RESEARCH

I am a graduate student working with Andrea Ghez and the UCLA Galactic Center Group. For my thesis, I am determining the orbits of ~100 young, massive stars in the Galactic center using high-precision astrometric measurements obtained with the Laser Guide Star Adaptive Optics system at the Keck Observatory.

Selected Publications can be found here.

[Photo taken by Andrew Cooper from WMKO; Keck II is pointed at the Galactic Center.]

NIRC2 OPTICAL DISTORTION:

High-precision astrometric measurements can only be made if systematic errors are properly characterized and taken into account. For Galactic center astrometry, we are currently limited by residual optical distortion. Thus, our group has created a new distortion solution for the NIRC2 narrow camera at Keck (Yelda et al. 2010) to help minimize this source of systematic error. We have significantly improved upon previous distortion solutions using, for the first time, on-sky observations of the globular cluster M92. Please forward any questions or comments regarding the distortion solution to me.

Download the NIRC2 distortion solution here.

YOUNG STARS AT THE GALACTIC CENTER:

I am currently working on using kinematic measurements of the young stars in the Galactic center in an attempt to determine their origin. Their proximity to Sgr A* is a mystery since it is difficult for stars to form in the face of the strong tidal forces from the supermassive black hole. Approximately half of these stars are known to orbit in a clockwise disk around Sgr A* (Lu et al. 2009, Paumard et al. 2006, Genzel et al. 2000), while the other half are on more randomly distributed orbits. We currently have a 16-year baseline of high precision astrometric measurements and are measuring plane-of-the-sky accelerations out to 1.5" away from Sgr A*, the furthest such measurements to date. With such acceleration measurements, we can determine direct stellar orbital parameter estimates, which we can then use to constrain star formation scenarios.

Previous research:

At the University of Michigan, I worked with Professor Sally Oey on HII regions and the warm ionized medium (WIM) in galaxies from the Survey for Ionization in Neutral-Gas Galaxies (SINGG). We measured the fraction of H-alpha luminosity contributed by the WIM for various types of galaxies and studied the WIM's relationship with different star formation properties. See our paper for more details.

I also worked with Professor Robert Mathieu at the University of Wisconsin during the summer of 2005 as part of the Research Experience for Undergraduates (REU) program. My project was on the tidal circularization of stellar binaries in the open cluster, NGC 6819. See my REU webpage for details of this project.

My first project in astronomy, with Diane Paulson, involved searching for substellar mass companions to young stars, which often are neglected in radial velocity searches because the increased level of stellar activity makes detecting companions more difficult. We did not find evidence for any companions, but we report the derived stellar parameters for dozens of nearby young stars in our paper.

Selected publications:

Clarkson, W., Ghez, A. M., Morris, M. R., Lu, J. R., Stolte, A., McCrady, N., Do, T., & Yelda, S. Proper motions of the Arches cluster with Keck LGS-Adaptive Optics: The First Kinematic Mass Measurement of the Arches, ApJ accepted.

Yelda, S., Lu, J. R., Ghez, A. M., Clarkson, W., Anderson, J., Do, T., & Matthews, K. Improving Galactic Center Astrometry by Reducing the Effects of Geometric Distortion, 2010, The Astrophysical Journal, 725, 331.

Yelda, S., Ghez, A. M., Lu, J. R., Do, T., Clarkson, W., & Matthews, K. Increasing the Scientific Return of Stellar Orbits at the Galactic Center, 2011, ASP Conference Proceedings: The Galactic Center: A Window on the Nuclear Environment of Disk Galaxies", ed. M. R. Morris, D. Q. Wang & F. Yuan, pp. 167

Do, T., Ghez, A. M., Morris, M. R., Lu, J. R., Matthews, K., Yelda, S., & Larkin, J. High angular resolution integral-field spectroscopy of the Galaxy's nuclear cluster: a missing stellar cusp? 2009, The Astrophysical Journal, 703, 1323.

Do, T., Ghez, A. M., Morris, M.R., Yelda, S., Meyer, L., Lu, J.R., Hornstein, S.D., Matthews, K. A Near-IR Variability Study of the Galactic Black Hole: A Red Noise Source with No Detected Periodicity, 2009, The Astrophysical Journal, 691, 1021.

Ghez, A.M., Salim, S., Weinberg, N., Lu, J., Do, T., Dunn, J.K., Matthews, K., Morris, M., Yelda, S., Becklin, E.E., Kremenek, T., Milosavijlevic, M., & Naiman, J. Measuring Distance and Properties of the Milky Way's Central Supermassive Black Hole with Stellar Orbits, 2008, The Astrophysical Journal, 689, 1044.

Oey, M.S., Meurer, G.R., Yelda, S., et al. The Survey for Ionization in Neutral Gas Galaxies. III. Diffuse, Warm Ionized Medium and Escape of Ionizing Radiation, 2007, The Astrophysical Journal, 661, 801.