A NLTE study of neutral boron in solar-type stars

Astronomy and Astrophysics (Impact Factor: 4.38). 05/1994; 286:169-180.
Source: arXiv


The formation of the resonance lines of neutral boron in solar-type
stellar atmospheres is investigated taking into account effects of
departures from local thermodynamic equilibrium (NLTE effects). The
latter are due to a combination of overionisation and optical pumping in
resonance lines, both caused by the hot, non-local, ultraviolet
radiation fields in the line-forming regions. They lead to an
underestimation of the boron abundance when analysis methods assuming
local thermodynamic equilibrium (LTE) are used. The abundance
correction, for the 249.7 nm resonance line, amounts to +0.56 dex for
the metal-poor star HD 140283 and +0.4 dex for Procyon. No significant
NLTE effects are predicted for the Sun. Applying the abundance
correction on the results for HD 140283 of Duncan et al. (1992) leads to
a B/Be ratio well above the minimum value required by spallation
production of beryllium. The reliability of the results in view of
atomic and atmospheric uncertainties is discussed. With the possible
exception of photospheric inhomogeneity, it seems unlikely that these
could remove the effect for HD 140283.

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    ABSTRACT: The boron 2500 spectral region has been observed with the Goddard High Resolution Spectrograph (GHRS) of the Hubble Space Telescope (HST) in a new set of metal-poor stars and analyzed by spectrum synthesis technique, adopting the most recent model atmospheres. By taking into account the Li and Be abundances available from the literature for this same set of objects, the resulting patterns of their light elements abundances cannot be easily justified with the currently known stellar structure scenarios. The finding of real differences in the B content between stars with very similar stellar characteristics suggest that also production effects, rather than depletion and/or mixing only, should be taken into account as a possible and valuable explanation.
    No preview · Article · Jan 1998 · Space Science Reviews