Over the last couple years, I've had the privilege to work with Samuel Yee, an exceptionally talented undergraduate. Last week, Sam graduated from Caltech and was awarded the George W. Housner Prize for Academic Excellence and Original Research. Sam will be starting grad school at Princeton in the fall. I couldn't be more proud.
I first met Sam when he was a sophomore and eager to get some research experience. I pitched him two projects: The first was a fairly straightforward summer project that involved the application of a standard analysis to an existing dataset. The second was a more off-the-wall idea to create a new method for analyzing stellar spectra. This project, I warned, would be about five times harder and may not even work at all. Sam eagerly jumped at the latter, and at that moment, I knew I had met a remarkable undergraduate.
The project eventually evolved into SpecMatch-Emperical, an open-source code for deriving fundamental stellar properties from spectra, such as a star's temperature, radius, and metallicity (Yee et al. 2017). This is a particular challenge for cool stars (K and M spectral types). These stars have complex spectra with many molecular lines that are hard to model ab initio with synthetic spectra. Sam's code circumvents inaccuracies in model spectra by using empirical spectra of "touchstone stars" with well measured properties. Today, SpecMatch-Empirical is an important tool in my team's efforts to characterize planet hosts discovered by Kepler and K2.
Over his junior year, Sam shifted his efforts to studying multiplanet dynamics in the HAT-P-11 system. HAT-P-11b was one of the first Neptune-size planets discovered outside the Solar System (Bakos et al. 2010). HAT-P-11b is an unusual planet. Even though its orbital period is only ~5 days it still has a moderately elliptical orbit (e = 0.2), about that of Mercury. Moreover, the planet is tilted by about 90 degrees with respect to the star's spin, in contrast to the Solar System planets, which are all aligned to a few degrees.
Over the past decade, the California Planet Search has been monitoring the HAT-P-11 system, looking for signs of other planets. Sam analyzed this dataset and discovered an new planet, HAT-P-11c (Yee et al. 2018). This planet is similar to Jupiter in terms of its mass and orbital period, but has a highly elliptical orbit (e = 0.6), higher than any Solar System planet. Working with Konstantin Batygin, we found that this distant giant planet can explain the tilted orbit of the inner planet through a process called "nodal precession."
Thanks to Sam's work, we now know that the star HAT-P-11 harbors both a close-in Neptune and a distant Jovian. Previous transit and RV surveys have shown that both classes of planets
are fairly common, but we rarely get to study them in the same system. As more such systems are found, we will learn more about the dynamical connections between the inner and outer regions of planetary systems.
Congrats again, Sam, and good luck at Princeton!