The Galactic Bulge Stellar Population
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A detailed investigation of the Galactic bulge stellar population, based predominantly on analysis of OGLE-III photometry, is reported. Significant progress is realized in the areas of variable stars, morphological structure, the red giant branch bump (RGBB), the age-helium-metallicity relationship, and the reddening toward the bulge.
It is demonstrated that there is vast discovery potential in the area of Galactic bulge variability studies that is accessible with available technology. The instruments in use for transit surveys are shown to be applicable to microlensing. Separately, detached red giant eclipsing binary pairs are shown to be plentiful, and to be a unique probe of the Galactic bulge age-helium-metallicity relation.
The discovery of the Galactic bulge double red clump (RC) is reported and discussed. The distance modulus distribution is shown to bifurcate into a bimodal distribution toward sightlines that are near the bulge minor axis and at least 5 degrees removed from the plane. The discovery of the Galactic bulge RGBB is also reported and discussed. It is shown to be slightly underpopulated and overluminous relative to expectations from stellar models and Galactic globular cluster calibrations, in a manner that can be explained by enhanced helium-enrichment for the Galactic bulge stellar population, with ${Delta}Y ~ + 0.06$ at the median metallicity. An investigation of the RGBB in Galactic globular clusters is conducted to better understand this uncalibrated feature of stellar evolution. Enhanced helium-enrichment is also demonstrated to be a possible solution to the Galactic bulge turnoff age discrepancy. An upper bound on the enhancement of the helium-enhancement, ${Delta}Y ~ + 0.10$, is derived.
Finally, the longstanding observational problem of the non-standard optical extinction toward the Galactic bulge is now solved. We combine OGLE-III $VI$ photometry with $VVV$ and $2MASS$ measurements in the near-IR to measure the extinction law $A_{I} = 0.7475{×}E(V-I) + 1.3655{×}E(J-K_{s})$. This two-parameter extinction law, which accounts for the variations in the steepness of the extinction curve, yields a Galactocentric distance $R_{0} = 8.20$ kpc, consistent with geometric determinations.
Document number: osu1343225619
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1343225619
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