Charting the Structure of the Milky Way Stellar Halo and Disk

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The investigator seeks to understand our Milky Way galaxy. The Milky Way has dozens of smaller dwarf galaxies in orbit around it. These dwarf galaxies are being ripped apart by our galaxy's gravity into long streams of stars. Some of these streams encircle the entire galaxy. The investigator recently discovered that the disk of the Milky Way, which includes the spiral structure, has previously unknown 'ripples'. These ripples are believed to form when smaller dwarf galaxies fall into the Milky Way, just as a pebble dropped into a pond produces ripples on the surface of the water. By mapping the density of stars throughout the Milky Way, this project model of the interaction between the Milky Way galaxy and the dwarf galaxies orbiting it. These models will help us understand where dark matter is located. The models also teach us how the spiral arms of galaxies are made and sustained. This project will train undergraduate students in science and computing. The investigator will engage the public in the scientific process through sustained public outreach initiatives. Public outreach will include science web pages, Facebook, Twitter, Instagram, YouTube videos, Reddit Ask Me Anything (AMA) sessions, opportunities to observe the sky through small telescopes, and hands-on outreach activities that will reach thousands of children, teens, adults, and seniors. A relationship will be maintained between the investigators and the ~20,000 people, at any given time, who volunteer their personal computers to create the MilkyWay@home supercomputer.The investigator will map the three dimensional stellar density in the disk and halo of our galaxy, using Sloan Digital Sky Survey main sequence and turnoff stars in the galaxy's halo. The investigator will use the technique of statistical photometric parallax to make the density maps. This technique recovers the underlying density distribution without measuring the distance to each individual star, because only the intrinsic brightness distribution is required.The outer disk and the stellar halo will be mapped with turnoff stars. Main sequence stars, which are intrinsically dimmer, will be used to trace the density of closer stars in the Milky Way disk. The investigator will map the dominant substructures, including the vertical oscillations of the stellar mid-plane.