The hot-Jupiter Kepler-17b: discovery, obliquity from stroboscopic starspots, and atmospheric characterization (original) (raw)
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HAT‐P‐7b: An Extremely Hot Massive Planet Transiting a Bright Star in the Kepler Field
The Astrophysical Journal, 2008
We report on the latest discovery of the HATNet project; a very hot giant planet orbiting a bright (V = 10.5) star with a small semi-major axis of a = 0.0377 ± 0.0005 AU. Ephemeris for the system is P = 2.2047299 ± 0.0000040 days, mid-transit time E = 2, 453, 790.2593 ± 0.0010 (BJD). Based on the available spectroscopic data on the host star and photometry of the system, the planet has a mass of M p = 1.78 +0.08 −0.05 M Jup and radius of R p = 1.36 +0.20 −0.09 R Jup. The parent star is a slightly evolved F6 star with M ⋆ = 1.47 +0.08 −0.05 M ⊙ , R ⋆ = 1.84 +0.23 −0.11 R ⊙ , T eff = 6350 ± 80 K, and metallicity [Fe/H] = +0.26 ± 0.08. The relatively hot and large host star, combined with the close orbit of the planet, yield a very high planetary irradiance of (4.71 +1.44 −0.05) × 10 9 erg cm −2 s −1 , which places the planet near the top of the pM class of irradiated planets as defined by Fortney et al. (2007). If as predicted by Fortney et al. (2007) the planet re-radiates its absorbed energy before distributing it to the night side, the day-side temperature should be about (2730 +150 −100) K. Because the host star is quite bright, measurement of the secondary eclipse should be feasible for ground-based telescopes, providing a good opportunity to compare the predictions of current hot Jupiter atmospheric models with the observations. Moreover, the host star falls in the field of the upcoming Kepler mission; hence extensive space-borne follow-up, including not only primary transit and secondary eclipse observations but also asteroseismology, will be possible.
The Astrophysical Journal Supplement Series, 2011
This paper reports the detection and the measurements of occultations of the two transiting hot giant exoplanets Kepler-5b and Kepler-6b by their parent stars. The observations are obtained in the near infrared with Warm-Spitzer Space Telescope and at optical wavelengths by combining more than a year of Kepler photometry. The investigation consists of constraining the eccentricities of these systems and of obtaining broad band emergent spectra for individual planets. For both targets, the occultations are detected at 3 σ level at each wavelength with mid-occultation times consistent with circular orbits. The brightness temperatures of these planets are deduced from the infrared observations and reach T Spitzer =1930 ± 100 K and T Spitzer =1660 ± 120 K for Kepler-5b and Kepler-6b respectively. We measure optical geometric albedos A g in the Kepler bandpass -2and find A g = 0.12 ± 0.04 for Kepler-5b and A g = 0.11 ± 0.04 for Kepler-6b leading to upper an limit for the Bond albedo A B ≤ 0.17 in both cases. The observations for both planets are best described by models for which most of the incident energy is redistributed on the dayside, with only less than 10% of the absorbed stellar flux redistributed to the night side of these planets. The data for Kepler-5b favor a model without a temperature inversion, whereas for Kepler-6b they do not allow distinguishing between models with and without inversion.
THE HIGH ALBEDO OF THE HOT JUPITER KEPLER-7 b
The Astrophysical Journal, 2011
Hot Jupiters are expected to be dark from both observations (albedo upper limits) and theory (alkali metals and/or TiO and VO absorption). However, only a handful of hot Jupiters have been observed with high enough photometric precision at visible wavelengths to investigate these expectations. The NASA Kepler mission provides a means to widen the sample and to assess the extent to which hot Jupiter albedos are low. We present a global analysis of Kepler-7 b based on Q0-Q4 data, published radial velocities, and asteroseismology constraints. We measure an occultation depth in the Kepler bandpass of 44±5 ppm. If directly related to the albedo, this translates to a Kepler geometric albedo of 0.32±0.03, the most precise value measured so far for an exoplanet. We also characterize the planetary orbital phase lightcurve with an amplitude of 42±4 ppm. Using atmospheric models, we find it unlikely that the high albedo is due to a dominant thermal component and propose two solutions to explain the observed planetary flux. Firstly, we interpret the Kepler-7 b albedo as resulting from an excess reflection over what can be explained solely by Rayleigh scattering, along with a nominal thermal component. This excess reflection might indicate the presence of a cloud or haze layer in the atmosphere, motivating new modeling and observational efforts. Alternatively, the albedo can be explained by Rayleigh scattering alone if Na and K are depleted in the atmosphere by a factor of 10-100 below solar abundances.
ATMOSPHERE AND SPECTRAL MODELS OF THE KEPLER -FIELD PLANETS HAT-P-7b AND TrES-2
The Astrophysical Journal, 2010
We develop atmosphere models of two of the three Kepler-field planets that were known prior to the start of the Kepler mission (HAT-P-7b and TrES-2). We find that published Kepler and Spitzer data for HAT-P-7b appear to require an extremely hot upper atmosphere on the dayside, with a strong thermal inversion and little day-night redistribution. The Spitzer data for TrES-2 suggest a mild thermal inversion with moderate day-night redistribution. We examine the effect of nonequilibrium chemistry on TrES-2 model atmospheres and find that methane levels must be adjusted by extreme amounts in order to cause even mild changes in atmospheric structure and emergent spectra. Our best-fit models to the Spitzer data for TrES-2 lead us to predict a low secondary eclipse planet-star flux ratio (∼ < 2×10 −5) in the Kepler bandpass, which is consistent with what very recent observations have found. Finally, we consider how the Kepler-band optical flux from a hot exoplanet depends on the strength of a possible extra optical absorber in the upper atmosphere. We find that the optical flux is not monotonic in optical opacity, and the non-monotonicity is greater for brighter, hotter stars.
Publications of the Astronomical Society of the Pacific, 2015
We present a comprehensive study of phase curves and secondary eclipses in the Kepler data set using all available data from 15 quarters. Our original sample consists of 489 Kepler Objects of Interest (KOI) with R p > 4R e , P < 10d, V mag < 15 from the latest data release. Here we focus on 20 confirmed planets from that sample and derive their temperatures and albedos. Our results confirm and in most cases improve parameters derived by previous studies. We present new results for Kepler 1b-8b, 12b-15b, 17b, 40b, 41b, 43b, 44b, 76b, 77b, and 412b derived in a consistent manner. Furthermore we present a lightcurve analysis of Kepler 91b and Kepler 74b. Both show extra dimmings at times other than of the expected primary and secondary eclipses. Corrected for thermal emission we find the 20 planets we analyzed separate into two groups of high (> 0.1) and low (< 0.1) albedos, with no significant correlation to any stellar or planetary parameters. However the most massive planets from our sample are all low in albedo.
Photometric analysis of the system Kepler-1
We have applied the close binary system analysis program WINFITTER to an intensive study of Kepler-1 (= TrES-2) using all the available photometry (14 quarters ; 1570640 measures) from the NASA Exoplanet Archive (NEA) at the Caltech website http://exoplanetarchive.ipac. caltech.edu. The mean individual data-point error of the normalized flux values is 0.00026, leading to the model's specification for the mean reference flux of the system to an accuracy of ∼0.5 ppm. Completion of the analysis requires a number of prior quantities, relating mainly to the host star, that are adopted from relevant literature. Our new results tend broadly to confirm those of previous authors, though there are a number of significant differences. Specifically, the applied photometric fitting function is more precise than those used before on the full Kepler data-set. The more complete discussion of the interdependent role of errors, using MCMC sampling, allows greater confidence in the obtained parameters themselves as well as understanding or their likely errors. Our photometrically derived values for the mass and radius of Kepler-1b are 1.18 ± 0.05 M Jup and 1.21 ± 0.05 R Jup. The mass of this Safronov Class I planet is closer to published spectroscopic values than found from previous photometric analysis, which can be attributed to the improved fitting function. The analysis determines a definite photometric Doppler effect from the orbit, but this is not independent of the tidal ('ellipticity') effect, and the two are consistently combined in our fitting function. A corresponding rotation-related Rossiter effect was not detected, allowing an upper limit on the rotation speed of ∼70 km s −1. The proportion of light coming from the known companion star is resolved, but turns out rather less than that inferred from the results of direct measurement. The fitting function also predicts a small secondary minimum ('occultation'), when the light reflected by the planet is eclipsed. However, the occultation depth cannot be measured directly from the data to the relevant accuracy, and so models for the planet's atmospheric properties based on this will be compromised by other assumptions and approximations in the light curve's fitting function. Suggestions of secular trends for the variation of parameters are considered, but the evidence of the Kepler data is not yet very persuasive.
DISCOVERY AND ATMOSPHERIC CHARACTERIZATION OF GIANT PLANET KEPLER-12b: AN INFLATED RADIUS OUTLIER
The Astrophysical Journal Supplement Series, 2011
We report the discovery of planet , which at 1.695 ± 0.030 R J is among the handful of planets with super-inflated radii above 1.65 R J . Orbiting its slightly evolved G0 host with a 4.438-day period, this 0.431 ± 0.041 M J planet is the least-irradiated within this largest-planet-radius group, which has important implications for planetary physics. The planet's inflated radius and low mass lead to a very low density of 0.111 ± 0.010 g cm −3 . We detect the occultation of the planet at a significance of 3.7σ in the Kepler bandpass. This yields a geometric albedo of 0.14 ± 0.04; the planetary flux is due to a combination of scattered light and emitted thermal flux. We use multiple observations with Warm Spitzer to detect the occultation at 7σ and 4σ in the 3.6 and 4.5 µm bandpasses, respectively. The occultation photometry timing is consistent with a circular orbit, at e < 0.01 (1σ), and e < 0.09 (3σ). The occultation detections across the three bands favor an atmospheric model with no dayside temperature inversion. The Kepler occultation detection provides significant leverage, but conclusions regarding temperature structure are preliminary, given our ignorance of opacity sources at optical wavelengths in hot Jupiter atmospheres. If Kepler-12b and HD 209458b, which intercept similar incident stellar fluxes, have the same heavy element masses, the interior energy source needed to explain the large radius of Kepler-12b is three times larger than that of HD 209458b. This may suggest that more than one radius-inflation mechanism is at work for Kepler-12b, or that it is less heavy-element rich than other transiting planets.
Kepler-77b: a very low albedo, Saturn-mass transiting planet around a metal-rich solar-like star
Astronomy & Astrophysics, 2013
We report the discovery of Kepler-77b (alias KOI-127.01), a Saturn-mass transiting planet in a 3.6-day orbit around a metal-rich solar-like star. We combined the publicly available Kepler photometry (quarters 1-13) with high-resolution spectroscopy from the Sandiford@McDonald and FIES@NOT spectrographs. We derived the system parameters via a simultaneous joint fit to the photometric and radial velocity measurements. Our analysis is based on the Bayesian approach and is carried out by sampling the parameter posterior distributions using a Markov chain Monte Carlo simulation. Kepler-77b is a moderately inflated planet with a mass of M p = 0.430 ± 0.032 M Jup , a radius of R p = 0.960 ± 0.016 R Jup , and a bulk density of ρ p = 0.603 ± 0.055 g cm −3 . It orbits a slowly rotating (P rot = 36 ± 6 days) G5 V star with M ⋆ = 0.95 ± 0.04 M ⊙ , R ⋆ = 0.99 ± 0.02 R ⊙ , T eff = 5520 ± 60 K, [M/H] = 0.20 ± 0.05 dex, that has an age of 7.5 ± 2.0 Gyr. The lack of detectable planetary occultation with a depth higher than ∼10 ppm implies a planet geometric and Bond albedo of A g ≤ 0.087 ± 0.008 and A B ≤ 0.058 ± 0.006, respectively, placing Kepler-77b among the gas-giant planets with the lowest albedo known so far. We found neither additional planetary transit signals nor transit-timing variations at a level of ∼0.5 minutes, in accordance with the trend that close-in gas giant planets seem to belong to single-planet systems. The 106 transits observed in short-cadence mode by Kepler for nearly 1.2 years show no detectable signatures of the planet's passage in front of starspots. We explored the implications of the absence of detectable spot-crossing events for the inclination of the stellar spin-axis, the sky-projected spin-orbit obliquity, and the latitude of magnetically active regions.
Kepler-423b: a half-Jupiter mass planet transiting a very old solar-like star
Astronomy & Astrophysics, 2015
We report the spectroscopic confirmation of the Kepler object of interest KOI-183b (also known as KOI-183.01), a half-Jupiter mass planet transiting an old solar-like star every 2.7 days. Our analysis is the first to combine the full Kepler photometry (quarters 1-17) with high-precision radial velocity measurements taken with the FIES spectrograph at the Nordic Optical Telescope. We simultaneously modelled the photometric and spectroscopic data-sets using Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that the Kepler pre-search data conditioned light curve of KOI-183 exhibits quarter-to-quarter systematic variations of the transit depth, with a peak-to-peak amplitude of ∼4.3 % and seasonal trends reoccurring every four quarters. We attributed these systematics to an incorrect assessment of the quarterly variation of the crowding metric. The host star KOI-183 is a G4 dwarf with M = 0.85 ± 0.04 M , R = 0.95 ± 0.04 R , T eff = 5560 ± 80 K, [M/H]=−0.10±0.05 dex, and with an age of 11 ± 2 Gyr. The planet KOI-183b has a mass of M p = 0.595 ± 0.081 M Jup and a radius of R p = 1.192 ± 0.052 R Jup , yielding a planetary bulk density of ρ p = 0.459 ± 0.083 g cm −3 . The radius of KOI-183b is consistent with both theoretical models for irradiated coreless giant planets and expectations based on empirical laws. The inclination of the stellar spin axis suggests that the system is aligned along the line of sight. We detected a tentative secondary eclipse of the planet at a 2-σ confidence level (∆F ec = 14.2 ± 6.6 ppm) and found that the orbit might have a small non-zero eccentricity of 0.019 +0.028 −0.014 . With a Bond albedo of A B = 0.037 ± 0.019, KOI-183b is one of the gas-giant planets with the lowest albedo known so far.
The Broadband Infrared Emission Spectrum of the Exoplanet HD 189733b
The Astrophysical Journal, 2008
We present Spitzer Space Telescope time series photometry of the exoplanet system HD 189733 spanning two times of secondary eclipse, when the planet passes out of view behind the parent star. We estimate the relative eclipse depth in 5 distinct bands and find the planet-to-star flux ratio to be 0.256±0.014% (3.6 µm), 0.214±0.020% (4.5 µm), 0.310 ± 0.034% (5.8 µm), 0.391 ± 0.022% (8.0 µm), and 0.598 ± 0.038% (24 µm). For consistency, we re-analyze a previously published time series to deduce a contrast ratio in an additional band, 0.519 ± 0.020% (16 µm). Our data are strongly inconsistent with a Planck spectrum, and we clearly detect emission near 4 µm as predicted by published theoretical models in which this feature arises from a corresponding opacity window. Unlike recent results for the exoplanet HD 209458b, we find that the emergent spectrum from HD 189733b is best matched by models that do not include an atmospheric temperature inversion. Taken together, these two studies provide initial observational support for the idea that hot Jupiter atmospheres diverge into two classes, in which a thermal inversion layer is present for the more strongly irradiated objects.