分类： 天文学 >> 天文学 提交时间： 2023-02-19
Taichi Uyama
Charles Beichman
Masayuki Kuzuhara
Markus Janson
Takayuki Kotani
Dimitri Mawet
Bun'ei Sato
Motohide Tamura
Hiroyuki Tako Ishikawa
Bryson Cale
Thayne Currie
Hiroki Harakawa
Thomas Henning
Teruyuki Hirano
Klaus Hodapp
Yasunori Hori
Masato Ishizuka
Shane Jacobson
Yui Kasagi
Eiichiro Kokubo
摘要： The Subaru telescope is currently performing a strategic program (SSP) using the high-precision near-infrared (NIR) spectrometer IRD to search for exoplanets around nearby mid/late-M~dwarfs via radial velocity (RV) monitoring. As part of the observing strategy for the exoplanet survey, signatures of massive companions such as RV trends are used to reduce the priority of those stars. However, this RV information remains useful for studying the stellar multiplicity of nearby M~dwarfs. To search for companions around such ``deprioritized" M~dwarfs, we observed 14 IRD-SSP targets using Keck/NIRC2 observations with pyramid wavefront sensing at NIR wavelengths, leading to high sensitivity to substellar-mass companions within a few arcseconds. We detected two new companions (LSPM~J1002+1459~B and LSPM~J2204+1505~B) and two new candidates that are likely companions (LSPM~J0825+6902~B and LSPM~J1645+0444~B) as well as one known companion. Including two known companions resolved by the IRD fiber injection module camera, we detected seven (four new) companions at projected separations between $\sim2-20$~au in total. A comparison of the colors with the spectral library suggests that LSPM~J2204+1505~B and LSPM~J0825+6902~B are located at the boundary between late-M and early-L spectral types. Our deep high-contrast imaging for targets where no bright companions were resolved did not reveal any additional companion candidates. The NIRC2 detection limits could constrain potential substellar-mass companions ($\sim10-75\ M_{\rm Jup}$) at 10~au or further. The failure with Keck/NIRC2 around the IRD-SSP stars having significant RV trends makes these objects promising targets for further RV monitoring or deeper imaging with JWST to search for smaller-mass companions below the NIRC2 detection limits.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Teruyuki Hirano
Fei Dai
John H. Livingston
Yui Kasagi
Norio Narita
Hiroyuki Tako Ishikawa
Sascha Grziwa
Kristine W. F. Lam
Kohei Miyakawa
Luisa M. Serrano
Yuji Matsumoto
Eiichiro Kokubo
Tadahiro Kimura
Masahiro Ikoma
Joshua N. Winn
John P. Wisniewski
Hiroki Harakawa
Huan-Yu Teng
William D. Cochran
Akihiko Fukui
摘要： We report on the discovery of an Earth-sized transiting planet ($R_p=1.015\pm0.051\,R_\oplus$) in a $P=4.02$ day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light curve data by the K2 mission, and is here shown to exist in the most recent data from TESS. Combining the light curves with the data secured by our follow-up observations including high-resolution imaging and near infrared spectroscopy with IRD, we rule out false positive scenarios, finding a low false positive probability of $2\times 10^{-4}$. Based on IRD's radial velocities of K2-415, which were sparsely taken over three years, we obtain the planet mass of $3.0\pm 2.7\,M_\oplus$ ($M_p<7.5\,M_\oplus$ at $95\,\%$ confidence) for K2-415b. Being one of the lowest mass stars ($\approx 0.16\,M_\odot$) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy.
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