The Classical Hyades Lithium Problem Revisited II.

Details The Classical Hyades Lithium Problem Revisited II. The Classical Hyades Lithium Problem Revisited II.

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.2608s&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #26.08; Bulletin of the American Astronomical Society, Vol. 24, p.768

Astronomy and Astrophysics

Astronomy

Scientific paper

Swenson, Stringfellow, and Faulkner (1990) suggested that deficiencies in interior opacities could be responsible for stellar models underestimating pre-main sequence (PMS) lithium depletion. They showed that models with increased interior opacities can produce excellent theoretical agreement with the pattern of depletion observed in the Hyades G-dwarfs. The first abstract in this series (1990, BAAS, 22, 1223) showed, as anticipated, that models using OPAL interior opacities instead of Cox-Tabor opacities experience considerably more PMS depletion. We now explore the consequences of a variety of physical improvements in both solar and Hyades models. We examine their impact on PMS lithium depletion, the depth of the solar convective zone, and the deduced helium abundance for the Sun and Hyades. (The deduction of the Hyades helium abundance is accomplished by making a detailed comparison between models and the observed Hyades Mass-Luminosity relationship.) Improvements are (1) the adoption of OPAL interior opacities (with photospheric or meteoritic iron abundances), (2) adoption of new surface opacities (Alexander 1992), (3) calibrated parameters for the pressure ionization prescription of the EFF equation of state (Proffitt & Michaud 1991), and (4) full inclusion of electrostatic corrections to the EFF EOS. (1) and (3) significantly increase depletion while (2) significantly decreases the depletion. While our ``best'' models deplete more lithium than our early models, they do not deplete enough to fit the observed pattern. We do, however, consider a number of changes that can produce an excellent fit to both the Hyades lithium depletion pattern and the Mass-Luminosity diagram. Two of which are: (i) an increase in opacity of ~ 13\ 1 to 4 million degree range (this also produces a solar model with the correct convective depth as determined from oscillations), and (ii) an increase in [Fe/H]_Hyades from 0.13 to ~ 0.26 (this also increases the deduced helium content of the Hyades to roughly the solar value).

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