Research keywords

Exoplanet, Lightcurve analysis, Kepler data, Alignment in all scales (planet, star, galaxy...), Exoplanetary ring, Sparse modeling , Star formation, Mapping of Exoplanets, the Tomo-e Gozen project, the HeSO survey

Papers (first-author)

・Global Mapping of an Exo-Earth using Sparse Modeling

(Masataka Aizawa, Hajime Kawahara & Siteng Fan, ApJ (2020))

- Directly imaged light curves of Exo-Earth are known to be used to create global maps of the planets (e.g. Ford+2001, Kawahara&Fujii 2010). Recently, Fan+2019 recovered the global map of the Earth from 2yrs-observations of the reflection light curves by DSCOVR. In this study, we introduced sparse modeling to the global mapping problem. Since our scheme can efficiently determine the coverage of the ocean, which is set to be zero in solving the problem, the recovered maps with the new technique can give the well-determined map. We also find that even if we consider associated noises and shorter observational duration (even 1 day/1 month!), we can recover the global map of the Earth.

・Search for Alignment of Disk Orientations in Nearby Star-forming Regions: Lupus, Taurus, Upper Scorpius, ρ Ophiuchi, and Orion

(Masataka Aizawa, Yasushi Suto, Yoko Oya, Shiro Ikeda, Takeshi Nakazato, ApJ (2020))

- Inspired by recent arguments on spin alignment in stellar clusters (e.g. Corsaro+2017), we attempted to search for alignment among orientations of proto-planetary disks. Spatial correlations among directions of angular momentum are likely to reflect global conditions of star formation if exist, so our approach can directly clarify the origins/implications of alignment. In the search, we exploited several surveys for disks, which are highly resolved by ALMA, to discuss the alignment. Except for a marginal detection of alignment in the Lupus III region, disk rotational axes are randomly oriented, consistently with the turbulent nature of angular momentum.

・Systematic Search for Rings around Kepler Planet Candidates: Constraints on Ring Size and Occurrence Rate

(Masataka Aizawa, Kento Masuda, Hajime Kawahara, Yasushi Suto, AJ (2018))

- On the basis of Aizawa+2017, we continued to search for exorings using the Kepler light curves. Since ring signatures are so tiny that they can be smoothed out in long-cadence data, we focus on short-cadence data in the analysis. Among pre-selected 168 candidates with sufficient S/Ns for the ring search, no system shows a robust evidence of a ring system. We found the frequency of Saturn-sized rings to be less than 15% for typical Kepler planets.

・Towards Detection of Exoplanetary Rings Via Transit Photometry: Methodology and a Possible Candidate

(Masataka Aizawa, Sho Uehara, Kento Masuda, Hajime Kawahara, Yasushi Suto, AJ (2017))

- Previous studies rely on pixel-by-pixel integrations for calculating transiting light curves by ringed planets (e.g. Ohta 2009). In this study, we gave a new analytical formulation for the calculation using quartic equations. We applied it to the Kepler light curves, mainly focusing on long-periods planets, since they are likely to harbor icy rings. Our attempt left one potential candidate (aasnova: "The Search for Ringed Exoplanets")