We report on a survey devoted for the search of exo-planets around young and nearby stars carried out with NACO at the VLT. The detection limit for 28 among the best available targets vs. the angular separation from the star is presented. The non-detection of any planetary mass companion in our survey is used to derive, for the first time, the frequency of the upper limit of the projected separation planet-stars. In particular, we find that in 50% of cases, no 5M J planet (or more massive) has been detected at projected separations larger than 14 AU and no 10M J planet (or more massive) has been detected at projected separations larger than 8.5 AU. In 100% of cases, these values increase to 36 AU and 65 AU respectively. The excellent sensitivity reached by our study leads to a much lower upper limit of the projected planet-star separation compared with previous studies. For example, for the β Pictoris group, (∼12 Myr), we did not detect any 10M J planet at distances larger than 15 AU. A previous study carried out with 4 m class telescopes put an upper limit for 10M J planets at ∼60 AU. For our closest target (V2306 Oph -d = 4.3 pc) it is shown that it would be possible to detect a 10M J planet at a minimum projected separation from the star of 1 AU and a 5M J planet at a minimum projected separation of 3.7 AU. Our results are discussed with respect to mechanisms explaining planet formation and migration and to forthcoming observational strategies and future planet finder observations from the ground.

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We present the results of a survey of 45 young (P250 Myr), close (P50 pc) stars with the Simultaneous Differential Imager (SDI) implemented at the VLT and the MMT for the direct detection of extrasolar planets. As part of the survey, we observed 54 objects, consisting of 45 close, young stars; two more distant (<150 pc), extremely young (10 Myr) stars; three stars with known radial velocity planets; and four older, very nearby (20 pc) solar analogs. Our SDI devices use a double Wollaston prism and a quad filter to take images simultaneously at three wavelengths surrounding the 1.62 m methane absorption bandhead found in the spectrum of cool brown dwarfs and gas giant planets. By differencing adaptive opticsYcorrected images in these filters, speckle noise from the primary star is significantly attenuated, resulting in photon (and flat-field)YnoiseYlimited data. In our VLT data, we achieved H-band contrasts k10 mag (5) at a separation of 0.5 00 from the primary star on 45% of our targets and H-band contrasts k 9 mag at a separation of 0.5 00 on 80% of our targets. With these contrasts, we can image (5 detection) a 7 M J planet 15 AU from a 70 Myr K1 star at 15 pc or a 7.8 M J planet at 2 AU from a 12 Myr M star at 10 pc. We detected no candidates with S/N > 2 which behaved consistently like a real object. From our survey null result, we can rule out (with 93% confidence) a model planet population where N (a) / constant out to a distance of 45 AU.

Statistical analysis of stellar scintillation on the pupil of a telescope, known as the scidar (scintillation, detection, and ranging) technique, is sensitive only to atmospheric turbulence at altitudes higher than a few kilometers. With the generalized scidar technique, recently proposed and tested under laboratory conditions, one can overcome this limitation by analyzing the scintillation on a plane away from the pupil. We report the first experimental implementation of this technique, to our knowledge, under real atmospheric conditions as a vertical profiler of the refractive-index structure constant C (N)(2) (h). The instrument was adapted to the Nordic Optical Telescope and the William Hershel Telescope at La Palma, Canary Islands. We measure the spatial autocorrelation function of double-star scintillation for different positions of the analysis plane, finding good agreement with theoretical expectations.

We examine the implications for the distribution of extrasolar planets based on the null results from two of the largest direct imaging surveys published to date. Combining the measured contrast curves from 22 of the stars observed with the VLT NACO adaptive optics system by Masciadri and coworkers and 48 of the stars observed with the VLT NACO SDI and MMT SDI devices by Biller and coworkers (for a total of 60 unique stars), we consider what distributions of planet masses and semimajor axes can be ruled out by these data, based on Monte Carlo simulations of planet populations. We can set the following upper limit with 95% confidence: the fraction of stars with planets with semimajor axis between 20 and 100 AU, and mass above 4 M Jup , is 20% or less. Also, with a distribution of planet mass of dN /dM / M À1:16 in the range of 0.5-13 M Jup , we can rule out a power-law distribution for semimajor axis (dN /da / a ) with index 0 and upper cutoff of 18 AU, and index -0.5 with an upper cutoff of 48 AU. For the distribution suggested by Cumming et al., a power-law of index À0.61, we can place an upper limit of 75 AU on the semimajor axis distribution. In general, we find that even null results from direct imaging surveys are very powerful in constraining the distributions of giant planets (0.5-13 M Jup ) at large separations, but more work needs to be done to close the gap between planets that can be detected by direct imaging, and those to which the radial velocity method is sensitive. Subject headingg s: planetary systems

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Abstract. These last years have seen the development of many devices to measure and monitor some atmospheric parameters characterizing the image degradation at the telescope focus. Many uncertainties about the possibility to forecast such parameters are real although this skill is fundamental for site testing, flexible scheduling and optimization of the performance of both interferometry and adaptive optics. We present our atmospheric numerical model, conceived to provide 3D maps of the classic meteorological parameters P , T and V , and also 3D maps of the C 2 N optical turbulent profiles. Knowing the wind V and the C 2 N profiles, the following integrated parameters are coded: seeing ε, coherence wavefront time τ AO , isoplanatic angle θ AO , scintillation rate σ 2 I and spatial coherence outer scale L 0 .The ability of the model to produce a 3D map of optical turbulence in the vicinity of a telescope and the effects of horizontal grid size are discussed. We demonstrate, for the same night, the global coherence of the different simulation outputs. Here we consider the use that this model could have in ground-based astronomy and we describe how it could be used to give a real forecast of the optical turbulence.

We have performed H and K S band observations of the planetary system around HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES Camera. The excellent instrument performance (Strehl ratios up to 80% in H band) enabled the detection of the innermost planet, HR 8799e, at H band for the first time. The H and K S magnitudes of HR 8799e are similar to those of planets c and d, with planet e being slightly brighter. Therefore, HR 8799e is likely slightly more massive than c and d. We also explored possible orbital configurations and their orbital stability. We confirm that the orbits of planets b, c and e are consistent with being circular and coplanar; planet d should have either an orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c. Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion resonances with c and d, while coplanar and circular orbits are allowed for a 5:2 resonance. The analysis of dynamical stability shows that the system is highly unstable or chaotic when planetary masses of about 5 M J for b and 7 M J for the other planets are adopted. Significant regions of dynamical stability for timescales of tens of Myr are found when adopting planetary masses of about 3.5, 5, 5, and 5 M J for HR 8799b, c, d, and e respectively. These masses are below the current estimates based on the stellar age (30 Myr) and theoretical models of substellar objects.