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Aditional Ultra-High-Resolution Observations of Ca+ Ions in the Local Insterstellar Medium

Crawford, IA; Lallement, R; Welsh, BY; (1998) Aditional Ultra-High-Resolution Observations of Ca+ Ions in the Local Insterstellar Medium. Monthly Notices of the Royal Astronomical Society , 300 (4) 1181 - 1188. 10.1046/j.1365-8711.1998.01980.x. Green open access

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Abstract

We present ultra-high-resolution (0.35 km s−1 FWHM) observations of the interstellar Ca K line towards seven nearby stars. The spectral resolution was sufficient to resolve the line profiles fully, thereby enabling us to detect hitherto unresolved velocity components, and to obtain accurate measurements of the velocity dispersions (b values). Absorption components with velocities similar to those expected for the Local Interstellar Cloud (LIC) and the closely associated ‘G cloud’ were identified towards six of the seven stars. However, in most cases the b values deduced for these components were significantly larger than the b ≈ 2.2 km s−1 (i.e. Tk ≈ 7000 K, vt ≈ 1 km s−1) expected for the LIC, and it is argued that this results from the presence of additional, spectrally unresolved, components having similar velocities and physical conditions. For two stars (δ Vel and α Pav) we detect interstellar components with much smaller b values (1.1 ± 0.3 and 0.8 ± 0.1 km s−1, respectively) than are expected for low-density clouds within the Local Bubble. In the case of the narrow α Pav component, we also find an anomalously large Na i/Ca ii column density ratio, which is indicative of a relatively high density. Thus it is possible that, in addition to LIC-type clouds, the local interstellar medium contains a population of previously undetected cooler and denser interstellar clouds.

Type: Article
Title: Aditional Ultra-High-Resolution Observations of Ca+ Ions in the Local Insterstellar Medium
Open access status: An open access version is available from UCL Discovery
DOI: 10.1046/j.1365-8711.1998.01980.x
Publisher version: http://dx.doi.org/10.1046/j.1365-8711.1998.01980.x
Language: English
Additional information: © 1998 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: Ions, ISM: Atoms, ISM: Structure, Line: Profiles
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/55394
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