Boron abundances in diffuse interstellar clouds

Abstract

Abstract. 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 (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 11 B 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 11 B synthesis.

Crossed Molecular Beam Study on the Ground State Reaction of Atomic Boron [B(2Pj)] with Hydrogen Cyanide [HCN(X1Σ+)]

“…Here, boron has been detected toward the Orion association, 43 specifically λ Ori, κ Ori, and ι Ori with column densities of 6.17, 4.26, and e1.99 × 10 10 cm -2 . [44][45][46][47][48] The potential precursor to the BCN molecule, hydrogen cyanide (HCN), was also monitored in the Orion KL nebula with a column density of 2.6 × 10 16 cm -2 . 49 Here, a reaction of atomic boron with hydrogen cyanide might lead to the BNC molecule with the emission of atomic hydrogen.…”