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Planet-star interactions with precise transit timing. II. The radial-velocity tides and a tighter constraint on the orbital decay rate in the WASP-18 system

Maciejewski, G. and Knutson, H. A. and Howard, A. W. and Isaacson, H. and Fernández-Lajús, E. and Di Sisto, R. P. and Migaszewski, C. (2020) Planet-star interactions with precise transit timing. II. The radial-velocity tides and a tighter constraint on the orbital decay rate in the WASP-18 system. Acta Astronomica, 70 (1). pp. 1-18. ISSN 0001-5237. doi:10.32023/0001-5237/70.1.1.

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From its discovery, the WASP-18 system with its massive transiting planet on a tight orbit was identified as a unique laboratory for studies on tidal planet-star interactions. In an analysis of Doppler data, which include five new measurements obtained with the HIRES/Keck-I instrument between 2012 and 2018, we show that the radial velocity signal of the photosphere following the planetary tidal potential can be distilled for the host star. Its amplitude is in agreement with both theoretical predictions of the equilibrium tide approximation and an ellipsoidal modulation observed in an orbital phase curve. Assuming a circular orbit, we refine system parameters using photometric time series from TESS. With a new ground-based photometric observation, we extend the span of transit timing observations to 28 yr in order to probe the rate of the orbital period shortening. Since we found no departure from a constant-period model, we conclude that the modified tidal quality parameter of the host star must be greater than 3.9×10⁶ with 95% confidence. This result is in line with conclusions drawn from studies of the population of hot Jupiters, predicting that the efficiency of tidal dissipation is 1 or 2 orders of magnitude weaker. As the WASP-18 system is one of the prime candidates for detection of orbital decay, further timing observations are expected to push the boundaries of our knowledge on stellar interiors.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Knutson, H. A.0000-0002-0822-3095
Howard, A. W.0000-0001-8638-0320
Isaacson, H.0000-0002-0531-1073
Additional Information:© 2020 Copernicus Foundation for Polish Astronomy. Received: March 31, 2020. We are grateful to Dr. Coel Hellier and Dr. Lucyna Kedziora- Chudczer for sharing the light curves with us. GM and CM acknowledge the financial support from the National Science Centre, Poland through grant no. 2016/23/B/ST9/00579. This work was based on observations at the W. M. Keck Observatory granted by the University of Hawaii, the University of California, and the California Institute of Technology. We thank the observers who contributed to the measurements reported here and acknowledge the efforts of the Keck Observatory staff. We extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This paper makes use of data from the DR1 of the WASP data (Butters et al. 2010) as provided by the WASP consortium, and the computing and storage facilities at the CERIT Scientific Cloud, reg. no. CZ.1.05/3.2.00/08.0144 which is operated by Masaryk University, Czech Republic.
Group:Astronomy Department
Funding AgencyGrant Number
National Science Centre (Poland)2016/23/B/ST9/00579
NASANAS 5-26555
Subject Keywords:Planet-star interactions - Stars: individual: WASP-18 - Planets and satellites: individual: WASP-18 b
Issue or Number:1
Record Number:CaltechAUTHORS:20200420-083848140
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102644
Deposited By: Tony Diaz
Deposited On:20 Apr 2020 15:46
Last Modified:16 Nov 2021 18:14

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