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OH maser mapping of the evolved star HD 179821: evidence for interacting outllows

Gledhill, TM; Yates, JA; Richards, AMS; (2001) OH maser mapping of the evolved star HD 179821: evidence for interacting outllows. Monthly Notices of the Royal Astronomical Society , 328 (1) 301 - 310. 10.1046/j.1365-8711.2001.04886.x. Green open access

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Abstract

The evolved star HD 179821 continues to be the subject of much debate as to whether it is a nearby post-asymptotic giant branch (post-AGB) star or a distant high initial mass post-red supergiant. We have mapped the OH maser emission around HD 179821 in the 1612- and 1667-MHz lines with the MERLIN interferometer array at a resolution of 0.4 arcsec and 0.35 km s−1. The OH emission lies in a thick shell with inner and outer radii of 1.3 and and expansion velocity of 30 km s−1. Although we find some evidence for acceleration and for deviations from spherical symmetry, the bulk of the maser emission is consistent with a constant-velocity spherical shell. The extent of the shell agrees with H2O and OH dissociation models and supports a distance estimate of 6 kpc. However, the shell is incomplete and appears to have been disrupted by more recent collimated outflow activity within the last 1500 yr. We suggest that this activity is also responsible for the active envelope chemistry (in particular the presence of HCO+) and for the apparent offset of the star from the centre of the shell. The luminous yellow hypergiant star IRC +10420 also shows signs of recent outflows, and HD 179821 may be at a similar, perhaps slightly earlier, phase of evolution. We suggest that the SiO thermal emission arises from the same detached envelope as the OH maser emission as in IRC +10420. If so then this would strengthen the connection between these two stars and probably rule out a post-AGB status for HD 179821.

Type: Article
Title: OH maser mapping of the evolved star HD 179821: evidence for interacting outllows
Open access status: An open access version is available from UCL Discovery
DOI: 10.1046/j.1365-8711.2001.04886.x
Publisher version: http://dx.doi.org/10.1046/j.1365-8711.2001.04886.x
Language: English
Additional information: © 2001 RAS Definitive versions of articles pre-2013 are available at http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2966, now published by http://mnras.oxfordjournals.org
Keywords: Astronomy, HD, mapping, Maser Mapping, Star
UCL classification: 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/140409
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