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Astron. Astrophys. 349, L13-L16 (1999)


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Letter to the Editor

Low deuterium abundance in the [FORMULA]=3.514 absorber towards APM 08279+5255 *

Paolo Molaro 1, Piercarlo Bonifacio 1, Miriam Centurion 1,2 and Giovanni Vladilo 1

1 Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste, Italy
2 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain

Received 29 June 1999 / Accepted 4 August 1999

Abstract

A high-resolution, high signal-to-noise HIRES-Keck spectrum of APM 08279+5255 reveals a feature in the HI Ly[FORMULA] profile of the [FORMULA]=3.514 absorber at the expected position of the corresponding DI Ly[FORMULA] line. The absorber shows a relatively simple velocity structure, with a major component detected in several metallic lines including CII, CIV, SiII, SiIII and Si IV. Modeling of the hydrogen column density with the minimum number of components yields [FORMULA]. However, a more complex structure for the hydrogen cloud with somewhat ad hoc components would allow a higher [FORMULA]. The system has a very low metallicity with [Si/H] [FORMULA] and [C/H] [FORMULA] and is therefore representative of essentially unprocessed material, with a deuterium abundance close to the primordial value. The present analysis favours the low D/H value of [FORMULA] =[FORMULA] measured towards QSO 1009+2956 and QSO 1937-1009 (Burles & Tytler 1998a, 1998b) as the fiducial value of deuterium at high redshift.

Key words: cosmology: observations – cosmology: early Universe – galaxies: quasars: individual: APM 08279+5255 – nuclear reactions, nucleosynthesis, abundances

* The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Send offprint requests to: P. Molaro

Correspondence to: molaro@oat.ts.astro.it

© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999

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