Evidence for Spin-Orbit Alignment in the TRAPPIST-1 System
Hirano, Teruyuki; Gaidos, Eric; Winn, Joshua N.; Dai, Fei; Fukui, Akihiko; Kuzuhara, Masayuki; Kotani, Takayuki; Tamura, Motohide; Hjorth, Maria; Albrecht, Simon; Huber, Daniel; Bolmont, Emeline; Harakawa, Hiroki; Hodapp, Klaus; Ishizuka, Masato; Jacobson,
ASTROPHYSICAL JOURNAL LETTERS
2020
VL / 890 - BP / - EP /
abstract
In an effort to measure the Rossiter-McLaughlin effect for the TRAPPIST-1 system, we performed high-resolution spectroscopy during transits of planets e, f, and b. The spectra were obtained with the InfraRed Doppler spectrograph on the Subaru 8.2 m telescope, and were supplemented with simultaneous photometry obtained with a 1 m telescope of the Las Cumbres Observatory Global Telescope. By analyzing the anomalous radial velocities, we found the projected stellar obliquity to be lambda = 1 28 degrees under the assumption that the three planets have coplanar orbits, although we caution that the radial-velocity data show correlated noise of unknown origin. We also sought evidence for the expected deformations of the stellar absorption lines, and thereby detected the "Doppler shadow" of planet b with a false-alarm probability of 1.7%. The joint analysis of the observed residual cross-correlation map including the three transits gave <CDATA <i degrees. These results indicate that the the TRAPPIST-1 star is not strongly misaligned with the common orbital plane of the planets, although further observations are encouraged to verify this conclusion.
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