We present the weak lensing analysis of the Wide-Field Imager SZ Cluster of galaxy (WISCy) sample, a set of 12 clusters of galaxies selected for their Sunyaev-Zel'dovich (SZ) effect. After developing new and improved methods for background selection and determination of geometric lensing scaling factors from absolute multi-band photometry in cluster fields, we compare the weak lensing mass estimate with public X-ray and SZ data. We find consistency with hydrostatic X-ray masses with no significant bias, no mass dependent bias and less than 20% intrinsic scatter and constrain f gas,500c = 0.128 +0.029 −0.023 . We independently calibrate the South Pole Telescope significance-mass relation and find consistency with previous results. The comparison of weak lensing mass and Planck Compton parameters, whether extracted selfconsistently with a mass-observable relation (MOR) or using X-ray prior information on cluster size, shows significant discrepancies. The deviations from the MOR strongly correlate with cluster mass and redshift. This could be explained either by a significantly shallower than expected slope of Compton decrement versus mass and a corresponding problem in the previous X-ray based mass calibration, or a size or redshift dependent bias in SZ signal extraction.

Context. GJ 1214b, the 6.55 Earth-mass transiting planet recently discovered by the MEarth team, has a mean density of ∼35% of that of the Earth. It is thought that this planet is either a mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. Aims. In the case of a hydrogen-rich atmosphere, molecular absorption and scattering processes may result in detectable radius variations as a function of wavelength. The aim of this paper is to measure these variations. Methods. We have obtained observations of the transit of GJ 1214b in the r-and I-band with the Isaac Newton Telescope (INT), in the g-, r-, i-and z-bands with the 2.2 m MPI/ESO telescope, in the K s -band with the Nordic Optical Telescope (NOT), and in the K c -band with the William Herschel Telescope (WHT). By comparing the transit depth between the the different bands, which is a measure for the planet-to-star size ratio, the atmosphere is investigated. Results. We do not detect clearly significant variations in the planet-to-star size ratio as function of wavelength. Although the ratio at the shortest measured wavelength, in g-band, is 2σ larger than in the other bands. The uncertainties in the K s and K c bands are large, due to systematic features in the light curves. Conclusions. The tentative increase in the planet-to-star size ratio at the shortest wavelength could be a sign of an increase in the effective planet-size due to Rayleigh scattering, which would require GJ 1214b to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have both clouds, to suppress planet-size variations at red optical wavelengths, as well as a sub-solar metallicity, to suppress strong molecular features in the near-and mid-infrared. However, star spots, which are known to be present on the hoststar's surface, can (partly) cancel out the expected variations in planet-to-star size ratio, because the lower surface temperature of the spots causes the effective size of the star to vary with wavelength. A hypothetical spot-fraction of ∼10%, corresponding to an average stellar dimming of ∼5% in the i-band, would be able to raise the near-and mid-infrared points sufficiently with respect to the optical measurements to be inconsistent with a water-dominated atmosphere. Modulation of the spot fraction due to the stellar rotation would in such case cause the observed flux variations of GJ 1214.

We present a weak lensing analysis of the cluster of galaxies RXC J2248.7-4431, a massive system at z = 0.3475 with prominent strong lensing features covered by the Cluster Lensing And Supernova survey with Hubble (CLASH). Based on UBVRIZ imaging from the Wide-Field Imager camera at the MPG/ESO 2.2-m telescope, we measure photometric redshifts and shapes of background galaxies. The cluster is detected as a mass peak at 5σ significance. Its density can be parametrized as a Navarro-Frenk-White (NFW) profile with two free parameters, the mass M 200m = 33.1 +9.6 −6.8 × 10 14 M ⊙ and concentration c 200m = 2.6 +1.5 −1.0 . We discover a second cluster inside the field of view at a photometric redshift of z ≈ 0.6, with an NFW mass of M 200m = 4.0 +3.7 −2.6 ×10 14 M ⊙ .

We present a sample of Cepheid variable stars towards M31 based on the first year of regular M31 observations of the PS1 survey in the r P1 and i P1 filters. We describe the selection procedure for Cepheid variable stars from the overall variable source sample and develop an automatic classification scheme using Fourier decomposition and the location of the instability strip. We find 1440 fundamental mode (classical δ) Cep stars, 126 Cepheids in the first overtone mode, and 147 belonging to the Population II types. 296 Cepheids could not be assigned to one of these classes and 354 Cepheids were found in other surveys. These 2009 Cepheids constitute the largest Cepheid sample in M31 known so far and the full catalog is presented in this paper. We briefly describe the properties of our sample in its spatial distribution throughout the M31 galaxy, in its age properties, and we derive an apparent period-luminosity relation (PLR) in our two bands. The Population I Cepheids nicely follow the dust pattern of the M31 disk, whereas the 147 Type II Cepheids are distributed throughout the halo of M31. We outline the time evolution of the star formation in the major ring found previously and find an age gradient. A comparison of our PLR to previous results indicates a curvature term in the PLR.

We report on the discovery of four ultra‐short‐period (P ≤ 0.18 d) eclipsing M‐dwarf binaries in the Wide‐Field Camera (WFCAM) Transit Survey. Their orbital periods are significantly shorter than that of any other known main‐sequence binary system, and are all significantly below the sharp period cut‐off at P ∼ 0.22  d as seen in binaries of earlier‐type stars. The shortest‐period binary consists of two M4‐type stars in a P = 0.112  d orbit. The binaries are discovered as part of an extensive search for short‐period eclipsing systems in over 260 000 stellar light curves, including over 10 000 M‐dwarfs down to J = 18 mag, yielding 25 binaries with P ≤ 0.23 d. In a popular paradigm, the evolution of short‐period binaries of cool main‐sequence stars is driven by the loss of angular momentum through magnetized winds. In this scheme, the observed P ∼ 0.22 d period cut‐off is explained as being due to time‐scales that are too long for lower‐mass binaries to decay into tighter orbits. Our discovery of low‐mass binaries with significantly shorter orbits implies that either these time‐scales have been overestimated for M‐dwarfs, e.g. due to a higher effective magnetic activity, or the mechanism for forming these tight M‐dwarf binaries is different from that of earlier‐type main‐sequence stars.

We present the largest M31 near-infrared (F110W (close to J band), F160W (H band)) Cepheid sample so far. The sample consists of 371 Cepheids with photometry obtained from the HST PHAT program. The sample of 319 fundamental mode Cepheids, 16 first overtone Cepheids and 36 type II Cepheids, was identified using the median absolute deviation (MAD) outlier rejection method we develop here. This method does not rely on priors and allows us to obtain this clean Cepheid sample without rejecting a large fraction of Cepheids.The obtained Period-Luminosity relations (PLRs) have a very small dispersion, i.e. 0.155 mag in F160W, despite using random phased observations. This remarkably small dispersion allows us to determine that the PLRs are significantly better described by a broken slope at ten days than a linear slope. The use of our sample as an anchor to determine the Hubble constant gives a 3.2% larger Hubble constant compared to the Riess et al. (2012) sample.

Context. The photometric observations of the OGLE-II microlens monitoring campaign have been taken in the period 1997−2000. All light curves of this campaign have recently become public. Our analysis of these data has revealed 13 low-amplitude transiting objects among ∼15 700 stars in three Carina fields towards the Galactic disk. One of these objects, OGLE2-TR-L9 (P ∼ 2.5 days), turned out to be an excellent transiting-planet candidate. Aims. We report on our investigation of the true nature of OGLE2-TR-L9. By re-observing the photometric transit, we attempt to determine the transit parameters to high precision, and, by spectroscopic observations, to estimate the properties of the host star and determine the mass of the transiting object by means of radial-velocity measurements. Methods. High precision photometric observations were obtained in g , r , i , and z band simultaneously, using the new GROND detector, mounted on the MPI/ESO 2.2 m telescope at La Silla. Eight epochs of high-dispersion spectroscopic observations were obtained using the fiber-fed FLAMES/UVES Echelle spectrograph, mounted on ESO's Very Large Telescope at Paranal. Results. The photometric transit, now more than 7 years after the last OGLE-II observations, was re-discovered only ∼8 min from its predicted time. The primary object is a rapidly rotating F3 star with v sin i = 39.33±0.38 km s −1 , T = 6933±58 K, log g = 4.25±0.01, and [Fe/H] = −0.05 ± 0.20. The transiting object is an extrasolar planet with M p = 4.5 ± 1.5 M Jup and R p = 1.61 ± 0.04 R Jup . Since this is the first planet detected orbiting a fast rotating star, the uncertainties in both the radial-velocity measurements and the planetary mass are larger than for most other planets discovered to date. The rejection of possible blend scenarios was based on a quantitative analysis of the multi-color photometric data. A stellar-blend scenario of an early F-star with a faint eclipsing-binary system is excluded, due to 1) the consistency between the spectroscopic parameters of the star and the mean density of the transited object as determined from the photometry, and 2) the excellent agreement between the transit signal as observed at four different wavelengths.

The Pan-Planets survey observed an area of 42 sq deg. in the galactic disk for about 165 h. The main scientific goal of the project is the detection of transiting planets around M dwarfs. We establish an efficient procedure for determining the stellar parameters T eff and log g of all sources using a method based on SED fitting, utilizing a three-dimensional dust map and proper motion information. In this way we identify more than 60 000 M dwarfs, which is by far the largest sample of low-mass stars observed in a transit survey to date. We present several planet candidates around M dwarfs and hotter stars that are currently being followed up. Using Monte Carlo simulations we calculate the detection efficiency of the Pan-Planets survey for different stellar and planetary populations. We expect to find 3.0 +3.3 −1.6 hot Jupiters around F, G, and K dwarfs with periods lower than 10 days based on the planet occurrence rates derived in previous surveys. For M dwarfs, the percentage of stars with a hot Jupiter is under debate. Theoretical models expect a lower occurrence rate than for larger main sequence stars. However, radial velocity surveys find upper limits of about 1% due to their small sample, while the Kepler survey finds a occurrence rate that we estimate to be at least 0.17( +0.67 −0.04 )%, making it even higher than the determined fraction from OGLE-III for F, G and K stellar types, 0.14( +0.15 −0.076 )%. With the large sample size of Pan-Planets, we are able to determine an occurrence rate of 0.11( +0.37 −0.02 )% in case one of our candidates turns out to be a real detection. If, however, none of our candidates turn out to be true planets, we are able to put an upper limit of 0.34% with a 95% confidence on the hot Jupiter occurrence rate of M dwarfs. This limit is a significant improvement over previous estimates where the lowest limit published so far is 1.1% found in the WFCAM Transit Survey. Therefore we cannot yet confirm the theoretical prediction of a lower occurrence rate for cool stars.