Galactic Evolution of D and 3He Including Stellar Production of 3He

New stellar models which track the production and destruction of ^3He (and D) have been evolved for a range of stellar masses (0.65\≤ M/M\\≤ 100), metallicities (0.01 \≤ Z/Z\ \≤ 1) and initial (main sequence) ^3He mass fractions (10⁻⁵ \≤ X3,MS \≤ 10⁻³). Armed with the ^3He yields from these stellar models we have followed the evolution of D and ^3He using a variety of chemical evolution models with and without infall of primordial or processed material. Production of new ^3He by the lower mass stars overwhelms any reasonable primordial contributions and leads to predicted abundances in the presolar nebula and/or the present interstellar medium in excess of the observationally inferred values. This result, which obtains even for zero primordial D and ^3He, and was anticipated by Rood, Steigman \& Tinsley (1976), is insensitive to the choice of chemical evolution model; it is driven by the large ^3He yields from low mass stars. In an attempt to ameliorate this problem we have considered a number of non-standard models in which the yields from low mass stars have been modified. Although several of these non-standard models may be consistent with the ^3He data, they may be inconsistent with observations of ¹²C/¹³C, ¹⁸O and, most seriously, the super-^3He rich planetary nebulae (Rood, Bania \& Wilson 1992). Even using the most extreme of these non-standard models (Hogan 1995), we obtain a generous upper bound to pre-galactic ^3He: X3P \≤ 3.2 \×10⁻⁵ which, nonetheless, leads to a stringent lower bound to the universal density of nucleons.