Detection of highly excited OH towards AGB stars: A new probe of shocked gas in the extended atmospheres
Journal article, 2019

We characterise the gas in the extended atmospheres of the oxygen-rich asymptotic giant branch (AGB) stars W Hya and R Dor using high angular resolution ALMA observations. Methods. We report the detection and investigate the properties of high-excitation Λ-doubling line emission of hydroxyl (OH). Results. The OH lines are produced very close to the central stars and seem optically thin and with no maser effect. We analyse the molecular excitation using a population diagram and find rotational temperatures of ∼2500 K and column densities of ∼10 19 cm -2 for both sources. For W Hya, we observe emission from vibrationally excited H 2 O arising from the same region as the OH emission. Moreover, CO v = 1, J = 3-2 emission also shows a brightness peak in the same region. Considering optically thin emission and the rotational temperature derived for OH, we find a CO column density ∼15 times higher than that of OH, within an area of (92 × 84) mas 2 centred on the OH emission peak. These results should be considered tentative because of the simple methods employed. The observed OH line frequencies differ significantly from the predicted transition frequencies in the literature, and provide the possibility of using OH lines observed in AGB stars to improve the accuracy of the Hamiltonian used for the OH molecule. We predict stronger OH Λ-doubling lines at millimetre wavelengths than those we detected. These lines will be a good probe of shocked gas in the extended atmosphere and are possibly even suitable as probes of the magnetic field in the atmospheres of close-by AGB stars through the Zeeman effect.

Stars: individual: R Dor

Stars: individual: W Hya

Stars: AGB and post-AGB

Line: identification

Circumstellar matter

Stars: individual: IK Tau

Author

Theo Khouri

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Luis Velilla Prieto

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Elvire De Beck

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Wouter Vlemmings

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Hans Olofsson

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Boy Lankhaar

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

John H Black

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

A. Baudry

Laboratoire d'Astrophysique de Bordeaux

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 623 L1

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Condensed Matter Physics

DOI

10.1051/0004-6361/201935049

More information

Latest update

4/8/2019 1