The Abundance of Boron in Diffuse Interstellar Clouds

Details The Abundance of Boron in Diffuse Interstellar Clouds The Abundance of Boron in Diffuse Interstellar Clouds

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21431001r&link_type=abstract

American Astronomical Society, AAS Meeting #214, #310.01; Bulletin of the American Astronomical Society, Vol. 41, p.745

Astronomy and Astrophysics

Astronomy

Scientific paper

I present a comprehensive survey of interstellar boron abundances from STIS observations of 56 diffuse Galactic sight lines in an effort to identify the sources responsible for light element nucleosynthesis. The present sample is the result of a complete search of archival STIS data for the B II λ1362 resonance line. Each detection is confirmed by the presence of absorption due to O I λ1355, Cu II λ1358, and Ga II λ1414 (when available) at the same velocity. Like B+, these species represent the dominant ion of their element in diffuse clouds and therefore should coexist. Profile templates, based on synthesized absorption profiles of O I, Cu II, and Ga II, are fitted to the B II line yielding line-of-sight abundances that are consistent within measurement uncertainties. By fitting components seen in high-resolution observations of Ca II λ3933 and K I λ7698, I show that unresolved structure in the UV data has little influence on final boron abundances. Derived values of B/H and B/O firmly establish that boron is depleted in diffuse gas. Trends of B/H and B/O with and f(H2) demonstrate that the depletion is greater in high-density sight lines. Elemental depletion increases with average gas density due to the larger fraction of cold clouds, relative to warm gas, along the line of sight. For boron, this amounts to an abundance difference of about 0.7 dex between the warm and cold phases of the diffuse ISM. By identifying the effect of depletion, my survey reveals sight lines with enhanced B/H and B/O ratios that I ascribe to recent production of 11B either by cosmic-ray or neutrino-induced spallation. These sight lines are key to discerning the relative importance of the two production routes for 11B synthesis.
This research was funded by the Space Telescope Science Institute through grant HST-AR-11247.01-A.

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