Journal Article

Metastable helium in absorption towards ζ Ophiuchi*

G. A. Galazutdinov and J. Krelowski

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 4, pages 3457-3459
Published in print June 2012 | ISSN: 0035-8711
Published online May 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20856.x
Metastable helium in absorption towards ζ Ophiuchi*

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We report on the detection of a metastable He i* absorption line at 3889 Å in a spectrum of ζ Ophiuchi from the Ultraviolet and Visual Echelle Spectrograph with an extremely high signal-to-noise ratio (∼3500), which was collected using the 8-m telescope UT2 at Paranal. We cannot conclusively determine whether the He i* absorption arises within the H ii region or within the foreground H i clouds, which are responsible for interstellar CH, CH+, Na i, Ca ii, K i, etc., absorption, because the radial velocities of the main mass of gas are nearly identical in both regions. The measured equivalent width (1.0 ± 0.07 mÅ) of the line gives a column density of 1.158(± 0.081) × 1011 cm−2, when we assume the absence of saturation effects, and an oscillator strength of f= 0.0645. We estimate the ionization rate of helium to be 1.491 × 10−13, if the helium relative abundance in the H i cloud (with respect to hydrogen) is solar, and 7.475 × 10−14 cm−2, if the helium abundance is enhanced by the nearby star.

Keywords: ISM: abundances; ISM: atoms; ISM: clouds

Journal Article.  1788 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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