Structure of the obscured galactic disk with pulsating variables.

Abstract

Bright pulsating variables, such as Cepheids and RR Lyrae, are prime probes of the structure of both the young and old stellar components of the Milky Way. However, the far side of the Galactic disk has not yet been mapped using such variables as tracers, due to the severe extinction caused by foreground interstellar dust. \nIn this thesis, the near-infrared light curves from the VISTA Variables in the Via Lactea survey are utilized to penetrate these regions of high extinction and thus discover thousands of previously “hidden” Cepheid and RR Lyrae variables. The analysis of the light curves of RR Lyrae variables, was performed with a newly developed fitting algorithm, and their metallicities determined from their near-infrared light-curve shapes, using a newly developed method. These photometric metal abundances, combined with their positions within the Galactic disk, lend support to theories of an early, inside-out formation of the Galactic disk. \nThe newly discovered Cepheids were classified into the old (Type II) and young (Classical) subtypes. A new near-infrared extinction law was determined using the Type II Cepheids, taking advantage of their concentration around the Galactic center. The distribution of the Classical Cepheids in the Galactic disk follows both the Galactic warp and the flare of the Galactic disk at large Galactocentric radii. A first attempt has been made to connect the current locations of the Classical Cepheids to the spiral arm structure of the Milky Way.