Astronomy Seminar: RR Lyrae variables as stellar tracers of distance and galaxy evolution

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Date/Time:Thursday, 26 Sep 2019 from 4:10 pm to 5:10 pm
Location:Rm. 18, Physics Hall
Contact:Curt Struck
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Dr. Jillian Neeley, Florida Atlantic University

Period-Luminosity relations for RR Lyrae stars have long been an important tool in the nearby Universe, but in recent years they have earned greater attention as constructing a Population II distance ladder that is independent of Cepheids has become more critical to the measurement of the Hubble Constant. Most of this work in this area has focused on the infrared, where the relations are tighter and steeper. Here, I will summarize recent progress on infrared period-luminosity as well as multi-wavelength period-Wesenheit relations, with calibrations coming from Gaia DR2 parallaxes of Galactic field stars. The effect of metallicity can now be measured empirically, and it is consistent with theoretical predictions. At present, the precision of the period-luminosity relations as distance indicators is still limited by the uncertainties in parallaxes of the calibration sample. The usefulness of RR Lyrae stars extends beyond measuring distances however, and they can also be used to measure the metallicity distribution, differential reddening, and the star formation histories of nearby galaxies. I will present some preliminary results on the variable star in dwarf galaxies, and what we can infer about the evolution of these galaxies.