New planetary and EB candidates from Campaigns 1-6 of the K2 mission

With only two functional reaction wheels, Kepler cannot maintain stable pointing at its original target field and entered a new mode of observation called K2. Our method is based on many years of experience in planet hunting for the CoRoT mission. Due to the unstable pointing, K2 light curves present systematics that are correlated with the target position in the CCD. Therefore, our pipeline also includes a decorrelation of this systematic noise. Our pipeline is optimised for bright stars for which spectroscopic follow-up is possible. We achieve a maximum precision on 6 hours of 6 ppm. The decorrelated light curves are searched for transits with an adapted version of the CoRoT alarm pipeline. We present 172 planetary candidates and 327 eclipsing binary candidates from campaigns 1, 2, 3, 4, 5 and 6 of K2. Both the planetary candidates and eclipsing binary candidates lists are made public to promote follow-up studies. The light curves will also be available to the community.Comment: 22 pages. 5 figures, 4 tables, Accepted for publication in A&

Detecting transit signatures of exoplanetary rings using SOAP3.0

CONTEXT. It is theoretically possible for rings to have formed around extrasolar planets in a similar way to that in which they formed around the giant planets in our solar system. However, no such rings have been detected to date. AIMS: We aim to test the possibility of detecting rings around exoplanets by investigating the photometric and spectroscopic ring signatures in high-precision transit signals. METHODS: The photometric and spectroscopic transit signals of a ringed planet is expected to show deviations from that of a spherical planet. We used these deviations to quantify the detectability of rings. We present SOAP3.0 which is a numerical tool to simulate ringed planet transits and measure ring detectability based on amplitudes of the residuals between the ringed planet signal and best fit ringless model. RESULTS: We find that it is possible to detect the photometric and spectroscopic signature of near edge-on rings especially around planets with high impact parameter. Time resolution $\leq$ 7 mins is required for the photometric detection, while 15 mins is sufficient for the spectroscopic detection. We also show that future instruments like CHEOPS and ESPRESSO, with precisions that allow ring signatures to be well above their noise-level, present good prospects for detecting rings.Comment: 13 pages, 16 figures, 2 tables , accepted for publication in A&

Light clusters and the pasta phase

The effects of including light clusters in nuclear matter at low densities are investigated within four different parametrizations of relativistic models at finite temperature. Both homogeneous and inhomogeneous matter (pasta phase) are described for neutral nuclear matter with fixed proton fractions. We discuss the effect of the density dependence of the symmetry energy, the temperature and the proton fraction on the non-homogeneous matter forming the inner crust of proto-neutron stars. It is shown that the number of nucleons in the clusters, the cluster proton fraction and the sizes of the Wigner Seitz cell and of the cluster are very sensitive to the density dependence of the symmetry energy.Comment: 14 pages, 14 figures; Accepted for publication in Phys. Rev.

Precise masses for the transiting planetary system HD 106315 with HARPS

Context. The multi-planetary system HD 106315 was recently found in K2 data. The planets have periods of P_b ~ 9.55 and P_c ~ 21.06 days, and radii of r_b = 2.44 ± 0.17 R⊕ and r_c = 4.35 ± 0.23 R⊕. The brightness of the host star (V = 9.0 mag) makes it an excellent target for transmission spectroscopy. However, to interpret transmission spectra it is crucial to measure the planetary masses. Aims. We obtained high precision radial velocities for HD 106315 to determine the mass of the two transiting planets discovered with Kepler K2. Our successful observation strategy was carefully tailored to mitigate the effect of stellar variability. Methods. We modelled the new radial velocity data together with the K2 transit photometry and a new ground-based partial transit of HD 106315c to derive system parameters. Results. We estimate the mass of HD 106315b to be 12.6 ± 3.2 M⊕ and the density to be 4.7 ± 1.7 g cm^(-3), while for HD 106315c we estimate a mass of 15.2 ± 3.7 M⊕ and a density of 1.01 ± 0.29 g cm^(-3). Hence, despite planet c having a radius almost twice as large as planet b, their masses are consistent with one another. Conclusions. We conclude that HD 106315c has a thick hydrogen-helium gaseous envelope. A detailed investigation of HD 106315b using a planetary interior model constrains the core mass fraction to be 5–29%, and the water mass fraction to be 10–50%. An alternative, not considered by our model, is that HD 106315b is composed of a large rocky core with a thick H–He envelope. Transmission spectroscopy of these planets will give insight into their atmospheric compositions and also help constrain their core compositions

A new model for gravitational potential perturbations in disks of spiral galaxies. An application to our Galaxy

We propose a new, more realistic, description of the perturbed gravitational potential of spiral galaxies, with spiral arms having Gaussian-shaped groove profiles. We investigate the stable stellar orbits in galactic disks, using the new perturbed potential. The influence of the bulge mass on the stellar orbits in the inner regions of a disk is also investigated. The new description offers the advantage of easy control of the parameters of the Gaussian profile of its potential. We find a range of values for the perturbation amplitude from 400 to 800 km^2 s^{-2} kpc^{-1} which implies a maximum ratio of the tangential force to the axisymmetric force between 3% and 6%, approximately. Good self-consistency of arm shapes is obtained between the Inner Lindblad resonance (ILR) and the 4:1 resonance. Near the 4:1 resonance the response density starts to deviate from the imposed logarithmic spiral form. This creates bifurcations that appear as short arms. Therefore the deviation from a perfect logarithmic spiral in galaxies can be understood as a natural effect of the 4:1 resonance. Beyond the 4:1 resonance we find closed orbits which have similarities with the arms observed in our Galaxy. In regions near the center, in the presence of a massive bulge, elongated stellar orbits appear naturally, without imposing any bar-shaped potential, but only extending the spiral perturbation a little inward of the ILR. This suggests that a bar is formed with a half-size around 3 kpc by a mechanism similar to that of the spiral arms. The potential energy perturbation that we adopted represents an important step in the direction of self-consistency, compared to previous sine function descriptions of the potential. Our model produces a realistic description of the spiral structure, able to explain several details that were not yet understood.Comment: 12 pag., 11 fig. Accepted for publication in A&A, 2012 December 1

Constraining planet structure and composition from stellar chemistry: trends in different stellar populations

The chemical composition of stars that have orbiting planets provides important clues about the frequency, architecture, and composition of exoplanet systems. We explore the possibility that stars from different galactic populations that have different intrinsic abundance ratios may produce planets with a different overall composition. We compiled abundances for Fe, O, C, Mg, and Si in a large sample of solar neighbourhood stars that belong to different galactic populations. We then used a simple stoichiometric model to predict the expected iron-to-silicate mass fraction and water mass fraction of the planet building blocks, as well as the summed mass percentage of all heavy elements in the disc. Assuming that overall the chemical composition of the planet building blocks will be reflected in the composition of the formed planets, we show that according to our model, discs around stars from different galactic populations, as well as around stars from different regions in the Galaxy, are expected to form rocky planets with significantly different iron-to-silicate mass fractions. The available water mass fraction also changes significantly from one galactic population to another. The results may be used to set constraints for models of planet formation and chemical composition. Furthermore, the results may have impact on our understanding of the frequency of planets in the Galaxy, as well as on the existence of conditions for habitability.Comment: Accepted for publication in Astronomy & Astrophysic

SOPHIE velocimetry of Kepler transit candidates VI. An additional companion in the KOI-13 system

We report the discovery of a new stellar companion in the KOI-13 system. KOI-13 is composed by two fast-rotating A-type stars of similar magnitude. One of these two stars hosts a transiting planet discovered by Kepler. We obtained new radial velocity measurements using the SOPHIE spectrograph at the Observatoire de Haute-Provence that revealed an additional companion in this system. This companion has a mass between 0.4 and 1 Msun and orbits one of the two main stars with a period of 65.831 \pm 0.029 days and an eccentricity of 0.52 \pm 0.02. The radial velocities of the two stars were derived using a model of two fast-rotating line profiles. From the residuals, we found a hint of the stellar variations seen in the Kepler light curve with an amplitude of about 1.41 km/s and a period close to the rotational period. This signal appears to be about three order of magnitude larger than expected for stellar activity. From the analysis of the residuals, we also put a 3-sigma upper-limit on the mass of the transiting planet KOI-13.01 of 14.8 Mjup and 9.4 Mjup, depending on which star hosts the transit. We found that this new companion has no significant impact on the photometric determination of the mass of KOI-13.01 but is expected to affect precise infrared photometry. Finally, using dynamical simulations, we infer that the new companion is orbiting around KOI-13B while the transiting planet candidate is expected to orbit KOI-13A. Thus, the transiting planet candidate KOI-13.01 is orbiting the main component of a hierarchical triple system.Comment: Accepted in A&A Letters. 4 pages including 4 figures and the RV tabl

Distinguishing the albedo of exoplanets from stellar activity

Light curves show the flux variation from the target star and its orbiting planets as a function of time. In addition to the transit features created by the planets, the flux also includes the reflected light component of each planet, which depends on the planetary albedo. This signal is typically referred to as phase curve and could be easily identified if there were no additional noise. As well as instrumental noise, stellar activity, such as spots, can create a modulation in the data, which may be very difficult to distinguish from the planetary signal. We analyze the limitations imposed by the stellar activity on the detection of the planetary albedo, considering the limitations imposed by the predicted level of instrumental noise and the short duration of the observations planned in the context of the CHEOPS mission. As initial condition, we have assumed that each star is characterized by just one orbiting planet. We built mock light curves that included a realistic stellar activity pattern, the reflected light component of the planet and an instrumental noise level, which we have chosen to be at the same level as predicted for CHEOPS. We then fit these light curves to try to recover the reflected light component, assuming the activity patterns can be modeled with a Gaussian process.We estimate that at least one full stellar rotation is necessary to obtain a reliable detection of the planetary albedo. This result is independent of the level of noise, but it depends on the limitation of the Gaussian process to describe the stellar activity when the light curve time-span is shorter than the stellar rotation. Finally, in presence of typical CHEOPS gaps in the simulations, we confirm that it is still possible to obtain a reliable albedo.Comment: Accepted for publication in A&A, 14 pages, 12 figure

Serological evidence of West Nile virus circulation in Portugal

The circulation of West Nile virus in Portugal was assessed by serological surveys conducted during 2004–2010 in horses and birds. The detection of WNV antibodies in both species in all the years covered by the study as well as the presence of anti-WNV IgM in symptomatic horses that had not traveled outside the country, support the notion that WNV circulates in Portugal

III.2 Activity modelling and impact on planet’s parameters

This book is dedicated to all the people interested in the CoRoT mission and the beautiful data that were delivered during its six year duration. Either amateurs, professional, young or senior researchers, they will find treasures not only at the time of this publication but also in the future twenty or thirty years. It presents the data in their final version, explains how they have been obtained, how to handle them, describes the tools necessary to understand them, and where to find them. It also highlights the most striking first results obtained up to now. CoRoT has opened several unexpected directions of research and certainly new ones still to be discovered