We present the optical transmission spectrum of the highly inflated Saturn- mass exoplanet WASP-21b, using three transits obtained with the ACAM instrument on the William Herschel Telescope through the LRG-BEASTS survey (Low Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy). Our transmission spectrum covers a wavelength range of 4635-9000{AA}, achieving an average transit depth precision of 197ppm compared to one atmospheric scale height at 246ppm. We detect NaI absorption in a bin width of 30{AA}, at >4{sigma} confidence, which extends over 100{AA}. We see no evidence of absorption from KI. Atmospheric retrieval analysis of the scattering slope indicates it is too steep for Rayleigh scattering from H_2, but is very similar to that of HD 189733b. The features observed in our transmission spectrum cannot be caused by stellar activity alone, with photometric monitoring of WASP-21 showing it to be an inactive star. We therefore conclude that aerosols in the atmosphere of WASP-21b are giving rise to the steep slope that we observe, and that WASP-21b is an excellent target for infra-red observations to constrain its atmospheric metallicity.
The sample of hot Jupiters that have been studied in great detail is still growing. In particular, when the planet transits its host star, it is possible to measure the planetary radius and the planet mass (with radial velocity data). For the study of planetary atmospheres, it is essential to obtain transit and occultation measurements at multiple wavelengths. We aim to characterize the transiting hot Jupiter WASP-19b by deriving accurate and precise planetary parameters from a dedicated observing campaign of transits and occultations. We have obtained a total of 14 transit lightcurves in the r'-Gunn, I-Cousins, z'-Gunn, and I+z' filters and 10 occultation lightcurves in z'-Gunn using EulerCam on the Euler-Swiss telescope and TRAPPIST. We also obtained one lightcurve through the narrow-band NB1190 filter of HAWK-I on the VLT measuring an occultation at 1.19 micron. We performed a global MCMC analysis of all new data, together with some archive data in order to refine the planetary parameters and to measure the occultation depths in z'-band and at 1.19 micron. We measure a planetary radius of R_p_=1.376+/-0.046R_J_, a planetary mass of M_p_=1.165+/-0.068M_J_, and find a very low eccentricity of e=0.0077(-0.0032/+0.0068), compatible with a circular orbit. We have detected the z'-band occultation at 3 sigma significance and measure it to be delta_F_occ,z'=352+/-116ppm, more than a factor of 2 smaller than previously published. The occultation at 1.19 micron is only marginally constrained at delta_F_occ,NB1190=1711(-726/+745)ppm. We show that the detection of occultations in the visible range is within reach, even for 1m class telescopes if a considerable number of individual events are observed. Our results suggest an oxygen-dominated atmosphere of WASP-19b, making the planet an interesting test case for oxygen-rich planets without temperature inversion.
Transmission spectroscopy has become a prominent tool for characterizing the atmospheric properties of close-in transiting planets. Recent observations have revealed a remarkable diversity in exoplanet spectra, which show absorption signatures of Na, K and H_2_O, in some cases partially or fully attenuated by atmospheric aerosols. Aerosols (clouds and hazes) themselves have been detected in the transmission spectra of several planets thanks to wavelength-dependent slopes caused by the particles' scattering properties. We present an optical 550-960nm transmission spectrum of the extremely irradiated hot Jupiter WASP-103b, one of the hottest (2500K) and most massive (1.5M_J_) planets yet to be studied with this technique. WASP-103b orbits its star at a separation of less than 1.2 times the Roche limit and is predicted to be strongly tidally distorted. We have used Gemini/GMOS to obtain multi-object spectroscopy throughout three transits of WASP-103b. We used relative spectrophotometry and bin sizes between 20 and 2nm to infer the planet's transmission spectrum. We find that WASP-103b shows increased absorption in the cores of the alkali (Na, K) line features. We do not confirm the presence of any strong scattering slope as previously suggested, pointing towards a clear atmosphere for the highly irradiated, massive exoplanet WASP-103b. We constrain the upper boundary of any potential cloud deck to reside at pressure levels above 0.01bar. This finding is in line with previous studies on cloud occurrence on exoplanets which find that clouds dominate the transmission spectra of cool, low surface gravity planets while hot, high surface gravity planets are either cloud-free, or possess clouds located below the altitudes probed by transmission spectra.
We present the analysis of TESS optical photometry of WASP-121b, which reveals the phase curve of this transiting ultra-hot Jupiter. Its hotspot is located at the sub-stellar point, showing inefficient heat transport from the dayside (2870+/-50K) to the nightside (<2500K at 3{sigma}) at the altitudes probed by TESS. The TESS eclipse depth, measured at the shortest wavelength to date for WASP-121b, confirms the strong deviation from blackbody planetary emission. Our atmospheric retrieval on the complete emission spectrum supports the presence of a temperature inversion, which can be explained by the presence of VO and possibly TiO and FeH. The strong planetary emission at short wavelengths could arise from an H^-^ continuum.
We report the discovery of WASP-117b, the first planet with a period beyond 10 days found by the WASP survey. The planet has a mass of M_p_=0.2755(+/- 0.0089)M_jup_, a radius of R_p_=1.021(-0.065/+0.076)R_jup_ and is in an eccentric (e=0.302(+/-0.023)), P=10.02165(+/-0.00055)d orbit around a main-sequence F9 star. The host star's brightness (V=10.15mag) makes WASP-117 a good target for follow-up observations, and with a periastron planetary equilibrium temperature of T_eq_=1225(-39/+36)K and a low planetary mean density (rho_p_=0.259(-0.048/+0.054)rho_jup_) it is one of the best targets for transmission spectroscopy among planets with periods around 10 days. From a measurement of the Rossiter-McLaughlin effect, we infer a projected angle between the planetary orbit and stellar spin axes of beta=-44(+/-11){deg}, and we further derive an orbital obliquity of psi=69.6(+4.7/-4.1){deg}. Owing to the large orbital separation, tidal forces causing orbital circularization and realignment of the planetary orbit with the stellar plane are weak, having had little impact on the planetary orbit over the system lifetime. WASP-117b joins a small sample of transiting giant planets with well characterized orbits at periods above ~8-days.
We report the discovery by the WASP transit survey of a giant planet in a close orbit (0.0295+/-0.0009AU) around a moderately bright (V=11.6, K=10) G9 dwarf (0.89+/-0.08M_{sun}_, 0.84+/-0.03R_{sun}_) in the Southern constellation Eridanus. Thanks to high-precision follow-up photometry and spectroscopy obtained by the telescopes TRAPPIST and Euler, the mass and size of this planet, WASP-50 b, are well constrained to 1.47+/-0.09M_Jup_ and 1.15+/-0.05R_Jup_, respectively. The transit ephemeris is 2455558.6120(+/-0.0002)+Nx1.955096(+/-0.000005) HJD_UTC_. The size of the planet is consistent with basic models of irradiated giant planets.
We report the discovery of WASP-34b, a sub-Jupiter-mass exoplanet transiting its 10.4-magnitude solar-type host star (1SWASP J110135.89-235138.4; TYC 6636-540-1) every 4.3177 days in a slightly eccentric orbit (e=0.038+/-0.012). We find a planetary mass of 0.59+/-0.01M_Jup_ and radius of 1.22^+0.11^_-0.08_R_Jup. There is a linear trend in the radial velocities of 55+/-4m/s/y indicating the presence of a long-period third body in the system with a mass >0.45M_Jup_ at a distance of >1.2AU from the host star. This third-body is either a low-mass star, white dwarf, or another planet. The transit depth ((R_P/R_*)^2^=0.0126) and high impact parameter (b=0.90) suggest that this could be the first known transiting exoplanet expected to undergo grazing transits, but with a confidence of only ~80%.
We report the discovery of WASP-13b, a low-mass M_p_=0.46^+0.06^_-0.05_ M_J_ transiting exoplanet with an orbital period of 4.35298+/-0.00004days. The transit has a depth of 9mmag, and although our follow-up photometry does not allow us to constrain the impact parameter well (0<b<0.46), with radius in the range R_p_~1.06-1.21R_J_ the location of WASP-13b in the mass-radius plane is nevertheless consistent with H/He-dominated, irradiated, low core mass and core-free theoretical models. The G1V host star is similar to the Sun in mass M_*_=1.03^+0.11^_-0.09_M_{sun}_ and metallicity ([M/H]=0.0+/-0.2, but is possibly older (8.5^+5.5^_-4.9_Gyr).
We report the discovery of the low-density, transiting giant planet WASP-31b. The planet is 0.48 Jupiter masses and 1.55 Jupiter radii. It is in a 3.4-day orbit around a metal-poor, late-F-type, V=11.7 dwarf star, which is a member of a common proper motion pair. In terms of its low density, WASP-31b is second only to WASP-17b, which is a more highly irradiated planet of similar mass.
We report the discovery of WASP-103 b, a new ultra-short-period planet (P=22.2h) transiting a 12.1 V-magnitude F8-type main-sequence star (1.22+/-0.04M_{sun}_, 1.44_-0.03_^+0.05^R_{sun}_, Teff=6110+/-160K). WASP-103 b is significantly more massive (1.49+/-0.09M_Jup_) and larger (1.53_-0.07_^+0.05^R_Jup_) than Jupiter. Its large size and extreme irradiation (~9x10^9^erg/s/cm2) make it an exquisite target for a thorough atmospheric characterization with existing facilities. Furthermore, its orbital distance is less than 20% larger than its Roche radius, meaning that it might be significantly distorted by tides and might experience mass loss through Roche-lobe overflow. It thus represents a new key object for understanding the last stage of the tidal evolution of hot Jupiters.
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