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Boron abundances in diffuse interstellar clouds

Published online by Cambridge University Press:  23 April 2010

Adam M. Ritchey
Affiliation:
Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA email: adam.ritchey@utoledo.edu, steven.federman@utoledo.edu, ysheffe@utnet.utoledo.edu
S. R. Federman
Affiliation:
Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA email: adam.ritchey@utoledo.edu, steven.federman@utoledo.edu, ysheffe@utnet.utoledo.edu
Y. Sheffer
Affiliation:
Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA email: adam.ritchey@utoledo.edu, steven.federman@utoledo.edu, ysheffe@utnet.utoledo.edu
D. L. Lambert
Affiliation:
W.J. McDonald Observatory, University of Texas at Austin, 1 University Station, Austin, TX 78712, USA email: dll@astro.as.utexas.edu
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Abstract

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We present a comprehensive survey of B abundances in diffuse interstellar clouds from HST/STIS observations along 56 Galactic sight lines. Our sample is the result of a complete search of archival STIS data for the B II λ1362 resonance line, with each detection confirmed by the presence of absorption from other dominant ions at the same velocity. The data probe a range of astrophysical environments including both high-density regions of massive star formation as well as low-density paths through the Galactic halo, allowing us to clearly define the trend of B depletion onto interstellar grains as a function of gas density. Many extended sight lines exhibit complex absorption profiles that trace both local gas and gas associated with either the Sagittarius-Carina or Perseus spiral arm. Our analysis indicates a higher B/O ratio in the inner Sagittarius-Carina spiral arm than in the vicinity of the Sun, which may suggest that B production in the current epoch is dominated by a secondary process. The average gas-phase B abundance in the warm diffuse ISM [log ϵ(B) = 2.38±0.10] is consistent with the abundances determined for a variety of Galactic disk stars, but is depleted by 60% relative to the solar system value. Our survey also reveals sight lines with enhanced B abundances that potentially trace recent production of 11B either by cosmic-ray or neutrino-induced spallation. Such sight lines will be key to discerning the relative importance of the two production routes for 11B synthesis.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2010

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