Osservatorio Astronomico di Roma

The two-families scenario of compact stars: signatures and implications on GRBs
2016-06-09 11:45 - 12:45 (Europe/Rome) | Aula Gratton
In the last years the possibility of discriminating between the various theoretically possible compositions of a compact “neutron” star has become more and more convincing and it is based on the measure of a few fundamental quantities, such as the radii (NICER, LOFT), the moment of inertia (SKA) and/or the gravitational wave signal before and after the merging of two compact stars (VIRGO, LIGO).
I will outline the so-called two-families scenario in which both stars having very small radii (of the order of about 10.5 km) and stars having very large masses (of the order or larger than about 2 Ms) can exist. In that scenario very dense stars, having small radii, are made of neutron, protons, hyperons and other hadronic resonances, while the most massive stars are strange-quark stars, i.e. objects entirely made of deconfined quark matter. I will discuss the implications of the two-families scenario on short and long Gamma Ray Bursts within the proto-magnetar model of GRBs, showing that quark deconfinement can be responsible both of the rapid termination of the prompt emission in short GRBs and of late time activity in long GRBs.

Dust-driven stellar winds in stellar evolution models
2016-05-31 11:45 - 12:45 | Aula Gratton
Mass loss from stars during their evolution in the HR-diagram is an essential ingredient in stellar evolution models. Mass loss on the AGB is of particular interest when dust production is included in the model, since it is well established that the winds of AGB stars are largely dust driven. For practical reasons, the wind models adopted in stellar evolution codes are relatively simplistic: the actual mass-loss rate is prescribed and net effect of thermal gas pressure is usually not taken into account. In this talk I will discuss how wind these models can be improved without turning them into inhibiting computational challenges. I will also discuss (or speculate about) the effects such an improved wind model can have on the resultant dust yields for AGB stars.

The square kilometre array
2016-05-24 11:45 - 12:45 | Aula Gratton
Building on the major scientific achievements of the current generation of centimetre and metre-wavelength telescopes, phase 1 of the Square Kilometre Array (SKA1) will be the next global radio astronomy observatory. It is currently being designed by engineers and scientists from around the world, with the aim of beginning construction in 2018 and early science operations in 2020. SKA1 will conduct key tests of general relativity through surveys and timing of pulsars in our Galaxy. It will help answer fundamental questions related to the evolution of atomic Hydrogen in the Universe, from the present day back to the Cosmic Dawn. I will give an overview of the wide breadth of science objectives that could be addressed by SKA1, along with a description of the planned telescopes and the sites that will host them

Serata Estiva
2016-05-20 20:00 - 23:00 | OAR Monte Porzio Catone, Via Frascati, 33, Monte Porzio Catone , RM, 00040, Italia
Birra e astronomia

Evolution of close binary systems
2016-05-17 11:45 - 12:45 | Aula Gratton
A general outlook of the evolution of close binary stars and of population synthesis as a method of their study will be presented. I will pay special attention to the evolution of low- and intermediate-mass stars (M < (8-10) solar) and to formation of different still hypothetical progenitors of SNe Ia. Next, I will consider evolution of massive binaries with an accent on scenarii of evolution leading to the recently discovered gravitational waves burst GW150914

A closer look at the reionization sources: clustering, line emission and feedback
2016-05-10 11:45 - 12:45 | Aula Gratton
The epoch of reionization marks a major phase transition of the Universe,
during which the intergalactic medium became transparent to UV photons.
Over the last few years, searches have intensified to identify the
population of high redshift galaxies that might be responsible for this
process and to constrain their properties. In this talk I will discuss
recent efforts to address the open problems in our understanding of the
sources of reionization. I will present the results from a deep HST
imaging program providing the first observational match to the theoretical
prediction that reionization fronts are generated within significant
overdensities of faint galaxies. I will show our ongoing analysis of the
HST Frontier Fields survey and the resulting limits on the cut-off
imprinted by photo-ionization feedback on the UV luminosity function at
high redshift. Finally, I will discuss a multi-band study of z~7 galaxies
providing evidence for strong line emission in the optical rest-frame
region and the first constraints on the escape fraction of ionizing
photons from these early galaxies.

The dawn of star formation: a local perspective
2016-05-03 11:45 - 12:45 | Aula Gratton
At the end of the Dark Ages gravity began to make matter
collapse around over-densities, resulting in the formation
of the first stars, the Pop III. These stars are very important in the
cosmological context, the most massive ones contributed ionizing
photons that played a role in the reionization of the Universe
and synthetised the first metals. We know that the formation mode
of these first stars was different than the one operating today.
The lack of metals implies it is difficult to cool a contracting cloud,
which would argue for a preferential formation of massive or very massive
stars. However from the theoretical point of view it is not yet possible
to determine the initial mass function of the first stars. Simulations
show that, even in the absence of metals, a collapsing cloud may fragment
into smaller clouds giving rise to stars that span a range of masses, even
sub-solar. Once the first metals begin to be shed in the clouds cooling
becomes possible, either through atomic lines or through dust. It is likely
that there is a transition from Pop III to “normal” Pop II star formation
at some critical metallicity, however the precise value of this critical
metallicity cannot be presently determined theoretically.
In this seminar I will describe the observational efforts that our group
is conducting in the local Universe, in order to derive as many constraints
as possible on the nature of the Pop III stars. These include searches
of the most metal-poor stars, and their chemical characterization.
Both the metallicity distribution function and the chemical pattern
of the most metal-poor stars contain precious information of the first stars.

Machine learning search for gamma-ray burst afterglows in optical images
2016-04-26 11:45 - 12:45 | Aula Gratton
Thanks to the rapid advances in robotic telescopes and wide field surveys, the time domain astronomy reveals a huge number of transient detections every night. Therefore, automatic classification of sources in the optical images is essential. A special attention is brought to the identification of gamma-ray burst afterglows using the combined observational data from the GROND telescope and the SDSS survey. Their successful identification can lead to further follow-up observations by dedicated telescopes and for statistical studies of these transients.

Escape of Lyman photons from galaxies
2016-04-12 11:45 - 12:45 | Aula Gratton
One of the key questions in observational cosmology is the identification of the sources responsible for cosmic
reionization. The general consensus is that a population of faint low-mass galaxies must be responsible for the
bulk of the ionizing photons. However, until recently, attempts at identifying individual galaxies showing
Lyman continuum (LyC) leakage have only found very few such galaxies, both at high and low redshifts.
We recently proposed a new indirect diagnostic for LyC leakage based on the shape of the Lyman-alpha line,
that I will first review (Verhamme+15).
A breakthrough was recently achieved by our team (Izotov et al. 2016a,b), detecting LyC emission in
low-redshift (z~0.3) luminous compact star-forming galaxies (LCGs) with high LyC escape fractions
using HST/COS observations. I will present these new results, and the Lyman-alpha emission from these galaxies,
confirming our theoretical predictions.
Finally, I will propose another complementary Lyman-alpha signature for LyC leakage, discussing theoretical predictions
on the Lyman-alpha spatial extend of LyC emitters: LyC leakers should have no/faint Lyman-alpha halos.

The final wind: stars in retirement
2016-04-05 11:45 - 12:45 | Aula Gratton
Catastrophic mass loss is at the heart of 90% of all stellar
death. Low and intermediate mass stars lose their hydrogen envelope
while on the Asymptotic Giant Branch stars. At the end, there is
insufficient hydrogen left and the star rapidly evolves into a white
dwarf, briefly illuminating a planetary nebula on the way. The ejected
gas can be used to study the superwind, the nuclear burning and dredge
up processes in the star, and even (with some difficulties) the star
formation histories of the dying stellar population. In this talk I
will discuss the planetary nebulae of the Galactic bulge, briefly
mention AGB stars in globular clusters, and finally discuss the origin
of the mysterious AGB J-type stars, believed to be the cause of the
A+B grains in the proto-solar system.

AGN feedback studies: combining SINFONI and ALMA
2016-03-31 11:45 - 12:45
From a mere ornament in the center of the galaxy, the Super Massive
Black Holes (SMBHs) turned in a potential major actor in shaping the
final stellar mass of its host via the so-called AGN feedback. From
the observations there is mounting evidence that AGN outflows are
ubiquitous, but what is still largely missing are observational proofs
of the impact that such AGN-driven outflows have on their hosts. I
will discuss two complementary approaches to tackle this topic.
The first involve the use of Integral Field Spectroscopy in the
near-infrared to use kinematical maps of the ionized gas, as traced by
the [OIII] line, to constrain the energetics of AGN outflows. Our
group has already obtained several results using SINFONI and it has
now started a more systematical study via a recently approved Large
Programme at VLT. The second approach involve the use of ALMA band-3 observations to
measure molecular gas masses, via the 12CO(2-1) transition line, in a
representative sample of ‘main-sequence’ z~ 1.5 AGNs. We compare the
star-formation efficiency and gas fraction of their hosts with those of inactive
galaxies in the same range of stellar masses, SFR and redshifts.

Substructures in protostellar discs: spirals, gaps and warps
2016-03-29 11:45 - 12:45 | Aula Gratton
The advent of high resolution imaging of protostellar discs, both in the sub-mm (thanks to ALMA) and in the near infrared, has radically changed our understanding of the evolution of such discs and of the planet formation process occuring within them. While in the past disc were modeled as simplified, axi-symmetric structures, often characterized by simple radial power-law for density and temperature, we now need more advanced modeling, able to describe the substructures observed. Such modeling needs to take into account both the gas component, that dominates the dynamics and the line emission, and the dust, which is responsible for the continuum mm band emission. Here, I present several aspects of such modeling. I will discuss the theory and some hydrodynamical simulations describing: (a) spiral density waves, for example induced by gravitational instabilities in young and massive discs; (b) gaps induced by the presence of a forming planet in the disc, with particular emphasis on the spectacular case of HL Tau, that we have recently successfully modeled; (c) warps, which are expected to develop in circumbinary discs, or in discs where a planet has been put on a very inclined orbit.

High ionisation absorption in low mass X-ray binaries
2016-03-22 11:45 - 12:45 | Aula Gratton
The advent of the new generation of X-ray telescopes yielded a significant step forward in our understanding of ionised absorption generated in the accretion discs of X-ray binaries. It appears now clear that these relatively weak and narrow absorption features, sporadically present in the X-ray spectra of some systems, are actually the signature of equatorial outflows, which might carry away more matter than that being accreted. Therefore, they play a major role in the accretion phenomenon. These outflows (or ionised atmospheres) are ubiquitous during the softer states but absent during the power-law dominated, hard states, suggesting a strong link with the state of the inner accretion disc, presence of the radio-jet and the properties of the central source. I will review the current understanding of this field.

Cool, luminous stars to probe chemistry & kinematics in dusty-extincted stellar systems
2016-03-15 11:45 - 12:45 | Aula Gratton
Evolved, cool giants and supergiants are among the brightest stars in any stellar system and are
easily observable out to large distances.
When observed at infrared wavelengths, these cool stars can be also used to probe the stellar content
in environments severely obscured by dust, such as the central regions of galaxies.
Progress in our astrophysical comprehension of the stellar content in such extreme environments
goes together with the technological advance of IR instrumentation.
In this talk I will first present briefly the IR instrument context over the last two decades,
and then I will review some of the most recent results in probing stellar chemistry
and kinematics in the center of the Milky Way and in nearby galaxies.

Extreme adaptive optics at the Large Binocular Telescope
2016-03-01 11:45 - 12:45 | Aula Gratton
After a brief introduction about adaptive optics and the Large Binoculare Telescope, I will present the LBT’s extreme adaptive optic system. I will show its current capabilities, main scientific results and the performance improvement offered by the upcoming upgrade. Finally, I will show how the LBT AO technology impacted the design of the 8m-class and the next generation of ground based telescopes.
