Nonprimordial deuterium in the interstellar medium

Contrary to a widespread assumption, deuterium is not simply destroyed in s tars: deuterium is also synthesized in the atmospheres of active stars. Thi s nonprimordial synthesis of D arises when protons accelerated in flares in teract with the atmosphere, create a flux of free neutrons, and these neutr ons then undergo radiative capture on atmospheric protons. Radiative captur e does not result in excess production of Li, Be, or B. Ejection of flare-p rocessed material contaminates the interstellar medium (ISM), as was origin ally suggested by Coleman & Worden. Estimates of the amount of flare-create d D are subject to considerable uncertainties, but we find, using stellar p arameters within permitted ranges, that flares may contribute significantly to the current ISM D content. Observational data indicate that different c louds of gas in the ISM exhibit variations in the value of D/H. We suggest that contamination of the ISM by D-enriched material ejected from stellar f lares contributes to the observed D/H inhomogeneity. More precise estimates of the efficiency of D ejection from flares into the solar wind are requir ed to evaluate this suggestion.