Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

Abstract

Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet's atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet-star interactions in HAT-P-2ʼs eccentric planetary system gained from the analysis of ∼350 hr of 4.5 μm observations with the Spitzer Space Telescope. The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b's 4.5 μm photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet's orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2ʼs pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.

The Telltale Heartbeat: Detection and Characterization of Eccentric Orbiting Planets via Tides on Their Host Star

“…Eccentric equilibrium tides will be the main focus of this paper. For high orbital eccentricity, these produce a characteristic cardiogram-like phase variability curve, explaining the shorthand for the well-studied binary "heartbeat" stars (Welsh et al 2011;Thompson et al 2012;Shporer et al 2016;Fuller 2017) and even a candidate "heartbeat planet" (de Wit et al 2017). It would not be unfair to call these tides "time-varying" or "eccentric" corrections to circular-orbit ellipsoidal variations, however by virtue of this time variability they hold considerably more information.…”

Mass loss from the exoplanet WASP-12b inferred from Spitzer phase curves

“…The previously favoured explanation for the double peaked phase curve reported for WASP-12b by Cowan et al (2012) was detector systematics, but this hypothesis is now strongly disfavoured. To date, 23 papers have been published with new Spitzer phase curves of 18 different exoplanets (Harrington et al 2006;Knutson et al 2007;Cowan et al 2007;Knutson et al 2009b,a;Laughlin et al 2009;Crossfield et al 2010;Cowan et al 2012;Knutson et al 2012;Crossfield et al 2012a;Lewis et al 2013;Maxted et al 2013;Zellem et al 2014;Wong et al 2015;de Wit et al 2016;Wong et al 2016;Krick et al 2016;Demory et al 2016;Wong et al 2016;Stevenson et al 2017;de Wit et al 2017;Zhang et al 2018;Dang et al 2018;Kreidberg et al 2018). Of these numerous observations, WASP-12 is the only system which has shown strong a double peaked phase curve not once, but twice.…”

Accelerated tidal circularization via resonance locking in KIC 8164262

“…KH acknowledges support through NASA ADAP grant (16-ADAP16-0201). This research was supported by the National Science Foundation under Grant 3 Resonance locking cannot explain the pulsations in HAT-P-2 reported by de Wit et al (2017) because those pulsations are larger than A N,max at the observed pulsation frequency.…”