New observations and models of circumstellar CO line emission of AGB stars in the<i>Herschel</i>SUCCESS programme

Danilovich, T.; Teyssier, D.; Justtanont, K.; Olofsson, H.; Cerrigone, L.; Bujarrabal, V.; Alcolea, J.; Cernicharo, J.; Castro-Carrizo, A.; García-Lario, P.; Marston, A. P.

doi:10.1051/0004-6361/201526705

Cited by 80 publications

(135 citation statements)

References 60 publications

(64 reference statements)

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“…This generally leads to overly resolved model line-profiles for the lower transitions, as evidenced by the double-peaked model line-profiles (specifically discussed for R Dor by Olofsson et al 2002). This is a common problem in CO radiative-transfer models (e.g., Justtanont et al 2005;Maercker et al 2008;Danilovich et al 2015). We attempted to fit the low-J line profiles by reducing the CO envelope size.…”

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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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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“…Herschel/HIFI observations: The 12 CO J=5-4, 9-8, and 14-13 observations were part of the Herschel SUCCESS program (Teyssier et al 2011;Danilovich et al 2015) and observed with the onboard instrument HIFI (de Graauw et al 2010). The signal-to-noise ratio of the 12 CO J=14-13 line was about 2 to 3 and because of this high uncertainty we decided to omit this line from our analysis.…”

Section: Previously Published Co Radio Line Observationsmentioning

confidence: 99%

“…1, respectively. The technical setup, data reduction, and line profiles were published in Danilovich et al (2015). The line profiles were plotted in main beam temperature scale with a noise rms of 15 mK at a channel resolution of 3 km s −1 .…”

Section: Previously Published Co Radio Line Observationsmentioning

confidence: 99%

The extended molecular envelope of the asymptotic giant branch star π¹ Gruis as seen by ALMA

Doan¹,

Ramstedt²,

Vlemmings³

et al. 2017

A&A

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Context. The S-type asymptotic giant branch (AGB) star π 1 Gru has a known companion at a separation of 2 ′′ . 7 (≈400 AU). Previous observations of the circumstellar envelope (CSE) show strong deviations from spherical symmetry. The envelope structure, including an equatorial torus and a fast bipolar outflow, is rarely seen in the AGB phase and is particularly unexpected in such a wide binary system. Therefore a second, closer companion has been suggested, but the evidence is not conclusive. Aims. The aim is to make a 3D model of the CSE and to constrain the density and temperature distribution using new spatially resolved observations of the CO rotational lines. Methods. We have observed the J=3-2 line emission from 12 CO and 13 CO using the compact arrays of the Atacama Large Millimeter/submillimeter Array (ALMA). The new ALMA data, together with previously published 12 CO J=2-1 data from the Submillimeter Array (SMA), and the 12 CO J=5-4 and J=9-8 lines observed with Herschel/Heterodyne Instrument for the Far-Infrared (HIFI), is modeled with the 3D non-LTE radiative transfer code SHAPEMOL. Results. The data analysis clearly confirms the torus-bipolar structure. The 3D model of the CSE that satisfactorily reproduces the data consists of three kinematic components: a radially expanding torus with velocity slowly increasing from 8 to 13 km s −1 along the equator plane; a radially expanding component at the center with a constant velocity of 14 km s −1 ; and a fast, bipolar outflow with velocity proportionally increasing from 14 km s −1 at the base up to 100 km s −1 at the tip, following a linear radial dependence. The results are used to estimate an average mass-loss rate during the creation of the torus of 7.7×10 −7 M ⊙ yr −1 . The total mass and linear momentum of the fast outflow are estimated at 7.3×10 −4 M ⊙ and 9.6×10 37 g cm s −1 , respectively. The momentum of the outflow is in excess (by a factor of about 20) of what could be generated by radiation pressure alone, in agreement with recent findings for more evolved sources. The best-fit model also suggests a 12 CO/ 13 CO abundance ratio of 50. Possible shaping scenarios for the gas envelope are discussed.

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“…The sample was chosen to cover a range of mass-loss rates across all three chemical types, and was largely drawn from stars covered by the SUC-CESS programme (Danilovich et al 2015), for which high quality CO observations and mass-loss rates derived from CO modelling were already available. Of this sample all but two sources were observed for at least one of three possible H 2 S transitions and H 2 S was detected in three of these.…”

Section: Sample and Observationsmentioning

confidence: 99%

Sulphur-bearing molecules in AGB stars

Danilovich

Sande

Beck

et al. 2017

A&A

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Context. Sulphur is a relatively abundant element in the local galaxy which is known to form a variety of molecules in the circumstellar envelopes of AGB stars. The abundances of these molecules vary based on the chemical types and mass-loss rates of AGB stars. Aims. Through a survey of (sub-)millimetre emission lines of various sulphur-bearing molecules, we aim to determine which molecules are the primary carriers of sulphur in different types of AGB stars. In this paper, the first in a series, we investigate the occurrence of H 2 S in AGB circumstellar envelopes and determine its abundance, where possible. Methods. We have surveyed 20 AGB stars with a range of mass-loss rates and of different chemical types using the APEX telescope to search for rotational transition lines of five key sulphur-bearing molecules: CS, SiS, SO, SO 2 and H 2 S. Here we present our results for H 2 S, including detections, non-detections and detailed radiative transfer modelling of the detected lines. We compare results based on different descriptions of the molecular excitation of H 2 S and different abundance distributions, including Gaussian abundances, where possible, and two different abundance distributions derived from chemical modelling results. Results. We detected H 2 S towards five AGB stars, all of which have high mass-loss rates ofṀ ≥ 5 × 10 −6 M yr −1 and are oxygenrich. H 2 S was not detected towards the carbon or S-type stars that fall in a similar mass-loss range. For the stars in our sample with detections, we find peak o-H 2 S abundances relative to H 2 between 4 × 10 −7 and 2.5 × 10 −5 . Conclusions. Overall, we conclude that H 2 S can play a significant role in oxygen-rich AGB stars with higher mass-loss rates, but is unlikely to play a key role in stars of other chemical types or the lower mass-loss rate oxygen-rich stars. For two sources, V1300 Aql and GX Mon, H 2 S is most likely the dominant sulphur-bearing molecule in the circumstellar envelope.

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New observations and models of circumstellar CO line emission of AGB stars in theHerschelSUCCESS programme

Cited by 80 publications

References 60 publications

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

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

The extended molecular envelope of the asymptotic giant branch star π¹ Gruis as seen by ALMA

Sulphur-bearing molecules in AGB stars

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New observations and models of circumstellar CO line emission of AGB stars in theHerschelSUCCESS programme

Cited by 80 publications

References 60 publications

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

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

The extended molecular envelope of the asymptotic giant branch star π1 Gruis as seen by ALMA

Sulphur-bearing molecules in AGB stars

Contact Info

Product

Resources

About

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

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

The extended molecular envelope of the asymptotic giant branch star π¹ Gruis as seen by ALMA