About me

Hi! I am an Astronomy grad student at Caltech. My interest lies in exoplanet astrophysics. Specifically, I am working on direct imaging and spectroscopy, a challenging yet rewarding technique that allows us to capture and analyze photons from an exoplanet

I received a BA in Physics from Pomona College (2019), where I spent 4 enriching years learning about the universe, widening my worldview through a philosophical reading club I organized, and developing a passion for the outdoors. I am grateful to my mentors Philip Choi and Elijah Quetin, among many other professors who lent me a guiding hand. While at Pomona, I got the opportunity to work at Caltech for the summers, and got my first intensive research experience in Dimitri Mawet's ETLab. For my first project, I worked on building the prototype for a fiber injection unit that links a high contrast imaging system with a downstream spectrograph. In my second project, I wrote a data reduction pipeline for images taken with the Keck/NIRC2 vortex coronagraph, and helped design a database and website for visualizing the data. For these projects, I worked closely with Garreth Ruane and Henry Ngo, who inspired me to continue research and taught me a tremendous amount. During my last summer, I worked with Marta Bryan and Heather Knutson on using Keck/NIRSPEC spectra to measure the rotation rate of a young super-Jupiter, and detect water and carbon monoxide in its atmosphere.

Before graduating Pomona, I won the Downing Fellowship to pursue a MPhil in Astronomy at the University of Cambridge (2020). There, I worked with Mark Wyatt on calculating the 3-D orbits of dynamical masses of giant planets discovered by the radial velocity technique. We applied our method on several systems, placing direct constraints on the mutual inclination between the giant planet and their inner transiting planets and/or outer debris disks. While at Cambridge, I learned cooking and punting, while serving as captain of an intramural badminton team.

Research Experience

Clouds and atmospheric composition of a brown dwarf companion with KPIC (2021-)

My main research focus is on The Keck Planet Imager and Characterizer (KPIC), a suite of instrument upgrades to Keck II, enabling high-resolution spectroscopy of directly imaged planets and brown dwarfs at high contrast. my primary mentor is Dimitri Mawet, and I also work closely with Jason Wang, Jean-Baptiste Ruffio, and Heather Knutson. I made an early contribution to KPIC in the summer of 2016, when I built and tested the fiber injection unit (FIU) that links the Keck II adaptive optics system and Keck/NIRSPEC. I helped publish this work as third-author in Mawet et al. 2017. I am currently studying the KPIC spectrum (R~35,000) and GPI spectrum (R~50) from a brown dwarf companion, an analog to young directly imaged giant planets, with the goal of studying exoplanet atmospheres and compositions, measuring rotation rates, and constraining the possibly different formation mechanisms of giant planets and brown dwarfs. Paper in preparation, stay tuned!

Mutual inclination between

Direct measurements of orbital mutual inclinations (2020-)

I'm also interested in combining different methods (imaging, radial velocity, astrometry) to constrain 3D orbital architectures and masses of exoplanets. I started this work at Cambridge with Mark Wyatt. Our results on π Men and HAT-P-11 in Xuan & Wyatt 2020, and results on the two debris disk systems in Xuan et al. 2020b .

How fast does a young planet rotate? (2018-2019)

I analyzed K-band NIRSPEC spectra of the exoplanet DH Tau b to measure its rotation rate, and found that it spins at only 10% of its breakup velocity despite its young age (~2 Myr) By comparing the rotation rates of giant, wide-separating exoplanets like DH Tau b to that of low-mass, isolated brown dwarfs, we probed whether these two populations share the same formation mechanism. We also detected carbon monoxide and water in the planet's atmosphere with high significance. This work has been published in Xuan et al. 2020a.

Characterizing the Keck/NIRC2 vortex coronagraph (2017-2018)

In the summer of 2017, I wrote software to automate the data processing workflow for the Keck/NIRC2 vortex coronagraph, and helped set up a Mongo database and a Flask website to organize and display the data products. These tools are still in use by the group. With the pipeline, I re-reduced archival data of more than 300 stars with Henry Ngo, and wrote a paper (Xuan et al. 2018) on characterizing the instrument's performance (i.e. how faint of a planet could we detect) as a function of observing conditions, stellar properties, and the observing modes. We systematically compared angular diffential imaging and reference differential imaging, and created a tool predicting contrast based on the archival data using random forests. This work has been published in Xuan et al. 2018.


I publish as Jerry W. Xuan. Previously, I've also published as Wenhao Xuan and W. Jerry Xuan.


Teaching and Outreach

In the summer of 2019, I worked for 6 weeks as Teaching and Residential Assistant for the Summer Science Program, where I am alumnus (2014). In the Astrophysics camp, students participate in an intensive research project on asteroid orbital determination, organizing their own observations and reducing real telescope data. As TA, I helped with late-night observing runs, homework sessions, and answering questions. I also lived together with the students, organized fun activites including sports, board games, boba and hiking trips. It was an incredibly rewarding experience to see the participants grow both as scientists and human beings.
During college, I worked as TA for several physics and astronomy classes, including Observational Astrophysics (twice), Intro to Astronomy, and Advanced Intro Physics.