arXiv subjects

Brice-Olivier Demory

Publications and source records attributed to Brice-Olivier Demory.

104 records · Page 6Linked to original sources

arXiv2013

The Mass of KOI-94d and a Relation for Planet Radius, Mass, and Incident Flux

We measure the mass of a modestly irradiated giant planet, KOI-94d. We wish to determine whether this planet, which is in a 22-day orbit and receives 2700 times as much incident flux as Jupiter, is as dense as Jupiter or rarefied like inflated hot Jupiters. KOI-94 also hosts 3 smaller transiting planets, all of which were detected by the Kepler Mission. With 26 radial velocities of KOI-94 from the W. M. Keck Observatory and a simultaneous fit to the Kepler light curve, we measure the mass of the giant planet and determine that it is not inflated. Support for the planetary interpretation of the other three candidates comes from gravitational interactions through transit timing variations, the statistical robustness of multi-planet systems against false positives, and several lines of evidence that no other star resides within the photometric aperture. The radial velocity analyses of KOI-94b and KOI-94e offer marginal (>2σ) mass detections, whereas the observations of KOI-94c offer only an upper limit to its mass. Using the KOI-94 system and other planets with published values for both mass and radius (138 exoplanets total, including 35 with M < 150 Earth masses), we establish two fundamental planes for exoplanets that relate their mass, incident flux, and radius from a few Earth masses up to ten Jupiter masses. These equations can be used to predict the radius or mass of a planet.

astro-ph.EP↗

arXiv2013

Spitzer Observations of GJ3470b: a Very Low-density Neptune-size Planet Orbiting a Metal-rich M dwarf

We present Spitzer/IRAC 4.5-micron transit photometry of GJ3470b, a Neptune-size planet orbiting a M1.5 dwarf star with a 3.3-day period recently discovered in the course of the HARPS M-dwarf survey. We refine the stellar parameters by employing purely empirical mass-luminosity and surface brightness relations constrained by our updated value for the mean stellar density, and additional information from new near-infrared spectroscopic observations. We derive a stellar mass of M_star = 0.539+0.047-0.043 M_sun and a radius of R_star = 0.568+0.037-0.031 R_sun. We determine the host star of GJ3470b to be metal-rich, with a metallicity of [Fe/H] = +0.20 +/- 0.10 and an effective temperature of Teff = 3600 +/- 100 K. The revised stellar parameters yield a planetary radius R_pl = 4.83+0.22-0.21 R_Earth that is 13 percent larger than the value previously reported in the literature. We find a planetary mass M_pl = 13.9+1.5-1.4 M_Earth that translates to a very low planetary density, rho_pl = 0.72+0.13-0.12 gcm-3, which is 33% smaller than the original value. With a mean density half of that of GJ436b, GJ3470b is an example of a very low-density low-mass planet, similar to Kepler-11d, Kepler-11e, and Kepler-18c but orbiting a much brighter nearby star that is more conducive to follow-up studies.

astro-ph.EP↗

arXiv2013

Confirmation of Hot Jupiter Kepler-41b via Phase Curve Analysis

We present high precision photometry of Kepler-41, a giant planet in a 1.86 day orbit around a G6V star that was recently confirmed through radial velocity measurements. We have developed a new method to confirm giant planets solely from the photometric light curve, and we apply this method herein to Kepler-41 to establish the validity of this technique. We generate a full phase photometric model by including the primary and secondary transits, ellipsoidal variations, Doppler beaming and reflected/emitted light from the planet. Third light contamination scenarios that can mimic a planetary transit signal are simulated by injecting a full range of dilution values into the model, and we re-fit each diluted light curve model to the light curve. The resulting constraints on the maximum occultation depth and stellar density combined with stellar evolution models rules out stellar blends and provides a measurement of the planet's mass, size, and temperature. We expect about two dozen Kepler giant planets can be confirmed via this method.

astro-ph.EP↗

arXiv2013

Spitzer Transits of the Super-Earth GJ1214b and Implications for Its Atmosphere

We observed the transiting super-Earth exoplanet GJ1214b using Warm Spitzer at 4.5 microns wavelength during a 20-day quasi-continuous sequence in May 2011. The goals of our long observation were to accurately define the infrared transit radius of this nearby super-Earth, to search for the secondary eclipse, and to search for other transiting planets in the habitable zone of GJ1214. We here report results from the transit monitoring of GJ1214b, including a re-analysis of previous transit observations by Desert et al. (2011). In total, we analyse 14 transits of GJ1214b at 4.5 microns, 3 transits at 3.6 microns, and 7 new ground-based transits in the I+z band. Our new Spitzer data by themselves eliminate cloudless solar composition atmospheres for GJ1214b, and methane-rich models from Howe & Burrows (2012). Using our new Spitzer measurements to anchor the observed transit radii of GJ1214b at long wavelengths, and adding new measurements in I+z, we evaluate models from Benneke & Seager (2012) and Howe & Burrows (2012) using a chi-squared analysis. We find that the best-fit model exhibits an increase in transit radius at short wavelengths due to Rayleigh scattering. Pure water atmospheres are also possible. However, a flat line (no atmosphere detected) remains among the best of the statistically acceptable models, and better than pure water atmospheres. We explore the effect of systematic differences among results from different observational groups, and we find that the Howe & Burrows (2012) tholin-haze model remains the best fit, even when systematic differences among observers are considered.

astro-ph.EP↗

arXiv2012

Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD189733b

Mapping distant worlds is the next frontier for exoplanet infrared photometry studies. Ultimately, constraining spatial and temporal properties of an exoplanet atmosphere will provide further insight into its physics. For tidally-locked hot Jupiters that transit and are eclipsed by their host star, the first steps are now possible. Our aim is to constrain an exoplanet's shape, brightness distribution (BD) and system parameters from its light curve. Notably, we rely on the eclipse scanning. We use archived Spitzer 8-μm data of HD189733 (6 transits, 8 secondary eclipses, and a phase curve) in a global MCMC procedure for mitigating systematics. We also include HD189733's out-of-transit radial velocity measurements. We find a 6-σ deviation from the expected occultation of a uniformly-bright disk. This deviation emerges mainly from HD189733b's thermal pattern, not from its shape. We indicate that the correlation of the orbital eccentricity, e, and BD (uniform time offset) does also depend on the stellar density, ρ*, and the impact parameter, b (e-b-ρ*-BD correlation). For HD189733b, we find that relaxing the e-constraint and using more complex BDs lead to lower stellar/planetary densities and a more localized and latitudinally-shifted hot spot. We obtain an improved constraint on the upper limit of HD189733b's orbital eccentricity, e<0.011 (95%), when including the RV measurements. Our study provides new insights into the analysis of exoplanet light curves and a proper framework for future eclipse-scanning observations. Observations of the same exoplanet at different wavelengths will improve the constraints on its system parameters while ultimately yielding a large-scale time-dependent 3D map of its atmosphere. Finally, we discuss the perspective of extending our method to observations in the visible, in particular to better understand exoplanet albedos.

astro-ph.EP↗

arXiv2012

Photometrically derived masses and radii of the planet and star in the TrES-2 system

We measure the mass and radius of the star and planet in the TrES-2 system using 2.7 years of observations by the Kepler spacecraft. The light curve shows evidence for ellipsoidal variations and Doppler beaming on a period consistent with the orbital period of the planet with amplitudes of 2.79+0.44-0.62 and 3.44+0.32-0.37 parts per million (ppm) respectively, and a difference between the day and night side planetary flux of 3.41+0.55-0.82 ppm. We present an asteroseismic analysis of solar-like oscillations on TrES-2A which we use to calculate the stellar mass of 0.94+/-0.05 MSun and radius of 0.95+/-0.02 RSun. Using these stellar parameters, a transit model fit and the phase curve variations, we determine the planetary radius of 1.162+0.020-0.024 RJup and derive a mass for TrES-2b from the photometry of 1.44+/-0.21 MJup. The ratio of the ellipsoidal variation to the Doppler beaming amplitudes agrees to better than 2σ with theoretical predications, while our measured planet mass and radius agree within 2-σ of previously published values based on spectroscopic radial velocity measurements. We measure a geometric albedo of 0.0136+0.0022-0.0033 and an occultation (secondary eclipse) depth of 6.5+1.7-1.8 ppm which we combined with the day/night planetary flux ratio to model the atmosphere of TReS-2b. We find an atmosphere model that contains a temperature inversion is strongly preferred. We hypothesize that the Kepler bandpass probes a significantly greater atmospheric depth on the night side relative to the day side.

astro-ph.SR↗

arXiv2012

Detection of Thermal Emission from a Super-Earth

We report on the detection of infrared light from the super-Earth 55 Cnc e, based on four occultations obtained with Warm Spitzer at 4.5 microns. Our data analysis consists of a two-part process. In a first step, we perform individual analyses of each dataset and compare several baseline models to optimally account for the systematics affecting each lightcurve. We apply independent photometric correction techniques, including polynomial detrending and pixel-mapping, that yield consistent results at the 1-sigma level. In a second step, we perform a global MCMC analysis including all four datasets, that yields an occultation depth of 131+-28ppm, translating to a brightness temperature of 2360+-300 K in the IRAC-4.5 micron channel. This occultation depth suggests a low Bond albedo coupled to an inefficient heat transport from the planetary dayside to the nightside, or else possibly that the 4.5-micron observations probe atmospheric layers that are hotter than the maximum equilibrium temperature (i.e., a thermal inversion layer or a deep hot layer). The measured occultation phase and duration are consistent with a circular orbit and improves the 3-sigma upper limit on 55 Cnc e's orbital eccentricity from 0.25 to 0.06.

astro-ph.EP↗

arXiv2012

Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data

New transiting planet candidates are identified in sixteen months (May 2009 - September 2010) of data from the Kepler spacecraft. Nearly five thousand periodic transit-like signals are vetted against astrophysical and instrumental false positives yielding 1,091 viable new planet candidates, bringing the total count up to over 2,300. Improved vetting metrics are employed, contributing to higher catalog reliability. Most notable is the noise-weighted robust averaging of multi-quarter photo-center offsets derived from difference image analysis which identifies likely background eclipsing binaries. Twenty-two months of photometry are used for the purpose of characterizing each of the new candidates. Ephemerides (transit epoch, T_0, and orbital period, P) are tabulated as well as the products of light curve modeling: reduced radius (Rp/R*), reduced semi-major axis (d/R*), and impact parameter (b). The largest fractional increases are seen for the smallest planet candidates (197% for candidates smaller than 2Re compared to 52% for candidates larger than 2Re) and those at longer orbital periods (123% for candidates outside of 50-day orbits versus 85% for candidates inside of 50-day orbits). The gains are larger than expected from increasing the observing window from thirteen months (Quarter 1-- Quarter 5) to sixteen months (Quarter 1 -- Quarter 6). This demonstrates the benefit of continued development of pipeline analysis software. The fraction of all host stars with multiple candidates has grown from 17% to 20%, and the paucity of short-period giant planets in multiple systems is still evident. The progression toward smaller planets at longer orbital periods with each new catalog release suggests that Earth-size planets in the Habitable Zone are forthcoming if, indeed, such planets are abundant.

astro-ph.EP↗

arXiv2011

Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star

A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 +/- 0.060 MSun and 0.979 +/- 0.020 RSun. The depth of 492 +/- 10ppm for the three observed transits yields a radius of 2.38 +/- 0.13 REarth for the planet. The system passes a battery of tests for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities obtained with HIRES on Keck 1 over a one year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3σ upper limit of 124 MEarth, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the Habitable Zone of any star other than the Sun.

astro-ph.EP↗

arXiv2011

Lack of Inflated Radii for Kepler Giant Planet Candidates Receiving Modest Stellar Irradiation

The most irradiated transiting hot Jupiters are characterized by anomalously inflated radii, sometimes exceeding Jupiter's size by more than 60%. While different theoretical explanations have been applied, none of them provide a universal resolution to this observation, despite significant progress in the past years. We refine the photometric transit light curve analysis of 115 Kepler giant planet candidates based on public Q0-Q2 photometry. We find that 14% of them are likely false positives, based on their secondary eclipse depth. We report on planet radii vs. stellar flux. We find an increase in planet radii with increased stellar irradiation for the Kepler giant planet candidates, in good agreement with existing hot Jupiter systems. We find that in the case of modest irradiation received from the stellar host, giant planets do not have inflated radii, and appear to have radii independent of the host star incident flux. This finding suggests that the physical mechanisms inflating hot Jupiters become ineffective below a given orbit-averaged stellar irradiation level of ~2 10^8 erg s^-1 cm^-2.

astro-ph.EP↗

arXiv2011

The hot-Jupiter Kepler-17b: discovery, obliquity from stroboscopic starspots, and atmospheric characterization

This paper reports the discovery and characterization of the transiting hot giant exoplanet Kepler-17b. The planet has an orbital period of 1.486 days, and radial velocity measurements from the Hobby-Eberly Telescope (HET) show a Doppler signal of 420+/-15 m.s-1. From a transit-based estimate of the host star's mean density, combined with an estimate of the stellar effective temperature T_eff=5630+/-100 K from high-resolution spectra, we infer a stellar host mass of 1.061+/-0.067 M_sun and a stellar radius of 1.019+/-0.033 R_jup. We estimate the planet mass and radius to be Mp=2.450+/-0.114 M_jup and Rp=1.312+/-0.018 R_jup and a planet density near 1.35 g.cm-3. The host star is active, with dark spots that are frequently occulted by the planet. The continuous monitoring of the star reveals a stellar rotation period of 11.89 days, 8 times the the planet's orbital period; this period ratio produces stroboscopic effects on the occulted starspots. The temporal pattern of these spot-crossing events shows that the planet's orbit is prograde and the star's obliquity is smaller than 15 deg. We detected planetary occultations of Kepler-17b with both the Kepler and Spitzer Space Telescopes. We use these observations to constrain the eccentricity, e, and find that it is consistent with a circular orbit (e<0.0011). The brightness temperatures of the planet the infrared bandpasses are T_3.6um=1880+/-100 K and T4.5um=1770+/-150 K. We measure the optical geometric albedo A_g in the Kepler bandpass and find A_g = 0.10+/-0.02. The observations are best described by atmospheric models for which most of the incident energy is re-radiated away from the day side.

astro-ph.EP↗

arXiv2011

Discovery and Atmospheric Characterization of Giant Planet Kepler-12b: An Inflated Radius Outlier

We report the discovery of planet Kepler-12b (KOI-20), which at 1.695\pm0.030 RJ is among the handful of planets with super-inflated radii above 1.65 RJ. Orbiting its slightly evolved G0 host with a 4.438-day period, this 0.431\pm0.041 MJ 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\pm0.010 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\pm0.04; 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.

astro-ph.EP↗

arXiv2011

The First Kepler Mission Planet Confirmed With The Hobby-Eberly Telescope: Kepler-15b, a Hot Jupiter Enriched In Heavy Elements

We report the discovery of Kepler-15b, a new transiting exoplanet detected by NASA's Kepler mission. The transit signal with a period of 4.94 days was detected in the quarter 1 (Q1) Kepler photometry. For the first time, we have used the High-Resolution-Spectrograph (HRS) at the Hobby-Eberly Telescope (HET) to determine the mass of a Kepler planet via precise radial velocity (RV) measurements. The 24 HET/HRS radial velocities (RV) and 6 additional measurements from the FIES spectrograph at the Nordic Optical Telescope (NOT) reveal a Doppler signal with the same period and phase as the transit ephemeris. We used one HET/HRS spectrum of Kepler-15 taken without the iodine cell to determine accurate stellar parameters. The host star is a metal-rich ([Fe/H]=0.36+/-0.07) G-type main sequence star with T_eff=5515+/-124 K. The amplitude of the RV-orbit yields a mass of the planet of 0.66+/-0.1 M_Jup. The planet has a radius of 0.96+/-0.06 R_Jup and a mean bulk density of 0.9+/-0.2 g/cm^3. The planetary radius resides on the lower envelope for transiting planets with similar mass and irradiation level. This suggests significant enrichment of the planet with heavy elements. We estimate a heavy element mass of 30-40 M_Earth within Kepler-15b.

astro-ph.EP↗

arXiv2011

The high albedo of the hot Jupiter Kepler-7b

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-7b 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-7b 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.

astro-ph.EP↗