Photometric Variability in the NGVS: Milky Way Halo RR Lyrae

RR Lyrae stars can give us insight into stellar pulsation mechanisms, measuring cosmic distances, and early galaxy formation; furthermore, their unique asymmetric pulsation makes them excellent markers of the accretion history and dark matter content of the Milky Way galaxy. Our research revolves around studying these RR Lyrae stars and devising an algorithm to determine the variability of a star given time series brightness measurements. With such capabilities, reliably identifying new RR Lyrae can give us more data to work with for these unique variable stars with cosmological and astrophysical value. Our primary research goals were thus to construct a rigorous approach towards calculating the completeness fraction (efficiency) and recovery ability of the variable star algorithm through the generation of a diverse set of mock light curves, and to calculate the line-of-sight velocity of two RR Lyrae stars using spectral analysis. In doing so, we were able to construct a light curve generation program simulating real life measurement cadences and photometric error data (caused by noise pollution and other sources) along with different magnitude stars and light curve phase shifts. We were able to generate a dataset of 2000 light curves using SESAR 2010 templates and a g-band average magnitude of 24 with phase shift values of 0.3, 0.6, and 0.9 for each template. The results from this process allow us to model the various aforementioned measurement imperfections and allow thorough testing for the effects of a diverse spectrum of factors, from sparsity to large error bars, on the detection algorithm’s efficiency and recovery ability. Furthermore, we determined the line-of-sight velocity of two RR Lyrae stars in the Milky Way Halo, discovered by the Pann-STARR survey. We used the spectral data obtained by the DEIMOS spectrograph via the Keck II Telescope and analyzed the spectral data along specific absorption lines with the Doppler Shift equation. Using spectroscopic analysis and barycentric velocity corrections, we then determined the line-of-sight velocity of two RR Lyrae stars as 46 km/s and 153 km/s and constructed an accurate velocity curve for each star.