WASP-25b: a 0.6 MJ planet in the Southern hemisphere

We report the detection of a 0.6 MJ extrasolar planet by WASP-South, WASP-25b, transiting its solar-type host star every 3.76 d. A simultaneous analysis of the WASP, FTS and Euler photometry and CORALIE spectroscopy yields a planet of Rp= 1.22 RJ and Mp= 0.58 MJ around a slightly metal-poor solar-type host star, [Fe/H]=- 0.05 ± 0.10, of R*= 0.92 Rsun and M*= 1.00 Msun. WASP-25b is found to have a density of ?p= 0.32 ?J, a low value for a sub-Jupiter mass planet. We investigate the relationship of planetary radius to planetary equilibrium temperature and host star metallicity for transiting exoplanets with a similar mass to WASP-25b, finding that these two parameters explain the radii of most low-mass planets well.

A high C/O ratio and weak thermal inversion in the atmosphere of exoplanet WASP-12b

The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O>=1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T>2,500K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.

WASP-34b: a near-grazing transiting sub-Jupiter-mass exoplanet in a hierarchical triple system

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±0.01 MJup and radius of 1.22-0.08+0.11 RJup. There is a linear trend in the radial velocities of 55±4 m s-1 y-1 indicating the presence of a long-period third body in the system with a mass ?0.45 MJup at a distance of ?1.2 AU from the host star. This third-body is either a low-mass star, a white dwarf, or another planet. The transit depth ((RP/Rstar)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%. Radial velocity and photometric data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/526/A130

WASP-41b: A Transiting Hot Jupiter Planet Orbiting a Magnetically Active G8V Star

We report the discovery of a transiting planet with an orbital period of 3.05 days orbiting the star TYC 7247-587-1. The star, WASP-41, is a moderately bright G8 V star (V=11.6) with a metallicity close to solar ([Fe/H]=-0.08±0.09). The star shows evidence of moderate chromospheric activity, both from emission in the cores of the Ca ii H and K ines and photometric variability with a period of 18.4 days and an amplitude of about 1%. We use a new method to show quantitatively that this periodic signal has a low false-alarm probability. The rotation period of the star implies a gyrochronological age for WASP-41 of 1.8 Gyr with an error of about 15%. We have used a combined analysis of the available photometric and spectroscopic data to derive the mass and radius of the planet (0.92±0.06 M, 1.20±0.06 R). Further observations of WASP-41 can be used to explore the connections between the properties of hot Jupiter planets and the level of chromospheric activity in their host stars.

WASP-40b: Independent Discovery of the 0.6 M Transiting Exoplanet HAT-P-27b

From WASP photometry and SOPHIE radial velocities we report the discovery of WASP-40b (HAT-P-27b), a 0.6 M planet that transits its 12th magnitude host star every 3.04 days. The host star is of late G-type or early K-type and likely has a metallicity greater than solar ([Fe/H]=0.14±0.11). The planet's mass and radius are typical of the known hot Jupiters, thus adding another system to the apparent pileup of transiting planets with periods near 3-4 days. Our parameters match those of the recent HATnet announcement of the same planet, thus giving confidence in the techniques used. We report a possible indication of stellar activity in the host star.

WASP-23b: a transiting hot Jupiter around a K dwarf and its Rossiter-McLaughlin effect

We report the discovery of a new transiting planet in the southern hemisphere. It was found by the WASP-south transit survey and confirmed photometrically and spectroscopically by the 1.2 m Swiss Euler telescope, LCOGT 2m Faulkes South Telescope, the 60 cm TRAPPIST telescope, and the ESO 3.6 m telescope. The orbital period of the planet is 2.94 days. We find that it is a gas giant with a mass of 0.88 ± 0.10 MJ and an estimated radius of 0.96 ± 0.05 RJ. We obtained spectra during transit with the HARPS spectrograph and detect the Rossiter-McLaughlin effect despite its small amplitude. Because of the low signal-to-noise ratio of the effect and a small impact parameter, we cannot place a strong constraint on the projected spin-orbit angle. We find two conflicting values for the stellar rotation. We find, via spectral line broadening, that v sin I = 2.2 ± 0.3 km s-1, while applying another method, based on the activity level using the index log R'_HK, gives an equatorial rotation velocity of only v = 1.35 ± 0.20 km s-1. Using these as priors in our analysis, the planet might be either misaligned or aligned. This result raises doubts about the use of such priors. There is evidence of neither eccentricity nor any radial velocity drift with time. Using WASP-South photometric observations confirmed with LCOGT Faulkes South Telescope, the 60 cm TRAPPIST telescope, the CORALIE spectrograph and the camera from the Swiss 1.2 m Euler Telescope placed at La Silla, Chile, as well as with the HARPS spectrograph, mounted on the ESO 3.6 m, also at La Silla, under proposal 084.C-0185. The data is publicly available at the CDS Strasbourg and on demand to the main author.RV data is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A24Appendix is available in electronic form at http://www.aanda.org

WASP-39b: a highly inflated Saturn-mass planet orbiting a late G-type star

We present the discovery of WASP-39b, a highly inflated transiting Saturn-mass planet orbiting a late G-type dwarf star with a period of 4.055259 +/- 0.000008 d, Transit Epoch T-0 = 2 455 342.9688 +/- 0.0002 (HJD), of duration 0.1168 +/- 0.0008 d. A combined analysis of the WASP photometry, high-precision follow-up transit photometry, and radial velocities yield a planetary mass of M-pl = 0.28 +/- 0.03 M-J and a radius of R-pl = 1.27 +/- 0.04 R-J, resulting in a mean density of 0.14 +/- 0.02 rho(J). The stellar parameters are mass M-star = 0.93 +/- 0.03 M-circle dot, radius R-star = 0.895 +/- 0.23 R-circle dot, and age 9(-4)(+3) Gyr. Only WASP-17b and WASP-31b have lower densities than WASP-39b, although they are slightly more massive and highly irradiated planets. From our spectral analysis, the metallicity of WASP-39 is measured to be [Fe/H] = -0.12 +/- 0.1 dex, and we find the planet to have an equilibrium temperature of 1116(-32)(+33) K. Both values strengthen the observed empirical correlation between these parameters and the planetary radius for the known transiting Saturn-mass planets.

WASP-31b: a low-density planet transiting a metal-poor, late-F-type dwarf star

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. Based in part on observations made with the HARPS spectrograph on the 3.6-m ESO telescope (proposal 085.C-0393) and with the CORALIE spectrograph and the Euler camera on the 1.2-m Euler Swiss telescope, both at the ESO La Silla Observatory, Chile.The photometric time-series and radial-velocity data used in this work are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A60

The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations

We present observations of the Rossiter–McLaughlin effect for the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b, and deduce the orientations of the planetary orbits with respect to the host stars’ rotation axes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde orbits and be well aligned, having sky-projected spin-orbit angles consistent with zero: λ=−4°.7 ± 4°.0, 15°+33−43 and Graphic, respectively. The host stars have Teff < 6250 K and conform with the trend of cooler stars having low obliquities. WASP-38b is a massive planet on a moderately long period, eccentric orbit so may be expected to have a misaligned orbit given the high obliquities measured in similar systems. However, we find no evidence for a large spin-orbit angle. By contrast, WASP-1b joins the growing number of misaligned systems and has an almost polar orbit, λ=Graphic. It is neither very massive, eccentric nor orbiting a hot host star, and therefore does not share the properties of many other misaligned systems.

WASP-50 b: a hot Jupiter transiting a moderately active solar-type star

We report the discovery by the WASP transit survey of a giant planet in a close orbit (0.0295 ± 0.0009 AU) around a moderately bright (V = 11.6, K = 10) G9 dwarf (0.89 ± 0.08 Msun, 0.84 ± 0.03 Rsun) 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 ± 0.09 MJup and 1.15 ± 0.05 RJup, respectively. The transit ephemeris is 2 455 558.6120 (±0.0002) + N × 1.955096 (±0.000005) HJDUTC. The size of the planet is consistent with basic models of irradiated giant planets. The chromospheric activity (log R'HK = -4.67) and rotational period (Prot = 16.3 ± 0.5 days) of the host star suggest an age of 0.8 ± 0.4 Gy that is discrepant with a stellar-evolution estimate based on the measured stellar parameters (?* = 1.48 ± 0.10 ?sun, Teff = 5400 ± 100 K, [Fe/H] = -0.12 ± 0.08) which favors an age of 7 ± 3.5 Gy. This discrepancy could be explained by the tidal and magnetic influence of the planet on the star, in good agreement with the observations that stars hosting hot Jupiters tend to show faster rotation and magnetic activity. We measure a stellar inclination of 84-31+6 deg, disfavoring a high stellar obliquity. Thanks to its large irradiation and the relatively small size of its host star, WASP-50 b is a good target for occultation spectrophotometry, making it able to constrain the relationship between hot Jupiters' atmospheric thermal profiles and the chromospheric activity of their host stars. The photometric time-series used in this work are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/533/A88

WASP-35b, WASP-48b, and HAT-P-30b/WASP-51b: Two New Planets and an Independent Discovery of a Hat Planet

We report the detection of WASP-35b, a planet transiting a metal-poor ([Fe/H] = -0.15) star in the Southern hemisphere, WASP-48b, an inflated planet which may have spun-up its slightly evolved host star of 1.75 R sun in the Northern hemisphere, and the independent discovery of HAT-P-30b/WASP-51b, a new planet in the Northern hemisphere. Using WASP, RISE, Faulkes Telescope South, and TRAPPIST photometry, with CORALIE, SOPHIE, and NOT spectroscopy, we determine that WASP-35b has a mass of 0.72 ± 0.06 MJ and radius of 1.32 ± 0.05RJ , and orbits with a period of 3.16 days, WASP-48b has a mass of 0.98 ± 0.09 MJ , radius of 1.67 ± 0.10 RJ , and orbits in 2.14 days, while HAT-P-30b/WASP-51b, with an orbital period of 2.81 days, is found to have a mass of 0.76 ± 0.05 MJ and radius of 1.42 ± 0.03 RJ , agreeing with values of 0.71 ± 0.03 MJ and 1.34 ± 0.07 RJ reported for HAT-P-30b.

A lower mass for the exoplanet WASP-21b

We present high-precision transit observations of the exoplanet WASP-21b, obtained with the Rapid Imager to Search for Exoplanets instrument mounted on the 2.0-m Liverpool Telescope. A transit model is fitted, coupled with a Markov chain Monte Carlo routine, to derive accurate system parameters. The two new high-precision transits allow us to estimate the stellar density directly from the light curve. Our analysis suggests that WASP-21 is evolving off the main sequence which led to a previous overestimation of the stellar density. Using isochrone interpolation, we find a stellar mass of 0.86 ± 0.04 Msun, which is significantly lower than previously reported (1.01 ± 0.03 Msun). Consequently, we find a lower planetary mass of 0.27 ± 0.01 MJup. A lower inclination (87?4 ± 0?3) is also found for the system than previously reported, resulting in a slightly larger stellar (R*= 1.10 ± 0.03 Rsun) and planetary radius (Rp= 1.14 ± 0.04 RJup). The planet radius suggests a hydrogen/helium composition with no core which strengthens the correlation between planetary density and host star metallicity. A new ephemeris is determined for the system, i.e. T0= 245 5084.519 74 ± 0.000 20 (HJD) and P= 4.322 5060 ± 0.000 0031 d. We found no transit timing variations in WASP-21b.

WASP-43b: the closest-orbiting hot Jupiter

We report the discovery of WASP-43b, a hot Jupiter transiting a K7V star every 0.81 d. At 0.6-Msun the host star has the lowest mass of any star currently known to host a hot Jupiter. It also shows a 15.6-d rotation period. The planet has a mass of 1.8 MJup, a radius of 0.9 RJup, and with a semi-major axis of only 0.014 AU has the smallest orbital distance of any known hot Jupiter. The discovery of such a planet around a K7V star shows that planets with apparently short remaining lifetimes owing to tidal decay of the orbit are also found around stars with deep convection zones.

Spitzer Secondary Eclipses of WASP-18b

The transiting exoplanet WASP-18b was discovered in 2008 by the Wide Angle Search for Planets project. The Spitzer Exoplanet Target of Opportunity Program observed secondary eclipses of WASP-18b using Spitzer's Infrared Array Camera in the 3.6 µm and 5.8 µm bands on 2008 December 20, and in the 4.5 µm and 8.0 µm bands on 2008 December 24. We report eclipse depths of 0.30% ± 0.02%, 0.39% ± 0.02%, 0.37% ± 0.03%, 0.41% ± 0.02%, and brightness temperatures of 3100 ± 90, 3310 ± 130, 3080 ± 140, and 3120 ± 110 K in order of increasing wavelength. WASP-18b is one of the hottest planets yet discovered—as hot as an M-class star. The planet's pressure-temperature profile most likely features a thermal inversion. The observations also require WASP-18b to have near-zero albedo and almost no redistribution of energy from the day side to the night side of the planet.

High-precision transit observations of the exoplanet WASP-13b with the RISE instrument

WASP-13b is a sub-Jupiter mass exoplanet orbiting a G1V type star with a period of 4.35 d.The current uncertainty in its impact parameter (0 < b < 0.46) results in poorly definedstellar and planetary radii. To better constrain the impact parameter, we have obtained highprecisiontransit observations with the rapid imager to search for exoplanets (RISE) instrumentmounted on 2.0-m Liverpool Telescope. We present four new transits which are fitted witha Markov chain Monte Carlo routine to derive accurate system parameters. We found anorbital inclination of 85. ◦ 2 ± 0. ◦ 3 resulting in stellar and planetary radii of 1.56 ± 0.04 Rand 1.39 ± 0.05RJup, respectively. This suggests that the host star has evolved off the mainsequence and is in the hydrogen-shell-burning phase.We also discuss how the limb darkeningaffects the derived system parameters.With a density of 0.17ρJ,WASP-13b joins the group oflow-density planets whose radii are too large to be explained by standard irradiation models.We derive a new ephemeris for the system, T0 = 245 5575.5136 ± 0.0016 (HJD) and P =4.353 011 ± 0.000 013 d. The planet equilibrium temperature (Tequ = 1500 K) and the brighthost star (V = 10.4mag) make it a good candidate for follow-up atmospheric studies.