Osservatorio Astronomico di Roma

A hard X-ray view of non-local AGNs
2016-11-22 11:45 - 12:45 (Europe/Rome) | Aula Gratton
The Cosmic X-ray Background (CXB) provides a record of cosmic accretion history
onto actively accreting supermassive black holes. The direct resolution of the
CXB into discrete sources can therefore provide a census of AGN populations
across cosmic time.
Population synthesis models are able to explain the CXB as mixture of AGN
populations with different luminosities and obscuration degree provided a
consistent population of heavily obscured AGN, called Compton Thick (CT),
expected to contribute significantly (20-30%) to the CXB peak at 20-30 keV, is
postulated. Unfortunately, several parameter degeneracies in the modelings at
energies > 10 keV result in an order of magnitude uncertainty in the estimation
of the fraction of CT AGN. Furthermore, the direct detection of these sources at
10 keV,
is capable of resolving a sizable part (>~ 30%) of the CXB at energies around
its peak of emissivity and of obtaining a direct and almost unobscured view of
obscured AGN up to z~3 therefore starting to address the main concerns in the
modelings of the CXB. In this regard I will report on the first spectral
characterization of these AGN populations, through broad-band (0.5-24 keV)
spectral analysis of a hard-band selected sample of AGN from the NuSTAR survey
program.

Storia della nascita e la sorte dei “telescopi Mussolini"
2016-11-24 11:45 - 12:45 | Aula Gratton
In May 1938, during the state visit to Italy Hitler asked Mussolini “to accept as a token of our reverence and friendship a Zeiss telescope and the complete equipment of an observatory”. This equipment included three big telescopes (a 26-inch refractor, a 1-m Schmidt refractor and a double astrograph) with three domes and auxiliary apparatus (a new-type transit instrument, a registering microphotometer, a comparator etc). All telescopes together with domes were going to be produced by Zeiss. It was decided to build the National Astronomical Observatory in Monte Porzio Catone for hosting the astronomical equipment. However, due to the WWII tragic events these plans were not fulfilled. Three domes for big telescopes (with necessary motors for rising floor and moving roof) were completed, moved to Italy and mounted. However, after 8 September, 1943 they were unmounted and moved back to Germany to the Zeiss factory. The domes and auxiliary instruments were distributed between German observatories. Three big telescopes were not paid by the German government and stayed in the Zeiss factory. They never came to Italy. In 1945 these telescopes were taken to the Soviet Union as war reparation. They were sent to Soviet observatories those most affected by the war.

Da Halley a Rosetta: esplorazione delle comete
2016-11-29 11:45 - 12:45 | Aula Gratton
Le analisi compositive dei nuclei cometari esplorati da vicino ( Halley/Giotto, Borrelly/DS1, Stardust/Wild-2, Tempel1/Deep Impact, soprattutto 67P-CG/Rosetta) hanno fornito informazioni decisive sull’origine delle comete, sul meccanismo della loro attività emissiva, sulla loro possibile fonte di molecole prebiologiche verso ambienti planetari abitabili.
Tutto questo è riassunto per la prima volta in un libro recentemente pubblicato da Hoepli (L’ ESPLORAZIONE DELLE COMETE, da Halley a Rosetta).

New channels of single and binary evolution and nucleosynthesis
2016-12-06 11:45 - 12:45 | Aula Gratton
In this talk I will present our new findings on an exotic group of evolved objects: post-asymptotic giant branch (post-AGB) and post-red giant branch (post-RGB) stars. These objects bear the signatures of the entire morphological and nucleosynthetic changes that occur during and prior to the red giant evolutionary phases. Therefore, they provide excellent constraints for single and binary star evolution and nucleosynthesis. These objects have also revealed new evolutionary channels and AGB nucleosynthesis which is vital for understanding the complex chemical evolution of our Galaxy as well as external galaxies.

Electromagnetic follow-up of gravitational wave candidates: perspectives and first results of the Italian project GRAWITA
2016-12-13 11:45 - 12:45
Detecting an electromagnetic (EM) emission associated with a gravitational wave (GW) signal is one of the main goal of the newly born gw astronomy. Merger of neutron stars and/or black holes and core-collapse of massive stars are expected to cause rapid transient EM signals like gamma-ray bursts (GRBs), core-collapse supernovae, soft-gamma ray repeaters and pulsar glitches.
The Advanced LIGO detectors on September 14th, for the first time, detected a binary black hole merger (GW150914) for which a detectable electromagnetic counterpart is little expected. This detection showed that EM follow-up facilities are able to react quickly to GW signals covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based over the entire gravitational sky localization even if they have to deal with large position uncertainties up to hundreds square degrees.
Therefore wide-field cameras and rapid follow-up observations are crucial to characterize the EM candidates and the first EM counterpart identification.
In this talk I want to present the activities we are currently currying on to optimize the response of the GRAWITA network of facilities to expected GW triggers and our first results. The GRAWITA project is representing an efficient operational framework capable of fast reaction on large error box triggers and direct identification and characterization of the candidates.
All the activities we will describe are expect to provide means and opportunities to the Italian and European astronomical communities to have a leading role in the GW astronomy and Time Domain Astronomy fields.

Chemical properties of distant Milky Way halo stars from current and future spectroscopic surveys
2016-12-20 11:45 - 12:45 | Aula Gratton
The study of elemental abundances of long-lived individual stars is one of the pillars of Galactic Archaeology, as a powerful way for retrieving information on the stars birth environment.
Through this approach, it has already been established that the inner Milky Way halo cannot have formed solely from the disruption of satellite galaxies experiencing as low an initial star formation rate as in the surviving Milky Way satellites.
However, the growing observational evidence for a dual nature of the Milky Way stellar halo raises the question of whether the elemental abundances of inner halo stars can be considered as representative of the whole Milky Way halo and if the inner and outer halo were formed through different dominant mechanisms.
In this talk I will present our investigation of the
chemical properties of the outer Milky Way halo, based on abundances of large samples of distant halo stars, both from SDSS-DR13
and proprietary spectroscopic campaigns at VLT, Magellan and HET. I will conclude with a
discussion of the prospects that future Galactic Archaeology surveys such as with the WHT/WEAVE spectrograph will open up for the study of the Milky Way halo properties.

Radial metallicity gradients of disk galaxies: The emission-line probes
2017-01-10 11:45 - 12:45 | Aula Gratton
The metallicity of stellar and interstellar probes thorough disk galaxies, including our own, is distributed non-uniformly, showing typically shallow radial metallicity gradients where the metallicity decreases radially, inside out. Ultimately, the chemical evolution models need to be constrained by observations to determine the existence and extent of gradient slope and evolution, which in turn are linked to the formation and evolution of the galaxy.
The use of emission-line probes to test metallicity gradients takes advantage of the brightness of the nebular emission lines, and of the fact that the two major nebular probes, planetary nebulae (PNe) and HII regions, probe different epochs since galaxy formation. The limitation is that direct abundances are within observational reach only in the Local Universe. On the Galactic side, additional complications are added to the problem by the uncertainty of the PN distance scale.
In this talk I review the radial metallicity gradients background and main observational results, the latest direct metallicity gradient determinations in the Galaxy and beyond, the Gaia solution to the PN distance problem, and the foreseen advances of this field with the next generation of observational capabilities.

Sensing the Universe in colour; Kinetic Inductance Detectors for optical and near-IR astronomy
2017-01-17 11:45 - 12:45 | Aula Gratton
I will describe the ongoing work in the development of Microwave Kinetic Inductance Detectors (MKIDs) for optical and infra-red astronomy. These super-conducting devices represent an important step towards the development of the ‘ultimate detector’; one that can measure the position, energy and arrival time of a photon. I will describe the operating principles of the devices and their current status. I will present the current MKID-based optical/IR instruments and show results from recent science demonstration runs. Finally, I will discuss the future promise of the technology and highlight some of the areas of astronomical instrumentation where they could have a transformational impact and our program at Oxford to exploit these devices.

Protoplanetary disk evolution: the key to planet formation
2017-01-24 08:00 - 17:00 | Aula Gratton
The evolution of protoplanetary disks in young stellar clusters is regulated by the interplay of various physical processes, such as accretion and winds, and by the interactions with other stars in the cluster. Accretion and winds are best studied spectroscopically. Instruments like the VLT/X-Shooter spectrograph allow us to observe simultaneously the signatures of the accretion process, such as the UV-excess and the emission lines, together with lines tracing winds and outflows, such as helium lines and forbidden lines. At the same time, these spectra allow us to robustly derive the physical parameters of the central objects, such as their temperature and their mass. These processes relate to the disk mass and size, which can nowadays be studied with ALMA. Finally, the coming Gaia data releases will open the field to new studies of dynamical evolution of stars in young clusters by means of kinematical modelling.
I will report on the stellar, accretion, and wind properties derived with X-Shooter of the complete samples of low-mass stars in the Lupus and Chamaeleon star forming regions, and discuss the dependence of stellar and accretion parameters with the disk properties obtained with ALMA surveys in these regions. I will present the results of the study of some peculiar dipping young stars recently discovered. Finally, I will show how we can use Gaia data to study young clusters and the effect of interactions on the evolution of disks.

The mystery of Fast Radio Bursts: are we closer to the solution?
2017-01-27 11:45 - 12:45 | Aula Gratton
With the recent firm localization of the host galaxy of the Fast Radio
Burst FRB 121102, the solution to the mystery of these peculiar signals
might be getting closer. FRB 121102 is, however, the only one showing
repeating pulses, leaving open the possibility that more classes, hence
different progenitors, of FRBs exist. In this talk I will give, following
the timeline of their observational milestones, an overview of FRBs. I
will presenting their main observational features, some of the many
theoretical models suggested to explain their characteristics, and some
possible use of FRBs as cosmological probes.

Sterile Neutrinos as Dark Matter: From Production to Predictions
2017-01-31 11:45 - 12:45 | Aula Gratton
Sterile neutrinos with masses of a few keV are very
well-motivated Dark Matter candidates. However, even though they have the
perfect properties for that job, it is unclear how to produce them in the
early Universe. In this talk, I will mainly focus on how to make this
production happen in the early Universe. While several proposals exist in
the literature, the production aspect unfortunately suffers from several
incorrect or at least oversimplified statements (e.g., that keV sterile
neutrino Dark Matter would usually be ‘warm’). I will make an attempt to
explain parts of the issues and how to resolve them, which ultimately
leads to means to distinguish the different mechanisms via their impact on
cosmic structure formation. While lab experiments are not well-suited to
probe this type of Dark Matter candidate, cosmology and astrophysics
provide the tools to do so. The whole talk is supposed to be more
pedagogical than technical, so I will avoid heavy formula whereever
possible.

High-contrast imaging observations of exoplanets: current status and future
2017-02-07 11:45 - 12:45 | Aula Gratton
Thanks to notable advancements in adaptive optics combined with
coronagraphic observational strategies, high-contrast imaging techniques
are rapidly progressing in the current years. The exploration of the
sub-stellar regime via direct imaging, hampered so far by technical limitations, is starting to provide us with a powerful tool, thanks to the advent of new-generation instruments, such as e.g., GPI or ScEXAO. SPHERE at VLT is a new facility that combining extreme adaptive optics with coronagraphy, dual-band imaging, and integral field spectroscopy has recently started its operations and aims at revealing relatively massive exoplanets at few tenths of arcsecond separations and contrasts better than 10^6. In this contribution I will present recent results obtained with SPHERE in the framework of the exoplanet detection and characterisation. Moreover, I will present a new system for coronagraphy with high-order adaptive optics that will be operating at LBT by the end of 2018: SHARK. This system will provide coronagraphic observations from visual to NIR bands, granting a very powerful tool that is not currently available for any other instrument in the world. Finally, I will discuss the employment of a brand-new technique that combines high-contrast imaging with high-dispersion spectroscopy, allowing in principle to reach contrasts down to 10^10. In the era of E-ELT, this will open the way to investigating earth-like planets in the habitable zones of their parent stars.

A main sequence for quasars
2017-02-14 14:30 - 15:30 | Aula Gratton
The last 15 years have seen a major step forward in the analysis of optical UV spectroscopic data of large quasar samples. Multivariate statistical approaches have proved to be especially helpful, as they have led to the definition of systematic trends (first and second eigenvector derived from Principal Component Analysis) in observed properties that are the basis of physical and dynamical modeling of quasar structure. In this talk I will discuss the empirical correlates of the so-called quasar “main sequence” associated with the quasar eigenvector 1, its governing physical parameters, as well as luminosity effects associated with the second eigenvector. I will also briefly discuss quasars in a segment of the main sequence which includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential “Eddington standard candles”.

The challenge of massive black hole binary coalescence; from galaxy formation to gravitational waves
2017-02-21 11:45 - 12:45 | Aula Gratton
I will review recent progress in understanding how a pair of massive black holes can evolve from galactic scale separations, kpc and above, to milliparsec separations, where gravitational wave emission takes over
and leads to signals that should be detected by the Laser Interferometer
Space Antenna (LISA). I will show how, contrary to common belief, the
orbital decay of massive black holes in gaseous environments can be
less efficient and more stochastic than in stellar backgrounds, where
the only two processes at play are dynamical friction and 3-body
encounters with passings stars. Novel supercomputer simulations that attempt to study orbital decay in realistic galactic hosts show that coalescence timescales
can become very short, about 10 Myr, in high redshit massive galaxies that are on their way to become quenched spheroids, but can be longer than a
Gyr in massive star forming gas-rich disks as those observed at z > 1.
Hosts of LISA black holes are expected to have a different nature. The complex interplay between
the physical properties of galactic nuclei and the orbital decay process
poses a huge challenge to computational model, but at the same time
holds the promise for LISA and other gravitational wave detection
experiments to become a powerful probe of galaxy formation and evolution.

AGB dust production: what we learn from the Local Group galaxies
2017-02-28 11:45 - 12:45 | Aula Gratton
Asymptotic giant branch (AGB) stars are among the most important gas and dust polluters of the Universe. The composition and the amount of dust produced in the winds of AGB stars is strongly correlated with the evolution of the central object. Detailed knowledge of the physical structure and chemical composition Is an essential ingredient to estimate the impact of these stars in the evolution history of their host environment.
A new release of AGB+dust models were developed in the last years to this scope. Their application in characterizing the AGB population and its contribution to the dust budget in the MCs, as well as in dwarf galaxies of the Local Group will be discussed in this talk.
