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Willacy, Karen; Millar, T. J.

doi:10.1023/a:1000779327010

Cited by 76 publications

(195 citation statements)

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“…A similar high abundance of HCN has also been derived for oxygen-rich (O-rich) asymptotic giant branch (AGB) stars Decin et al 2010). Photochemical predictions for the outer envelope of O-rich AGB stars (Willacy & Millar 1997) are clearly too low by at least an order of magnitude. Pulsation driven shock models can account for this high concentration of HCN, yielding a HCN fractional abundance in the inner wind (between 2.2 and 5 R ) ranging from 2 × 10 −6 to 1 × 10 −5 (Duari et al 1999;Cherchneff 2006).…”

Section: Modeling the Envelope: Co H 2 O Hcn And Siosupporting

confidence: 56%

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PACS and SPIRE spectroscopy of the red supergiant VY CMa

Royer¹,

Decin

Wesson

et al. 2010

A&A

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With a luminosity >10 5 L and a mass-loss rate of ∼2 × 10 −4 M yr −1 , the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55-672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as ∼1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.

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Section: Modeling the Envelope: Co H 2 O Hcn And Siosupporting

confidence: 56%

“…Both inner wind shock-induced nonequilibrium chemistry (Duari et al 1999;Cherchneff 2006) and outer wind photochemical processes (Willacy & Millar 1997) predict almost the same abundance value. Zubko & Elitzur (2000) and 1:1 by Barlow et al (1996)).…”

Section: Hcnmentioning

confidence: 93%

PACS and SPIRE spectroscopy of the red supergiant VY CMa

Royer¹,

Decin

Wesson

et al. 2010

A&A

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“…1). Using the analytical formula from Groenewegen (1994), we calculated a photodissociation radius of 2.8 × 10 16 cm or 1870 R , while the theoretical models by Willacy & Millar (1997) predict a value around 1600 R . Assuming the same photodissociation radius for all isotopologs and isomers, we deduced (see Appendix B) a water-abundance [ortho-H 16 2 O/H 2 ] = 5 × 10 −5 and an orthoto-para water ratio (OPR) of 3:1.…”

Section: Resultsmentioning

confidence: 99%

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

Decin

Justtanont

Beck

et al. 2010

A&A

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During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the highresolution HIFI spectrometer onboard Herschel. We report on the first detection of H 16 2 O and the rarer isotopologues H 17 2 O and H 18 2 O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10 −5 , and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H 2 O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12 CO, 13 CO, 28 SiO, 29 SiO, 30 SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.

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“…τ d is the dust optical depth at 10 µm, υ ∞ the terminal gas expansion velocity, β the exponent of the velocity law, d/g the derived dust-to-gas ratio,Ṁ the gas mass-loss rate, R e the CO-photodissociation radius, δ the average ratio between integrated model and observed line intensities, and χ 2 red the reduced χ 2 value of the best-fit model. AGB stars, Willacy & Millar (1997) use α = −0.6 for R Dor, TX Cam, and IK Tau.…”

Section: Co Modelsmentioning

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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Cited by 76 publications

References 5 publications

PACS and SPIRE spectroscopy of the red supergiant VY CMa

PACS and SPIRE spectroscopy of the red supergiant VY CMa

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

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

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Untitled

Cited by 76 publications

References 5 publications

PACS and SPIRE spectroscopy of the red supergiant VY CMa

PACS and SPIRE spectroscopy of the red supergiant VY CMa

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

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

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