RESEARCH
Photo taken by Andrew Cooper from WMKO; Keck II is pointed at the Galactic Center.
NIRC2 OPTICAL DISTORTION:
I have created a new optical distortion solution for the NIRC2 narrow camera at Keck (Yelda et al. 2010). This solution provides a factor of ~3 improvement over previous distortion solutions.
Download the NIRC2 distortion solution here
THIRTY METER TELESCOPE SIMULATIONS OF THE GALACTIC CENTER:
I am currently investigating the astrometric performance of the future Adaptive Optics imager for the future Thirty Meter Telescope, NFIRAOS/IRIS, by simulating images of the Galactic center, which include ~300,000 stars. Various sources of astrometric error, including spatially-variable point spread functions, optical distortion, and source confusion are being tested in order to develop an astrometric error budget for the Galactic center science case.
YOUNG STARS AT THE GALACTIC CENTER:
My thesis work involved using high-precision kinematic measurements of the young stars in the Galactic center to determine their orbits and constrain star formation scenarios. The young stars' proximity to the supermassive black hole, Sgr A*, is a mystery since it is difficult for stars to form in such a hostile environment. 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 use a 16-year baseline of high precision astrometric measurements and measured plane-of-the-sky accelerations out to 1.5" away from Sgr A*, the furthest such measurements to date. With such acceleration measurements, direct stellar orbital parameter estimates are determined, which place useful constraints on star formation scenarios.
Some fun movies and images I've made:
Animation of the central arcsecond stars orbiting the supermassive black hole
Image of the central arcsecond orbits around the supermassive black hole
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:
Yelda, S., Ghez, A. M., Lu, J. R., Do, T., Meyer, L., & Morris, M. R. Adaptive Optics Observations of the Galactic Center Young Stars, 2012, Proceedings of the SPIE: Astronomical Telescopes and Instrumentation.
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.