Heavy-element Rydberg transition line emission from the post-giant-evolution star HD101584

Abstract

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 HD101584 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. We aim to determine whether or not these lines can be attributed to the Rydberg transitions -- X30alpha and X26alpha -- of neutral atoms of elements heavier than carbon. A simple model in strict local thermodynamic equilibrium for a warm-gas environment of the moderate-temperature star (T_eff about 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. The observed flux densities of the lines and the continuum at 232 and 354 GHz can be reproduced using 10^(-3) M_sun of gas at a temperature of about 2800 K and a hydrogen density of about 10^(12) 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, about 3x10^(-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 1G is set using the Zeeman effect in these lines. 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.

arXiv comment19 pages, 6 figures

References in corpus (19)

• The chemical composition of the Sun
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• An atomic and molecular database for analysis of submillimetre line observations
• The ExoMol database: molecular line lists for exoplanet and other hot atmospheres
• Theory and applications of atomic and ionic polarizabilities
• Accurate determination of the free-free Gaunt factor; I - non-relativistic Gaunt factors
• Imaging the Radio Photospheres of Mira Variables
• Resolving the extended stellar atmospheres of Asymptotic Giant Branch stars at (sub-)millimetre wavelengths
• Phosphorus in the Diffuse Interstellar Medium
• The inhomogeneous sub-millimeter atmosphere of Betelgeuse
• Revisiting the Chlorine Abundance in Diffuse Interstellar Clouds from Measurements with the Copernicus Satellite
• Measuring angular diameters of extended sources
• A pilot search for mm-wavelength recombination lines from emerging ionized winds in pre-planetary nebulae candidates
• The Evolving Radio Photospheres of Long-Period Variable Stars
• HD101584: Circumstellar characteristics and evolutionary status
• First detection of methanol towards a post-AGB object, HD101584
• ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907
• VLTI/PIONIER reveals the close environment of the evolved system HD101584

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