Abstract:

One of the most perplexing problems associated with the supermassive black hole at the center of our Galaxy is the origin of the young stars in its close vicinity. In this thesis, the question of the young stars' origins is addressed using high-resolution infrared images obtained at the W. M. Keck telescopes to study both the distribution and kinematics of the young stellar population.

First, using proper motion measurements and stellar number density counts based on 9 years of diffraction-limited K(2.2 ? m)-band speckle imaging at the W. M. Keck 10-meter telescopes, we have identified a new comoving group of stars, which we call the IRS 16SW comoving group, located [Special characters omitted.] (0.08 pc, in projection) from the central black hole. Four of the five members of this comoving group have been spectroscopically identified as massive young stars, specifically He I emission-line stars and OBN stars. This is the second young comoving group within the central parsec of the Milky Way to be recognized and is the closest, by a factor of 2, in projection to the central black hole.

Second, we present new proper motions from the 10 m Keck telescopes for a puzzling population of massive, young stars located within a parsec of the supermassive black hole at the Galactic Center. Our proper motion measurements have uncertainties of only 0.07 mas/yr (3 km/s), which is [Special characters omitted.] 7 times better than previous proper motion measurements for these stars, and enables us to measure accelerations as low as 0.2 mas/yr 2 (7 km/s/yr). These measurements, along with stellar line-of-sight velocities from the literature, constrain the true orbit of each individual star and allow us to directly test the hypothesis that the massive stars reside in two stellar disks as has been previously proposed. Analysis of the stellar orbits reveals only one disk of young stars. No second disk was detected using a method that is capable of detecting disks with half-opening angles of 19? and containing at least 7 stars. The detected disk contains 50% of the young stars and is inclined by ~115? from the plane of the sky and oriented at a position angle of ~100? East of North. Additionally, the on-disk and off-disk populations have similar K-band luminosity functions and radial distributions that decrease at larger radii as r-2 . The disk has a finite thickness as expressed by an out-of-the-disk velocity dispersion of 28 ? 6 km/s, and several candidate disk members have eccentricities greater than 0.2. The comoving group, IRS 16SW, makes up the South-Eastern component of the disk as stars on the other side of the disk are less apparent due to higher extinction. Our findings suggest that the young stars may have formed in situ but in a more complex geometry than a simple thin circular disk.

Finally, future astrometric studies of the young stars in the Galactic Center will take advantage of the factor of 5 improvement in astrometric precision that is possible with new laser guide star adaptive optics imaging techniques. We show that careful data calibration and analysis, including correcting for differential atmospheric refraction, results in a relative astrometric accuracy of ~0.2 mas over multi-year time scales. To achieve this level of accuracy, we find that many individual images of the Galactic Center should be combined to produce a long integration time (~25-50 minutes) in order to average down the short time scale, high-order astrometric fluctations that are apparent in individual 30 second exposures. These improvements in astrometric precision and accuracy not only offers the opportunity to measure the accelerations for more young stars at larger radii than has previously been possible, but is also applicable to a much broader range of scientific experiments beyond the Galactic Center.