D. Juncher

Three regimes of extrasolar planet radius inferred from host star metallicities

Approximately half of the extrasolar planets (exoplanets) with radii less than four Earth radii are in orbits with short periods. Despite their sheer abundance, the compositions of such planets are largely unknown. The available evidence suggests that they range in composition from small, high-density rocky planets to low-density planets consisting of rocky cores surrounded by thick hydrogen and helium gas envelopes. Here we report the metallicities (that is, the abundances of elements heavier than hydrogen and helium) of more than 400 stars hosting 600 exoplanet candidates, and find that the exoplanets can be categorized into three populations defined by statistically distinct (∼4.5σ) metallicity regions. We interpret these regions as reflecting the formation regimes of terrestrial-like planets (radii less than 1.7 Earth radii), gas dwarf planets with rocky cores and hydrogen–helium envelopes (radii between 1.7 and 3.9 Earth radii) and ice or gas giant planets (radii greater than 3.9 Earth radii). These transitions correspond well with those inferred from dynamical mass estimates, implying that host star metallicity, which is a proxy for the initial solids inventory of the protoplanetary disk, is a key ingredient regulating the structure of planetary systems.

High-precision photometry by telescope defocussing - VI. WASP-24, WASP-25 and WASP-26

We present time series photometric observations of 13 transits in the planetary systems WASP-24, WASP-25 and WASP-26. All three systems have orbital obliquity measurements, WASP-24 andWASP-26 have been observed with Spitzer, andWASP-25 was previously comparatively neglected. Our light curves were obtained using the telescope-defocussing method and have scatters of 0.5-1.2 mmag relative to their best-fitting geometric models. We use 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.

Modelling the local and global cloud formation on HD 189733b

G.L. and Ch.H. highlight the financial support of the European community under the FP7 ERC starting grant 257431.

High-precision photometry by telescope defocusing - VII. The ultrashort period planet WASP-103

We present 17 transit light curves of the ultrashort period planetary system WASP-103, a strong candidate for the detection of tidally-induced orbital decay. We use these to establish a high-precision reference epoch for transit timing studies. The time of the reference transit mid-point is now measured to an accuracy of 4.8 s, versus 67.4 s in the discovery paper, aiding future searches for orbital decay. With the help of published spectroscopic measurements and theoretical stellar models, we determine the physical properties of the system to high precision and present a detailed error budget for these calculations. The planet has a Roche lobe filling factor of 0.58, leading to a significant asphericity; we correct its measured mass and mean density for this phenomenon. A high-resolutionLucky Imaging observation shows no evidence for faint stars close enough to contaminate the point spread function of WASP-103. Our data were obtained in the Bessell RI and the SDSS griz passbands and yield a larger planet radius at bluer optical wavelengths, to a confidence level of 7.3σ. Interpreting this as an effect of Rayleigh scattering in the planetary atmosphere leads to a measurement of the planetary mass which is too small by a factor of 5, implying that Rayleigh scattering is not the main cause of the variation of radius with wavelength.

EMCCD photometry reveals two new variable stars in the crowded central region of the globular cluster NGC 6981

Two previously unknown variable stars in the crowded central region of the globular cluster NGC 6981 are presented. The observations were made using the Electron Multiplying CCD (EMCCD) cameraat the Danish 1.54m Telescope at La Silla, Chile. The two variables were not previously detected by conventional CCD imaging because of their proximity to a bright star. This discovery demonstrates that EMCCDs are a powerful tool for performing high-precision time-series photometry in crowded fields and near bright s tars, especially when combined with difference image analysis (DIA).

An Attractor for Dark Matter Structures

Cosmological simulations of dark matter (DM) structures have identified a set of universal profiles, and similar characteristics have been seen in non-cosmological simulations. There has therefore been speculation as to whether these profiles of collisionless systems relate to accretion and merger history, or if there is an attractor for the DM systems. Here, we identify such a one-dimensional attractor in the three-dimensional space spanned by the two radial slopes of the density and velocity dispersion, and the velocity anisotropy. This attractor effectively removes 1 degree of freedom from the Jeans equation. It also allows us to speculate on a new fluid interpretation for the Jeans equation, with an effective polytropic index for the DM particles between 1/2 and 3/4. If this attractor solution holds for other collisionless structures, then it may hold the key to breaking the mass-anisotropy degeneracy, which presently prevents us from uniquely measuring the mass profiles in dwarf galaxies.

Absolute dimensions of eclipsing binaries - XXVIII. BK Pegasi and other F-type binaries: Prospects for calibration of convective core overshoot

We present a detailed study of the F-type detached eclipsing binary BK Peg, based on new photometric and spectroscopic observations. The two components, which have evolved to the upper half of the main-sequence band, are quite different with masses and radii of (1.414 +/- 0.007 Msun, 1.988 +/- 0.008 Rsun) and (1.257 +/- 0.005 Msun, 1.474 +/- 0.017 Rsun), respectively. The 5.49 day period orbit of BK Peg is slightly eccentric (e = 0.053). The measured rotational velocities are 16.6 +/- 0.2 (primary) and 13.4 +/- 0.2 (secondary) km/s. For the secondary component this corresponds to (pseudo)synchronous rotation, whereas the primary component seems to rotate at a slightly lower rate. We derive an iron abundance of [Fe/H] =-0.12 +/- 0.07 and similar abundances for Si, Ca, Sc, Ti, Cr and Ni. Yonsei-Yale and Victoria-Regina evolutionary models for the observed metal abundance reproduce BK Peg at ages of 2.75 and 2.50 Gyr, respectively, but tend to predict a lower age for the more massive primary component than for the secondary. We find the same age trend for three other upper main-sequence systems in a sample of well studied eclipsing binaries with components in the 1.15-1.70 Msun range, where convective core overshoot is gradually ramped up in the models. We also find that the Yonsei-Yale models systematically predict higher ages than the Victoria-Regina models. The sample includes BW Aqr, and as a supplement we have determined a [Fe/H] abundance of -0.07 +/- 0.11 for this late F-type binary. We propose to use BK Peg, BW Aqr, and other well-studied 1.15-1.70 Msun eclipsing binaries to fine-tune convective core overshoot, diffusion, and possibly other ingredients of modern theoretical evolutionary models.

Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry

Aims. We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the clusters parameters. Methods. We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible. We also derive an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). Results. Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H](ZW) = -2.01 +/- 0.04, or [Fe/H](UVES) = -2.11 +/- 0.06, and a distance of 8.32 +/- 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 +/- 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 +/- 1.0 Gyr for M 30.

A detailed census of variable stars in the globular cluster NGC 6333 (M9) from CCD differential photometry

We report CCD V and I time series photometry of the globular cluster NGC 6333 (M9). The technique of difference image analysis has been used, which enables photometric precision better than 0.05 mag for stars brighter than V ∼ 19.0 mag, even in the crowded central regions of the cluster. The high photometric precision has resulted in the discovery of two new RRc stars, three eclipsing binaries, seven long-term variables and one field RRab star behind the cluster. A detailed identification chart and equatorial coordinates are given for all the variable stars in the field of our images of the cluster. Our data together with the literature V-data obtained in 1994 and 1995 allowed us to refine considerably the periods for all RR Lyrae stars. The nature of the new variables is discussed. We argue that variable V12 is a cluster member and an Anomalous Cepheid. Secular period variations, double-mode pulsations and/or the Blazhko-like modulations in some RRc variables are addressed. Through the light-curve Fourier decomposition of 12 RR Lyrae stars we have calculated a mean metallicity of [Fe/H]ZW = −1.70 ± 0.01(statistical) ± 0.14(systematic) or [Fe/H]UVES = -1.67 ± 0.01(statistical) ± 0.19(systematic). Absolute magnitudes, radii and masses are also estimated for the RR Lyrae stars. A detailed search for SX Phe stars in the Blue Straggler region was conducted but none were discovered. If SX Phe exist in the cluster then their amplitudes must be smaller than the detection limit of our photometry. The colour–magnitude diagram has been corrected for heavy differential reddening using the detailed extinction map of the cluster of Alonso-Garcia et al. This has allowed us to set the mean cluster distance from two independent estimates; from the RRab and RRc absolute magnitudes, we find 8.04 ± 0.19 and 7.88 ± 0.30 kpc, respectively.

High-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP): I. Lucky imaging observations of 101 systems in the southern hemisphere

(abridged) Context. Wide binaries are a potential pathway for the formation of hot Jupiters. The binary fraction among host stars is an important discriminator between competing formation theories, but has not been well characterised. Additionally, contaminating light from unresolved stars can significantly affect the accuracy of photometric and spectroscopic measurements in studies of transiting exoplanets. Aims. We observed 101 transiting exoplanet host systems in the Southern hemisphere in order to create a homogeneous catalogue of both bound companion stars and contaminating background stars. We investigate the binary fraction among the host stars in order to test theories for the formation of hot Jupiters, in an area of the sky where transiting exoplanetary systems have not been systematically searched for stellar companions. Methods. Lucky imaging observations from the Two Colour Instrument on the Danish 1.54m telescope at La Silla were used to search for previously unresolved stars at small angular separations. The separations and relative magnitudes of all detected stars were measured. For 12 candidate companions to 10 host stars, previous astrometric measurements were used to evaluate how likely the companions are to be physically associated. Results. We provide measurements of 499 candidate companions within 20 arcseconds of our sample of 101 planet host stars. 51 candidates are located within 5 arcseconds of a host star, and we provide the first published measurements for 27 of these. Calibrations for the plate scale and colour performance of the Two Colour Instrument are presented. Conclusions. We find that the overall multiplicity rate of the host stars is 38 +17 -13%, consistent with the rate among solar-type stars in our sensitivity range, suggesting that planet formation does not preferentially occur in long period binaries compared to a random sample of field stars.