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Evidence for Spin–Orbit Alignment in the TRAPPIST-1 System

Hirano, Teruyuki and Gaidos, Eric and Winn, Joshua N. and Dai, Fei and Fukui, Akihiko and Kuzuhara, Masayuki and Kotani, Takayuki and Tamura, Motohide and Hjorth, Maria and Albrecht, Simon and Huber, Daniel and Bolmont, Emeline and Harakawa, Hiroki and Hodapp, Klaus and Ishizuka, Masato and Jacobson, Shane and Konishi, Mihoko and Kudo, Tomoyuki and Kurokawa, Takashi and Nishikawa, Jun and Omiya, Masashi and Serizawa, Takuma and Ueda, Akitoshi and Weiss, Lauren M. (2020) Evidence for Spin–Orbit Alignment in the TRAPPIST-1 System. Astrophysical Journal Letters, 890 (2). Art. No. L27. ISSN 2041-8213. doi:10.3847/2041-8213/ab74dc.

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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° 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_(-15)^(+13)°. 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hirano, Teruyuki0000-0003-3618-7535
Gaidos, Eric0000-0002-5258-6846
Winn, Joshua N.0000-0002-4265-047X
Dai, Fei0000-0002-8958-0683
Fukui, Akihiko0000-0002-4909-5763
Tamura, Motohide0000-0002-6510-0681
Huber, Daniel0000-0001-8832-4488
Bolmont, Emeline0000-0001-5657-4503
Harakawa, Hiroki0000-0002-6197-5544
Hodapp, Klaus0000-0003-0786-2140
Konishi, Mihoko0000-0003-0114-0542
Kudo, Tomoyuki0000-0002-9294-1793
Weiss, Lauren M.0000-0002-3725-3058
Additional Information:© 2020. The American Astronomical Society. Received 2019 December 29; revised 2020 February 5; accepted 2020 February 11; published 2020 February 25. This work is based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and makes use of observations from the LCOGT network. The data analysis was carried out, in part, on the Multi-wavelength Data Analysis System operated by the Astronomy Data Center (ADC), National Astronomical Observatory of Japan. This work is supported by JSPS KAKENHI grant Nos. 16K17660, 19K14783, 18H05442, 15H02063, and 22000005, and by the Astrobiology Center Program of National Institutes of Natural Sciences (NINS; grant No. AB311017). J.N.W. thanks the Heising-Simons foundation for support. L.M.W. is supported by the Beatrice Watson Parrent Fellowship. S.A. and M.H. acknowledge support from the Danish Council for Independent Research through the DFF Sapere Aude Starting grant No. 4181-00487B, and the Stellar Astrophysics Centre which funding is provided by The Danish National Research Foundation (grant agreement No. DNRF106). This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation. Software: batman (Kreidberg 2015), emcee (Foreman-Mackey et al. 2013), IRAF (Tody 1986, 1993).
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)16K17660
Japan Society for the Promotion of Science (JSPS)19K14783
Japan Society for the Promotion of Science (JSPS)18H05442
Japan Society for the Promotion of Science (JSPS)15H02063
Japan Society for the Promotion of Science (JSPS)22000005
National Institutes of Natural Sciences (Japan)AB311017
Heising-Simons FoundationUNSPECIFIED
Beatrice Watson Parrent FellowshipUNSPECIFIED
Danish Council for Independent Research4181-00487B
Danish National Research FoundationDNRF106
Swiss National Science Foundation (SNSF)UNSPECIFIED
Subject Keywords:Transit photometry ; High resolution spectroscopy ; Extrasolar rocky planets ; Radial velocity
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Transit photometry (1709); High resolution spectroscopy (2096); Extrasolar rocky planets (511); Radial velocity (1332)
Record Number:CaltechAUTHORS:20200225-135943496
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Official Citation:Teruyuki Hirano et al 2020 ApJL 890 L27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101547
Deposited By: George Porter
Deposited On:26 Feb 2020 16:00
Last Modified:16 Nov 2021 18:03

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