Welcome!
Welcome to my web page! My name is Zhexing Li and I am a PhD candidate in the Department of Earth and Planetary Sciences at University of California, Riverside (UCR) working in Prof. Stephen Kane's group. My research interests are detection and characterization of exoplanets using radial velocity and direct imaging methods, and pretty much any other things related to these.
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Before coming to UCR, I received a Bachelor of Science degree from University of California, Santa Barbara (UCSB), with a major in Physics and a minor in Astronomy and Planetary Sciences. After graduation, I interned at Las Cumbres Observatory (LCO) for a year, then moved to Boston and earned a Master of Arts degree in Astronomy from Boston University (BU) after another two years of study.
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Feel free to browse through other sections of my webpage for more on my work and personal life. If you have any questions, please don't hesitate to contact me.
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RESEARCH
My research interest covers a range of topics, all related to detection and characterization of exoplanets. My current work involves the radial velocity (RV) and direct imaging (DI) techniques, and I have past experience with the microlensing method as well.
Radial Velocity
RV detection of exoplanets employs the measurement of periodic line-of-sight red and blue shifts observed in the stellar spectral lines due to the gravitational tugs exerted by the planets on the star as the planets orbit around it. Through long term observations, periodic oscillations due to exoplanets around stars ranging from days to years can be revealed, if there're any. I'm currently using data from telescopes such as Automated Planet Finder, Keck, and Anglo-Australian Telescope, combining with modeling tools to search for new exoplanet candidates. I'm also interested in the characterization of periodic and non-periodic stellar activity signals such as magnetic cycle and stellar jitter to identify any false postive detections as well as to minimize the effect of random noises on low mass planetary signals, all are important for future extreme precision RVs.
Radial velocity demonstration. Credit: ESO
Direct Imaging
Unlike other indirect detection methods, DI is able to see the planets directly using infrared emission, or light reflected off the surface or the atmosphere of the planets. It relies heavily on instrumentaion (such as coronagraph, starshade, wavefront sensing and control) and image processing techniques to block out the starlight, achieve high instrumental contrast ratio, and remove various sources of noise. I'm currently involved in the exoplanet direct imaging precursor science preparation of NASA's Nancy Grace Roman Space Telescope. Using RV data and simulations, I'm trying to refine the orbital ephemerides of known planets that are ideal DI candidates as part of the target selection process to ensure future imaging observations happen at the right times when the planets are at the right places in their orbits. In addition, I'm working on combining RV and DI detection limits, along with dynamical simulations, to predict the possibility of discovering new low mass exoplanets within known systems with future imaging missions.
Direct imaging time series of HR 8799 system. Credit: Jason Wang & Christian Marois
Microlensing
Exoplanets microlensing event happens when the gravitational field of a foreground planetary system acts as a lens, bending and magnifying the light from the background, more distance object, when the planetary system passes in front of the background object along our line of sight. Planetary microlensing events are rare and easy to miss, and thus requires global effort for 24/7 monitoring when such event occurs. During my time at Las Cumbres Observatory, I helped develop and improve the microlensing observation and data pipeline there and was part of several microlensing projects. On one of the key projects, we carried out first-time-ever simultaneous microlensing observations with two space telescopes, Spitzer and Swift, as well as ground observations that resulted in a brown dwarf discovery.
Microlensing demonstration. Left: Observed lightcurve, middle: slightly exaggerated what we see, right: top down view of the geometry. Credit: NASA
Personal
I'm interested in a variety of things outside my research. I play the trumpet and the piano. I picked up my rudimentary keyboard skills during college but I have been playing the trumpet since early elementary school. I had been in several wind ensembles and orchestras during middle school, high school, and college years. AND, I was the principal trumpet player in my middle school and high school's wind ensembles. Though how often I practice them now is a big question...
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I'm a huge sports fan: soccer (calling it football like the rest of the world makes much more sense!!!), basketball, and Formula One. I'm a die hard fan of Real Madrid and Ferrari. I rarely miss a Formula 1 grand prix despite the mediocare performances of the Ferrari cars for the recent seasons. Sorting out my sleeping schedule is a pain though when the race weekends are in Europe, which is over half of each year's racing calendar.
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I enjoy the movie going experience (when there's no pandemic of course). With my experience in orchestras, naturally I'm a big fan of orchestral music. I collect soundtracks from movies, tv shows, documentaries, movie trailers, and sometimes even games. I have a massive collection with over 18,000 tracks collected and still counting. Being a lossless aficionado, of course these are all of premium quality.
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I like hiking, video games sometimes (World of Warships), and of course, good food (I mean... who doesn't).
My Yamaha-8445 B-flat trumpet with all my mouthpieces and mutes...
One of the many pandemic hikes: Mount Baldy in SoCal. Elevation:10,064 ft (3068 m).