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    First results from the UHRF: ultra-high-resolution observations of atomic interstellar lines towards ζ Ophiuchi

    Barlow, M.J. and Crawford, Ian and Diego, F. and Dryburgh, M. and Fish, A.C. and Howarth, I.D. and Spyromilio, J. and Walker, D.D. (1995) First results from the UHRF: ultra-high-resolution observations of atomic interstellar lines towards ζ Ophiuchi. Monthly Notices of the Royal Astronomical Society 272 (2), pp. 333-345. ISSN 0035-8711.

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    Abstract

    We present ultra-high-resolution observations of optical interstellar lines towards ζOph obtained during the commissioning phase of the new Ultra-High-Resolution Facility (UHRF) at the AAT. The UHRF has achieved its design resolving power of R≈106, and has very clearly resolved hyperfine splitting in three of the 11 identified Na I D-line velocity components towards ζ Oph. In addition, the intrinsic line profiles of the 3s-4p Na I doublet at 3302 Å have been measured for the first time. 12 velocity components are identified in the interstellar Ca II K-line absorption profile, of which seven have definite velocity counterparts in the Na I profile. Three of the Na I velocity components have b-values which correspond to a gas temperature of about 200 K, for the case of pure thermal broadening. The strongest component in the sightline (-14.8 km s-1) was found to have a b-value of 0.6+0.2−0.1kms−1⁠, corresponding to a temperature of 500 K. If a true gas kinetic temperature of 54 K is assumed to apply to this component, from the H2 rotational excitation temperature previously measured for the ζ Oph sightline, then the observed Na I and Fe I line profiles both imply an rms turbulent velocity of 0.4 km s-1 within the cloud, just less than the local sound speed. The observed Ca II linewidths are all significantly larger than those of the corresponding Na I components. The Ca IIcomponents are interpreted as arising from warm neutral material (intercloud medium) surrounding cooler clouds, while half of the Na I components arise from cool clouds and half arise from warm intercloud material. The measured Na I/CaII column density ratios, and the inferred temperatures, are consistent with a model in which calcium is heavily depleted on to grains in cool clouds but is restored to the gas phase by impact desorption in the warm intercloud medium.

    Metadata

    Item Type: Article
    School: School of Science > Earth and Planetary Sciences
    Depositing User: Sarah Hall
    Date Deposited: 13 Aug 2019 15:12
    Last Modified: 10 Feb 2021 05:01
    URI: https://eprints.bbk.ac.uk/id/eprint/28552

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