Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared

The TRAPPIST-1 planetary system is a favorable target for the atmospheric characterization of temperate earth-sized exoplanets by means of transmission spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible obstacle to this technique could come from the photospheric heterogeneity of the host star that could affect planetary signatures in the transit transmission spectra. To constrain further this possibility, we gathered an extensive photometric data set of 25 TRAPPIST-1 transits observed in the near-IR J band (1.2 $\mu$m) with the UKIRT and the AAT, and in the NB2090 band (2.1 $\mu$m) with the VLT during the period 2015-2018. In our analysis of these data, we used a special strategy aiming to ensure uniformity in our measurements and robustness in our conclusions. We reach a photometric precision of $\sim0.003$ (RMS of the residuals), and we detect no significant temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the period of three years. The few transit depths measured for planets d and f hint towards some level of variability, but more measurements will be required for confirmation. Our depth measurements for planets b and c disagree with the stellar contamination spectra originating from the possible existence of bright spots of temperature 4500 K. We report updated transmission spectra for the six inner planets of the system which are globally flat for planets b and g and some structures are seen for planets c, d, e, and f.Comment: accepted for publication in MNRA

Mean and extreme precipitation over European river basins better simulated in a 25km AGCM

Limited spatial resolution is one of the factors that may hamper applications of global climate models (GCMs), in particular over Europe with its complex coastline and orography. In this study, the representation of European mean and extreme precipitation is evaluated in simulations with an atmospheric GCM (AGCM) at different resolutions between about 135 and 25km grid spacing in the mid-latitudes. The continent-wide root-mean-square error in mean precipitation in the 25km model is about 25% smaller than in the 135km model in winter. Clear improvements are also seen in autumn and spring, whereas the model's sensitivity to resolution is very small in summer. Extreme precipitation is evaluated by estimating generalised extreme value distributions (GEVs) of daily precipitation aggregated over river basins whose surface area is greater than 50000km2. GEV location and scale parameters are measures of the typical magnitude and of the interannual variability of extremes, respectively. Median model biases in both these parameters are around 10% in summer and around 20% in the other seasons. For some river basins, however, these biases can be much larger and take values between 50% and 100%. Extreme precipitation is better simulated in the 25km model, especially during autumn when the median GEV parameter biases are more than halved, and in the North European Plains, from the Loire in the west to the Vistula in the east. A sensitivity experiment is conducted showing that these resolution sensitivities in both mean and extreme precipitation are in many areas primarily due to the increase in resolution of the model orography. The findings of this study illustrate the improved capability of a global high-resolution model in simulating European mean and extreme precipitation

Rock magnetic investigation of possible sources of the Bangui magnetic anomaly

International audienceThe Bangui magnetic anomaly (BMA) is the largest lithospheric magnetic field anomaly on Earth at low latitudes. Previous studies investigated its geological source using constraints from satellite and ground magnetic field measurements, as well as from surface magnetic susceptibility measurements on rocks from the Panafrican Mobile Belt Zone (PMBZ). Here we combine magnetic field data modelling and rock magnetic property measurements (susceptibility and natural remanent magnetization, NRM) on many samples from this PMBZ and the surrounding formations. It reveals that NRM is a significant component of the total magnetization (Mt) of the BMA source, which reaches 4.3 A/m with maximum thicknesses of 38 and 54 km beneath the western and eastern parts of the BMA. Only the isolated and relatively thin banded iron formations and some migmatites show such Mt values. Thus we suggest that the thick BMA source may be composed either by overlapped slices of such metamorphic rocks, or by an iron-rich mafic source, or by a combination of these two geological structures

Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ3470b

GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing variation (TTV) and transmission spectroscopy analyses of multiwavelength optical photometry from 2.4-m and 0.5-m telescopes at the Thai National Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows us to place an upper mass limit for a second planet in the system. The presence of a hot Jupiter with a period of less than 10 d or a planet with an orbital period between 2.5 and 4.0 d are excluded. Combined optical and near-infrared transmission spectroscopy favour an H/He-dominated haze (mean molecular weight 1.08 ± 0.20) with high particle abundance at high altitude. We also argue that previous near-infrared data favour the presence of methane in the atmosphere of GJ3470b

The TRAPPIST survey of southern transiting planets. I. Thirty eclipses of the ultra-short period planet WASP-43 b

We present twenty-three transit light curves and seven occultation light curves for the ultra-short period planet WASP-43 b, in addition to eight new measurements of the radial velocity of the star. Thanks to this extensive data set, we improve significantly the parameters of the system. Notably, the largely improved precision on the stellar density (2.41+-0.08 rho_sun) combined with constraining the age to be younger than a Hubble time allows us to break the degeneracy of the stellar solution mentioned in the discovery paper. The resulting stellar mass and size are 0.717+-0.025 M_sun and 0.667+-0.011 R_sun. Our deduced physical parameters for the planet are 2.034+-0.052 M_jup and 1.036+-0.019 R_jup. Taking into account its level of irradiation, the high density of the planet favors an old age and a massive core. Our deduced orbital eccentricity, 0.0035(-0.0025,+0.0060), is consistent with a fully circularized orbit. We detect the emission of the planet at 2.09 microns at better than 11-sigma, the deduced occultation depth being 1560+-140 ppm. Our detection of the occultation at 1.19 microns is marginal (790+-320 ppm) and more observations are needed to confirm it. We place a 3-sigma upper limit of 850 ppm on the depth of the occultation at ~0.9 microns. Together, these results strongly favor a poor redistribution of the heat to the night-side of the planet, and marginally favor a model with no day-side temperature inversion.Comment: 14 pages, 6 tables, 11 figures. Accepted for publication in A&

Planetary Candidates Observed by Kepler IV: Planet Sample From Q1-Q8 (22 Months)

We provide updates to the Kepler planet candidate sample based upon nearly two years of high-precision photometry (i.e., Q1-Q8). From an initial list of nearly 13,400 Threshold Crossing Events (TCEs), 480 new host stars are identified from their flux time series as consistent with hosting transiting planets. Potential transit signals are subjected to further analysis using the pixel-level data, which allows background eclipsing binaries to be identified through small image position shifts during transit. We also re-evaluate Kepler Objects of Interest (KOI) 1-1609, which were identified early in the mission, using substantially more data to test for background false positives and to find additional multiple systems. Combining the new and previous KOI samples, we provide updated parameters for 2,738 Kepler planet candidates distributed across 2,017 host stars. From the combined Kepler planet candidates, 472 are new from the Q1-Q8 data examined in this study. The new Kepler planet candidates represent ~40% of the sample with Rp~1 Rearth and represent ~40% of the low equilibrium temperature (Teq<300 K) sample. We review the known biases in the current sample of Kepler planet candidates relevant to evaluating planet population statistics with the current Kepler planet candidate sample.Comment: 12 pages, 8 figures, Accepted ApJ Supplemen

Ultra-precise Masses and Magnitudes for the Gliese 268 M-dwarf Binary

Recent advances in astrometry using interferometry and precision radial velocity techniques combined allow for a significant improvement in the precision of masses of M‐dwarf stars in visual systems. We report recent astrometric observations of Gliese 268, an M‐dwarf binary with a 10.4 day orbital period, with the IOTA interferometer and radial velocity observations with the ELODIE instrument. Combining these measurements leads to preliminary masses of the constituent stars with uncertainties of 0.4%. The masses of the components are 0.22596±0.00084 M_⊙ for the primary and 0.19230±0.00071 M_⊙ for the secondary. The system parallax is determined by these observations to be 0.1560±.0030 arcsec (2.0% uncertainty) and is within Hipparcos error bars (0.1572±.0033). We tested these physical parameters, along with the near‐infrared luminosities of the stars, against stellar evolution models for low‐mass stars. Discrepancies between the measured and theoretical values point toward a low‐level departure from the predictions. These results are among the most precise masses measured for visual binaries

WASP-42 b and WASP-49 b: two new transiting sub-Jupiters

We report the discovery of two new transiting planets from the WASP survey. WASP-42 b is a 0.500 +/- 0.035 M_jup planet orbiting a K1 star at a separation of 0.0548 +/- 0.0017 AU with a period of 4.9816872 +/- 7.3 x 10^-6 days. The radius of WASP-42 b is 1.080 +/- 0.057 R_jup while its equilibrium temperature is T_eq = 995 +/- 34 K. We detect some evidence for a small but non-zero eccentricity of e=0.060 +/- 0.013. WASP-49 b is a 0.378 +/- 0.027 M_jup planet around an old G6 star. It has a period of 2.7817387 +/- 5.6 x 10^-6 days and a separation of 0.0379 +/- 0.0011 AU. This planet is slightly bloated, having a radius of 1.115 +/- 0.047 R_jup and an equilibrium temperature of T_eq = 1369 +/- 39 K. Both planets have been followed up photometrically, and in total we have obtained 5 full and one partial transit light curves of WASP-42 and 4 full and one partial light curves of WASP-49 using the Euler-Swiss, TRAPPIST and Faulkes South telescopes

Mapping Exoplanets

The varied surfaces and atmospheres of planets make them interesting places to live, explore, and study from afar. Unfortunately, the great distance to exoplanets makes it impossible to resolve their disk with current or near-term technology. It is still possible, however, to deduce spatial inhomogeneities in exoplanets provided that different regions are visible at different times---this can be due to rotation, orbital motion, and occultations by a star, planet, or moon. Astronomers have so far constructed maps of thermal emission and albedo for short period giant planets. These maps constrain atmospheric dynamics and cloud patterns in exotic atmospheres. In the future, exo-cartography could yield surface maps of terrestrial planets, hinting at the geophysical and geochemical processes that shape them.Comment: Updated chapter for Handbook of Exoplanets, eds. Deeg & Belmonte. 17 pages, including 6 figures and 4 pages of reference