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The dynamics of the Galactic bulge: Uncovering the old populations that formed before the bar

Physics/Astro Auditorium

Andrea Kunder (St. Martin’s University)

February 21 @ 4:00 PM - 5:00 PM

Using mainly bulge red clump giants (RCG) and giants as tracers, a picture has emerged of the Galactic bulge consisting of a rotating peanut-shaped structure made up largely of old and metal-rich stars (~10 Gyr, [Fe/H] falling between -0.5 and +0.5 dex).  However, there is a more metal-poor population of stars present in the bulge, a scarcer, lesser explored population of stars. I will present results from our spectroscopic survey of bulge RR Lyrae variables, tracers of possibly the oldest and most metal-poor stars in the bulge ([Fe/H] peaking at -1.0 dex).  To date, we have obtained spectra of ~2000 OGLE bulge RR Lyrae stars in eight 2 degree windows. Our results indicate that the RR Lyrae stars exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy.  Our RR Lyrae stars predate these structures, and have metallicities, kinematics, and spatial distribution that are consistent with a “classical” bulge, or an inner halo.