TY - JOUR
T1 - A HIFI preview of warm molecular gas around χ Cygni: First detection of H2O emission toward an S-type AGB star
AU - Justtanont, K.
AU - Decin, L.
AU - Schöier, F. L.
AU - Maercker, M.
AU - Olofsson, H.
AU - Bujarrabal, V.
AU - Marston, A.P.
AU - Teyssier, D.
AU - Alcolea, J.
AU - Cernicharo, J.
AU - Dominik, C.
AU - de Koter, A.
AU - Melnick, G.
AU - Menten, K.
AU - Neufeld, D.
AU - Planesas, P.
AU - Schmidt, M.
AU - Szczerba, R.
AU - Waters, R.
AU - De Graauw, T.
AU - Whyborn, N.
AU - Finn, T.
AU - Helmich, F.
AU - Siebertz, O.
AU - Schmülling, F.
AU - Ossenkopf, V.
AU - Lai, R.
N1 - Herschel/HIFI: first science highlights
PY - 2010
Y1 - 2010
N2 - Aims. A set of new, sensitive, and spectrally resolved, sub-millimeter line observations are used to probe the warm circumstellar gas around the
S-type AGB star χ Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency
data, make it possible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of χ Cyg.
Methods. The data were obtained using the HIFI instrument aboard Herschel, whose high spectral resolution provides valuable information about
the line profiles. Detailed, non-LTE, radiative transfer modelling, including dust radiative transfer coupled with a dynamical model, has been
performed to derive the temperature, density, and velocity structure of the circumstellar envelope.
Results. We report the first detection of circumstellar H2O rotational emission lines in an S-star. Using the high-J CO lines to derive the parameters
for the circumstellar envelope, we modelled both the ortho- and para-H2O lines. Our modelling results are consistent with the velocity structure
expected for a dust-driven wind. The derived total H2O abundance (relative to H2) is (1.1 ± 0.2) × 10−5, much lower than that in O-rich stars. The
derived ortho-to-para ratio of 2.1 ± 0.6 is close to the high-temperature equilibrium limit, consistent with H2O being formed in the photosphere.
AB - Aims. A set of new, sensitive, and spectrally resolved, sub-millimeter line observations are used to probe the warm circumstellar gas around the
S-type AGB star χ Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency
data, make it possible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of χ Cyg.
Methods. The data were obtained using the HIFI instrument aboard Herschel, whose high spectral resolution provides valuable information about
the line profiles. Detailed, non-LTE, radiative transfer modelling, including dust radiative transfer coupled with a dynamical model, has been
performed to derive the temperature, density, and velocity structure of the circumstellar envelope.
Results. We report the first detection of circumstellar H2O rotational emission lines in an S-star. Using the high-J CO lines to derive the parameters
for the circumstellar envelope, we modelled both the ortho- and para-H2O lines. Our modelling results are consistent with the velocity structure
expected for a dust-driven wind. The derived total H2O abundance (relative to H2) is (1.1 ± 0.2) × 10−5, much lower than that in O-rich stars. The
derived ortho-to-para ratio of 2.1 ± 0.6 is close to the high-temperature equilibrium limit, consistent with H2O being formed in the photosphere.
KW - stars: AGB and post-AGB
KW - circumstellar matter
KW - stars: kinematics and dynamics
KW - stars: individual: chi Cyg
KW - stars: late-type
KW - stars: mass-loss
U2 - 10.1051/0004-6361/201015092
DO - 10.1051/0004-6361/201015092
M3 - Article
SN - 0004-6361
VL - 521
SP - L6/1-L6/5
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
IS - 1
ER -