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Detached Red Giant Eclipsing Binary Twins: Rosetta Stones to the Galactic Bulge

Nataf D. M., Gould A., Pinsonneault M. H.

Acta Astronomica

2012

Vol. 62, No. 1

33--65

We identify 34 highly-probable detached, red giant eclipsing binary pairs among 315 candidates in Devor's catalog of ≈10 000 OGLE-II eclipsing binaries. We estimate that there should be at least 200 such systems in OGLE-III. We show that spectroscopic measurements of the metallicities and radial-velocity-derived masses of these systems would independently constrain both the age-metallicity and helium-metallicity relations of the Galactic bulge, potentially breaking the age-helium degeneracy that currently limits our ability to characterize the bulge stellar population. Mass and metallicity measurements alone would be sufficient to immediately validate or falsify recent claims about the age and helium abundance of the bulge. A spectroscopic survey of these systems would constrain models of Milky Way assembly, as well as provide significant auxiliary science on research questions such as mass loss on the red giant branch. We discuss the theoretical uncertainties in stellar evolution models that would need to be accounted for to maximize the scientific yield.

Protecting Life in the Milky Way: Metals Keep the GRBs Away

Stanek K. Z., Gnedin O. Y., Beacom J. F., Gould A. P., Johnson J. A., Kollmeier J. A., Modjaz M., Pinsonneault M. H., Pogge R., Weinberg D. H.

Acta Astronomica

2006

Vol. 56, No. 4

333--345

The host galaxies of the five local, z≤0.25, long-duration gamma-ray bursts (GRBs 980425, 020903, 030329, 031203 and 060218), each of which had a well-documented associated supernova, are all faint and metal-poor compared to the population of local star-forming galaxies. We quantify this statement by using a previous analysis of star-forming galaxies (0.005iso, steeply decreases with increasing host oxygen abundance. This might further indicate that (low) metallicity plays a fundamental physical role in the GRB phenomenon, and suggesting an upper metallicity limit for "cosmological" GRBs at ≈0.15 Z_solar.