Evidence for Spin-orbit Alignment in the TRAPPIST-1 System

By Keith Cowing
Press Release
February 17, 2020
Filed under
Evidence for Spin-orbit Alignment in the TRAPPIST-1 System

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 λ=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 λ=19+13−15 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.

Teruyuki Hirano, Eric Gaidos, Joshua N. Winn, Fei Dai, Akihiko Fukui, Masayuki Kuzuhara, Takayuki Kotani, Motohide Tamura, Maria Hjorth, Simon Albrecht, Daniel Huber, Emeline Bolmont, Hiroki Harakawa, Klaus Hodapp, Masato Ishizuka, Shane Jacobson, Mihoko Konishi, Tomoyuki Kudo, Takashi Kurokawa, Jun Nishikawa, Masashi Omiya, Takuma Serizawa, Akitoshi Ueda, Lauren M. Weiss
(Submitted on 14 Feb 2020)
Comments: 9 pages, 3 figures, accepted for publication in ApJ Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2002.05892 [astro-ph.EP] (or arXiv:2002.05892v1 [astro-ph.EP] for this version)
Submission history
From: Hirano Teruyuki
[v1] Fri, 14 Feb 2020 07:17:38 UTC (337 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻