The Gaia astrometric mission holds the promise for crucial contributions to almost every subject of astrophysics and astronomy, including planetary systems astrophysics. We focus on the potential of the Gaia mission as perfect tool for a complete screening of nearby stars in search for exoplanets. We build our dissertation on the most recent results of the satellites astrometric payload performances and data reduction capabilities. We put the identified capabilities in context by illustrating the outstanding contribution to planetary sciences, in combination with nowadays and next decade exoplanets search programs, as a complement to other indirect and direct methods for the detection and characterization of planetary systems. We conclude by highlighting the crucial improvements in the optimization of the target lists of future dedicated observatory projects.

Spurred by the recent large number of radial velocity detections and the discovery of several transiting system and among those two planets, that are consistent with rocky composition, the study of planets orbiting nearby stars has now entered an era of characterizing massive terrestrial planets (aka super-Earths). One prominent question is, if such planets could be habitats. Here we focuss on one particular planet Gl581d. For Earth-like assumptions, we investigate the minimal atmospheric conditions for Gl581d to be potentially habitable at its current position, and if habitability could be remotely detected in its spectra. The model we present here only represents one possible nature an Earth-like composition - of a planet like Gl581d in a wide parameter space. Future observations of atmospheric features of such super-Earths can be used to examine if our concept of habitability and its dependence on the carbonate-silicate cycle is correct, and also assess whether Gl581d is indeed the first detected habitable super-Earth. We will need spectroscopic measurements to probe the atmosphere of such planets to break the degeneracy of mass and radius measurements and characterize a planetary environment.

Recently we were able to retrieve the Earth's transmission spectrum through lunar eclipse observations. This spectrum showed that the depth of most molecular species was stronger than models had anticipated. The presence of other atmospheric signatures, such as atmospheric dimers, were also present in the spectrum. We have been developing a radiative transfer code able to reproduce the Earth's transmission spectra at different depths into the penumbra and umbra, and taking into account transmission, refraction, and multiple scattering. Here we discuss the results to date and the work ahead.

The effects of turbulence on the dynamics of dust grains in protoplanetary discs is of relevant importance in the study of pre-planetesimal formation. The complex interplay between gas and dust and the modelling of turbulence require numerical simulations.

A statistical study of the noise in SPH simulations of gas-only protoplanetary accretion discs is performed in order to determine if it could mimic turbulence and to what extent.

The outcome of collisions between pre-planetesimals is important in the theory of planetesimal formation by collisional growth and strongly depends on their internal structure. Since pre-planetesimals are highly porous, reaching 90% porosity, they could show the so called anomalous behaviour (decrease of density during shock compression, e.g. Bolkhovitinov & Khvostov 1978). Due to involved sizes (>dm), laboratory experiments are unfeasible therefore numerical simulations equipped with adequate porosity models are necessary.

Here we focus on the P-α model and its variations. We found that they are suitable for applications in the high porosity range only after a modification of the basic equations, that avoids an inconsistency and takes into account the effect of dissipated energy, is performed.

A close stellar companion influences the formation of planets in the system. The occurrence of stellar companions and characteristics of the stars and planets in the system provide constraints on the formation processes. We present results from our high-resolution Lucky Imaging survey for binary exoplanet host stars, including the discovery of stellar companion candidates to the transiting planet hosts WASP-12 and HAT-P-8.

High-precision radial-velocimetry (RV) is until now the more efficient way to discover planetary systems. Moreover, photometric transit search missions like CoRoT and Kepler, need spectroscopic RV measurements to establish the planetary nature of a transit candidate and to measure the true mass. An active star has on its photosphere dark spots and bright plages rotating with the star. These inhomogeneities of the stellar surface can induce a variation of the measurement of the RV, due to changes in lines shapes and not to a Doppler motion of the star (e.g. Queloz et al. 2001; Desort et al. 2007; Boisse et al. 2009). We study how the Keplerian fit used to search for planets in RV data is confused by spots and we test an approach to subtract RV jitter based on harmonic decomposition of the star rotation. We use simulations of spectroscopic measurements of rotating spotted stars and validate our approach on active stars monitored by high-precision spectrograph HARPS: CoRoT-7 and ι Hor.

We investigate the coupling between solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. We find that fragments can become differentiated at birth. Even if an entire clump does not survive, differentiation could create solids cores that survive to accrete gaseous envelopes later.

We present preliminary results of the radial velocity survey on going at TNG targeting binaries with similar components.

To form meter-sized pre-planetesimals in protoplanetary discs, dust aggregates have to decouple from the gas at a distance far enough from the central star so they are not accreted. Dust grains are affected by gas drag, which results in a vertical settling towards the mid-plane, followed by radial migration. To have a better understanding of the influence of growth on the dust dynamics, we use a simple grain growth model to determine the dust distribution in observed discs. We implement a constant growth rate into a gas+dust hydrodynamics SPH code and vary the growh rate to study the resulting effect on dust distribution. The growth rate allows us to determine the relative importance between friction and growth.We show that depending on the growth rate, a range of dust distribution can result. For large enough growth rates, grains can decouple from the gas before being accreted onto the central star, thus contributing as planetary building rocks.

3D global MHD simulations of magneto-driven turbulence are performed for the disk of 100 AU with reduced amount of 10μm fluffy dust grains. We use X-ray and cosmic ray ionization, as well as simplified treatment of recombination on dust grains. The ionization of gas and charging of dust grains are dynamically evolving during the simulation, making the zone of high magnetic dissipation (’dead’ zone) variable. In our simulations, the jump in MRI-driven turbulent viscosity inside and outside of dead zone is insignificant. We find no hard edge, but rather a smooth transition between active and dead zone. Subsequently, there is no visible pressure bump at outer edge of the dead zone.

If it is commonly agreed that the presence of a (moderately) close stellar companion affects the formation and the dynamical evolution of giant planets, the frequency of giant planets residing in binary systems separated by less than 100 AU is unknown. To address this issue, we have conducted with VLT/NACO a systematic adaptive optics search for moderately close stellar companions to 130 nearby solar-type stars. According to the data from Doppler surveys, half of our targets host at least one planetary companion, while the other half show no evidence for short-period giant planets. We present here the final results of our survey, which include a new series of second-epoch measurements to test for common proper motion. The new observations confirm the physical association of two companion candidates and prove the unbound status of many others. These results strengthen our former conclusion that circumstellar giant planets are slightly less frequent in binaries with mean semimajor axes between 35 and 100 AU than in wider systems or around single stars.

Discoveries of extrasolar planets in tight binaries are of great scientific value since these systems can be used to gain new insights in planetary development processes. Gamma Cephei, one of the most thoroughly investigated double star systems is hosting a Jovian planet at a distance of about 2 AU from its primary, a 1.4 solar-mass K1 III-IV star (Neuhäuser et al. 2007; Torres 2007). We comprise aspects of dynamical stability, disc heating processes and different giant planet (GP) formation scenarios in order to gain a better understanding of the open questions that remain in explaining the formation of gamma Cephei b.

The Earth's comparatively massive moon, formed via a giant impact on the proto-Earth, has played an important role in the development of life on our planet. Here we study how frequently Earth-Moon planetary systems occur. We derive limits on the collision parameters that may guarantee the formation of a circumplanetary disk after a protoplanet collision that could form a satellite. Based on a large set of simulations, we observe potential moon forming impacts and conclude that giant impacts with the required energy and orbital parameters for producing a binary planetary system occur frequently with more than one in ten terrestrial planets hosting a massive moon.

Photometric observations of transits can be used to derive physical and orbital parameters of the system, like the planetary and stellar radius, orbital inclination and mean density of the star. Furthermore, monitoring possible periodic variations in transit timing of planets is important, since small changes can be caused by the presence of other planets or moons in the system. On the other hand, long term changes in the transit length can be due to the orbital precession of the planets. For these reasons we started an observational program dedicated to observe transits of known exoplanets with the aim of contributing to a better understanding of these planetary systems. In this work we present our first results obtained using the observational facilities in Argentina including the 2.15 telescope at CASLEO.

We present 3D global non-ideal MHD simulations with a self consistent dynamic evolution of ionization fraction of the gas as result of reduced chemical network. We include X-ray ionization from the star as well as cosmic ray ionization. Based on local gas density and temperature in our chemical network, we determine the magnetic resistivity, which is fed back in MHD simulations. Parameters for dust size and abundance are chosen to have accreting layers and a laminar “dead” mid-plane.

We present the spatially-resolved polarization measurements for the disk around the Herbig Ae star, AB Aurigae. The images were obtained in J, H, and Ks bands with the coronagraphic camera HiCIAO on the Subaru Telescope. The inner region beyond 30 AU from the star was imaged, which reveals an azimuthal dip, a radial gap at around 80 AU, and complex spiral-like emission in polarized light.

We have analysed very high-quality HARPS and UVES spectra of 95 solar analogs, 24 hosting planets and 71 without detected planets, to search for any possible signature of terrestial planets in the chemical abundances of volatile and refractory elements with respect to the solar abundances.

We demonstrate that stars with and without planets in this sample show similar mean abundance ratios, in particular, a sub-sample of 14 planet-host and 14 “single” solar analogs in the metallicity range 0.14 < [Fe/H] < 0.36. In addition, two of the planetary systems in this sub-sample, containing each of them a super-Earth-like planet with masses in the range ~ 7-11 Earth masses, have different volatile-to-refratory abundance ratios to what would be expected from the presence of a terrestial planets.

Finally, we check that after removing the Galactic chemical evolution effects any possible difference in mean abundances, with respect to solar values, of refratory and volatile elements practically dissappears.

Planet formation theory is founded on the concept of dust coagulation and subsequent growth into planetesimals. This process is by no means an isolated one, but possibly happens in a turbulent nebula. It is therefore crucial to understand how particles of different sizes are affected by their gaseous environment via stochastic forcing and aerodynamic damping. We here report on the effects of magneto-rotational (MRI) turbulence in the presence of non-uniform ionisation leading to the formation of a magnetically inactive dead-zone. While we find that collisional growth is impeded by fully-active MRI, it may be possible within a dead-zone.

Four new transit light curves of XO-2b obtained in 2008 and 2009, are analyzed by using MCMC algorithm, and the system parameters are derived. The result demonstrates that the orbital period of the system obtained from new observations is almost the same as Burke et al.'s one (2007), which does not confirm the result of Fernandez et al. (2009).