D. Queloz

An Earth-sized planet with an Earth-like density

Recent analyses of data from the NASA Kepler spacecraft have established that planets with radii within 25 per cent of the Earth’s () are commonplace throughout the Galaxy, orbiting at least 16.5 per cent of Sun-like stars. Because these studies were sensitive to the sizes of the planets but not their masses, the question remains whether these Earth-sized planets are indeed similar to the Earth in bulk composition. The smallest planets for which masses have been accurately determined are Kepler-10b (1.42) and Kepler-36b (1.49), which are both significantly larger than the Earth. Recently, the planet Kepler-78b was discovered and found to have a radius of only 1.16. Here we report that the mass of this planet is 1.86 Earth masses. The resulting mean density of the planet is 5.57u2009gu2009cm−3, which is similar to that of the Earth and implies a composition of iron and rock.

Doppler follow-up of OGLE transiting companions in the Galactic bulge

Two years ago, the OGLE-III survey (Optical Gravitational Lensing Experiment) announced the detection of 54 short period multi-transiting objects in the Galactic bulge (Udalski et al. 2002a,b). Some of these objects were considered to be po- tential hot Jupiters. In order to determine the true nature of these objects and to characterize their actual mass, we conducted a radial velocity follow-up of 18 of the smallest transiting candidates. We describe here our procedure and report the char- acterization of 8 low-mass star-transiting companions, 2 grazing eclipsing binaries, 2 triple systems, 1 confirmed exoplanet (OGLE-TR-56b), 1 possible exoplanet (OGLE-TR-10b), 1 clear false positive and 3 unsolved cases. The variety of cases en- countered in our follow-up covers a large part of the possible scenarios occurring in the search for planetary transits. As a by-product our program yields precise masses and radii of low mass stars.

Characterizing K2 Planet Discoveries: A Super-Earth Transiting the Bright K Dwarf HIP 116454

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 ± 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with (Fe/H) =− 0.16 ± 0.08 and has a radius R� = 0.716 ± 0.024 Rand mass M� = 0.775 ± 0.027 M� . The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of Rp = 2.53 ± 0.18 R⊕. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 ± 1.33 M⊕ planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.

The HARPS search for southern extra-solar planets XXXV. The interesting case of HD 41248: stellar activity, no planets?

Context. The search for planets orbiting metal-poor stars is of utmost importance for our understanding of planet formation models. However, no dedicated searches have been conducted so far for very low mass planets orbiting such objects. Only a few cases of low-mass planets orbiting metal-poor stars are thus known. Amongst these, HD 41248 is a metal-poor, solar-type star on the orbit of which a resonant pair of super-Earth-like planets has been announced. This detection was based on 62 radial velocity measurements obtained with the HARPS spectrograph (public data). Aims. We present a new planet search program that is using the HARPS spectrograph to search for Neptunes and super-Earths that orbit a sample of metal-poor FGK dwarfs. We then present a detailed analysis of 162 additional radial velocity measurements of HD 41248, obtained within this program, with the goal of confirming the existence of the proposed planetary system. Methods. We analysed the precise radial velocities, obtained with the HARPS spectrograph, together with several stellar activity diagnostics and line profile indicators. Results. A careful analysis shows no evidence for the planetary system. One of the signals, with a period of similar to 25 days, is shown to be related to the rotational period of the star, and is clearly seen in some of the activity proxies. We were unable to convincingly retrieve the remaining signal (P similar to 18 days) in the new dataset. Conclusions. We discuss possible causes for the complex (evolving) signals observed in the data of HD 41248, proposing that they might be explained by the appearance and disappearance of active regions on the surface of a star with strong differential rotation, or by a combination of the sparse data sampling and active region evolution.

On the Age of Stars Harboring Transiting Planets

Results of photometric surveys have brought to light the existence of a population of giant planets orbiting their host stars even closer than the hot Jupiters (HJ), with orbital periods below 3 days. The reason why radial velocity surveys were not able to detect these very-hot Jupiters (VHJ) is under discussion. A possible explanation is that these close-in planets are short-lived, being evaporated on short time-scales due to UV flux of their host stars. In this case, stars hosting transiting VHJ planets would be systematically younger than those in the radial velocity sample.u2029We have used the UVES spectrograph (VLT-UT2 telescope) to obtain high resolution spectra of 5 faint stars hosting transiting planets, namely, OGLE-TR-10, 56, 111, 113 and TrES-1. Previously obtained CORALIE spectra of HD189733, and published data on the other transiting planet-hosts were also used. The immediate objective is to estimate ages via Li abundances, using the Caxa0II activity-age relation, and from the analysis of the stellar rotational velocity.u2029For the stars for which we have spectra, Li abundances were computed as in Israelian et al. (2004, A&A, 414, 601) using the stellar parameters derived in Santos et al. (2006, A&A, 450, 825). The chromospheric activity index S US was built as the ratio of the flux within the core of the Ca II H & K lines and the flux in two nearby continuum regions. The index S US was calibrated to Mount Wilson index S MW allowing the computation of the Ca II H & K corrected for the photospheric contribution. These values were then used to derive the ages by means of the Henry et al. (1996) activity-age relation.u2029Bearing in mind the limitations of the ages derived by Li abundances, chromospheric activity, and stellar rotational velocities, none of the stars studied in this paper seem to be younger than 0.5 Gyr.

High resolution spectroscopy of stars with transiting planets ⋆ The cases of OGLE-TR-10, 56, 111, 113, and TrES-1

Context: During the past years photometric surveys, later complemented by follow-up radial-velocity measurements, have revealed the presence of several new extra-solar transiting planets, in very short period orbits. Many of the host stars are extremely faint (V

WASP-103 b: a new planet at the edge of tidal disruption

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Astrometric planet search around southern ultracool dwarfs - I. First results, including parallaxes of 20 M8–L2 dwarfs

16), making high-precision spectroscopic measurements challenging. Aims: We have used the UVES spectrograph (VLT-UT2 telescope) to obtain high resolution spectra of 5 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111, 113 and TrES-1. The immediate objective is to derive accurate stellar parameters and chemical abundances. Methods: The stellar parameters were derived from an LTE analysis of a set of FeI and FeII lines. Results: Complementing the spectroscopic information with photometric transit curves and radial-velocity data from the literature, we have then refined the stellar and planetary radii and masses. The obtained data were also used to study and discuss the relation between the stellar metallicity and orbital period of the planets.

Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star

We report the discovery of WASP-103 b, a new ultra-short-period planet (P = 22:2 hr) transiting a 12.1 V-magnitude F8-type mainsequence star (1:22 0:04 M , 1:44 +0:05

Transiting planets from WASP-South, Euler, and TRAPPIST - WASP-68 b, WASP-73 b, and WASP-88 b, three hot Jupiters transiting evolved solar-type stars

Context. Extrasolar-planet searches that target very low-mass stars and brown dwarfs are hampered by intrinsic or instrumental limitations. Time series of astrometric measurements with precisions better than one milli-arcsecond can yield new evidence on the planet occurrence around these objects. Aims. We present first results of an astrometric search for planets around 20 nearby dwarf stars with spectral types M8‐L2. Methods. Over a time-span of two years, we obtained I-band images of the target fields with the FORS2 camera at the Very Large Telescope. Using background stars as references, we monitored the targets’ astrometric trajectories, which allowed us to measure parallax and proper motions, set limits on the presence of planets, and to discover the orbital motions of two binary systems. Results. We determined trigonometric parallaxes with an average accuracy of 0.09 mas (’ 0.2 %), which resulted in a reference sample for the study of ultracool dwarfs at the M/L transition, whose members are located at distances of 9.5‐40 pc. This sample contains two newly discovered tight binaries (DE0630 18 and DE0823 49) and one previously known wide binary (DE1520 44). Only one target shows I-band variability >5 mmag r.m.s. We derived planet exclusion limits that set an upper limit of 9 % on the occurrence of giant planets with masses & 5 MJ in intermediate-separation (0.01‐0.8 AU) orbits around M8‐L2 dwarfs. Conclusions. We demonstrate that astrometric observations with an accuracy of 120 as over two years are feasible from the ground and can be used for a planet-search survey. The detection of two tight very low-mass binaries shows that our search strategy is e cient and may lead to the detection of planetary-mass companions through follow-up observations.