UC Santa Barbara

The relatively young field of exoplanets promises exciting new discoveries and insights into other planetary systems much like and unlike our own, thanks to the development of advanced instrumentation, observing techniques and analysis techniques. To date, thousands of nearby exoplanets have been discovered via various methods such as transit detection, radial velocity, astrometry, micro-lensing, and direct imaging. Among these methods, direct imaging is the only method to directly receive photons from the sub-stellar companions that are distinguishable from their host stars. As such, it offers unique characterizations to the surface properties of these companions and offer us rich information on the astrometry, mass, atmospheres and evolution of these objects, especially when combined with all other methods.

Throughout my Astrophysics PhD thesis titled "Characterizing Exoplanets, Brown Dwarfs, and Proto-planetary Disks with High Contrast Imaging", I present an exploration into the development of advanced data analysis techniques for high contrast imaging data, alongside their application in characterizing celestial objects. The introductory chapter provides overviews for the subjects covered in each subsequent chapter. In Chapter 2, I contextualize the significance of direct imaging in characterizing these celestial objects, emphasizing the challenges posed by their extreme contrast and close angular separations from their host stars in ground based imaging. Leveraging sophisticated instrumentation and post-processing algorithms, I introduce the pyKLIP-CHARIS Post-Processing Pipeline within the pyKLIP framework, offering a Python-based data analysis tool for reducing and analyzing observation data taken by the CHARIS instrument on the Subaru Telescope in Hawaii. This pipeline incorporates state-of-the-art algorithms and observing techniques like KLIP, ADI, SDI, and forward modeling for PSF subtraction, facilitating the extraction of precise positions and calibrated planet spectra.

In subsequent chapters, I demonstrate the application of various imaging analysis techniques to measure properties of sub-stellar companions and the scientific insights gained from them. In Chapter 3, I delve into the characterization of a binary brown dwarf system, , utilizing long-term relative orbit monitoring and absolute astrometry data from the VLT. This comprehensive analysis yields precise individual dynamical masses for the binary components, shedding light on their mass-luminosity relationship and providing invaluable benchmarks for substellar cooling models.

In Chapter \ref{chap:disk}, my research extends to the investigation of a proto-planetary disk around HD 34700 A. Leveraging CHARIS' unique capability to obtain polarized integral field images, I gain access to the intricate structures of the disk at multiple wavelengths, and explore their implications through 3D Monte Carlo radiative transfer simulations. These simulations, combined with observed polarized intensity data, offer insights into the dust grain properties and scattering mechanisms within the disk, highlighting the complexities inherent in modeling such systems.

Finally, in Chapter \ref{chap:gl504}, I conclude my research with an on-going investigation on the infra-red spectra of two ultra-cool T-dwarfs, Gl~758~B and Gl~504~b. These are two of the coldest brown dwarfs observed so far. They share very similar host star properties and provides invaluable insight to understanding brown dwarfs atmospheres at temperatures of 500-600 K. A special beam-steering mode on the \SCExAO and \CHARIS instrument was required to capture these widely separated companions and poses unique data analysis challenges. I emphasize these challenges and the solutions that employed to address them, along with preliminary results on the astrometry and the extracted spectra of these two brown dwarfs.