow from a luminous carbon star

Decin, L.; Agúndez, M.; Barlow, M. J.; Daniel, F.; Cernicharo, J.; Lombaert, R.; Beck, E. De; Royer, P.; Vandenbussche, B.; Wesson, R.; Polehampton, E. T.; Blommaert, J. A. D. L.; Meester, W. De; Exter, Katrina; Feuchtgruber, H.; Gear, Walter Kieran; Gomez, Haley Louise; Groenewegen, M. A. T.; Guèlin, M.; Hargrave, Peter Charles; Huygen, R.; Imhof, P.; Ivison, R. J.; Jean, C.; Kahane, C.; Kerschbaum, F.; Leeks, S. J.; Lim, T.; Matsuura, M.; Olofsson, G.; Posch, Th.; Regibo, S.; Savini, G.; Sibthorpe, B.; Swinyard, Bruce; Yates, J. A.; Waelkens, C.

doi:10.1038/nature09344

Cited by 89 publications

(122 citation statements)

References 38 publications

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“…The total H 2 O abundance is then ≈1.2 × 10 −5 placing it in between the values typically determined for M-type AGB stars (Justtanont et al 2005;Maercker et al 2008Maercker et al , 2009Decin et al 2010c) and carbon stars (Melnick et al 2001;Hasegawa et al 2006;Decin et al 2010a;Neufeld et al 2010Neufeld et al , 2011. Justtanont et al (2010) derived a total H 2 O abundance of ≈1.1 × 10 −5 for χ Cyg in excellent agreement with the analysis performed here.…”

Section: Oxygen-bearing Moleculessupporting

confidence: 76%

“…Such H 2 O abundances can be explained by a stellar atmosphere equilibrium chemistry. In contrast, to explain the detection of H 2 O in the extreme carbon star IRC +10216 (Melnick et al 2001;Hasegawa et al 2006), even higher abundances in the carbon star V Cyg (Neufeld et al 2010), and the ubiquitous occurrence of H 2 O in CSEs around carbon stars (Neufeld et al 2011), requires some effective nonequilibrium chemical process (Willacy 2004), the influx of H 2 O through the evaporation of icy-bodies (Melnick et al 2001), or, as recently suggested by Decin et al (2010a), the penetration of interstellar ultraviolet photons deep into a clumpy CSE, thereby affecting the chemistry. A study of the S-type AGB star χ Cyg suggests that this type of stars has an intermidiate circumstellar H 2 O abundance (Justtanont et al 2010).…”

Section: Introductionmentioning

confidence: 99%

“…Possibly, a shock-induced chemistry which is very sensitive to the physical conditions could be important, as the C/O ratio appears to only have a minor effect for S-stars (Cherchneff 2006). Also clumpiness can possibly lead to chemical signatures that deviate from the expected (Agúndez et al 2010;Decin et al 2010a). …”

Section: Carbon-bearing Moleculesmentioning

confidence: 99%

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A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

Schöier

Maercker

Justtanont

et al. 2011

A&A

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Context. S-type AGB stars (C/O ≈ 1) are thought to be transition objects from M-type (O-rich) AGB stars to carbon stars and as such are interesting objects in themselves. Of particular interest is to determine accurate circumstellar properties and molecular abundances, due to their predicted sensitivity to the photospheric C/O-ratio. Aims. Presented here are new sensitive sub-millimetre line observations of molecules towards the S-type AGB star χ Cyg, using the HIFI instrument on-board the Herschel Space Observatory. The observed lines predominantly probe warm gas relatively close to the central star. Methods. Detailed, non-LTE, radiative transfer modelling has been used in order to interpret the circumstellar molecular line observations performed using HIFI, assuming a spherically symmetric, smooth, accelerating wind. Results. Lines from common molecules such as H 2 O, CO and SiO, which are expected to be abundant in an S-type AGB star, are clearly detected (as well as some of their isotopologues) in the HIFI spectra. In addition, we detect lines from carbon-bearing molecules such as HCN and CN. The CO line modelling indicates that the mass-loss rate has not undergone any significant modulations during the past ≈1000 yr. The derived o-H 2 O fractional abundance is ≈7 × 10 −6 , i.e., lower than those obtained for a small sample of M-type AGB stars but higher than what has been derived for a few carbon stars. We further obtain a p-H 2 O fractional abundance of ≈5 × 10 −6 giving an o/p-ratio of ≈1.4. Molecular line cooling is dominated by H 2 O only in a region close to the star ( 6 × 10 14 cm). The SiO abundance is estimated to be ≈1 × 10 −5 . The 12 CO/ 13 CO ratio is 43 ± 6. The high-excitation rotational lines clearly probe the acceleration region of the stellar wind ( 2 × 10 15 cm) and put constraints on dynamical wind models. We are unable to fit consistently the combined ground-based and HIFI data for HCN and CN. Conclusions. The derived H 2 O abundance is reasonably consistent with recent chemical model predictions and so is the SiO abundance. The o/p-ratio of ≈1.4 supports a chemical formation under non-LTE conditions for the H 2 O molecules, and the presence of carbon-bearing molecules at relatively large abundances is also indicative of the importance of non-LTE chemical processes in regulating the circumstellar chemistry. The velocity field derived from the molecular line modelling is consistent with that obtained from solving for the wind dynamics through the coupled momentum equations of the dust and gas particles.

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Section: Oxygen-bearing Moleculessupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

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A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

Schöier

Maercker

Justtanont

et al. 2011

A&A

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“…In particular, observations of CO emission lines have proven to be a useful tool to describe the mass loss (e.g., Schöier et al 2002;González Delgado et al 2003;Ramstedt et al 2008;De Beck et al 2010;Khouri et al 2014a). Observations of other molecules have led to important insights in the chemistry and structure of AGB CSEs (e.g., González Delgado et al 2003;Schöier et al 2007;Maercker et al 2008Maercker et al , 2009Decin et al 2010a;Cernicharo et al 2010Cernicharo et al , 2011De Beck et al 2012;Justtanont et al 2012;Khouri et al 2014b; Lombaert et al 2016).…”

Section: Introductionmentioning

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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“…T he great advances experienced by radioastronomy during recent years have depicted the interstellar medium (ISM) and circumstellar envelopes (CSE) as supporting an active and rich chemistry 1 . In these cosmic regions, both simple molecules, such as H 2 or CO, and complex ones, such as C 60 and polycyclic aromatic hydrocarbons (PAHs), are routinely detected by their characteristic infrared spectrum 2,3 .…”

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confidence: 99%

Graphene etching on SiC grains as a path to interstellar polycyclic aromatic hydrocarbons formation

et al. 2014

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Polycyclic aromatic hydrocarbons as well as other organic molecules appear among the most abundant observed species in interstellar space and are key molecules to understanding the prebiotic roots of life. However, their existence and abundance in space remain a puzzle. Here we present a new top-down route to form polycyclic aromatic hydrocarbons in large quantities in space. We show that aromatic species can be efficiently formed on the graphitized surface of the abundant silicon carbide stardust on exposure to atomic hydrogen under pressure and temperature conditions analogous to those of the interstellar medium. To this aim, we mimic the circumstellar environment using ultra-high vacuum chambers and investigate the SiC surface by in situ advanced characterization techniques combined with first-principles molecular dynamics calculations. These results suggest that top-down routes are crucial to astrochemistry to explain the abundance of organic species and to uncover the origin of unidentified infrared emission features from advanced observations.

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Warm water vapour in the sooty outflow from a luminous carbon star

Cited by 89 publications

References 38 publications

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

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

Graphene etching on SiC grains as a path to interstellar polycyclic aromatic hydrocarbons formation

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Warm water vapour in the sooty outflow from a luminous carbon star

Cited by 89 publications

References 38 publications

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

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

Graphene etching on SiC grains as a path to interstellar polycyclic aromatic hydrocarbons formation

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