Research theme

I conduct research on exoplanets which are planets found outside our Solar system. My research aims to deepen our understanding of planets in the Solar system, especially Earth, by studying the properties of diverse planetary systems in the Universe. During my PhD, I led and supported various international projects that focused on discovering and characterizing planets with various sizes and ages, revealing valuable information about their diversity, formation, and evolution. This research resulted in three first-author and 60+ other high-impact publications in scientific journals. Here is a summary of my past research.

Past research

  1. Discovered 37 new exoplanets using the Kepler telescope. The Kepler/K2 space telescope have successfully identified thousands of planet candidates, but many more await to be validated as planets. My work contributed to the mission’s planet yield by discovering and validating new exoplanets using data from the K2 mission. I employed a novel approach by combining data from multiple observation campaigns to uncover otherwise hidden planet signals and precisely measure their properties. Notably, I discovered the exoplanet with the longest known orbital period observed by K2 (de Leon et al., 2021; See also Fig. 1). Together with related studies, our research group has confirmed a total of 156 exoplanets smaller than Jupiter, including the largest exoplanet haul for Japan. These findings enhance our understanding of the diversity of exoplanetary systems and support future studies.
Fig. 1. The planets discovered in de Leon et al. (2021) in the context of all known planets found by K2 telescope shown in density contours.
  1. Characterized a young exoplanet with precisely measured mass found using the TESS telescope. Studying exoplanets younger than 1 billion years old is important because they provide insights into the early stages of planetary evolution that shape them into maturity. However, out of the thousands of known exoplanets, fewer than 30 young stars with transiting planets have been identified to date (See Fig. 2). This is mainly due to the technical difficulty in detecting the planet signal that is drowned by the noise from the host star. In my most recent work, I focused on the discovery of young exoplanets by specifically targeting young stars observed by the Transiting Exoplanet Survey Satellite (TESS) space telescope. I led a large international team of astronomers to discover and validate a young Neptune-sized exoplanet named TOI-179b (de Leon et al., 2023). This benchmark discovery is important because it is one of the only ten young planets where fundamental parameters including planet mass are precisely measured. The result of this work is very crucial for future detailed studies of young exoplanets that allow direct comparison between the results of observations and theoretical predictions. Other related works I co-authored about the discovery or follow-up characterization of other young planet systems include: (1) A grazing Saturn-sized planet in TOI-837 in a young star cluster (Bouma et al., 2020); (2) One of the first transiting multi-planet systems discovered in the Praesepe open cluster (Livingston et al., 2018c); and (3) the first ever mass measurement of a young low-density Neptune-sized planet in K2-100 (Barragan et al., 2019).
Fig. 2. The discovered young planets in the context of all known planets found by K2+TESS shown in density contours, of which very few have measured masses including the planet discovered in de Leon et al. (2023).
  1. Conducted detailed studies of the environments where young stars and planets form using the Subaru telescope. My current research on exoplanets orbiting young stars builds upon my previous work focused on characterizing young stellar objects (YSOs), which are believed to be the birthplaces of planets. These studies include the observation of unique tail structures in the disk around the pre-main sequence star SU Aur observed in high resolution for the first time using the 8-m class Subaru telescope (de Leon et al., 2015; See also Fig. 3). For more details, see also my report submitted for my internship at Academia Sinica. Other related works I co-authored about YSOs include: (1) a follow-up investigation of the tail structure associated with the SU Aur disk observed in radio wavelength (Akiyama et al., 2018); (2) Detection of other disk features such as gap and spiral-like structures in LKHa 330 in multiple wavelengths (Uyama et al., 2018); and (3) Characterization of misaligned disks around the SR 24 triple star system (Mayama et al., 2019).
Fig. 3. Polarized intensity image in log-scale overlaid with polarization vector map of what resembles a tail structure associated with SU Aur in de Leon et al. (2015). The region 0. 15" (~20 AU) around the star is masked to emphasize only the disk morphology

Present research

Currently, I lead our research laboratory’s efforts in discovering young transiting exoplanets using the analysis pipeline I developed, and characterizing them in detail using a suite of state-of-the-art instruments like MuSCAT. MuSCAT is a high precision simultaneous multi-band imager which I helped build and operate remotely across 4 continents in the past seven years. In fact, we just commissioned MuSCAT4 in Siding Spring Observatory in October 2023. The MuSCAT series project is part of a large multinational program called TESS Follow-up Observing Program (TFOP) where our team provides time series photometry data taken using MuSCATs and other instruments in the Las Cumbres Observatory (LCO) network to validate planetary candidates found by the TESS telescope. In this project, my role in our laboratory is to develop and maintain our analysis softwares to deliver fresh data products (mainly taken with MuSCAT2) to the exoplanet research community almost on a weekly basis.

Projects (work in progress)

  • Searching for transiting planets in (open) star clusters and young moving groups using quicklook
  • Detecting Transit Timing Variations (TTVs) in young multi-planet systems
  • Discovery and mass confirmation of a rare short-period gas giant planet transiting a wide M dwarf binary (de Leon et al., in prep)