PI: Joleen Carlberg, jcarlberg@stsci.edu
Website: https://www.stsci.edu/~jcarlberg/
Graduate Student: 1 year rotation (potential thesis option)
Undergraduate: Summer
Abstract: The elemental abundances of red giant stars are exciting potential tools for understanding the pollution of stellar hosts by planet formation processes, as well as the bulk composition of exoplanets tidally engulfed by their host stars. Utilizing ground based, high S/N echelle observations, we propose to measure the relative abundances of 16 elements in a sample of ~100 red giant stars that both do and do not host planetary companions and that both do and do not show signs of enhanced rotation (a potential signature of planet engulfment). The goal is to identify differences in the abundances patterns of these different sub-groups of red giants to better understand when and how planet engulfment occurs.
Student Work:
All of the data are in hand, reduced, and partially analyzed. The student will work with and have the opportunity to further develop a custom equivalent width (EW) measuring tool in python. The project is at the stage where iron abundances have been measured for all stars, but the EW tool needs to be run and vetted for the remaining spectral features. The student will learn about precision stellar abundance measurements and standard stellar LTE line analysis codes used in the field. The other remaining task is searching for abundance pattern variations among the subsamples of stars (planet hosts, non-hosts, and planet engulfing candidates) and interpreting results. Students will have the opportunity to contribute to and/or lead resulting papers.
Fig 1. Motivation for this study showing the distribution of known exoplanets' masses and orbital separations (as of 2015). Overlaid as vertical lines are typical red giant radii at various stages of red giant evolution, showing how many planets' orbits are within the future radius of their host stars. Tidal forces will allow engulfment of even farther exoplanets.
Fig 2. Example screenshot of the custom equivalent width fitting tool. Currently written as a Jupyter notebook, this code allows a good balance of automation with the ability to fine tune fitting parameters to allow good continuum fit. Many automated routines fail because the optimal fitting window for defining the continuum in stars with high density of lines varies line-to-line and sometimes star-to-star.
