Osservatorio Astronomico di Roma

The mystery of Fast Radio Bursts: are we closer to the solution?
2017-01-27 11:45 - 12:45 (Europe/Rome) | 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.

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.

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.

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.

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.

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.

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.

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).

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.

A hard X-ray view of non-local AGNs
2016-11-22 11:45 - 12:45 | 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.

Extreme-Adaptive-Optics observations of protostellar jets
2016-11-15 11:45 - 12:45 | Aula Gratton
The ejection of matter in form of protostellar jets/outflows plays a fundamental role in the star-formation process as it is tightly connected to the mass accretion mechanism and is expected to directly affect the evolution of the circumstellar disk in which planet formation occurs. Since the typical angular scales of the jet-formation region are of the order of tens of mas for the closest star-forming regions, such region has so far remained unknown from an observational point of view. New instruments equipped with extreme Adaptive Optics systems offer now the opportunity to observe the jets as close as possible to the driving sources so as to gather crucial pieces of information on the ejection process and its connection to the disk.
In this context, I will present the first VLT/SPHERE observations jets from a young object. Using the ZIMPOL instrument we have taken optical images of the young binary Z CMa, which is composed by two eruptive variables: a Herbig star showing recurrent EXor-like outbursts and a FUor source, both driving a jet. The morphology of the two jets, which we trace down to ~70 mas, looks fairly different: the Herbig star appears to emit a poorly collimated compact flow, while the FU Ori drives a highly collimated precessing jet.
For the FUor jet, we discuss the mechanism responsible for the observed jet precession and we provide the first direct measurement of the mass ejection rate and of the ejection efficiency in a FUor source, which we can compare to the same quantities measured in other classes of young stellar objects.
Finally, I will give an overview of what we can expect for protostellar jet observations with other upcoming extreme-AO instruments, such as SHARK at LBT.

Can supermassive black holes influence the evolution of galaxies?
2016-11-10 11:45 - 12:45 | Aula Gratton
Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this “quasar mode” feedback came from the recent X-ray observations of a mildly relativistic accretion disk winds in an ultraluminous infrared galaxies and their connection with a large-scale molecular outflows, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. Fundamental improvements on these studies will come from the unprecedented energy resolution and sensitivity of upcoming X-ray missions, such as Athena, and the synergy with future large facilities at other wavelengths, such as ALMA, E-ELT, SKA.

AGILE highlights in gamma-ray astrophysics and the hunt for GW counterparts
2016-11-08 11:45 - 12:45 | Aula Gratton

Swinging between accretion and rotation power in binary millisecond pulsars
2016-10-25 11:45 - 12:45 | Aula Gratton
Neutron stars in low mass X-ray binaries are spun-up to millisecond spin periods during a Gyr-long phase of accretion of the matter transferred by a companion star. When the rate of mass transfer decreases at the end of this Gyr-long X-ray bright phase, a radio pulsar powered by the rotation of the neutron star magnetic field turns on. After decades of searches, the evolutionary link between these two classes of sources has been recently proven by the discovery of three sources that were observed to swing between accretion (X-ray bright) and rotation (radio bright) pulsar behaviour. These sources are the prototype of a new class of transitional systems that alternate between accretion and rotation-powered states in response to variations of the rate of mass in-flow, on time scales as short as a couple of weeks. Observations of this and other similar systems indicate that transitions to the accretion phase not only involve bright X-ray outbursts, but also a fainter intermediate X-ray state, possibly caused by centrifugal inhibition and ejection of the matter flow. Transitional ms pulsars are ideal test beds for theories describing the accretion-ejection coupling around a fast magnetized rotator, as well as the evolution of old binary systems. I will review the main observed properties, the prospects of catching more state transitions, and the possibilities to fully exploit the unique observable features of this newly established class.

Ascende superius - Seek higher things - Moving to higher order statistics in weak lensing
2016-10-18 11:45 - 12:45 | Aula Gratton
Weak lensing has emerged as one of the most promising tool to constrain
cosmological parameters and modified gravity theories by measuring second
order statistical probes such as the cosmic shear two points correlation
function and tomographic power spectra. Thanks to both the wide area and
large redshift range probed, future surveys will deliver such an exquisite
quality dataset that it is worth wondering whether one can move to higher
order statistics. We review here some interesting possibilities showing
that they can be recovered with sufficient precision from future data and
shed further light on the dark energy mystery.
