The Oldest Extremely Metal-poor Stars

Speaker: 
Henrique Reggiani (JHU)
Date: 
Friday, February 14, 2020 - 12:15pm to 1:00pm

It is tempting to assert that the most metal-poor stars in the Galaxy are the direct descendants of the first stars. This is not necessarily the case though, as metal-poor stars form over a range of redshift. Other properties beyond metallicity are therefore necessary to separate the old from the genuinely ancient metal-poor stars. It has recently been proposed that the location of a metal-poor star within the Galaxy provides some extra information about its age. The bulge is the oldest component of the Milky Way, and numerous groups have used simulations to predict that the oldest stars at a given metallicity are found on bulge-like orbits. These tightly bound metal-poor stars have been impossible to find in the past, as most metal-poor stars have been discovered using short-wavelength data. These classical techniques fail in the bulge due to strong reddening and extinction. We have used the mid-infrared metal-poor star selection of Schlaufman & Casey (2014) on Spitzer/GLIMPSE data to overcome these problems and discover the first three extremely metal-poor stars in the inner bulge. I'll present the results of a detailed abundance and orbital analysis of three stars using Magellan/MIKE spectroscopy and Gaia DR2 astrometry. I'll conclude by outlining the constraints these data provide for Pop III stars and the earliest stage of the Milky Way's formation.

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