UCLA

This thesis performs unprecedented investigations for spectroscopic binaries at the Galactic center and utilizes the development and extended observing baseline of integral field spectroscopy behind adaptive optics. The second chapter of this thesis describes the first direct search for binarity of its kind for the star S0-2, the most well-studied star of the S-star cluster. Almost two decades of spectroscopic with adaptive optics has led to the capability to look for a binary signal in S0-2's spectroscopic data. We introduce a methodology for investigating periodicity and placing limits on binary parameters with radial velocity data. We do not detect any signs of binarity for S0-2 and place limits on a hypothetical companion mass for S0-2 to be 1.6 solar masses, which is below current detection limits. We also investigate and find that a feasible spectroscopic binary system would not bias the detection of relativistic redshift, a post-Newtonian spectroscopic measurement.

The third chapter of this thesis explains the improvements in spectral analysis that lead to greater sensitivity to spectroscopic binary systems. We use a new method for measuring radial velocity measurements of stars at the Galactic center. This new method utilizes spectral fitting software and a new infrared spectral grid that finally covers effective temperatures of 30,000 K, putting the young, massive S-stars at the Galactic center within reach. We improve the precision of our radial velocities by a factor of 1.7. We also test our methodology on radial velocity standard stars and find that the new method eliminates the slight bias of our previous method. These characteristics of this method make us more sensitive to detecting the radial velocity variations of spectroscopic binary stars.

The fourth chapter presents a systematic search for spectroscopic binaries at the Galactic Center. With over two decades of integral field spectroscopy data, advanced tools for fitting mid-infrared stellar spectra, and 1000 radial velocity data points, we conduct a spectroscopic binary search of 29 stars at the Galactic center. After subtracting a star's motion around the supermassive black hole, we search for a periodic signal using a Lomb-Scargle analysis and fitting the residual radial velocity curve to a binary system radial velocity curve. We find no significant periodic detections in our sample, suggesting there are no binaries among the S-stars. We also place limits on the hypothetical companion masses of these S-stars. We also place a limit on the intrinsic binary fraction of these stars at 42%, which disagrees with the binary fraction for massive field stars. These results favor S-star formation mechanisms that result in a low binary fraction.

The final chapter presents new integral field spectroscopic observations of stars in the nuclear star cluster. We present data taken over 6 years and add the spectral types of 169 stars: 47 of which are Wolf-Rayet and O/B stars, and the remaining 122 are K and M giants. This addition to the rich Galactic center integral field spectroscopy data set provides opportunities to further study stellar demographics and dynamics of the nuclear star cluster.