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RR Lyrae stars: Substructures and the Oosterhoff dichotomy in the Halo of the Milky Way

Abbas, Mohamad

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Abstract

We present the detection of 6371 RR Lyrae (RRL) stars distributed across 14000 deg2 of the sky from the combined data of the Sloan Digital Sky Survey (SDSS), the Panoramic Survey Telescope and Rapid Response System 1 3pi survey (PS1), and the repeated observations from the second photometric catalogue from the Catalina Survey (CSDR2). Around 2000 of these stars are new discoveries. The completeness level of our RRL stars (4800 RRab and 1571 RRc stars) is 50 % while the efficiency levels for RRab and RRc stars are 99 % and 87 %, respectively. We show that our method for selecting RRL stars allows us to recover halo substructures. Moreover, we present a method for selecting RRL stars and other types of variable stars in the absence of a large number of multi-epoch data and light curve analyses. Our method uses a Gaussian Mixture Bayesian Generative technique (GMM) to apply SDSS color and PS1 variability cuts instead of the commonly used rectangular cuts. A comparison between our efficiency and completeness levels using the GMM method to the efficiency and completeness levels using rectangular cuts that are commonly used yielded a significant increase in the efficiency level from 13% to 77% and an insignificant change in the completeness levels. Although we develop it over the SDSSxPS1 footprint, our technique would work well on any multi-band, multi-epoch survey for which the number of epochs is limited. Additionally, we study the different Oosterhoff populations (OoI and OoII) in the Milky Way’s halo using the largest catalog of RRab stars from the Catalina Sky Survey (CSS). We show that 73% of the halo RRab stars are of OoI type (RRabOoI ) and that the latter stars are more metal-rich compared to RRabOoII stars. By examining the change of RRabOoI and RRabOoII stars with Galactocentric distances (Rgc), we detect two turning points at Rgc 25 kpc and Rgc 45 kpc. We believe that these turning points are associated with breaks in the power-laws of the halo and that they divide the stellar halo into three main components: the inner halo, the outer halo, and the “extreme outer halo” components. We also study the Oosterhoff populations of the RRL stars in the direction of the trailing arm of the Sagittarius dwarf spheroidal (dSph) galaxy, the Virgo substructure, and the Hercules-Aquila Cloud and we conclude that these substructures are dominated by RRabOoI stars (80%) and that the mean periods of their RRab stars fall near the boundary of the Oosterhoff gap; results that suggest that they had dSph galaxy progenitors.

Item Type: Dissertation
Supervisor: Grebel, Prof. Dr. Eva
Date of thesis defense: 12 December 2014
Date Deposited: 18 Dec 2014 07:12
Date: 2014
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 520 Astronomy and allied sciences
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