SuperWASP Results

Edasich wrote:Nice, but no hints about the host stars.

We report on the discovery of WASP-37b, a transiting hot Jupiter orbiting a mv = 12.7 G2-type dwarf, with a period of 3.577471 +/- 0.00001 d, transit epoch T0 = 2455338.6189 +/- 0.0006 (HJD), and a transit duration 0.1307 +/- 0.0019 d. The planetary companion has a mass Mp = 1.696(+0.123)(-0.128) MJ and radius Rp = 1.136(+0.060){-0.051} RJ, yielding a mean density of 1.169(+0.119)(-0.152) times that of Jupiter. From a spectral analysis and comparisons with stellar models, we find the host star has M* = 0.849(+0.067)(-0.040) Msun, R* = 0.977(+0.045)(-0.042) Rsun, Teff = 5800 +/- 150 K and [Fe/H] = -0.40 +/- 0.12. WASP-37 is therefore one of the lowest metallicity stars to host a transiting planet.

Transit timing variation and activity in the WASP-10 planetary system
Transit timing analysis may be an effective method of discovering additional bodies in extrasolar systems which harbour transiting exoplanets. The deviations from the Keplerian motion, caused by mutual gravitational interactions between planets, are expected to generate transit timing variations of transiting exoplanets. In 2009 we collected 9 light curves of 8 transits of the exoplanetWASP-10b. Combining these data with published ones, we found that transit timing cannot be explained by a constant period but by a periodic variation. Simplified three-body models which reproduce the observed variations of timing residuals were identified by numerical simulations. We found that the configuration with an additional planet of mass of 0.1 MJ and orbital period of 5.23 d, located close to the outer 5:3 mean motion resonance, is the most
likely scenario. If the second planet is a transiter, the estimated flux drop will be 0.3 per cent and can be observable with a ground-based telescope. Moreover, we present evidence that the spots on the stellar surface and rotation of the star affect the radial velocity curve giving rise to spurious eccentricity of the orbit of the first planet. We argue that the orbit of WASP-10b is essentially circular. Using the gyrochronology method, the host star was found to be 270 ± 80 Myr old. This young age can explain the large radius reported for WASP-10b.

The existence of WASP-10c could be independently confirmed if it is a transiter. Assuming that its radius is 0.4 RJ, i.e. similar to exoplanets of the similar mass like HAT-P-11b (Bakos et al. 2010) or Kepler-4b (Borucki et al. 2010), the expected flux drop during a transit would be 0.3
per cent or even greater if we consider the young age of the system. This could be observable with a large ground-based telescope.

Assuming the hypothetical second planet is also a transiting exoplanet, it would cause periodic flux drops of the host star. The depth of these transits would be in the range of 0.03–0.35 per cent (or 0.3–3.8 mmag) depending on the adopted mean planetary density – for a rocky planet (e.g. CoRoT-7b, L´eger et al. 2009; Queloz et al. 2009) or an ultra-low-density hot Neptune (e.g. WASP-17b, Anderson et al. 2010), respectively. If one considers the mass of the hypothetical second planet and its proximity to the host star, the latter scenario seems to be less probable, causing transits to be shallow and difficult to detect.

We have observed 7 new transits of the 'hot Jupiter' WASP-5b using a 61 cm telescope located in New Zealand, in order to search for transit timing variations (TTVs) which can be induced by additional bodies existing in the system. When combined with other available photometric and radial velocity (RV) data, we find that its transit timings do not match a linear ephemeris; the best fit \chi^2 values of 32.2 with 9 degrees of freedom indicates that a marginal TTV signal has been observed at a confidence level of 99.982 %, or 3.7 \sigma. The standard deviation of the TTVs is as large as 70 s, and if this is real, it cannot be explained by other effects than that due to an additional body or bodies. We put the upper limit on the RV amplitude due to the possible secondary body as 21 m s^{-1}, which corresponds to its mass of 22-70 M_{Earth} over the period ratio from 0.2 to 5.0. From the TTVs data, using the numerical simulations, we place more stringent limits down to 2 M_{Earth} near 1:2 and 2:1 MMRs at the 3 \sigma level, assuming that the two planets are co-planer. We also put the upper limit on Trojan mass as 43 M_{Earth} (3 \sigma) using both RV and photometric data. Further follow-up photometric and spectroscopic observations will be required to confirm the reality of the TTV signal. Results such as these will provide important information for the migration mechanisms of planetary systems.

We report the detection of a 0.6 M_J extrasolar planet by WASP-South, WASP-25b, transiting its solar-type host star every 3.76 days. A simultaneous analysis of the WASP, FTS and Euler photometry and CORALIE spectroscopy yields a planet of R_p = 1.22 R_J and M_p = 0.58 M_J around a slightly metal-poor solar-type host star, [Fe/H] = -0.05 \pm 0.10, of R_{\ast} = 0.92 R_{\odot} and M_{\ast} = 1.00 M_{\odot}. WASP-25b is found to have a density of \rho_p = 0.32 \rho_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.

Recently, Fossati et al. observed that the UV transit of WASP-12b showed an early ingress compared to the optical transit. We suggest that the resulting early ingress is caused by a bow shock ahead of the planetary orbital motion. In this Letter we investigate the conditions that might lead to the formation of such a bow shock. We consider two scenarios: (1) the stellar magnetic field is strong enough to confine the hot coronal plasma out to the planetary orbit and (2) the stellar magnetic field is unable to confine the plasma, which escapes in a wind. In both cases, a shock capable of compressing plasma to the observed densities will form around the planet for plasma temperatures T < (4 - 5) x 10^6 K. In the confined case, the shock always forms directly ahead of the planet, but in the wind case the shock orientation depends on the wind speed and hence on the plasma temperature. For higher wind temperatures, the shock forms closer to the line of centers between the planet and the star. We conclude that shock formation leading to an observable early UV ingress is likely to be a common feature of transiting systems and may prove to be a useful tool in setting limits on planetary magnetic field strengths Bp. In the case of WASP-12b, we derive an upper limit of about Bp=24 G.

We report the discovery of WASP-38b, a long period transiting planet in an eccentric $6.871815$ day orbit. The transit epoch is $2455335.92050 \pm 0.00074$ (HJD) and the transit duration is $4.663$ hours. We performed a spectral analysis of the host star HD 146389/BD+10 2980 that yielded $T_{eff} = 6150 \pm 80 $K, \logg$=4.3 \pm 0.1$, \vsini=$8.6 \pm 0.4 $\kms, $M_*=1.16 \pm 0.04$\Msun\ and $R_* =1.36 \pm 0.05 $\Rsun, consistent with a dwarf of spectral type F8. The radial velocity variations and the transit light curves were fitted simultaneously to estimate the orbital and planetary parameters. The planet has a mass of $2.71 \pm 0.07 $ \Mjup\ and a radius of $1.08 \pm 0.05\, $\Rjup\, giving a density, $ \rho_p = 2.2 \pm 0.3 \rho_J$. The high precision of the eccentricity $e=0.032 \pm 0.0045$ is due to the relative transit timing from the light curves and the RV shape. The planet equilibrium temperature is estimated at $1311 \pm 45$K. WASP-38b is the longest period planet found by WASP-North and with a bright host star (V = $9.4\,$ mag), is a good candidate for followup atmospheric studies.

We report the discovery of photometric oscillations in the host star of the exoplanet WASP-33 b (HD 15082). The data were obtained in the R band both in transit and out-of-transit phases from the Montcabrer (0.3-m telescope) and Montsec (0.8-m telescope) observatories. Proper fitting and subsequent removal of the transit signal reveals stellar photometric variations with an amplitude of about 1 mmag and a period of 67.57+/-0.08 min, which is typical of delta Scuti-type variable stars. Furthermore, the oscillation period is commensurable with the orbital period of the planet with a factor of 26. These findings make WASP-33 the first transiting exoplanet host star with pulsation variability and possibly experiencing tidally induced planet-star interactions. Several possible explanations for the existence of the observed high-order ressonance such as perturbations due to an eccentric orbit, rotational distortion of the star or tidal locking during planet migration are proposed.

We report the discovery of a transiting planet orbiting the star TYC 2-1155-1. The star, WASP-32, is a moderately bright (V=11.3) solar-type star (Teff=6100 +- 100K, [Fe/H] = -0.13 +- 0.10). The lightcurve of the star obtained with the WASP-South and WASP-North instruments shows periodic transit-like features with a depth of about 1% and a duration of 0.10d every 2.72d. The presence of a transit-like feature in the lightcurve is confirmed using z-band photometry obtained with Faulkes Telescope North. High resolution spectroscopy obtained with the CORALIE spectrograph confirms the presence of a planetary mass companion. From a combined analysis of the spectroscopic and photometric data, assuming that the star is a typical main-sequence star, we estimate that the planet has a mass M_p = 3.60 +- 0.07 M_Jup and a radius R_p = 1.19 +- 0.06R_Jup. WASP-32 is one of a small group of hot Jupiters with masses M_p > 3M_Jup. We find that some stars with hot Jupiter companions and with masses M_* =~ 1.2M_sun, including WASP-32, are depleted in lithium, but that the majority of these stars have similar lithium abundances to field stars.

We report the discovery of a 61-Jupiter-mass brown dwarf, which transits its F8V, rotationally-synchronised host star, WASP-30, every 4.16 days. From a range of age indicators, we estimate the system age to be 1-2 Gyr. We derive a radius (0.89 \pm 0.02 RJup) for the companion that is consistent with that predicted (0.914 RJup) by a model of a 1-Gyr-old, non-irradiated brown dwarf with a dusty atmosphere.