High-order harmonics in light curves of <i>Kepler</i> planets

Armstrong, Caden; Rein, Hanno

doi:10.1093/mnrasl/slv112

Cited by 27 publications

(6 citation statements)

References 13 publications

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“…Finally, planetary tides have been detected in the power spectra of certain Kepler planets, although not recognised as such. In particular, oscillations at 3 times the transiting companion's orbital frequency have been noted in the power spectra of a number of Kepler light curves (Esteves et al 2013;Armstrong & Rein 2015;Cowan et al 2017). We demonstrate here that this pervasive quirk can in fact be a natural consequence of eccentric planetary orbits.…”

Section: Previous Work On Tides Raised By Planetssupporting

confidence: 53%

Higher order harmonics in the light curves of eccentric planetary systems

Penoyre

Sandford

2019

Monthly Notices of the Royal Astronomical Society

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As a planet orbits, it causes periodic modulations in the light curve of its host star. Due to the combined effects of the planet raising tides on the host star, relativistic beaming of the starlight, and reflection of light off the planet's surface, these modulations occur at the planet's orbital frequency, as well as integer multiples of this frequency. In particular, planets on eccentric orbits induce third and higher-order harmonics in the stellar light curve which cannot be explained by circular-orbit models. Even at moderate eccentricities, such as those typical of Solar System planets, these harmonics are detectable in current and future photometric data. We present an analysis of the harmonics caused by tides, beaming, and reflection in eccentric planetary systems. We explore the dependence of these signals on the parameters of the system, and we discuss prospects for current and future observations of these signals, particularly by the NASA TESS mission. Finally, we present publicly available code for computation of light curves with tidal, beaming, and reflection signals, OoT.

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Section: Previous Work On Tides Raised By Planetssupporting

confidence: 53%

Higher order harmonics in the light curves of eccentric planetary systems

Penoyre

Sandford

2019

Monthly Notices of the Royal Astronomical Society

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“…There is also the strong possibility of this periodic behaviour being detectable in the power spectrum (the measure of energy in oscillations of different frequencies) of the light curve. The signals, as we will show, are not sinusoidal and hence there will not be a sharp peak but rather excitation of higher order harmonics (Esteves et al 2013;Armstrong & Rein 2015;Cowan et al 2017; see also the power spectra of heartbeat stars, e.g. Fuller 2017).…”

Section: Observing Heartbeat Planetsmentioning

confidence: 72%

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

Penoyre¹,

Stone

2019

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We present an analytic description of tides raised on a star by a small orbiting body. In particular, we highlight the disproportionate effect of eccentricity and thus the scope for using these tides to detect and characterise the orbits of exoplanets and brown dwarfs. The tidal distortions of the star produced by an eccentric orbit are, in comparison to a circular orbit, much richer in detail, and potentially visible from any viewing angle. The magnitude of these variations is much larger than that in a circular orbit of the same semi-major axis. These variations are visible in both photometric and spectroscopic data, and dominate other regular sources of phase variability (e.g reflection and Doppler beaming) over a particularly interesting portion of parameter space. These tidal signatures will be a useful tool for planet detection on their own, and used in concert with other methods provide powerful constraints on planetary and stellar properties.

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“…Many authors have attributed each Fourier coefficient in a phase curve to a distinct astrophysical cause (Welsh et al 2010;Faigler & Mazeh 2011;Faigler et al 2013;Faigler & Mazeh 2015;Barclay et al 2012;Shporer et al 2011;Shporer & Hu 2015;Jackson et al 2012;Angerhausen et al 2015;Armstrong & Rein 2015). Although this approach is suitable to search for non-transiting planets or obtain rough estimates of planetary mass, using over-simplified astrophysical models may lead to imperfect fits and therefore spurious claims of new physics.…”

Section: Discussionmentioning

confidence: 99%

“…If interpreted as solely due to the planet, these correspond to A 3 /A 0 = 0.06 and 0.08, respectively (A 3 is the planet's third harmonic semi-amplitude and A 0 is the orbit-averaged planetary flux). Armstrong & Rein (2015), henceforth A&R15, performed a uniform analysis of all Kepler Objects of Interest and reported significant n = 3 amplitudes for 16 short-period systems. They found that the amplitude of these odd modes was too great (10 −6 -10 −3 ) to attribute to tidal effects of the planet on the its star.…”

Section: Introductionmentioning

confidence: 99%

Odd Harmonics in Exoplanet Photometry: Weather or Artifact?

Cowan¹,

Chayes²,

Bouffard³

et al. 2017

Mon. Not. R. Astron. Soc.

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Photometry of short-period planetary systems allows astronomers to monitor exoplanets, their host stars, and their mutual interactions. In addition to the transits of a planet in front of its star and the eclipses of the planet by its star, researchers have reported flux variations at the orbital frequency and its harmonics: planetary reflection and/or emission and Doppler beaming of starlight produce one peak per orbit, while ellipsoidal variations of a tidally distorted star and/or planet produce two maxima per orbit. Researchers have also reported significant photometric variability at three times the orbital frequency, sometimes much greater than the predictions of tidal theory. The reflected phase variations of a homogeneous planet contains power at even orbital harmonics-important for studies of ellipsoidal variations-but cannot contain odd orbital harmonics. We show that odd harmonics can, however, be produced by an edge-on planet with a time-variable map, or an inclined planet with a NorthSouth (N-S) asymmetric map. Either of these scenarios entail weather: short-period planets are expected to have zero obliquity and hence N-S symmetric stellar forcing. North-South asymmetry in a giant planet would therefore suggest stochastic localized features, such as weather. However, we find that previous claims of large-amplitude odd modes in Kepler photometry are artifacts of removing planetary transits rather than modeling them. The only reliable claims of odd harmonics remain HAT-P-7b and Kepler-13Ab, for which the third mode amplitude is 6-8% of the planetary flux. Although time-variable albedo maps could in principle explain these odd harmonics, upper-limits on the infrared variability of hot Jupiters make this hypothesis unlikely. We urge theorists to study the effects of close-in planets on stellar atmospheres, as this remains the only plausible hypothesis.

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High-order harmonics in light curves of Kepler planets

Cited by 27 publications

References 13 publications

Higher order harmonics in the light curves of eccentric planetary systems

Higher order harmonics in the light curves of eccentric planetary systems

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

Odd Harmonics in Exoplanet Photometry: Weather or Artifact?

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