TY - JOUR
T1 - Sulphur-bearing molecules in AGB stars
T2 - I. The occurrence of hydrogen sulphide
AU - Danilovich, T.
AU - Van De Sande, M.
AU - De Beck, E.
AU - Decin, L.
AU - Olofsson, H.
AU - Ramstedt, S.
AU - Millar, T. J.
N1 - Funding Information:
Acknowledgements. The authors would like to acknowledge John H. Black for his compilation of the H2S molecular data file used in our modelling. L.D. and T.D. acknowledge support from the ERC consolidator grant 646758 AEROSOL and the FWO Research Project grant G024112N. M.V.d.S. and L.D. acknowledge support from the Research Council of the KU Leuven under grant number GOA/2013/012. T.J.M. acknowledges support from the STFC, grant reference ST/P000312/1. Based on observations made with APEX under programme IDs O-097.F-9318 and O-098.F-9305. APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France and the US Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-NAF; The Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observato-rio Astronómico Nacional (IGN), Centro de Astrobiología (CSIC-INTA). Sweden: Chalmers University of Technology – MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC.
Publisher Copyright:
© ESO 2017.
PY - 2017/10/1
Y1 - 2017/10/1
N2 - Context. Sulphur is a relatively abundant element in the local Galaxy that 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 H2S in AGB circumstellar envelopes and determine its abundance, where possible. Methods. We surveyed 20 AGB stars with a range of mass-loss rates and different chemical types using the Atacama Pathfinder Experiment (APEX) telescope to search for rotational transition lines of five key sulphur-bearing molecules: CS, SiS, SO, SO2, and H2S. Here we present our results for H2S, including detections, non-detections, and detailed radiative transfer modelling of the detected lines. We compared results based on various descriptions of the molecular excitation of H2S and different abundance distributions, including Gaussian abundances, where possible, and two different abundance distributions derived from chemical modelling results. Results. We detected H2S towards five AGB stars, all of which have high mass-loss rates of M ≥ 5 × 10-6 M⊙ yr-1 and are oxygen rich. H2S 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-H2S abundances relative to H2 between 4 × 10-7 and 2.5 × 10-5. Conclusions. Overall, we conclude that H2S 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 in lower mass-loss rate oxygen-rich stars. For two sources, V1300 Aql and GX Mon, H2S is most likely the dominant sulphur-bearing molecule in the circumstellar envelope.
AB - Context. Sulphur is a relatively abundant element in the local Galaxy that 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 H2S in AGB circumstellar envelopes and determine its abundance, where possible. Methods. We surveyed 20 AGB stars with a range of mass-loss rates and different chemical types using the Atacama Pathfinder Experiment (APEX) telescope to search for rotational transition lines of five key sulphur-bearing molecules: CS, SiS, SO, SO2, and H2S. Here we present our results for H2S, including detections, non-detections, and detailed radiative transfer modelling of the detected lines. We compared results based on various descriptions of the molecular excitation of H2S and different abundance distributions, including Gaussian abundances, where possible, and two different abundance distributions derived from chemical modelling results. Results. We detected H2S towards five AGB stars, all of which have high mass-loss rates of M ≥ 5 × 10-6 M⊙ yr-1 and are oxygen rich. H2S 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-H2S abundances relative to H2 between 4 × 10-7 and 2.5 × 10-5. Conclusions. Overall, we conclude that H2S 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 in lower mass-loss rate oxygen-rich stars. For two sources, V1300 Aql and GX Mon, H2S is most likely the dominant sulphur-bearing molecule in the circumstellar envelope.
KW - Circumstellar matter
KW - Stars: AGB and post-AGB
KW - Stars: evolution
KW - Stars: mass-loss
UR - http://www.scopus.com/inward/record.url?scp=85032353244&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/201731203
DO - 10.1051/0004-6361/201731203
M3 - Article
AN - SCOPUS:85032353244
SN - 0004-6361
VL - 606
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
M1 - A124
ER -