Osservatorio Astronomico di Roma

The MESSIER surveyor: lifting the veil on the ultra low surface brightness universe
2018-10-09 11:45 - 12:45 (Europe/Rome) | Aula Gratton
The MESSIER satellite has been designed to explore the extremely low surface brightness universe at UV and optical wavelengths. The two driving science cases target the mildly- and highly non-linear regimes of structure formation to test two key predictions of the LCDM scenario: (1) the detection of the putative large number of galaxy satellites, and (2) the identification of the filaments of the cosmic web. The science requirements imply challenging instrumentation issues which have only recently been solved. The satellite will drift scan the entire sky in 6 bands covering the 200-1000 nm wavelength range to reach the unprecedented surface brightness levels of 34 mag/arcsec^2 in the optical and 37 mag/arcsec^2 in the UV. As usual when uncovering new volumes in parameter space, many important secondary science cases will also result as free by-products and will be discussed in some detail: the actual luminosity function of galaxies, the contribution and role of intracluster light, the fluctuations of the cosmological background radiation at UV and optical wavelengths, the warm molecular hydrogen content of galaxies at z=0.25, time-domain studies of supernovae and tidal disruption events, the chemical enrichment of the interstellar medium through mass loss of red giant stars and the accurate measure of the BAO scale at z=0.7 with over 30 million galaxies detected in Lyman-alpha at this redshift. It will provide the first space-based reference UV-optical photometric catalogue of the entire sky, and synergies with GAIA, EUCLID and WFIRST will also be discussed.

Four years of science with SPHERE/VLT
2018-10-02 11:45 - 12:45 | Aula Gratton
SPHERE/VLT is an extreme adaptive optics instrument designed to directly image exoplanets. It was designed and build by a European consortium (including laboratories from France, Italy, Germany, Switzerland and the Netherlands) from and saw its first light in 2014. Most of the guaranteed time observations (GTO) are related to exoplanets and young disk. I will briefly present some results from these programs. I will then focus on the “Other Science” part of the GTO, aiming at showing that SPHERE is a versatile instrument able to answer key question in a variety of topics. I will present the results obtained via this program, ranging from 3D mapping of asteroids to star clusters via jets from young stars and evolved stars, including the first direct image of the surface of stars.

SHARK-VIS: the upcoming high-resolution high-contrast visible imager for LBT
2018-09-18 11:45 - 12:45 | Aula Gratton
SHARK-VIS is the visual channel (400-1000 nm) of SHARK, the upcoming extreme-AO instrument for the LBT optimized for high-contrast observations. The project is led by the OAR AO group and the instrument is currently being built at OAR with the first light foreseen in 2019.
SHARK-VIS will provide LBT with unprecedented high-contrast and high-resolution imaging capabilities in the visible band, thanks to both several technical solutions, aimed at optimizing the PSF stability, and its “fast cadence imaging” approach, based on the use of a high-frame-rate low-noise camera exploited by specific custom algorithms. The instrument will produce diffraction-limit images with an angular resolution down to 15 mas and with frame rates up to 1kHz.
In the first part of the talk, instrument details, expected performances, and the project status will be discussed.
In the second part of the presentation, we will present a summary of the main scientific cases for which SHARK-VIS is expected to provide breakthrough results, also considering the simultaneous use of the SHARK-NIR companion instrument (built at OAPd) and LMIRCAM, which will turn LBT into a unique high-resolution facility with continuous wavelength coverage from 0.4 to 3.5 um. Main science cases include identification of accreting planets in star-forming regions, morphology of jets and disks in young stars, characterization of minor bodies of the Solar system, and investigation of the central regions of bright AGNs.

The planet formation seen through high-resolution images of protoplanetary disks
2018-09-11 11:45 - 12:45 | Aula Gratton
The high occurrence of exoplanets around solar-type stars suggests that planets form very efficiently in protoplanetary disks. Yet, numerical simulations and laboratory experiments show that the planet formation is a complicated process. The onset of optical/NIR and (sub-)mm surveys of young stars has been a game changer for our understanding of protoplanetary disks and planet formation. Thanks to the contributed effort of VLT/SPHERE, GPI, and ALMA we could resolve with unprecedented resolution several sub-structures at the disk surface and midplane from few to hundreds of au from the star. I show the method and the recent improvement of this type of observations and discuss the implications to the recurrent existence of these disk features.

CTA: Scientific perspective and current status
2018-09-04 11:45 - 12:45 | Aula Gratton
The Cherenkov Telescope Array (CTA) is the major ground-based gamma-ray observatory planned for the next
decade and beyond. Consisting of two large atmospheric Cherenkov telescope arrays (one in the southern
hemisphere and one in the northern hemisphere), CTA will have superior energy and angular resolutions, a much
wider energy range, and up to an order of magnitude improvement in sensitivity, as compared to existing
instruments. The CTA science program will be rich and diverse, covering the major aspects of cosmic particle
acceleration, understanding extreme astrophysical environments, and probing physics frontiers beyond the
Standard Model. This talk will outline the scientific persective for CTA and will cover the most recent status of the project.

seminar by Cristina Raimos Almeida
2018-06-12 11:45 - 12:45 | Aula Gratton

Zooming into Dark Matter and primordial Star Formation with massive Lensing Clusters
2018-05-15 11:45 - 12:45 | Aula Gratton

seminar by Antonio Frasca
2018-05-08 11:45 - 12:45 | Aula Gratton

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

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

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.

Bright and dustiest stars in the JWST era: powerful tools to constrain the recent star formation history
2018-03-27 11:45 - 12:45, 2018-02-27 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.

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.

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.
