Debris Disk Chemistry

The processes that produce exoplanets begin early in the life of the host star, with formation of an equatorial disk of gas and dust. Extrasolar planetary studies focus on these circumstellar disks, which are found at various stages of stellar life and ultimately give rise to the diverse range of planets we see today. There are important stages of disk evolution that are not well understood. For my senior Honors Capstone at American University, I studied debris disks, representing an intermediate stage between gas-rich protoplanetary disks and mature planetary systems.  I worked Dr. Alycia Weinberger at the Department of Terrestrial Magnetism (Carnegie Institute of Washington), in collaboration with Dr. Aki Roberge of the GSFC. At the DTM I examined Magellan Inamori Kyocera Echelle (MIKE) spectra from young, rapidly-rotating ‘shell’ stars for chemical signatures of gas components in debris disk candidates, and possible variability in the observed lines caused by planetesimals. These stars are known to have circumstellar gas, and some also show evidence of dust, indicating that they harbor debris disks. My work built upon the paper by Drs. Roberge and Weinberger extending the sample of known disks containing gas and dust. Such a sample is vital to investigating the mysterious and complicated interaction between gas and dust during terrestrial planet formation – how do these components influence each other as the host star evolves, what causes the initial coagulation of particles, and what subsequent mixing may bring organics and volatiles to the newly forming planets? I measured the positions and strengths of absorption lines, then compared these measurements to nearby stars and detailed stellar models in order to eliminate lines originating from the interstellar medium. Additionally, I calculated velocity variations to look for evidence of binary companions. More details and results can be read here.