Heavy-element Rydberg transition line emission from the post-giant-evolution star HD 101584
Journal article, 2021

Context.
We report the detection of two lines at millimetre wavelengths towards the immediate surroundings of the post-giant and most likely post-common-envelope star HD 101584 using high-angular-resolution ALMA observations. The circumstellar environment of this object is rich in different molecular species, but we find no viable identifications in terms of molecular lines.
Aims.
We aim to determine whether or not these lines can be attributed to the Rydberg transitions - X30α and X26α - of neutral atoms of elements heavier than carbon.
Methods.
A simple model in strict local thermodynamic equilibrium for a warm-gas environment of the moderate-temperature star (Teff ≈ 8500 K) was constructed to corroborate our findings. A geometrically thin, disc-like geometry seen face-on was chosen and a distance of 1 kpc. Results. The observed flux densities of the lines and the continuum at 232 and 354 GHz can be reproduced using ≈10-3 M⊙ of gas at a temperature of ≈2800 K and a hydrogen density of ≈1012 cm-3, assuming solar abundances for the elements. The gas lies within a distance of about 5 au from the star (assuming a distance of 1 kpc). The ionisation fraction is low, ≈3 × 10-5. The origin of such a region is not clear, but it may be related to a common-envelope-evolution phase. With these conditions, the line emissions are dominated by Rydberg transitions within the stable isotopes of Mg. A turbulent velocity field in the range 5.5-7.5 km s-1 is required to fit the Gaussian line shapes. An upper limit to the average magnetic field in the line-emitting region of 1 G is set using the Zeeman effect in these lines.
Conclusions.
We speculate that Rydberg transitions of heavy elements may be an interesting probe for the close-in environments of other moderate-temperature objects like AGB stars, red supergiants, yellow hypergiants, and binaries of various types.

Circumstellar matter

Radio lines: stars

Stars: individual: HD 101584

Stars: AGB and post-AGB

Author

Hans Olofsson

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

John H Black

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

Theo Khouri

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Wouter Vlemmings

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

E. Humphreys

European Southern Observatory (ESO)

Michael Lindqvist

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Observation Support

Matthias Maercker

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

L.-Å. Nyman

European Southern Observatory Santiago

S. Ramstedt

Uppsala University

Daniel Tafoya

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Observation Support

Astronomy and Astrophysics

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

Vol. 651 A35

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Condensed Matter Physics

DOI

10.1051/0004-6361/202140537

More information

Latest update

7/22/2021