**Student:** Keith Doore, Undergraduate Student in Earth Science, University of Northern Iowa

**Research Mentor:** Siobahn Morgan

**Using Fourier Coefficients to Examine the Metallicity of the Milky Way ****and Other Galaxies**

The research project I am pursuing is examining RR Lyrae stars in the region of the Galactic bulge from OGLE (Optical Gravitational Lensing Experiment) IV data acquired in 2014. Using the *I *band light curves of these variables, I have derived the Fourier coefficients, *R** _{ij}* and

*ϕ*

*, from a Fourier transform.*

_{ij}*R*

*and*

_{ij}*ϕ*

*relate to the amplitude and phase terms respectively, of the light variation over a pulsation period. In order to use these terms, I have had to take into account the use of*

_{ij}*I*magnitudes since most other studies use

*B*or

*V*magnitude

*values. I am doing this by revising a current*

*I*to

*V*band Fourier coefficient relation from Morgan et al., 1998. To revise this relation, I have gathered other RR Lyrae data from various globular clusters within the galaxy that contain both

*I*and

*V*band data. With this data, I have had to determine “well-behaved” stars, which can be used to determine a relation between the

*I*and

*V*band Fourier coefficients. Then, these new Fourier coefficients along with the pulsation period of the stars will be used to derive the metallicity of the OGLE IV RR Lyrae. The metallicity of these stars will then be compared to similar stars in this location from other metallicity studies. If successful, this

*I*to

*V*band formula will replace existing formulas and be applied to other datasets in the OGLE database, including the larger RR Lyrae catalogs for the Large and Small Magellanic Clouds.