Physics
Scientific paper
Jun 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........6k&link_type=abstract
Proquest Dissertations And Theses 2009. Section 0059, Part 0606 314 pages; [Ph.D. dissertation].United States -- New Hampshire:
Physics
Extinction, Galactic Bar, Galactic Halo, Milky Way Galaxy, Rr Lyrae, Sagittarius Dwarf Galaxy, Galactic Bulge
Scientific paper
This dissertation details the use of a new catalog of Galactic bulge field RR Lyrae variables to advance the understanding of the structure of the Milky Way Galaxy. The catalog contains 3667 RR0 Lyrae stars from the eight-year MACHO Project light-curve database. I use these stars to explore four topics:
(1) Reddening toward the Galactic bulge: A reddening map of the central Galactic region from 3525 RR Lyrae stars is presented. These reddenings are based upon my findings that the mean dereddened RR Lyrae color at minimum light is ( V - R ) min,0 = 0.28 ± 0.02 mag, which is determined from new observations of 18 local RR Lyrae variables as well as 14 RR Lyrae from the literature.
(2) Structure of the Galactic bulge: I find metallicities of 2690 RR Lyrae stars from the Fourier coefficients of their light-curves, which are accurate to ± 0.2 dex. Hence their absolute magnitudes and distances can be found. A correlation between metallicity and galactocentric distance is found. For the metal-poor RR0 Lyrae stars ([Fe/H] < -1.5 dex), the closer a star is to the Galactic center, on average, the more metal rich it is. For the metal-rich RR0 Lyrae stars ([Fe/H] > -1.2 dex), this trend is reversed. I searched for the evidence of the Galactic bar, and found marginal evidence of a bar. This suggests that the RR Lyrae in the bulge represent a different population than the majority of the bulge stars, which are metal rich and are part of a bar.
(3) Distance to the Sagittarius Dwarf Galaxy: I find a distance of D = 24.8 ± 0.8 kpc at l = 5° and b = -8°, and that the body of Sgr is inclined toward us. This distance is based on 203 Sgr RR Lyrae stars determined differentially with respect to 288 Galactic bulge RR Lyrae stars.
(4) Limitations on using RR Lyrae stars has distance indicators: I find that reliance upon a single [Special characters omitted.] - [Fe/H] relation may be discrepant by up to 0.2 mags when considering populations with different period- V -amplitude relations.
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