Notte Europea dei Ricercatori 2023
In occasione della Notte Europea dei Ricercatori 2022, l’INAF-Osservatorio Astrofisico di Catania ha organizzato varie attività per il pubblico che si svolgeranno tra il 28 e il 30 settembre.
Pagina di caricamento
eventi-seminari
Gravitational entropy proposals adaptable to structure formation in Cosmology
Sede A. Riccò Via Santa Sofia 78, CataniaI would like to summarize and present cosmological applications of two proposals of Gravitational entropy, which are distinct from the standard holographic approach and from the entropy of the sources. One is the proposal by Clifton-Ellis and Tabakol (CET) based on the Bel-Robinson tensor, the other by Hosoya and Buchert (HB), based on the Leibler-Kullbach functional of Information Theory. By applying these proposals to inhomogenous dust solutions of Einstein’s equations (LTB and Szekeres models), we have shown in various published articles that both proposals are equivalent in their predictions, but CET is local and HB is non-local. Both yield entropy production in spacetime regions that can be characterized by generation and growth of structure (either overdensities or voids). The CET proposal provides an interesting interpretation of the cosmological constant as an asymptotic gravitational temperature that characterizes a finite entropy saturation value.
Determination of fundamental stellar parameters on massive stars
Sede A. Riccò Via Santa Sofia 78, CataniaMassive stars (i.e. the progenitors of core-collapse supernovae) are quite scarce, but play a crucial role in several important astrophysical phenomena, as for example, the chemical evolution of their host galaxies. Even so, their fundamental stellar parameters (as mass, radii, temperature and luminosity) are poorly known. This relates to important uncertainties about their formation processes, structure and evolution. We are attempting to face this challenge at the research group GEMAE (Grupo de investigación en Estrellas Masivas y Agrupaciones Estelares) at the University of La Plata, together with collaborators in Chile and Spain. We rely mainly on high-quality and high-resolution spectroscopic data collected by 18 years by the OWN Survey of the O-type and WN-stars in the Southern hemisphere. In this talk I will outline the work that we are developing at GEMAE, focusing on determinations of masses of close binary stars by spectroscopy and photometry in the optic and near-infrared bands.
The evolution of young low-mass stars: focus on rotation and activity
Sede A. Riccò Via Santa Sofia 78, CataniaBetween its formation stage as an active accreting seed and today, the Sun underwent large structural changes as well as variation in magnetic activity, rotation rate and its relation to the surrounding environment. I will go through the different processes that are responsible for these changes and present our latest results on the subject. We will go from the early interaction between the star and its proto-planetary disc bathing in UV radiations emitted from the massive neighbours, to the internal mixing happening in the inner layers of solar-like stars that are probed by asteroseismology.
Finally, I will review the possible applications of this work to other types of stars at different stages of the evolution in the context of the current or future surveys.
Challenges for the forthcoming CMB polarization experiments
Sede A. Riccò Via Santa Sofia 78, CataniaOne of the major challenges in the context of the Cosmic Microwave Background (CMB) radiation is to detect a polarization pattern, the so called B-modes of CMB polarization, that are thought to be directly linked to the space-time fluctuations present in the Universe at the very first instants of life. To date, several challenges have prevented to detect the B-modes partly because of the lower sensitivity of the detectors. Our own Galaxy is observed in this context as a foreground contamination. However the awareness of improving the modeling of its polarized emission has been constantly increase not only to assess the cosmological signals but also to provide new insights onto the Galactic magnetic field probed with the Galactic polarized emissions, e.g. synchrotron and thermal dust. This is particularly relevant in order to better characterize the foreground contamination for future CMB experiments (e.g. SO, LiteBIRD, CMB-S4 ), where unprecedented polarization sensitivities are expected to be achieved in the coming decades.
Astronomical Observations & Optical Communication through Atmospheric Turbulence
Sede A. Riccò Via Santa Sofia 78, CataniaThe atmospheric parameters have a strong impact on the image formation through the atmosphere. Indeed, the effect of atmospheric turbulence on wavefronts reduces severely the resolution of ground-based astronomical observations. Thus, in the context of astronomical observations, the site-selection has now become essential with the advent of the next generation of Extremely Large Telescopes (ELT). Indeed, it is important to choose sites with reduced cloud coverage, weak turbulence and low aerosol distribution in order to enhance observations time and to improve their scientific performance. It is also important to remember that the choice of sites hosting astronomical projects must meet very strict criteria in terms of optical quality. Future optical communications and telemetry stations will be forced to meet the same
requirements.
Space-Weathering on Primitive Asteroids
Sede A. Riccò Via Santa Sofia 78, CataniaStudying small bodies in our solar system is fundamental for understanding its youth and evolution. These small "primitive" bodies are "undifferentiated" (they did not undergo phase density separation, irreversibly altering their mineralogy). They have evolved little since their creation, spurring a composition relatively close to the primordial proto-planetary disk. However, other processes, such as thermal alteration, aqueous alteration, shocks, or space-weathering, can affect these bodies' surfaces.
The Gravitational-Wave breakthrough we can(‘t) wait for
Sede A. Riccò Via Santa Sofia 78, CataniaLess than a decade after the first historical Gravitational Wave (GW) detection GW150914, the field of GW astronomy has grown at a phenomenal pace, going from less than an event per month, to the currently observed rate of few events a week.
Despite the exceptional contributions the field has brought to fundamental physics, astronomy, cosmology, computational physics as well as the unavoidable collateral progress in fields related to the experimental development of GW detectors, the picture is anything but complete.
Amongst the missing pieces of the puzzle we find Continuous Gravitational Waves (CGWs).
In this seminar I am going to talk about CGWs, what are they and what astrophysical sources and mechanisms can produce them, with a particular focus on non-axisymmetric spinning Neutron Stars.
I will also briefly discuss the different search implementations, what is done, or can be done, to increase our chances to arrive to what is probably going to be the next breakthrough in GW Astronomy, the first CGW detection, including a discussion about prospects in view of future observation runs as well as GW detectors operational in the close future.
The contribution of laboratory experiments in the study of organic matter in Solar-system bodies
Sede A. Riccò Via Santa Sofia 78, CataniaOrganic matter is revealed in a variety of extraterrestrial bodies, including comets, asteroids, satellites, and trans-Neptunian objects. On atmosphere-less surfaces, organics are detected in the visible and near-infrared thanks to observations performed with the instruments on-board space probes and telescopes. Further information on the properties of organics comes from the analysis of meteorites, interplanetary dust particles, and unique samples collected on comets and asteroids during dedicated space missions.
Understanding the properties of organic matter present in small bodies would allow us to shed light on processes that happened at the dawn of the Solar System, when these objects formed by the aggregation of the materials available in the protoplanetary disk. However, since their formation, atmosphere-less surfaces were continuously exposed to energetic photons, solar particles, and cosmic rays that cause the alteration of organics, hindering to draw firm conclusions on their pristine composition and origin.
With the aim to support the interpretation of recent remote sensing observations and the analysis of extraterrestrial samples, we performed laboratory experiments to study the spectral properties of organics revealed in Solar System bodies, to shed light on the alteration induced by energetic charged particles, and to suggest possible pathways for the organics’ formation thanks to processes that involved molecular precursors already available in the pre-solar cloud.
RU Lup: the accretion environment of a prototypical Classical T Tauri star
Sede A. Riccò Via Santa Sofia 78, CataniaWhile it is well established that Classical T Tauri stars accrete material from a circumstellar disk through magnetic fields, the physics regulating the processes in the inner (0.1 AU) disk is still not well understood. With its long observational history and its rich emission line spectrum, RU Lup is a prime example to study this environment.
RU Lup is a monitoring target within the ULLYSES survey for Classical T Tauri stars. Optical spectroscopic observations with CHIRON and ESPRESSO were obtained simultaneously with the two epochs of the ULLYSES monitoring program for RU Lup.
In this talk, I will discuss the main results obtained by analyzing this collection of data, supplemented by the two TESS observations and the archival AAVSO photometry of RU Lup.
Using the high resolution ESPRESSO spectra, we improved the measurements of the stellar parameters, especially the projected rotational velocity (vsini).
We determined the veiling fraction for the ESPRESSO spectra, showing that the veiling consists of two components: a continuum emission likely originating in the accretion shock and line emission that fills in the photospheric absorption lines.
We detected a periodic modulation in the narrow component (NC) of the He I 5876 line with a period that is compatible with the stellar rotation period, indicating the presence of a compact region on the stellar surface that we identified as the footprint of the accretion shock. Although the brightness of RU Lup changed drastically both on daily and yearly timescales, this region is overall stable over the 3 years covered by the observations.
An analysis of the high-cadence TESS light curves revealed quasi-periodic oscillations (QPO) on timescales shorter than the stellar rotation period. This suggests that the accretion disk in RU Lup extends inward of the corotation radius and the star accretes through a magnetic boundary layer (MBL). The rich metallic emission line spectrum of RU Lup might be characteristic of this accretion regime.