Characterizing the Hercules Thick Disk Cloud
Abstract
Astronomical observations show that there is an excess of faint blue stars located towards and to the left of the Constellation Sagittarius near the Galactic center, as we see it from Annapolis, indicating an asymmetry in the thick disk of the Milky Way. This region, originally discovered by Larsen and Humphreys in 1996, has been named the Hercules Thick Disk Cloud and originally had three origin theories: a galactic merger, rotation of the stellar bar, and triaxiality of the Thick Disk. This project examined the types and motions of the excess stars in order to explain their existence using the method of star counts. We completed and analyzed a survey of Quadrants 1 and 4 of the Galaxy (those in the direction of the galactic center). Using image reduction procedures, we converted the observations into stellar catalogs organized by magnitude and color, then used data mining techniques to identify stars that appear to be part of the excess. Color and magnitude indicated the distance and type of the excess stars through the method of photometric parallax. Spectral observations, taken by collaborators at the University of Minnesota, were to be used to determine the motion of the excess stars due to the gravitational effects from the Galaxy. We then incorporated the data into an updated model of the Galaxy and applied an optimization technique known as a ?genetic algorithm? to find the best fit parameters of the galactic model. This model helped us to better study the galactic asymmetry and the ranges of color, magnitude, and spatial motion of these excess stars. We showed that the excess is located entirely above the galactic plane, which suggests that the Hercules Thick Disk Cloud is the remnant of a galactic merger.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2009
- Accession Number
- ADA524072
Entities
People
- Aaron P. Haviland
Organizations
- United States Naval Academy