Ultracool dwarfs (UCDs) are the lowest-mass stars and brown dwarfs (effective temperatures < 3,000 K), with trillions of years for their lifetime, so they are excellent tracers for our Milky Way's formation history and evolution. Due to their intrinsic faintness and peak in near-infrared waveband, the majority of these objects found to date are in our immediate solar neighborhood.
My thesis work is mainly on measuring precise radial and rotational velocity of ultracool dwarfs (UCDs), using a Markov chain Monte Carlo forward-modeling technique, to model high-resolution spectroscopic data including the Keck NIRSPEC spectrometer (R~25,000-35,000) and SDSS/APOGEE (R~22,500) spectrometers, for a sample of size of ~1,000. Studying these two parameters enables us to study their population and individual kinematics, binaries, and rotations. The ultimate science goal is to understand their formation history and evolution through population kinematics, and therefore to examine and constrain the fundamental parameters at lowest-mass end including mass function, star formation history, and brown dwarf evolutionary models.
We also develope a modified data reduction pipeline from the NIRSPEC Data Reduction Pipeline (NSDRP) and a forward-modeling routine code. The foward-modeling tool has been used in multiple peer-reviewed publications, including Wilcomb et al. (2020) and Sahlmann et al. (2021).
As an international student from Taiwan, I got my B.S. in Physics at National Tsing Hua University (NTHU) in 2014 (and a member of NTHU's astronomy club) and started as a physics graduate student at UC San Diego from 2016. When I am free, I like to listen to classical, pop, R&B musics, to sing/karaoke, to brew coffee, and to play tennis.
Physics PhD student, UC San Diego
B.S. Physics, National Tsing Hua University, Taiwan
lowest-mass stars and brown dwarfs, medium-/high-resolution spectroscopy, stellar kinematics, binaries, stellar rotations
Radial and Rotational Velocities of Ultracool Dwarfs Using Keck/NIRSPEC and SDSS/APOGEE High-Resolution Spectrometer
Precise RV time series are essential for identifying binaries and measuring their orbital parameters and masses, combining relative and absolute astrometry measurements. Here is an example that shows the modeling fit of a likely brown dwarf triple system using the forward-modeling technique. One of my research projects includes modeling all archival and obtained NIRSPEC UCD spectra using such techique (number of sources > 450). I have modeled 37 nearby (<20 pc) T dwarfs and achieved median precisions of 0.5 km/s, 0.9 km/s for RV and vsin i, respectively. The project expands the understanding of the T dwarfs in the solar neighborhood by >4 times larger compared to the previous local T dwarf 6D kinematics studies. Interested readers can check out my poster presented at the Cool Stars 20.5 virtual conference. The result is available on arXiv and was accepted in ApJS!
Besides research, I am also interested in teaching and outreach activities.
undergraudate stellar astrophysics (PHYS5, PHYS 160)
undergraudate stellar classical mechanics (PHYS 1A)
undergraduate physics lab: classical mechanics (PHYS 2BL)
undergraduate physics lecture/lab: modern physics (PHYS 2D/2DL)
California Professoriate for Access to Physics Careers (CPAPC) Southern California Physics GRE Bootcamp
Python Workshop for Physics Undergraduate Students (2019, 2020)
2019 Institute for Scientist & Engineer Educations (ISEE) Professional Development Program (PDP)
2017 IOA Science Innovation Camp Physics Outreach
2019 The Barrio Logan Science & Art Expo