Osservatorio Astronomico di Roma

Unravelling the Andromeda Galaxy's most important merger
2019-06-25 11:45 - 12:45 (Europe/Rome)
The Andromeda Galaxy (M31), our nearest large galactic neighbour, offers a unique opportunity to test how mergers affect galaxy properties. M31’s stellar halo caused by the tidal disruption of satellite galaxies is the best tracer of the galaxy’s accretion history. Despite a decade of effort in mapping out M31’s large stellar halo, we are unable to convert M31’s stellar halo into a merger history. Here we use cosmological models of galaxy formation to show that M31’s massive and metal-rich stellar halo containing intermediate age stars implies that it merged with a large (M* ~ 2.5 x 10^10 M_sun) galaxy ~2 Gyr ago. The simulated properties of the merger debris help to interpret a broader set of observations of M31’s stellar halo and satellites than previously considered: its compact and metal-rich satellite M32 is the tidally-stripped core of the disrupted galaxy, M31’s rotating and flattened inner stellar halo contains most of the merger
debris, and the giant stellar stream is likely to have been thrown out during the merger. This accreted galaxy was the third largest member of the Local Group. This merger may explain the global burst of star formation ~2 Gyr ago in the disk of M31 in which ~1/5 of its stars were formed. Moreover, M31’s disk and bulge were already in place before its most important merger, suggesting that mergers of this magnitude do not dramatically affect galaxy structure.

Absorption and accretion properties of local Active Galactic Nuclei
2019-09-16 11:45 - 12:45 | Aula Gratton
Active Galactic Nuclei (AGN) are powered by accretion onto supermassive black holes and, besides being among the most luminous sources of radiation in the Universe, are also widely believed to play an important role in the evolution of their host galaxies.
X-ray emission is an ubiquitous property of AGN and, being produced within a few gravitational radii from the supermassive black hole, can provide fundamental information about the structure and geometry of the circumnuclear material, as well as on the characteristics of the accretion flow. In my talk I will present recent studies of the obscuration and accretion properties of local AGN in the X-ray band, focussing on the results obtained from the Swift/BAT AGN Spectroscopic Survey.

Lars Mattsson - colloquium
2019-09-24 14:30 - 15:30 | Aula Gratton

Modeling stellar winds on the asymptotic giant branch accurately
2019-09-26 11:45 - 12:45 | Aula Gratton
I present the latest progress on our ongoing work with our state-of-the-art
models of stellar winds of asymptotic giant branch stars. I will both depict
features and assumptions of our model code T-800 and show some of the results
that set our work apart; because, results are in several a case drastically
different from earlier results. In particular, I focus on effects of
gas-to-dust drift and higher-than-before spatial resolution.

colloquium - Chris Sneden
2019-10-01 11:45 - 12:45 | Aula Gratton

Early galaxy formation and its large-scale effects
2019-10-03 11:45 - 12:45 | Aula Gratton
Galaxy formation in the first billion years mark a time of great upheaval in the history of the Universe: as the first sources of light, these galaxies ended the ‘cosmic dark ages’ and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of cosmic reionization. As the earliest building blocks, the galaxies that formed in the first billion years also determine the physical properties of all subsequent galaxy populations. I will start by introducing the reionization process and detail the reasons foe which the history and topology of reionization remain debated. I will then show how cross-correlations of 21cm data with the underlying galaxy population, in the forthcoming era of 21cm cosmology, will yield tantalising constraints on the average intergalactic medium ionization state as well as the reionization toplogy (outside-in versus inside-out). Time permitting, I will try to give a flavour of how the assembly of early galaxies, accessible with the forthcoming James Webb Space Telescope, can provide a powerful testbed for Dark Matter models beyond “Cold Dark Matter”.

Dynamic relations in sampled processes
2019-10-10 11:45 - 12:45 | Aula Gratton
I will start my talk by a short description of a historical connection between my university, Shanghai Jiao Tong University (SJTU), and Collegio Romano. There is an interesting chain from Clavius, who led the Gregorian calendar reform, via Matteo Ricci and Xu Guangqi, the first modern scientist of China, to the founding of the two elite universities on Shanghai, Fudan and SJTU. The technical part of my talk is based on joint work with Tryphon Georgiou. Linear dynamical relations that may exist in continuous-time, or at some natural sampling rate, are not directly discernable at reduced observational sampling rates. Indeed, at reduced rates, matrix-valued spectral densities of vector-valued time series have maximal rank and thereby cannot be used to ascertain potential dynamic relations between their entries. This hitherto undeclared source of inaccuracies appears to plague off-the-shelf identification techniques seeking remedy in hypothetical observational noise. In this paper we explain the exact relation between stochastic models at different sampling rates and show how to construct stochastic models at the finest time scale that data allows. We then point out that the correct number of dynamical dependences can only be ascertained by considering stochastic models at this finest time scale, which in general is faster than the observational sampling rate.

Horizontal Branch morphologies in the age of multi-band photometry
2019-10-15 11:45 - 13:45
The Horizontal Branch (HB) stars have always played a crucial role in the study of the galactic globular clusters (GC). They are the direct offspring of the low mass, Red Giant Branch (RGB) stars and the final product of the helium flash taking place at the Tip of the RGB. The colour and the luminosity of a HB star are tied to its mass which, in turn, is tied to the mass of the star undergoing the flash. The sensitivity of this value to the chemistry of the cluster allows for a large variety of HB morphologies which is one of the culprits that led to the discovery of the multiple populations phenomenon. A leap forward in our understanding of GCs has been made when recent works, based on a large collection of HST data, measured, albeit indirectly, the helium abundance in a large collection of GCs, allowing the characterization of these old stellar populations in unprecedented ways. In spite of this richness of information, however, we still lack the key to fully understand the populations hosted along the HB, especially due to the complex interplay between the parameters regulating their evolution. In this talk, I will provide a review of the current state of the HB study and discuss how the synergy with the recent advancements in the field of multi-band photometry can provide solutions to some new and decades-old problems.

Linear spectropolarimetry in stars different than the Sun: what can we learn?
2019-10-22 11:45 - 12:45 | Aula Gratton
Polarimetry is considered as an important searching tool in Astronomy and it deserves to be a standard observational technique for a variety of astrophysical contexts: from stellar photospheric inhomogeneities to protoplanetary nebulae, as well as in the exoplanet research field. Despite this, however, the difficulties involved in the measurements and in the theoretical interpretation made this technique not as widespread as it deserves. In this talk I will review the results of my research about the diagnostic potential of optical high resolution linear spectropolarimetry in stars different than the Sun. At this purpose, after an introduction on the observational technique, I will focus on the polarised spectrum of the post-AGB binary system 89 Herculis: from the very inner regions of the stellar envelope to the first observational evidence of a micro-Gauss level magnetic field. Finally, I will discuss on the applicability and future prospect of this technique in the more general context of stellar physics.

Post-AGB stars as tracers of the origin of elements in the Universe
2019-10-29 11:45 - 12:45 | Aula Gratton
The chemical evolution of galaxies is governed by the chemical yields from stars, especially from Asymptotic Giant Branch (AGB) stars. This underlines the importance of understanding how AGB stars produce their elements by obtaining accurate stellar nucleosynthetic yields. Although AGB nucleosynthesis has general validity, critical uncertainties (such as the treatment of convective-driven mixing processes and mass loss) exist in current stellar models. Observations from Post-Asymptotic Giant Branch (post-AGB) stars serve as excellent tools to confront predictions from a dedicated suite of stellar models, quantify the strongest discrepancies, and eliminate crucial uncertainties that hamper stellar modelling. Our recent studies of post-AGB stars have shown an intriguing chemical diversity that ranges from stars that are extremely enriched in carbon and s-process elements to the discovery of the first post-AGB star with no traces of carbon nor s-process elements. Additionally, our studies have also shown that AGB nucleosynthesis is significantly affected by a binary companion. These results reflect the complexity that surrounds the element production in AGB stars. In this talk, I will present the intriguing chemical diversity observed in post-AGB stars and its implications on element/isotope production in AGB stars and stellar nucleosynthetic yields.

The impact of AGB stars on the life of stellar systems
2019-11-05 11:45 - 12:45 | Aula Gratton
During the latest phases of their lives, low-intermediate mass stars (M<8Msun) evolve through the Asymptotic Giant branch (AGB) phase. Although very rapid, the AGB phase represents a crucial step for the chemical evolution of the system where these stars form. The reason is that AGB stars undergo an advanced nucleosynthesis and experiment dredge-up events, while they progressively lose the majority of their mass through stellar winds. Furthermore, the low temperature and high densisty of their stellar winds prove extremely favourable conditions for dust condensation in the circumstellar envelopes. All the reprocessed gas and dust lost by the AGB stars enrich the insterstellar medium of the host system. Detailed modelling of these complex physical processes are essential to reconstruct the impact that these stars had on the history of formation and chemical evolution of stellar clusters and galaxies. In this talk I will present how the latest generation of AGB+dust evolutionary models has been recently used to this scope in different environments: from globular clusters, to unveil the origine of multiple populations, to Local Group dwarf galaxies, to infer star formation history and dust production rate.

The ultraluminous X-ray pulsar NGC 5907 ULX-1 and its nebula
2019-11-08 11:45 - 12:45 | Aula Gratton
Ultraluminous X-ray pulsars are accretion-powered pulsars whose X-ray
luminosity, if isotropic, largely exceeds their Eddington limit. Only a handful
are known to date and NGC 5907 ULX-1, distant 17 Mpc from us, is the most luminous of them,
at 1e41 erg/s 500 times its Eddington limit. We constrained through
pulsar timing its orbit and spin behavior, estimating a 5d orbital period and a spin-up
time <40 yr. We detected an extended X-ray feature surrounding the source: likely a young and
powerful bubble driven by the wind from the accreting pulsar system. The nebula
has been powered at ~1e41 erg/s for ~70 kyr proving that a highly super-Eddington
regime can be sustained for much longer than the spin-up time of the pulsar.
I will present the current status of the observations and understanding of this system
and the prospects to solve the still open problems it raises.

Lithium in the local Volume
2019-11-14 11:45 - 12:45 | Aula Gratton
We present our recent study on the chemical evolution of lithium in the thin disc of the Milky Way.
We found that the best agreement with the observed Li abundances in the thin disc is obtained
considering novae as the main source of lithium. We assumed a delay time of ≈1 Gyr for nova
production and an effective 7Li yield of 1.8(± 0.6)×10−5 Msun over the whole nova lifetime.
The possibility to check our detailed assumptions on lithium production on other stellar systems, such
as the satellites of our Milky Way, is seriously hampered by their distance from us. In these systems
dwarf stars (where the original lithium can be measured) are too faint to detect lithium lines.
However, thanks to the Gaia mission, it was recently possible to disentangle the stars of a disrupted
dwarf galaxy in the Galactic halo (called Enceladus or Galactic sausage). Adopting a chemical evolution
model able to match the chemical enrichment in alpha elements and the metallicity distribution function
of Enceladus, we present our prediction for the lithium abundance of the stars of this disrupted galaxy.

Dal Sole a Sedna: una passeggiata per il sistema solare, e uno sguardo più in là
2019-11-15 16:00 - 17:00 | Aula Gratton
Dal 1959 ad oggi più di cento sonde spaziali hanno lasciato la Terra verso la Luna e lo spazio profondo. Queste appendici robotica dei nostri sensi hanno visitato tutti i pianeti e i principali satelliti del sistema solare, rivelando una straordinaria e inattesa varietà di forme e fenomeni. Ripercorrere vent’anni di scoperte sarà un tributo all’ingegno di quanti le hanno rese possibili. Grazie alle immagini più belle raccolte negli ultimi anni, la conferenza ripercorrerà le scoperte più significative nell’esplorazione del sistema solare, gettando infine uno sguardo ai pianeti delle stelle vicine. Forse tra questi ne esiste qualcuno che ospita la vita? Come trovarlo?

Lithium in the Universe: to Be or not to Be
2019-11-18 09:00 - 2019-11-22 18:00 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia

workshop Stamerra
2019-11-25 08:00 - 2019-11-28 17:00 | Aula Gratton

LSST: an opportunity for the Italian Community
2019-11-26 11:45 - 12:45 | Aula Gratton
We review the current status of the LSST project, its expected performances, the key science goals and the involvment of the Italian Community

Acoustic oscillations and dynamo action in giants
2019-12-03 11:45 - 12:45 | Aula Gratton
The role of the magnetic field in determining the angular momentum transport in stellar interior is still an open issue. Acoustic oscillations are directly affected by the presence of a large-scale magnetic field but their study can provide fundamental information on the properties of the magnetic fields in solar-like stars. As an example the case of EK Eridani, a slowly rotating, overactive G8 giant, will be presented. Moreover the possibility to use asteroseismology to solve the long-lasting mystery on the origin of magnetic fields in Ap stars will be discussed.

Characterizing multi-phase gas outflows and their powering mechanism in nearby AGN
2019-12-10 11:45 - 12:45 | Aula Gratton
Active Galactic Nuclei are thought to play a crucial role in
the evolution of massive galaxies. In particular, fast outflows are
frequently observed in AGN covering various gas phases which may remove
a significant fraction of the gas content from the galaxies. I will
review the current state of research in this very active field of
ongoing research together with the advantages and disadvantages of
previous approaches. In particular, I will highlight the importance of
multi-wavelength observations to unravel the true multi-phase nature of
outflows by combining state-of-the-art observational facilities. In this
context I will present the first results from the ongoing Close AGN
Reference Survey (CARS), a multi-wavelength survey of 39 luminous
low-redshift unobscured AGN with extensive observations from VLT/MUSE,
ALMA, VLA, Chandra, SOFIA and many more. In addition, I will present the
multi-phase view of the famous ultra-luminous Quasar 3C273 where we
unlocked a few unknown secrets.

Gamma-ray bursts under a new light: the TeV emission from GRB190114C seen by the MAGIC telescopes
2019-12-18 11:45 - 12:45 | Aula Gratton
Gamma-ray bursts (GRBs) are the most luminous sources of electromagnetic radiation known in the Universe. GRBs had been observed over a broad energy range from the radio band up to GeV gamma rays, but the TeV gamma-ray band had remained terra incognita for a long time. Thanks to the MAGIC telescopes, designed to catch the fast glimpses of the GRBs, the first ever clear detection in this band was achieved for GRB 190114C, a bright, long GRB. The TeV emission from GRB190114C belongs to a new energetic component, providing an energy output comparable at the one at lower energies. We will discuss the details of the observations by MAGIC and the accompanying multi-frequency measurements by more than 20 instruments, from radio to gamma- rays, and the inferences on the emission mechanisms. This historical, highly significant detection has followed an intriguing hint of TeV emission from GRB 160821B, a short GRB with an associated kilonova. This hint, if real, has potential multi-messenger implications on the detectability of gravitational wave alerts in high-energy gamma-rays.

The two-families scenario: what does it predict?
2020-01-14 11:45 - 12:45 | Aula Gratton
I will revisit the two-families scenario in which neutron stars coexist with strange quark stars, i.e. with compact objects made almost
entirely of deconfined quarks. I will outline the differences between this scenario and other schemes in which quark matter appears only at the center of compact stars and I will discuss how it compares with GW170817, GRB170817A, AT2017gfo and with the existing limits on masses and radii of compact stars.

colloquium - Matteo Bachetti
2020-01-21 11:45 - 12:45 | Aula Gratton

3D magnetic structure, and brightening in sunspot penumbra
2020-01-28 11:45 - 12:45 | Aula Gratton
We analyzed spectropolarimetric data in the Fe I 617.3 nm and Ca II 854.2 nm lines of the sunspot in AR 12546 observed with the IBIS at the Dunn Solar Telescope on 20th May 2016 and co-temporal filtergrams by space-borne (Hinode, IRIS and SDO) instruments. The observed sunspot is one among the largest such features occurred over the last solar cycle. The IBIS data, taken under excellent seeing conditions that lasted more than three hours, were inverted with the NICOLE code, in order to retrieve the temperature, magnetic field, and plasma velocity of the studied sunspot as a function of optical depth and time. The umbral and penumbral regions are for the most part stable in the photosphere, while co-spatial chromospheric areas show waves in the umbra-penumbra boundary and intense brightening along penumbral filaments. We explored the origin of these chromospheric processes and their relation to changes in the 3D magnetic structure of the observed sunspot.

The X-ray universe at microarsec resolution: the power and promise of X-ray interferometry
2020-02-04 11:45 - 12:45 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia
The spectacular image of a supermassive black hole `shadow’ taken by the Event Horizon Telescope last year highlights the potential of being able to resolve microarcsecond scale structures in astrophysical sources. Given the ~Angstrom scale of X-ray wavelengths, similar resolutions are theoretically possible with only a 1 m diameter telescope, which could be accommodated on a single spacecraft. Conventional X-ray imaging capability remains far from from this goal however.
In this talk I will explore the possibility, recently proposed to ESA’s Voyage 2050 program, of developing X-ray interferometry to break the resolution barrier in the X-rays, starting from X-ray fringes which have already been observed in the lab and examining what would be required for an X-ray interferometric space observatory, from the possibilities with single spacecraft to formation flyers which could push to sub-microarcsecond resolution. Such revolutionary observatories would enable detailed imaging-spectroscopy of stellar coronae and transiting exoplanets within ~100 pc, direct observation of X-ray binary orbits, supermassive black hole accretion flows and event horizons, and imaging of luminous transients and binary supermassive black holes across the observable universe.

The quest for observational evidence of the hierarchical formation process at the smallest galaxy scales
2020-02-11 11:45 - 12:45 | Aula Gratton
I will present our ongoing project devoted to the search and study of satellites, stellar streams, and substructures around dwarf galaxies. Deep, wide field imaging acquired with the Large Binocular Telescope and follow-up observations performed with the WFC3 on the Hubble Space Telescope provide evidence of multiple satellites associated with the very metal-poor star-forming dwarf galaxy DDO 68. This is a striking example of the few observed cases of hierarchical merging in action at the dwarf galaxy scales. To perform a systematic search of substructures around dwarf galaxies, we have started a Strategic Program at the LBT, named SSH (i.e. The Smallest Scales of Hierarchy Survey) to acquire deep, wide-field imaging of a sample of 45 late-type dwarf galaxies located within 10 Mpc. The survey, which is now close to completion, will provide one of the first systematic observational studies of the hierarchical formation process down to very small galaxy scales. In this talk I will introduce SSH and discuss the results obtained so far.

The interstellar medium at high redshift
2020-02-18 11:45 - 12:45 | Aula Gratton
The gaseous content of galaxies is one of the key ingredients of galaxy evolution: It fuels star formation and nuclear activity, and at the same time it is the main receiver of any feedback mechanism from these two processes. However, we have only very limited knowledge of the gas content and of its physical properties in galaxies beyond the local universe. As a result, no description of galaxy formation can be fully validated without a better understanding of 1) how much gas was available for star formation in different cosmic times; 2) how the star formation efficiency, i.e., the capability of a galaxy to form stars from a given amount of gas, evolve through cosmic history, and which are physical conditions that governed this evolution; 3) what was the interplay between the interstellar medium, star formation, and nuclear activity. These questions are particularly critical at the very high redshifts (z>6, when the universe was <1 Gyr old), where our census of galaxies is highly incomplete, especially at the high-mass end, and galaxies followed very different evolution according to the mass of their initial gas reservoir. In this talk I will present the results of various observational campaigns aimed at addressing these questions, in particular by capitalizing on the unprecedented capabilities offered by the Atacama Large Millimeter Array and the Northern Extended Millimeter Array. These findings will guide the next generation of simulations and theoretical models, thus marking a transformational step in our understanding of galaxy evolution.

colloquium - Roberta Zanin
2020-02-28 11:45 - 12:45 | Aula Gratton

colloquium - Ester Marini
2020-03-03 11:45 - 12:45 | Aula Gratton

The role of starburst galaxies and mergers in the distant Universe
2020-03-10 11:45 - 12:45 | Aula Gratton
Starburst galaxies are the most luminous star-forming powered objects in the Universe. A long standing problem in galaxy evolution is to understand whether these systems are caused by merger events, or they are just gas rich galaxies undergoing stochastic accretion events. To properly characterize them, we need infrared data, given the huge dust attenuations affecting their UV and optical emission.
I will present a unique set of near-infrared rest-frame spectral observations of star-forming galaxies at redshift ~ 0.7, and show how these can be used to understand the dust properties and origin of starbursts. Furthermore, I will explain how additional multiwavelength information (from radio to X-rays) is crucial to trace the whole sequence of mergers, test the merger-AGN connection and the formation mechanism of passive galaxies. Finally, I will exploit high-resolution HST images to investigate the role of mergers on the origin of bright star-forming clumps in high-redshift galaxies. A complete study of near-infrared rest-frame lines will allow JWST to probe the physical properties (e.g., dust attenuation, metallicity) and the nature of the most dust-embedded systems up to the reionization epoch.

colloquium - Brian Chaboyer
2020-03-17 11:45 - 12:45 | Aula Gratton
