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WASP-4 Is Accelerating toward the Earth

Bouma, L. G. and Winn, J. N. and Howard, A. W. and Howell, S. B. and Isaacson, H. and Knutson, H. and Matson, R. A. (2020) WASP-4 Is Accelerating toward the Earth. Astrophysical Journal Letters, 893 (2). Art. No. L29. ISSN 2041-8213. doi:10.3847/2041-8213/ab8563.

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The orbital period of the hot Jupiter WASP-4b appears to be decreasing at a rate of −8.64 ± 1.26 ms yr⁻¹, based on transit-timing measurements spanning 12 yr. Proposed explanations for the period change include tidal orbital decay, apsidal precession, and acceleration of the system along the line of sight. To investigate further, we performed new radial-velocity measurements and speckle imaging of WASP-4. The radial-velocity data show that the system is accelerating toward the Sun at a rate of −0.0422 ± 0.0028 m s⁻¹ day⁻¹. The associated Doppler effect should cause the apparent period to shrink at a rate of −5.94 ± 0.39 ms yr⁻¹, comparable to the observed rate. Thus, the observed change in the transit period is mostly or entirely produced by the line-of-sight acceleration of the system. This acceleration is probably caused by a wide-orbiting companion of mass 10–300 M_(Jup) and orbital distance 10–100 au, based on the magnitude of the radial-velocity trend and the nondetection of any companion in the speckle images. We expect that the orbital periods of one out of three hot Jupiters will change at rates similar to WASP-4b, based on the hot-Jupiter companion statistics of Knutson et al. Continued radial-velocity monitoring of hot Jupiters is therefore essential to distinguish the effects of tidal orbital decay or apsidal precession from line-of-sight acceleration.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bouma, L. G.0000-0002-0514-5538
Winn, J. N.0000-0002-4265-047X
Howard, A. W.0000-0001-8638-0320
Howell, S. B.0000-0002-2532-2853
Isaacson, H.0000-0002-0531-1073
Knutson, H.0000-0002-0822-3095
Matson, R. A.0000-0001-7233-7508
Additional Information:© 2020 The American Astronomical Society. Received 2020 February 28; revised 2020 March 27; accepted 2020 March 30; published 2020 April 17. Facilities: Gaia (Gaia Collaboration et al. 2016, 2018), Gemini:South (Zorro; Scott et al. 2018), Keck:I (HIRES; Vogt et al. 1994), Euler1.2m (CORALIE), ESO:3.6m (HARPS; Mayor et al. 2003), CTIO:1.0 m (Y4KCam), Danish 1.54 m Telescope, El Sauce:0.356 m, Elizabeth 1.0 m at SAAO, Euler1.2 m (EulerCam), Magellan:Baade (MagIC), Max Planck:2.2 m (GROND; Greiner et al. 2008) NTT, SOAR (SOI), TESS (Ricker et al. 2015), TRAPPIST (Jehin et al. 2011), VLT:Antu (FORS2). Software: astrobase (Bhatti et al. 2018), astropy (Astropy Collaboration et al. 2018), astroquery (Ginsburg et al. 2018), corner (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013), IPython (Pérez & Granger 2007), matplotlib (Hunter 2007), MESA (Paxton et al. 2011, 2013, 2015) numpy (van der Walt 2011), pandas (McKinney 2010), radvel (Fulton et al. 2018), scipy (Jones et al. 2001).
Group:Astronomy Department
Subject Keywords:Exoplanet tides ; Exoplanet dynamics ; Radial velocity ; Transit timing variation method
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet tides (497); Exoplanet dynamics (490); Radial velocity (1332); Transit timing variation method (1710)
Record Number:CaltechAUTHORS:20200417-141914566
Persistent URL:
Official Citation:L. G. Bouma et al 2020 ApJL 893 L29
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102614
Deposited By: Tony Diaz
Deposited On:17 Apr 2020 21:27
Last Modified:16 Nov 2021 18:13

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