Rossby number calculations for fully convective stars
2018-01-16 11:45 - 12:45 (Europe/Rome) | Aula Gratton
The Rossby number is a quantity that gauges the relative importance of
rotation in astrophysical flows. In particular, it plays a significant role
in mean-field, alpha-Omega dynamo models as it is directly related to the
“dynamo number” which, in turn, measures the efficiency of the magnetic field
generation. From an observational standpoint, the Rossby number has been
widely used to correlate either coronal or chromospheric magnetic activity of
low-mass stars with their rotation. A fundamental problem with this
rotation-activity relationship is the determination of the convective turnover
time tau_c, on which the Rossby number depends, and that can be obtained
from some empirical relations or from stellar models. The ATON stellar
evolution code has been used in the near past to calculate Rossby numbers
for solar-type stars and now, in view of the recent discovery of fully
convective stars in the non-saturated region of the rotation-activity
relationship, is being used to extend those calculations to very low mass
stars.

Deep, multi-band photometry of low-mass stars to reveal young clusters: a blind study of the NGC 2264 region
2018-01-23 11:45 - 12:45 | Aula Gratton
The LSST survey will provide multi-epoch, multi-wavelength (u,g,r,i,z,y) mapping of the Southern Hemisphere, with a single-visit depth of r~24.5 and a gain of three magnitudes by the end of the program. This unprecedented spatial coverage will enable detection of young, pre-main sequence stars and stellar clusters down to distances of 5-10 kpc. A crucial and challenging step for spatial analyses of large stellar populations is measuring the extinction Av of individual objects. Multi-color photometry on a (r-i, g-r) or (i-J, r-i) diagram offers a direct solution to this issue for M-type stars: indeed, while the color locus of early-type (< K7) stars on these diagrams is parallel to the reddening vector, the color locus traced by M-type stars is tilted with respect to the reddening vector, which enables a straightforward and empirical measurement of their Av. By investigating the correlation between extinction and spatial properties of M-type stars in a given field, it is therefore possible to reconstruct the structure of the region and probe the nature of its population. In this study, we test the method on the NGC 2264 field. We selected a 2°x2° area centered on the NGC 2264 cluster, and collected the available r,i,J photometry from existing large-scale surveys (notably Pan-STARRS and UKIDSS). Then, assuming no prior knowledge on the nature of stars in the field, we used the (i-J, r-i) diagram to identify and deredden M-type stars in the sample, and the (r-i, r) + (RA, Dec) diagrams to investigate the nature and spatial distribution of stars as a function of their Av. We derived a non-uniform distribution of Av across the region, and could distinguish between a diffuse field population and a clustered stellar population toward the center of the field. An a posteriori comparison between the inferred spatial density map of the clustered population and the literature census of the NGC 2264 cluster enabled us to assess the performance of the method and its predictive capability.

Modern core-collapse supernova nucleosynthesis
2018-01-25 11:45 - 12:45 | Aula Gratton
Massive stars and their core-collapse supernovae are key contributors to the evolution and chemical enrichment of galaxies. Despite over 50 years of research, the explosion mechanism of core-collapse supernovae is still not fully understood, which hinders nucleosynthesis predictions. In a previous, proof-of-principle study, we have established a modern method to induced explosions in spherically symmetric (otherwise non-exploding) simulations to calculate the nucleosynthesis. This method (PUSH method) includes two aspects that are crucial for nucleosynthesis: One, the mass cut is emerging from the simulation, consistently with the explosion energy. And two, neutrino-interactions with matter are included. In this talk, I will discuss the nucleosynthesis predictions from our PUSH models and put the results in the context of other nucleosynthesis predictions

The wee free magnetic elements on the photosphere: a turbulent story
2018-01-30 08:00 - 17:00 | Aula Gratton
The study of the dynamics of the photosphere allow us to investigate the physical processes occurring in both the interior of the Sun and in the higher layers of the solar atmosphere due the magnetic coupling between the photosphere and the corona. This field concerns many basic stellar processes such as: global dynamo, turbulent convection and super-hot corona.
In this talk, we report on the recent results on the transport of small scale magnetic field by advection/diffusion as seen on different data-sets from ground-based and space telescopes. We compare those results with simplified advective models that mimic the motion scales observed on the solar surface.
We will digress on how the advection of the smallest magnetic elements on the solar surface affects the toroidal-to-poloidal conversion in the solar cycle, on how it can be used to estimate the possible nano-flare contribution to the coronal heating and on its consequences on transiting exo-planet detection.

A Panchromatic View of High-Redshift Quasar Host Galaxies
2018-02-06 11:45 - 12:45 | Aula Gratton
While it is now widely accepted that the growth of supermassive black-holes in galaxies is fundamentally linked to the process of galaxy formation, the host galaxies of the most luminous and massive accreting black-holes or quasars are still poorly understood. Quasars out-shine their host galaxies at most wavelengths making these studies difficult, and the space-density of luminous quasars is also such that very wide-field surveys are required to be able to assemble statistical samples. I will present new observations of the host galaxies of a population of heavily reddened, luminous quasars at redshifts of 2-3. Exploiting wide-field optical surveys together with the dust obscuration towards the quasar line-of-sight, we are, for the first time, able to probe the rest-frame UV emission from the star-forming hosts of these high-luminosity quasars. Observations of the quasar host galaxies at sub-millimetre and millimetre wavelengths with SCUBA2, ALMA and the VLA are also revealing complex gas morphologies, diverse interstellar medium properties and evidence for significant over-densities and major-mergers.

Electromagnetic Counterparts of Gravitational Waves
2018-02-13 11:45 - 12:45 | Aula Gratton
Compact binary systems composed by neutron stars (NS) and black holes (BH) are one of the principal sources of gravitational waves (GW) in the terrestrial interferometers frequency range (10 Hz -1 kHz). While BH binary coalescences are not expected in general to be accompanied by any electromagnetic signal, detectable electromagnetic counterparts, such as Short Gamma-Ray Bursts (SGRB) and Kilonovae, could follow binary NS and NS-BH mergers.
The recent join GW and electromagnetic observation of a binary NS coalescence (GW170817) marked the down of multimessenger astronomy era that open a new way to explore the high energetic universe and test the fundamental physics under extreme conditions.
The coincident detection of gravitational and electromagnetic radiation is important because these messengers carry different and complementary informations: while from a GW detection it is possible to infer the masses and the spins of the binary progenitors, electromagnetic emission is essential to localize the source, thus enabling the host galaxy identification.
In this talk I will show how a joint detection of SGRB and GW from a NS-BH progenitor could be used to measure the neutron star radius and thus constrain the dense matter equation of state.
I will also provide a brief description of isotropic electromagnetic counterpart of compact binary coalescence such as Kilonova and Spindown powered transients.

Lyα-Lyman Continuum connection in 3.5 ≤ z ≤ 4.3 star-forming galaxies from the VUDS survey
2018-02-20 11:45 - 12:45 | Aula Gratton
Understanding the processes that led to the reionization of the Universe is among the most challenging tasks of modern extra-galactic astronomy. The main responsible for this phenomenon are thought to be high redshift star-forming galaxies. However, it is very difficult to constrain their contribution and only few detections of Lyman Continuum (LyC) emitters have been reported so far. Following theoretical models, several so-called indirect indicators of LyC radiation have been proposed, such as a strong Lyα emission, a large OIII/OII ratio, the compactness of the UV continuum and others. Using these pre-selection criteria has indeed proved to be a powerful method to identify LyC leakers at low redshift but there is a lack of consistent studies that relates these indicators to the LyC emission at high redshifts.
We have used ultra-deep spectra from the Vimos Ultra Deep Survey (VUDS) to investigate the LyC properties of z~4 star-forming galaxies. We initially investigated the LyC emission from a stack of ~33 sources free from foreground contamination, selected after a very careful cleaning procedure based on the inspection of multi-wavelength high resolution HST imaging. We found for this sample a mean fesc,rel=0.09±0.04 with no individual detections. We also observed a tentative correlation between the individual limits given in the LyC flux and the EW of the Lyα emission line. To better investigate this trend and other expected correlations with LyC properties of high redshift galaxies, we then analysed a much larger sample of more than 200 objects also from the VUDS survey. We found evidence that LyC is strongly related to a large Lyα EW and to the UV compactness, in agreement with theoretical expectations and observational studies at low redshift. In addition we found that galaxies with a small Lyα spatial extent have higher LyC flux compared to the rest of the population: such a correlation had never been analysed before and seems even stronger than the correlation with high Lyα EW and small UV effective radius.

Assemblea del Personale.
2018-02-27 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia
RICERCATORI, TECNICI, AMMINISTRATIVI, PRECARI e STRUTTURATI DELL’ INAF – OAR

ASSEMBLEA DEL PERSONALE
Martedì 27 febbraio ore 10:00
INAF– Monte Porzio
Per discutere di:
1) Stabilizzazioni e Piano Fabbisogno Personale INAF 2018/2020;
2) Contrattazione integrativa;
3) Nuovo contratto Istruzione e Ricerca;
4)Elezioni RSU;

Saranno presenti all’ iniziativa :
Stefano Bernabei – Coordinatore nazionale C.d.E. INAF FLC-CGIL
Carlo Buttarelli – Coordinatore territoriale FLC – CGIL

Bright and dustiest stars in the JWST era: powerful tools to constrain the recent star formation history
2018-02-27 11:45 - 12:45, 2018-03-27 11:45 - 12:45 | Aula Gratton
With the advent of the JWST, the horizon of our knowledgies will be amazingly enlarged, providing an unprecedent look of a large volume of galaxies with a broad properties range. This will be possible in the IR domain where the extinction is low and bright cool evolved stars have their emission peak. This is the case of asymptotic giant branch stars (AGB), luminous objects and main dust producers for the galaxy. We present how the large release of AGB+dust evolutionary models developed in the last years, will enable a detailed study of these sources in different systems. The distribution of these objects in the IR colour-magnitude diagrams is a powerful instrument to determine the recent star formation history of the galaxy in detail.

An experiment in Astrobiology: exploring the climate parameter space of rocky planets
2018-03-06 11:45 - 12:45 | Aula Gratton
Astrobiology is a relatively new and fast-growing science, whose main
characteristic is to need expertises from different science fields.
I’ll show how the climate of a planet influences its abitability.
Astronomers from OATs, climatologists from CNR and experts in
databases from OATs joined their efforts to build a fast, simplified,
yet effective climate model and database for extra-solar planets. I
will describe
the model, its main feature, its validation, its application to a
specific exo-planet (Kepler 452b). I will then show how such a model
can be used to explore a huge parameter space and build a database
that can be used to characterize classes of habitable planets. I will
point out how this particular case is an good example of
High-Throughput Computing (HTC). Our database can also be used, e.g.,
as a tool to get a first estimate of the habitability of a newly
discovered rocky planet.
Then I will describe possible future developements of such a research
line, including the study of the effect of the biosphere itself on the
habitability.

Drag and drift - decoupling of the dust and gas phases in astrophysical flows
2018-03-14 11:45 - 12:45
Simulating the dynamics of gas and dust in various astrophysical contexts is a topic of intense research. It includes simulations of the turbulent interstellar medium (ISM), active galactic nuclei (AGN), proto-planetary discs, and dusty stellar winds. I will focus on the ISM and dust-driven stellar winds, however, and only briefly mention a few other examples.
Using high-resolution (1024^3) simulations of homogeneous isothermal hydrodynamic turbulence, including a multi-disperse population of 10^7 dust grains imbedded in the gas, one may assess the efficiency of condensation, destruction and coagulation in molecular clouds. Due to hydrodynamic drag, large grains will decouple from a turbulent gas flow, while small grains will tend to follow the motions of the gas. Dust grains of various sizes will also cluster and increase the rate of grain-grain interaction. This may in turn lead to turbulence-driven coagulation and fragmentation.
In a stellar-wind context the decoupling between gas and dust is often called “drift”, which is referring to the fact that the two phases may develop different mean-flow velocities. In a spherically-symmetric setting, a mean-flow model of drift is fairly simple. But there are significant 3D effects, as well as instabilities, which we must take into account. For instance, dust grains of various sizes will cluster and increase the rate of grain-grain interaction. Moreover, due to spatial separation of dust and gas, condensation is likely less effective than in a velocity-coupled case. There are several implications for dust-driven stellar winds which arise from this. One is that the momentum-transfer efficiency (from dust to gas) of large grains may be low as they cluster where the gas is not; another is that the sublimation rate increases as grains are more exposed to the radiation field.

The science of HERMES: a constellation of nano-satellites for high energy astrophysics and fundamental physics
2018-04-10 11:45 - 12:45 | Aula Gratton
A distributed instrument, such that consisting of nano-satellites carrying simple X-ray detectors, can provide accurate (arcmin to arcsec) and prompt (within minutes) localisation of high energy transients, such as gamma ray bursts and the electromagnetic counterparts of gravitational wave events. In addition, once the position of the transient is computed, the signals registered by the different detectors can be realigned in time and added together to improve the statistics. This can allow the investigation of the temporal structure of transients down to a fraction of microsecond, providing crucial information on one hand on the physics of the transient inner engine, and, on the other hand, on the granular structure of space-time, through the study of light-travel effects.
The advantages of a distributed instrument based on nano-satellites are: a) modularity, which allows redundancies with the associated lower risks; b) the possibility to expand (and/or improve) the experiment with the time; c) low cost and quick development.

seminar by Filippo Ambrosino
2018-04-17 11:45 - 12:45 | Aula Gratton

seminar by Ambra Nanni
2018-04-24 11:45 - 12:45 | Aula Gratton
