Calendar

The early stages of a star birth are characterised by a variety of mass ejection phenomena, including outflows and collimated jets, that are strongly related with the accretion process developed in the context of the star-disc interaction. After been ejected, jets move through the ambient medium, interacting and producing shocks and complex structures that are observed at different wavelength bands. In particular, X-ray observations show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary and have been interpreted as shock diamonds. We aim at investigating the physical properties of the shocked plasma and the role of the magnetic field on the collimation of the jet and the location, stability and detectability in X-rays of the stationary shock formed. We performed 2.5D MHD simulations, including the effects of the thermal conduction and the radiative losses. We modelled the propagation of a jet ramming with a supersonic speed into an initially isothermal and homogeneous magnetized medium. We studied the physics that guides the formation of a stationary shock (for instance a shock diamond) and compared the results with observations, via the distribution of emission measure vs. temperature and the luminosity synthesized from the simulations output data.

Coupling high-power lasers and high-strength B-fields helps gaining unique insight and understanding of a variety of phenomena of crucial importance for astrophysics. We have shown that such platform could be used to mimic the expansion of a young star isotropic disk wind threaded by a co-axial poloidal magnetic field. It reveals that long-range collimated jets can indeed by result from such system, complementing toroidal B-fields that help shape the initial matter from the star into a jet. The same system can then be used to study the dynamics of the accretion of magnetized plasma columns onto star surfaces and help decipher the underlying physics, or also the issue of particle energization in astrophysical plasmas. Our investigations on these topics will be reviewed and prospects discussed.

The first characteristic measured for Cepheids is their periods. The next step is to determine their pulsation mode. We have made month long observations with the MOST satellite of a fundamental mode Cepheid (RT Aur) and an overtone Cepheid (SZ Tau). The quantity and quality of the satellite data have shown that the Fourier parameters of the overtone are far more variable than those of the fundamental. A series of studies have been made of the binary properties of Cepheids, providing insight into star formation and dynamical evolution. A survey of 70 Cepheids was made with HST WFC3 to identify possible resolved companions. This was followed up with XMM-Newton observations to determine which possible companions are young X-ray active stars, and hence physical companions of Cepheids. This provides information about the frequency, separations, and mass ratios. Finally, the measured masses of Cepheids will be summarized, and new developments discussed.

Evidence for some super-hot plasma (> 4 MK) has been found in the core of active region loops. This is a signature of impulsive heating (nano-flaring). We study the EUV light curves in one or a few pixels with a model of multi-stranded coronal loop. Each strand is pulse-heated. In the hypothesis of an energy distribution of the heat pulses, we first generate a grid of strand models with different heating rates, and then we combine them randomly to generate simulated light curves similar to the observed ones. We make 10000 realisations for each set of model parameters (the power law index of the energy distribution, the duration of the heat pulse, the number of strands) and compare them to the observed light curves to find the best one by means of an artificial intelligence system (Probabilistic Neural Network, PNN). Cross-Correlation is used as a cross-check. We find that a shallow (but not flat) distribution of short-duration pulses in a relatively high number of strands (1000) best describes the observed data. A space-resolved loop model with these parameters predicts different fluctuations of the emission from the bottom to the top of the loop: we compare with observation.

We are using the GMOS integral field unit on the Gemini telescopes to investigate the kinematics of the circum-nuclear ionized gas in a sample of nearby AGNs spanning a wide range of nuclear hard X-ray luminosity (a proxy for the SBH accretion rate). The study aims at investigating the mechanisms channeling gas (the supermassive black hole fuel) from the inner kiloparsec down to few tens of parsecs from the supermassive black hole. The galaxy NGC 1386 turned out to be one of the most interesting sources: we found that the dominant kinematic components can be explained as a combination of rotation in the large-scale galactic disk and compact outflows along the axis of the AGN “radiation cone”. However, there is also compelling evidence for an equatorial outflow. A new clue to the physical processes operating in AGNs?

In our Galaxy, star formation occurs in a variety of environments, with a large fraction of stars formed in clusters hosting massive stars. OB stars have an important feedback on the evolution of protoplanetary disks orbiting around nearby young stars and likely on the process of planet formation occurring in them. The nearby massive association Cygnus OB2 is an outstanding laboratory to study this feedback. It is the closest massive association to our Sun, and hosts hundreds of massive stars and thousands of low mass members, both with and without disks. We have analyzed the spatial variation of the disk fraction (i.e. the fraction of cluster members bearing a disk) in Cygnus OB2 and and studied its correlation with the local values of Far and Extreme ultraviolet radiation fields and the local stellar surface density. We found evidence that disks are more rapidly dissipated in the regions of the association characterized by intense local UV field and large stellar density. In particular, the FUV radiation dominates disks dissipation timescales in the proximity (i.e. within 0.5 pc) of the O stars. In the rest of the association, EUV photons potentially induce a significant mass loss from the irradiated disks across the entire association, but the efficiency of this process is reduced at increasing distances from the massive stars due to absorption by the intervening intracluster material. Comparing our results to what has been found in other young clusters with different massive populations, it is possible to conclude that massive associations like Cygnus OB2 are potentially hostile to protoplanetary disks, but that the environments where disks can safely evolve in planetary systems are likely quite common in our Galaxy.

The race towards the discovery and characterization of terrestrial extrasolar planets, possibly in the habitable zone of their host stars, that recent statistical analyses revealed to have high occurrence rates, represents a scientific adventure rich of great expectations, but also of great challenges. I will address the subject starting from my experience in planet hunting as a collaborator of the Italian ground-based surveys GAPS and APACHE, that aim for a similar goal in complementary ways: through the analysis of the stellar radial velocity variations the first, with the photometric transit method the second. In particular, I will explore the limits imposed by signals of stellar origin to the detection and mass determination of another Earth in precise radial velocity measurements, discussing some proposed strategies to mitigate the impact of stellar noise. Moreover, I will focus the discussion on M dwarfs, which represent a treasure trove for the search of Earth-like planets, but demand particular attention both for the detection and characterization of small planets.

Colliding neutron stars (NSs) are strong sources of gravitational radiation, and one of the most promising candidates for direct detection by advanced LIGO. Following the spectacular observations of gravitational waves from GW150914 – produced by the collision of two black holes – we can now expect that the direct detection of NS collisions is just around the corner. Growing observational evidence shows that NS collisions also produce bright electromagnetic signals: gamma-ray bursts, and macronovae. The former are brief flashes of gamma-ray radiation, the latter are short-lived infrared transients powered by the radioactive decay of heavy nuclei. The simultaneous detection of both electromagnetic and gravitational radiation arising from NS collisions would be a revolutionary observation. This exciting prospect makes these systems prime targets in the era of multi-messenger astronomy. In this talk, I present ongoing observational efforts to characterize the electromagnetic signatures of NS collisions, and outline future initiatives aimed at exploring the gravitational wave sky.

CARMENES, the brand-new, Spanish-German, two-channel, ultra-stabilised, high-resolution spectrograph at the 3.5 m Calar Alto telescope, started its science survey on 01 Jan 2016. In one shot, it covers from 0.52 to 1.71 mum with resolution R = 94,600 (lambda less then 0.96) and 80,400 (lambda larger than 0.96 mum). During guaranteed time observations, CARMENES carries out the programme for which the instrument was designed: radial-velocity monitoring of bright, nearby, low-mass dwarfs with spectral types between M0.0 V and M9.5 V. Carmencita is the CARMEN(ES) Cool dwarf Information and daTa Archive, our input catalogue, from which we select the about 300 targets being observed during guaranteed time. Besides that, Carmencita is perhaps the most comprehensive database of bright, nearby M dwarfs ever built, as well as a useful tool for forthcoming exo-planet hunters: ESPRESSO, HPF, IRD, SPIRou, TESS or even PLATO. Carmencita contains dozens of parameters measured by us or compiled from the literature for about 2,200 M dwarfs in the solar neighbourhood brighter than J = 11.5 mag: accurate coordinates, spectral types, photometry from ultraviolet to mid-infrared, parallaxes and spectro-photometric distances, rotational and radial velocities, Halpha pseudo-equivalent widths, X-ray count rates and hardness ratios, close and wide multiplicity data, proper motions, Galactocentric space velocities, metallicities, full references, homogeneously derived astrophysical parameters, and much more. I will briefly describe the instrument CARMENES, the consortium that built it and now operates it, the sample, the status of the science survey, and some ideas for the future.