Elena Masciadri

A Search for Hot Massive Extrasolar Planets around Nearby Young Stars with the Adaptive Optics System NACO

We report on a survey devoted to the search of exoplanets around young and nearby stars carried out with NACO at the VLT. The detection limit for 28 among the best available targets versus the angular separation from the star is presented. The nondetection 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 planet-star separation. In particular, we find that in 50% of the cases, no 5MJ (or more massive) planet has been detected at projected separations larger than 14 AU, and no 10MJ (or more massive) planet has been detected at projected separations larger than 8.5 AU. In 100% of the cases, these values increase to 36 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 10MJ planet at distances larger than 15 AU. A previous study carried out with 4 m class telescopes put an upper limit for 10MJ 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 10MJ planet at a minimum projected separation from the star of 1 AU and a 5MJ planet at a minimum projected separation of 3.7 AU. Our results are discussed with respect to mechanisms explaining planet formation and migration and forthcoming observational strategies and future planet-finder observations from the ground.

An imaging survey for extrasolar planets around 45 close, young stars with the simultaneous differential imager at the very large telescope and MMT

Wepresent theresultsof asurveyof 45young(P250Myr), close(P50pc) starswiththeSimultaneous 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 ( 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.

Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations

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 MJup, is 20% or less. Also, with a distribution of planet mass of -->dN/dM M?1.16 in the range of 0.5-13 MJup, 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 ?0.61, 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 MJup) 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.

A survey for massive giant planets in debris disks with evacuated inner cavities

The commonality of collisionally replenished debris around main-sequence stars suggests that minor bodies are frequent around Sun-like stars.Whether or not debris disks in general are accompanied by planets is yet unknown, but debris disks with large inner cavities—perhaps dynamically cleared—are considered to be prime candidates for hosting large-separation massive giant planets. We present here a high-contrast VLT/NACO angular differential imaging survey for eight such cold debris disks. We investigated the presence of massive giant planets in the range of orbital radii where the inner edge of the dust debris is expected. Our observations are sensitive to planets and brown dwarfs with masses >3-7 Jupiter mass, depending on the age and distance of the target star. Our observations did not identify any planet candidates. We compare the derived planet mass upper limits to the minimum planet mass required to dynamically clear the inner disks.While we cannot exclude that single giant planets are responsible for clearing out the inner debris disks, our observations constrain the parameter space available for such planets. The nondetection of massive planets in these evacuated debris disks further reinforces the notion that the giant planet population is confined to the inner disk (<15 AU).

Generalized SCIDAR Measurements at San Pedro Martir. I. Turbulence Profile Statistics

We present the results of monitoring optical-turbulence profiles at San Pedro Martir, Mexico, during 11 nights in 1997 March and April, and 16 nights in 2000 May. The data were collected using the generalized scintillation detection and ranging (SCIDAR) technique from Nice University at the 1.5 and 2.1 m telescopes. A total of 6414 turbulence profiles were measured and statistically analyzed. The principal results are as follows: the seeing produced by the turbulence in the first 1.2 km at the 1.5 m and 2.1 m telescopes, not including turbulence inside the domes, have median values of 063 ± 001 and 044 ± 002, respectively. The dome seeing at those telescopes have median values of 064 ± 001 and 031 ± 002. The median values of the seeing produced above 1.2 km and in the whole atmosphere are 039 ± 001 and 071 ± 001. The isoplanatic angle for full-correction adaptive optics has a median value of 187 ± 004. The decorrelation time (defined as the time lag for which the temporal correlation drops to 50%) of the turbulence strength at altitudes below and above 16 km above sea level is approximately equal to 2 and 0.5 hr, respectively. The isoplanatic-angle decorrelation time is estimated to be equal to 2 hr. The turbulence above ~8 km remained notably calm during nine consecutive nights, which is encouraging for adaptive optics observations at the site. The results obtained here places San Pedro Martir among the best suited sites for installing next-generation optical telescopes.

MOSE: operational forecast of the optical turbulence and atmospheric parameters at European Southern Observatory ground-based sites – I. Overview and vertical stratification of atmospheric parameters at 0–20 km

We present the overview of the MOSE project (MOdeling ESO Sites) aiming at proving the feasibility of the forecast of the classical atmospherical parameters (wind speed intensity and direction, temperature, relative humidity) and the optical turbulence OT (C N profiles and the most relevant integrated astro-climatic parameters derived from the C N : the seeing ε, the isoplanatic angle θ0 , the wavefront coherence time τ0 ) above the two ESO ground-based sites of Cerro Paranal and Cerro Armazones. The final outcome of the study is to investigate the opportunity to implement an automatic system for the forecast of these parameters at these sites. In this paper we present results related to the Meso-Nh model ability in reconstructing the vertical stratification of the atmospherical parameters along the 20 km above the ground. The very satisfactory performances shown by the model in reconstructing most of these parameters (and in particular the wind speed) put this tool of investigation as the most suitable to be used in astronomical observatories to support AO facilities and to calculate the temporal evolution of the wind speed and the wavefront coherence time at whatever temporal sampling. The further great advantage of this solution is that such estimates can be available in advance (order of some hours) with respect to the time of interest.

Comparison of the atmosphere above the South Pole, Dome C and Dome A: first attempt

The atmospheric properties above three sites (Dome C, Dome A and the South Pole) on the Internal Antarctic Plateau are investigated for astronomical applications using the monthly median of the analyses from ECMWF (the European Centre for Medium-Range Weather Forecasts). Radiosoundings extended on a yearly time-scale at the South Pole and Dome C are used to quantify the reliability of the ECMWF analyses in the free atmosphere as well as in the boundary and surface layers, and to characterize the median wind speed in the first 100 m above the two sites. Thermodynamic instability properties in the free atmosphere above the three sites are quantified with monthly median values of the Richardson number. We find that the probability to trigger thermodynamic instabilities above 100 m is smaller on the Internal Antarctic Plateau than on mid-latitude sites. In spite of the generally more stable atmospheric conditions of the Antarctic sites compared to mid-latitude sites, Dome C shows worse thermodynamic instability conditions than those predicted above the South Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to the strength of the wind speed in the free atmosphere (ECMWF analyses) as well as the wind shear in the surface layer (radiosoundings) is presented.

Mesoscale optical turbulence simulations at Dome C

In recent years, ground-based astronomy has been looking towards Antarctica, especially its summits and the internal continental plateau, where the optical turbulence appears to be confined in a shallow layer close to the icy surface. Preliminary measurements have so far indicated rather good values for the seeing above 30–35 m: around 0.3 arcsec at Dome C. Site-testing campaigns are however extremely expensive; instruments provide only local measurements and atmospheric modelling might represent a step ahead in the search and selection of astronomical sites, thanks to the possibility of reconstructing three-dimensional (3D) C 2 maps over a surface of several km. The Antarctic Plateau therefore represents an important benchmark test to evaluate the possibility of discriminating between sites on the same plateau. Our group has proven that the analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) global model do not describe the Antarctic boundary and surface layers in the plateau with the required accuracy. A better description could be obtained with a mesoscale meteorological model. The mesoscale model Meso-NH has proven to be reliable in reproducing 3D maps of optical turbulence above mid-latitude astronomical sites. In this paper we study the ability of the Meso-NH model to reconstruct the meteorological parameters as well as the optical turbulence above Dome C with different model configurations (monomodel and grid-nesting). We concentrate our attention on the abilities of the model in reproducing the optical turbulence surface-layer thickness (hsl) and the integral of C 2 in the free atmosphere and in the surface layer. It is worth highlighting that these are the first estimates ever made with a mesoscale model of the optical turbulence above the internal Antarctic Plateau.

Generalized SCIDAR Measurements at Mount Graham

We present the results of optical turbulence measurements conducted with a Generalized SCIDAR (scintillation detection and ranging) at Mount Graham during 16 nights in 2004 and 2005 at the Vatican Advanced Technology Telescope. The principle of the data reduction process is shown, as is the validation of the obtained results. From the measured and wind speed profiles, the astroclimatic parameters, such as seeing , isoplanatic 2 C e N 0 angle , wave-front coherence time , and isopistonic angle , are calculated, and their seasonal variation is ct c 00 P studied. With subtraction of the dome seeing, we obtained median values for (0.67), (2.7), (3.6 ms), ec t 00 0 and (3.3) that indicate that the astronomical seeing at Mount Graham is comparable to the best sites in the cP world. The seasonal variation of the vertical structure of the profiles is studied, and the contribution by the 2 CN ground-layer turbulence is analyzed. Furthermore, typical discretized profiles that are suitable for numerical 2 CN simulations are determined. Online material: color figures

Meteorological Parameter Analysis above Dome C Using Data from the European Centre for Medium‐Range Weather Forecasts

In this paper we present the characterization of all the principal meteorological parameters (wind speed and direction, pressure, absolute and potential temperature) extended up to 25 km from the ground and over two years (2003 and 2004) above the Antarctic site of Dome C. The data set is composed by ’analyses’ provided by the General Circulation Model (GCM) of the European Center for Medium Weather Forecasts (ECMWF) and they are part of the catalog MARS. A monthly and seasonal (summer and winter time) statistical analysis of the results is presented. The Richardson number is calculated for each month of the year over 25 km to study the stability/instability of the atmosphere. This permits us to trace a map indicating where and when the optical turbulence has the highest probability to be triggered on the whole troposphere, tropopause and stratosphere. We finally try to predict the best expected isoplanatic angle and wavefront coherence time (θ0,max and a τ0,max) employing the Richardson number maps, the wind speed profiles and simple analytical models of C N vertical profiles. Subject headings: atmospheric effects — turbulence — site testing