Science and Technology News

The recently discovered transiting very hot Jupiter, HAT-P-7b, a planet detected by the telescopes of HATNet, turned out to be among the ones subjected to the highest irradiation from the parent star. As known, the combination of photometric and spectroscopic data for such an object yields the stellar, orbital and planetary parameters. In order to best characterize this particular planet, we carried out a complex analysis based on a complete and simultaneous Monte-Carlo solution using all available data. We included the discovery light curves, partial follow-up light curves, the radial velocity data, and we used the stellar evolution models to infer the stellar properties. This self-consistent way of modeling provides the most precise estimate of the a posteriori distributions of all of the system parameters of interest, and avoids making assumptions on the values and uncertainties of any of the internally derived variables describing the system. This analysis demonstrates that even partial light curve information can be valuable. This may become very important for future discoveries of planets with longer periods -- and therefore longer transit durations -- where the chance of observing a full event is small.

We present the discovery of optical/X-ray flux correlations on rapid timescales in the low/hard state of the Galactic black hole GX 339-4. The source had recently emerged from outburst and was associated with a relatively-faint counterpart with mag V~17. The optical (VLT/ULTRACAM) and X-ray (RXTE/PCA) data show a clear positive cross-correlation function (CCF) signal, with the optical peak lagging X-rays by ~ 150 ms, preceded by a shallow rise and followed by a steep decline along with broad anti-correlation dips. Examination of the light curves shows that the main CCF features are reproduced in superpositions of flares and dips. The CCF peak is narrow and the X-ray auto-correlation function (ACF) is broader than the optical ACF, arguing against reprocessing as the origin for the rapid optical emission. X-ray flaring is associated with spectral hardening, but no corresponding changes are detected around optical peaks and dips. The variability may be explained in the context of synchrotron emission with interaction between a jet and a corona. The complex CCF structure in GX 339-4 has similarities to that of another remarkable X-ray binary XTE J1118+480, in spite of showing a weaker maximum strength. Such simultaneous multi-wavelength, rapid timing studies provide key constraints for modeling the inner regions of accreting stellar sources.

We present the optical and cryo-mechanical solutions for the Spectrograph of VSI (VLTI Spectro-Imager), the second generation near-infrared (J, H and K bands) interferometric instrument for the VLTI. The peculiarity of this spectrograph is represented by the Integrated Optics (IO) beam-combiner, a small and delicate component which is located inside the cryostat and makes VSI capable to coherently combine 4, 6 or even 8 telescopes. The optics have been specifically designed to match the IO combiner output with the IR detector still preserving the needed spatial and spectral sampling, as well as the required fringe spacing. A compact device that allows us to interchange spectral resolutions (from R=200 to R=12000), is also presented.

We simulate the dynamics and the evolution of quiet Sun magnetic elements to produce a probability density function of the field strengths associated with such elements. The dynamics of the magnetic field are simulated through a numerical model in which magnetic elements are passively driven by an advection field presenting spatio-temporal correlations which mimicks the granulation and the mesogranulation scales observed on the solar surface. The field strength can increase due to an amplification process which takes place where the magnetic elements converge. Starting from a delta-like probability density function centered on B=30 G, we obtain magnetic field strengths up to 2 kG (in absolute value). To derive the statistical properties of the magnetic elements several simulation runs are performed. The model is able to produce kG magnetic fields in a time interval of the order of the granulation time scale. The mean unsigned flux density and the mean magnetic energy density of the synthetic quiet Sun reach respectively 100 G and 350 G in the stationary regime. The derived probability density function of the magnetic field strength decreases rapidly from B=30 G to B=100 G and presents a secondary maximum for B=2 kG. From this result it follows that magnetic fields >700 G dominate the unsigned flux density and magnetic energy density although the probability density function of the field strength presents a maximum for B=30 G.

We study the stability and the modes of non -- isothermal coronal loop models with different intensity values of the equilibrium twisted magnetic field.We use an energy principle obtained via non -- equilibrium thermodynamic arguments. The principle is expressed in terms of Hermitian operators and allows to consider together the coupled system of equations: the balance of energy equation and the equation of motion, to obtain modes and eigenmodes in a spectrum ranging from short to long--wavelength disturbances without having to use weak varying approximations of the equilibrium parameters. Long--wavelength perturbations introduce additional difficulties because the inhomogeneous nature of the medium determines disturbances leading to continuous intervals of eigenfrequencies which cannot be considered as purely sinusoidal.We analyze the modification of periods, modes structure and stability when the helicity, the magnetic field strength and the radius of the fluxtube are varied. The efficiency of the damping due to the resonant absorption mechanism is analyzed in a context of modes that can either impulsively release or storage magnetic energy.We find that the onset of the instability is associated to a critical value of the helicity and that the magnetic energy content has a determinant role on the instability of the system with respect to the stabilizing effect of the resonant absorption mechanism.