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Ultra-high-resolution observations of circumstellar K I and C2 around the post-AGB star HD 56126

Crawford, IA; Barlow, MJ; (2000) Ultra-high-resolution observations of circumstellar K I and C2 around the post-AGB star HD 56126. Monthly Notices of the Royal Astronomical Society , 311 (2) pp. 370-376. 10.1046/j.1365-8711.2000.03055.x. Green open access

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Abstract

We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s−1 (FWHM), to observe K I and C2 absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K I, two of which are also present in C2. We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions (b-values) of 0.2–0.3 km s−1 for the K I components, and 0.54 ± 0.03 km s−1 for the strongest (and best defined) C2 component. These correspond to rigorous kinetic temperature upper limits of 211 K for K I and 420 K for C2, although the b-value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C2 implies low kinetic temperatures (Tk ≈10 K) and high densities (n ≈ 106 to 107 cm−3) within the shell responsible for the main C2 component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell.

Type: Article
Title: Ultra-high-resolution observations of circumstellar K I and C2 around the post-AGB star HD 56126
Open access status: An open access version is available from UCL Discovery
DOI: 10.1046/j.1365-8711.2000.03055.x
Publisher version: https://doi.org/10.1046/j.1365-8711.2000.03055.x
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: molecular processes, stars: AGB and post-AGB, circumstellar matter, stars: individual: HD 56126
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10096053
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