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T. P. Ashenfelter, G. J. Mathews (University of Notre Dame), K. A. Olive (University of Minnesota)
The many-multiplet method applied to high redshift quasar absorption spectra has been interpreted as evidence for a possible time variation of the fine structure constant. This is a very interesting possibility. However, before accepting a time variation of a fundamental constant, one should carefully scrutinize other possible explanations. In this context it is of interest that the value of the fine structure constant can be made consistent with the observational analysis if a non-solar isotopic ratio of 24,25,26Mg occurs at large (0.5 < z < 1.8) redshifts . In particular, higher abundances of the heavier isotopes 25,26Mg are required to explain the observed multiplet splitting. We show that new stellar evolution calculations enhance the synthesis of 25,26Mg at the base of the convective envelope in low-metallicity asymptotic giant branch stars. Furthermore, there is evidence for a burst of intermediate-mass stars at low metallicities. Hence, a simple model of galactic chemical evolution can produce the required isotopic ratios. This model is supported both by recent observations of high abundances for neutron-rich Mg isotopes in metal-poor globular-cluster stars, and evidence of an enhancement in the population of carbon-enriched stars at low metallicity. We conclude that the present data based on quasar absorption spectra may be providing interesting information on the nucleosynthetic history of such systems, rather than a time variation of fundamental constants.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.