Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012mnras.tmp.2772g&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Online Early
Astronomy and Astrophysics
Astronomy
Ism: Abundances, Ism: Atoms, Ism: Clouds
Scientific paper
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. a He abundances are normalized to E(B‑V) = 0.32.
Galazutdinov G. A.
Krelowski Jacek
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