Elenco dei seminari passati

The Carte du Ciel project is considered the mother of all astrometric enterprises. It was conceived at the end of 19th century and was aimed at photographing the entire sky vault, to produce a catalogue of stars up to magnitude 11 and a chart containing stars up to magnitude 14.. This international endeavour was promoted by Paris Observatory in 1887: 18 observatories from both hemispheres participated in it, more or less successfully. This talk will illustrate how the project was originated and developed, why it remained partially inachieved and what was its impact on the astrometric missions which preceded the current GAIA mission.

High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in Classical T Tauri stars (CTTS). In particular the accretion-shock region, where the accreting material is heated to temperatures of a few million degrees, can be probed by X-ray spectroscopy. MHD models predict that this hot post-shock plasma should have an inward bulk motion, with v_post ~ 100 km/s, with respect to the surrounding stellar atmosphere. To verify this prediction we searched for a Doppler shift in the deep Chandra/HETG observation of the CTTS TW Hya, perfectly suited for this task because of the excellent S/N and spectral resolution of the dataset, and because of the ideal target inclination. This test should allow us to constrain definitively the nature of this X-ray emitting plasma component in CTTS, and infer constraints on the accretion stream geometry. We searched for a Doppler shift in the X-ray emission from TW Hya by measuring the position of a selected sample of emission lines. To check the absolute wavelength calibration of the Chandra gratings, and to check whether or not bulk motions with respect to the photosphere are observed in coronal plasma, we also analyzed a sample of Chandra/HETG spectra of non-accreting active stars. We found that the soft part of the X-ray spectrum of TW Hya is significantly red-shifted by ~40 km/s with respect to the known radial velocity of the stellar photosphere. Conversely no X-ray redshift is observed in the X-ray emission of non-accreting active stars. The evidence that the X-ray emitting plasma on TW Hya is moving inward with respect to the stellar surface definitively confirms that it originates in the post-shock region, at the base of the accretion stream, and not in coronal structures. The observed radial velocity indicates that the base of the accretion stream on TW Hya is located at low latitudes on the stellar surface. Moreover the observed velocity of the soft X-ray emitting plasma is very similar to the velocity of the narrow component of the CIV resonance doublet at 1550 A, suggesting that they both originate from the same post-shock regions, that the hypothesis of free-fall regime in the accretion streams holds, and that complex magnetic field geometries, as that of TW Hya, allow low latitude accretion spots.

Space missions are very complex projects with peculiar characteristics such as: strategic importance, extent of international participation, specialized industrial sector, high investment costs, long-term program duration, impossibility of intervening in space for repairs and/or maintenance. These peculiarities strongly influence the realization process since its conception. This talk provides an introduction to methods and tools of project management of a space mission under the guidance of the European Space Agency. The following topics will be covered: General section: – Introduction to management of complex projects; – Key elements for the design of a space mission; – Main phases for the development of a space mission; – The life cycle of ESA programs; – The European Cooperation for Space Standardization (ECSS) documentation for project management and quality control. Phase A study: – Objectives of a phase A; – The main activities of analysis and development; – Preliminary Requirements Review (PRR) documentation.

I will present results from my recent papers based on XMM-Newton observations of young stars in Star Forming Regions near Orion A (Kappa Ori) and Rho Ophiuchi. These observations were aimed at discovering new young stars and infer their ages, their distances and the relationship with the parent cloud. In Kappa Ori, with 40 ks of XMM/EPIC we have derived X-ray fluxes and luminosities of about 120 young stars with and without disks near Kappa Ori (B0 type). X-ray luminosity functions provided a “yardstick” to infer that these stars form a separate cluster centered on Kappa Ori (~250 pc), much closer than ONC (~410 pc) and unrelated to it. In Rho Ophiuchi, with 50+140 ks we have discovered a group of disk-less stars around Rho Oph itself and significantly older (5-10 Myr) than the bulk of YSOs (1 Myr) in the main core of the cloud, L1688. As an unexpected discovery, Rho Oph itself is a periodic emitter of hard X-rays, mimicking a “X-ray lighthouse”, and hinting that either a strong magnetism or an unseen companion are the source of such X-rays.

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.

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.

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.

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.

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?

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.