A high-resolution line survey of IRC +10216 with<i>Herschel</i>/HIFI

Cernicharo, J.; Waters, L. B. F. M.; Decin, L.; Encrenaz, P.; Tielens, A. G. G. M.; Agúndez, M.; Beck, E. De; Müller, H. S. P.; Goicoechea, J. R.; Barlow, M. J.; Benz, A. O.; Crimier, N.; Daniel, F.; Giorgio, A. M. Di; Fich, M.; Gaier, T.; García-Lario, P.; Koter, A. de; Khouri, T.; Liseau, R.; Lombaert, R.; Erickson, N. R.; Pardo, J. R.; Pearson, John C.; Shipman, R.; Contreras, C. Sánchez; Teyssier, D.

doi:10.1051/0004-6361/201015150

Cited by 80 publications

(79 citation statements)

References 38 publications

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“…In these cases the uncertainties on the predicted frequencies were below 0.1 MHz. Moreover, the J = 7-6 line of several vibrational levels of HCN have been observed by Cernicharo et al (2010) using these predictions. The observed minus calculated frequencies never exceed 2 MHz.…”

Section: Observations and Resultsmentioning

confidence: 85%

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Cernicharo

Agúndez

Kahane

et al. 2011

A&A

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We report the detection in IRC +10216 of 63 rotational transitions of HCN, most of them with quantum numbers J = 3-2, pertaining to 28 different vibrational states with energies up to 10 700 K (ν 1 +3ν 2 +ν 3 ). Some of the transitions were also observed for the rare isotopologue H 13 CN. The observations were carried out with the IRAM 30-m telescope. The HCN lines with level energies above 5000 K arise within 1.5 stellar radius from the photosphere. Their intensities imply a vibrational temperature of T vib 2400 K and a fractional HCN abundance relative to H 2 , x(HCN) = 5-7 × 10 −5 . These high-energy levels are mainly populated by photospheric radiation, and their vibrational temperature yields a direct measurement of the stellar photospheric temperature. The lines with energy levels between 2000 and 5000 K yield T vib 1300 K and x(HCN) 0.8-2 × 10 −5 . They are radiatively excited and arise from a shell extending between 1.5 and 5 stellar radii. Finally, the lines from the low-energy vibrational states (<2000 K) trace a larger region of the envelope (5-28 stellar radii) with T vib = 400-600 K and x(HCN) = 4-6× 10 −6 . They are strongly affected by mid and near-infrared pumping. The line widths increase from 5 km s −1 near the 2400 K photosphere, to 19 km s −1 in the warm 400 K shell. This provides a unique insight into the physical conditions of the gas acceleration and dust formation region.

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Section: Observations and Resultsmentioning

confidence: 85%

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Cernicharo

Agúndez

Kahane

et al. 2011

A&A

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“…The cited column density for this molecule in Table 3 is 2.0 ×10 14 cm −2 (Thaddeus et al 1984). However, according to a more recent study by Cernicharo et al (2010) employing high quality Herschel/HIFI spectra an average column density of ∼6.4 × 10 15 cm −2 was found. Our computed value, 2.6 × 10 15 cm −2 , is in better agreement with the latter observed value.…”

Section: Column Densitymentioning

confidence: 79%

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

Millar

Walsh

et al. 2014

A&A

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Context. The envelopes of asymptotic giant branch (AGB) stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N 2 and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N 2 has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. Aims. For the first time, we use accurate N 2 and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. Methods. We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N 2 photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. Results. The transition of N 2 → N (also, CO → C → C + ) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, C n N (n = 1, 3, 5), C n N − (n = 1, 3, 5), HC n N (n = 1, 3, 5, 7, 9), H 2 CN and CH 2 CN. Conclusions. The chemistry of many species is directly or indirectly affected by the photodissociation of N 2 and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N 2 and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.

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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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A high-resolution line survey of IRC +10216 withHerschel/HIFI

Cited by 80 publications

References 38 publications

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

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

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A high-resolution line survey of IRC +10216 withHerschel/HIFI

Cited by 80 publications

References 38 publications

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Photodissociation and chemistry of N2in the circumstellar envelope of carbon-rich AGB stars

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

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Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

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