Gravity-Darkened Seasons: Insolation Around Rapid Rotators

Ahlers, John P.

doi:10.3847/0004-637x/832/1/93

Cited by 35 publications

(16 citation statements)

References 41 publications

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“…From the gravity darkening and oblateness modeling in Ahlers et al (2020a), we produced an effective temperature map of the host star and generated the total irradiance I experienced by KELT-9b as a function of orbital phase, using the model described in Ahlers (2016). The equilibrium dayside temperature of KELT-9b is related to the incident irradiance via T day ∝I 1/4 , and we computed the relative change in thermal emission from the planet associated with the varying dayside temperature (see the numerator in the first term of Equation (9)).…”

Section: Consequences Of Rapid Stellar Rotation and Kelt-9b's Polar Omentioning

confidence: 99%

Exploring the Atmospheric Dynamics of the Extreme Ultrahot Jupiter KELT-9b Using TESS Photometry

Wong¹,

Shporer²,

Kitzmann³

et al. 2020

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We carry out a phase-curve analysis of the KELT-9 system using photometric observations from NASA's Transiting Exoplanet Survey Satellite (TESS). The measured secondary eclipse depth and peak-to-peak atmospheric brightness modulation are-+ 650 15 14 and 566±16 ppm, respectively. The planet's brightness variation reaches maximum 31±5minutes before the midpoint of the secondary eclipse, indicating a 5°.2±0°.9 eastward shift in the dayside hot spot from the substellar point. We also detect stellar pulsations on KELT-9 with a period of 7.58695±0.00091hr. The dayside emission of KELT-9b in the TESSbandpass is consistent with a blackbody brightness temperature of 4600±100 K. The corresponding nightside brightness temperature is 3040±100 K, comparable to the dayside temperatures of the hottest known exoplanets. In addition, we detect a significant phase-curve signal at the first harmonic of the orbital frequency and a marginal signal at the second harmonic. While the amplitude of the first harmonic component is consistent with the predicted ellipsoidal distortion modulation assuming equilibrium tides, the phase of this photometric variation is shifted relative to the expectation. Placing KELT-9b in the context of other exoplanets with phase-curve observations, we find that the elevated nightside temperature and relatively low day-night temperature contrast agree with the predictions of atmospheric models that include H 2 dissociation and recombination. The nightside temperature of KELT-9b implies an atmospheric composition containing about 50% molecular and 50% atomic hydrogen at 0.1bar, a nightside emission spectrum that deviates significantly from a blackbody, and a 0.5-2.0 μm transmission spectrum that is featureless at low resolution.

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Section: Consequences Of Rapid Stellar Rotation and Kelt-9b's Polar Omentioning

confidence: 99%

Exploring the Atmospheric Dynamics of the Extreme Ultrahot Jupiter KELT-9b Using TESS Photometry

Wong¹,

Shporer²,

Kitzmann³

et al. 2020

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“…Additionally, the star's abundant centrifugal force near its equator distorts its hydrostatic equilibrium, causing its effective temperature to vary by nearly a thousand Kelvin over the surface of the star. These two effects of stellar oblateness and varying effective temperature -together commonly referred to as gravity darkening (Barnes 2009)-change the total irradiance on KELT-9 b (Ahlers 2016). The star's oblateness changes the overall shape and size of the projected disk in the sky that KELT-9 b sees depending on its location in the system, and the star's decreased temperature decreases output stellar radiation near its equator.…”

Section: Introductionmentioning

confidence: 99%

“…4 via Doppler tomography, meaning KELT-9 b resides in a polar orbital configuration. Therefore, KELT-9 b varies in exposure to the host star's hotter poles and cooler equator, which has been shown to significantly impact a planet's total irradiation in similar systems (Ahlers 2016;Ahlers et al 2020).…”

Section: Introductionmentioning

confidence: 99%

KELT-9 b’s Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin–Orbit Misalignment

Ahlers

Johnson

Stassun

et al. 2020

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KELT-9 b is an ultra-hot Jupiter transiting a rapidly rotating, oblate early-A-type star in a polar orbit. We model the effect of rapid stellar rotation on KELT-9 b's transit light curve using photometry from the Transiting Exoplanet Survey Satellite to constrain the planet's true spin-orbit angle and to explore how KELT-9 b may be influenced by stellar gravity darkening. We constrain the host star's equatorial radius to be 1.089±0.017 times as large as its polar radius and its local surface brightness to vary by ∼38% between its hot poles and cooler equator. We model the stellar oblateness and surface brightness gradient and find that it causes the transit light curve to lack the usual symmetry around the time of minimum light. We take advantage of the light-curve asymmetry to constrain KELT-9 b's true spin-orbit angle (- +  87 11 10), agreeing with Gaudi et al. that KELT-9 b is in a nearly polar orbit. We also apply a gravity-darkening correction to the spectral energy distribution model from Gaudi et al. and find that accounting for rapid rotation gives a better fit to available spectroscopy and yields a more reliable estimate for the star's polar effective temperature.

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“…Recent observing programs such as the Kepler mission have demonstrated that stellar variability in high mass stars often renders transit light curves unusable . Additionally, high-mass stars often rotate rapidly, inducing an oblate shape and a pole-to-equator luminosity gradient across the stellar surface ; Ahlers 2016). These two effects add challenges to traditional light curve analysis, radial velocity measurements, Doppler tomography, and Rossiter McLaughlin measurements (Gimenez 2006;.…”

Section: Introductionmentioning

confidence: 99%

LASR-guided stellar photometric variability subtraction

Ahlers

Barnes

Horvath

et al. 2018

A&A

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We develop a technique for removing stellar variability in the light curves of δ-Scuti and similar stars. Our technique, which we name the Linear Algorithm for Significance Reduction (LASR), subtracts oscillations from a time series by minimizing their statistical significance in frequency space. We demonstrate that LASR can subtract variable signals of near-arbitrary complexity and can robustly handle close frequency pairs and overtone frequencies. We demonstrate that our algorithm performs an equivalent fit as prewhitening to the straightforward variable signal of KIC 9700322. We also show that LASR provides a better fit to seismic activity than prewhitening in the case of the complex δ-Scuti KOI-976.

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Gravity-Darkened Seasons: Insolation Around Rapid Rotators

Cited by 35 publications

References 41 publications

Exploring the Atmospheric Dynamics of the Extreme Ultrahot Jupiter KELT-9b Using TESS Photometry

Exploring the Atmospheric Dynamics of the Extreme Ultrahot Jupiter KELT-9b Using TESS Photometry

KELT-9 b’s Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin–Orbit Misalignment

LASR-guided stellar photometric variability subtraction

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