Context. We wish to determine accurate ages for open clusters and use this, in conjunction with colour-magnitude diagrams, to constrain models of stellar structure and evolution. Aims. The detached eclipsing binary V20 in the old, metal-rich ([Fe/H] = +0.40) open cluster NGC 6791 is studied in order to determine highly accurate masses and radii of its components. This allows the cluster age to be established with high precision, using isochrones in the mass-radius diagram. Methods. We employ high-resolution UVES spectroscopy of V20 to determine the spectroscopic orbit and time-series V, I photometry to obtain the photometric elements. Results. The masses and radii of the V20 components are found to be 1.074 ± 0.008 M and 1.399 ± 0.016 R (primary) and 0.827 ± 0.004 M and 0.768 ± 0.006 R (secondary). The primary is located almost exactly at the hottest point along the cluster isochrone, and the secondary is a ∼7 times fainter main-sequence star. We determine an apparent cluster distance-modulus of (m − M) V = 13.46 ± 0.10 (average of primary and secondary). The cluster age is obtained from comparisons with theoretical isochrones in the mass-radius diagram. Using the isochrones from Victoria-Regina with [Fe/H] = +0.37 we find 7.7 ± 0.5 Gyr, whereas the Yonsei-Yale (Y 2 ) isochrones lead to 8.2 ± 0.5 Gyr, and BaSTI isochrones to 9.0 ± 0.5 Gyr. In a mass-radius diagram, the 7.7 Gyr VRSS and 9.0 Gyr BaSTI isochrones overlap nearly perfectly despite the age-difference. This model dependence, which is significantly larger than the precision determined from mass, radius, and abundance uncertainties, prevents a definitive age-determination of the cluster. Conclusions. Using detached eclipsing binaries for determination of cluster ages, the dominant error is due to differences among stellar models and no longer to observational errors in cluster reddening and distance. By observing a suitable number of detached eclipsing binaries in several open clusters it should be possible to calibrate the age-scale and provide firm constraints which stellar models must reproduce.

c 0000 RAS 2 L. Mancini et al. ABSTRACT We present new ground-based, multi-colour, broad-band photometric measurements of the physical parameters, transmission and emission spectra of the transiting extrasolar planet WASP-19 b. The measurements are based on observations of eight transits and four occultations through a Gunn i filter using the 1.54 m Danish Telescope, 14 transits through an R c filter at the PEST observatory and one transit observed simultaneously through four optical (Sloan g ′ , r ′ , i ′ , z ′ ) and three near-infrared (J, H, K) filters, using the GROND instrument on the MPG/ESO 2.2m telescope. The GROND optical light curves have a point-to-point scatter around the best-fitting model between 0.52 and 0.65 mmag rms. We use these new data to measure refined physical parameters for the system. We find the planet to be more bloated (R b = 1.410 ± 0.017 R Jup ; M b = 1.139 ± 0.030 M Jup ) and the system to be twice as old as initially thought. We also used published and archived data sets to study the transit timings, which do not depart from a linear ephemeris. We detected an anomaly in the GROND transit light curve which is compatible with a spot on the photosphere of the parent star. The starspot position, size, spot contrast and temperature were established. Using our new and published measurements, we assembled the planet's transmission spectrum over the 370-2350 nm wavelength range and its emission spectrum over the 750-8000 nm range. By comparing these data to theoretical models we investigated the theoretically predicted variation of the apparent radius of WASP-19 b as a function of wavelength and studied the composition and thermal structure of its atmosphere. We conclude that: (i) there is no evidence for strong optical absorbers at low pressure, supporting the common idea that the planet's atmosphere lacks a dayside inversion; (ii) the temperature of the planet is not homogenized, because the high warming of its dayside causes the planet to be more efficient in re-radiating than redistributing energy to the night side; (iii) the planet seems to be outside of any current classification scheme.

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA 2010-BLG-477. The measured planet-star mass ratio is q = (2.181 ± 0.004) × 10 −3 and the projected separation is s = 1.1228 ± 0.0006 in units of the Einstein radius. The angular Einstein radius is unusually large θ E = 1.38 ± 0.11 mas. Combining this measurement with constraints on the "microlens parallax" and the lens flux, we can only limit the host mass to the range 0.13 < M/M < 1.0. In this particular case, the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses. However, we find that adding Bayesian priors from two effects (Galactic model and Keplerian orbit) each independently favors the upper end of this mass range, yielding star and planet masses of M * = 0.67 +0.33 −0.13 M and m p = 1.5 +0.8 −0.3 M JUP at a distance of D = 2.3 ± 0.6 kpc, and with a semi-major axis of a = 2 +3 −1 AU. Finally, we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects, photometric and astrometric.

We present time-series photometric observations of thirteen transits in the planetary systems WASP-24, WASP-25 and WASP-26. All three systems have orbital obliquity measurements, WASP-24 and WASP-26 have been observed with Spitzer, and WASP-25 was previously comparatively neglected. Our light curves were obtained using the telescope-defocussing method and have scatters of 0.5 to 1.2 mmag relative to their best-fitting geometric models. We used these data to measure the physical properties and orbital ephemerides of the systems to high precision, finding that our improved measurements are in good agreement with previous studies. High-resolution Lucky Imaging observations of all three targets show no evidence for faint stars close enough to contaminate our photometry. We confirm the eclipsing nature of the star closest to WASP-24 and present the detection of a detached eclipsing binary within 4.25 arcmin of WASP-26.

We present the analysis of the light curves of nine high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011. For all of the events, we measure the linear limb-darkening coefficients of the surface brightness profile of source stars by measuring the deviation of the light curves near the peak affected by the finite-source effect. For seven events, we measure the Einstein radii and the lens-source relative proper motions. Among them, five events are found to have Einstein radii of less than 0.2 mas, making the lenses very low mass star or brown dwarf candidates. For MOA-2011-BLG-274, especially, the small Einstein radius of θ E ∼ 0.08 mas combined with the short timescale of t E ∼ 2.7 days suggests the possibility that the lens is a free-floating planet. For MOA-2009-BLG-174, we measure the lens parallax and thus uniquely determine the physical parameters of the lens. We also find that the measured lens mass of ∼0.84 M is consistent with that of a star blended with the source, suggesting that the blend is likely to be the lens. Although we did not find planetary signals for any of the events, we provide exclusion diagrams showing the confidence levels excluding the existence of a planet as a function of the separation and mass ratio.