Advances in stellar and galactic evolution with the population of planetary nebula progenitors from the APOGEE DR17 survey
20/02/2024
Planetary nebulae (PNe) are the ejected gas and dust shells of Asymptotic Giant Branch (AGB) stars, which represent the late life of low- and intermediate-mass stars (LIMS). With the advent of the APOGEE DR17 survey, there is a purpose in comparing Red Giants (RGs) and PNe abundances to disclose their similarities and differences since such a comparison has been rarely, and not recently, done in the Milky Way. While we expect similarities in most of the alpha-element distributions across the two populations, given their limited evolution in LIMS, differences in Fe and S abundances allow us to determine their depletion due to grain condensation in post-AGB phases. Differences in N and C between PNe and their progenitors set new limits to their production in the late stages of LIMS evolution. Finally, we use radial metallicity gradients from RGs and PNe and Gaia-calibrated distances to constrain galaxy evolution in the framework of the current chemical evolution models.
|
Opening up the radio sky with VLBI
16/02/2024
In the past few decades, radio surveys have provided us with unique insights into many areas of astrophysics such as star formation, supernovae, active galactic nuclei, pulsars, cosmology and much more. A key aspect of these surveys is the technique of Very Long Baseline Interferometry (VLBI) which can provide some of the highest resolutions possible in astronomy. This method has been crucial in understanding the inner workings of galaxies such as AGN-star-formation feedback, dark-matter substructures in gravitational lenses, and providing the first two direct images of a black hole shadow. VLBI has been typically limited where the largest surveys require many years of observations to build up an extensive sample. However, computational improvements have enabled us to map multiple sources within a single VLBI survey and push into the lower frequency regime through the International LOFAR telescope. In this talk, I will talk about the scientific and technical discoveries arising from such surveys and focus on the bright future of VLBI surveys. This includes the transition from the current modus operandi of a small number of surveys of a few 'famous' deep fields to a ubiquitous VLBI survey instrument. I will conclude the talk by talking about the upcoming developments in VLBI, such as the incorporation of SKA and MeerKAT, ultra-wideband receivers, and GPU-accelerated correlation and calibration.
|
The long and winding road towards precise and accurate ages of stars: a traveller’s perspective
14/02/2024
Our understanding of the formation and evolution of the Milky Way and galaxies is often blurred and biased by the lack of precise and accurate stellar ages. Asteroseismology, i.e., the study of global, resonant oscillation modes in stars, is providing us with a formidable tool to unveil detailed insights into the internal structure of stars, paving the path for robust age determinations.
In this presentation I will discuss the ongoing efforts and recent results of the asterochronometry project, which aims to test our knowledge of stellar physics while providing precise and accurate age estimates (within 10-20%) for stars in the regions of the Galaxy surveyed by the space telescopes Kepler, K2, CoRoT, and TESS.
While I will showcase examples of asteroseismology's role in reconstructing the early assembly history of the Milky Way, I will also highlight the limitations we encounter emphasising that these hurdles can only be truly overcome via an improved understanding of stellar physics.
Finally, I will discuss the prospects for extending these studies to larger samples, and outline the scientific rationale for a future space mission dedicated to asteroseismology in “controlled environments”. Such a mission would transform stars into laboratories, enabling us to test stellar physics catalysing the development of next-generation stellar models.
|
The Imaging X-ray Polarimetry Explorer: Making History in High-Energy Astrophysics
7/02/2024
IXPE represents the momentary culmination of a long history of determined scientists with the goal of introducing two brand-new observables to the usual ones in High Energy Astrophysics. In this talk, I will illustrate how this goal was achieved, starting from the late '80s, progressing to the development of IXPE, which began with the proposal in 2014 and led to the launch on December 9, 2021, amid a pandemic and an American Government shutdown. Over the past two years, IXPE has been actively observing a variety of celestial sources, such as neutron star and black hole binaries, AGNs, magnetars, Supernova Remnants and Pulsar Wind Nebulae, just to name a few categories. The main findings for each class of objects will be presented in a cycle of seminars, starting with this one, where I will focus specifically on the scientific results that have been obtained for galactic black hole binaries, AGNs, and magnetars.
|
SHARP - A Near-IR Multi-mode Spectrograph conceived for the Multi-Conjugate Adaptive Optics Module MORFEO@ELT
6/02/2024
The world's largest aperture combined with state-of-the-art Adaptive Optics systems will enable the ELT to capture better data than the JWST in both sharpness and depth. Therefore, the spectrograph intended for the 2nd port of the Multi-Conjugate Adaptive Optics (MCAO) system MORFEO@ELT will be the most powerful instrument of the JWST era, revealing phenomena beyond the reach of others. SHARP (http://sharp.brera.inaf.it) is a near-IR (0.95-2.45 mu) spectrograph designed for the 2nd port of MORFEO@ELT, intended to be submitted in the upcoming ESO instrument call. Comprising a Multi-Object Spectrograph, NEXUS, and a multi-Integral Field Unit, VESPER, SHARP extends its wavelength range to ~2.45 μ. Coupled with MCAO-assisted observations, it delivers unprecedented high angular (~30 mas) and spectral resolution, outperforming NIRSpec@JWST (100 mas). MORFEO-SHARP will allow us to study the nearby and the early Universe in unprecedented detail, resolving the first galaxies and the star forming regions within galaxies far back in cosmic time, and providing spectra of individual nearby young stellar objects. This presentation introduces the scientific rationale behind SHARP, showcasing its features and inviting those interested to join the SHARP team.
|
Rapidly-rotating Population III stellar models
1/02/2024
The first stars, also known as Population III stars, began the process of reionization in the Universe and contributed to the metal enrichment. It is believed that they might have been fast rotators, which can have significant consequences for their radiative, mechanical, and chemical feedback. In this talk, I will present recent models using the Geneva stellar evolution code (GENEC) with fast initial rotation velocity, corresponding to 70% of the critical one in the mass range of 9 to 120Msol. I will compare the outputs of these models with those obtained with lower initial rotations, focusing on the primary nitrogen production. Other aspects of the rapidly-rotating models will be discussed, including their impact on the early chemical evolution of galaxies. Moreover, I will discuss the possibility that rapidly-rotating Pop III stars may, at least in part, explain the high N/O ratios measured in certain high-redshift galaxies, such as GN-z11 and CEERS-1019.
|
Searching for light dark matter
31/01/2024
The Standard Model (SM) of particle physics has been highly successful in describing the fundamental particles and their interactions in the last decades. Nevertheless, the SM leaves unanswered questions, like the origin of matter over anti-matter asymmetry in the Universe, the strong CP problem. On the other hand, the existence of dark matter (DM) is required by the cosmological and astrophysical observations. The scenario in which DM is the thermal relic of the early Universe is thus well justified.
Even though well justified if the governing force is the weak interaction, the parameter space available to GeV-TeV WIMPs has reduced over recent years, so that interest has grown in “hidden” or “dark" sector models. These models assume that DM is made of particles which interact feebly with SM particles via a portal particle, thus greatly enlarging the allowed parameter space.
In addition to solving the DM problem, those models postulating light dark particles could also address some anomalies in particles physics, such as the discrepancy between the experimental results and the calculated SM value of the anomalous magnetic moment of the muon, or the strong CP problem. Another indication of the existence of new, light (MeV-GeV) states seems to come from anomalous e+e- pairs production in nuclear physics measurements of light even-even nuclei.
A panorama of ongoing and proposed experiments, capable of testing different models, is presented; those experiments explore different mass ranges and sensitivities, using different production and detection techniques. In particular, the feeble interaction with SM particles opens the possibility of producing these new particles at accelerators.
|
RU Lup: the accretion environment of a prototypical Classical T Tauri star
30/01/2024
While 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.
|
Relativistic jets from black hole X-ray binaries: a MeerKAT view
30/01/2024
Black hole X-ray binaries (BH XRBs) can launch powerful outflows in the form of radio-emitting discrete jet ejecta, which are generally observed to be produced during bright outburst phases and to propagate at apparently superluminal speeds. However, little is known about the powering mechanism, the formation and composition of these jets, and studying them is important for understanding both their physics and their feedback on the surrounding environment.
While discrete ejecta have been historically difficult to detect and to follow in their motion away from the central black hole, the MeerKAT radio-interferometer (precursor of the SKA) is now revolutionizing the field with its exceptional sensitivity at GHz frequencies. In this talk, I will present some of the most interesting advancements that we have obtained with MeerKAT observations of BH XRBs in the last five years, as part of the ThunderKAT collaboration.
More in detail, I will present the MeerKAT detection of a number of new ejecta that we observed to interact with the interstellar medium (ISM) and to strongly decelerate at parsec scales far from the black hole. In this context, covering the deceleration phase is essential for the physical modelling of the jet kinematics, and I will discuss what is possible to learn from the application of these models on the jet physical parameters and on the properties of the environment surrounding BH XRBs.
|
ICY SATELLITES: A MULTI-SCALE ANALYSIS TO UNDERSTAND THEIR TECTONICS
24/01/2024
The icy satellites, such as Jupiter’s Europa and Ganymede or Saturn’s Enceladus, are first class targets for future missions focused on the search of biosignatures in the Solar System. In fact, evidence of subsurface oceans indicates that such bodies may harbor potentially habitable environments and the investigation of the surface features contributes to their detection. The icy satellites show widespread deformation structures that provide insights to infer the tectonics and the mechanical properties of their crusts. Such structures represent discontinuities between crustal layers and conduits for fluid circulation that connect the surface with the deep layers, such as the ocean. Therefore, structural investigation is pivotal for the understanding of icy satellite geology, which still presents open issues. Their surfaces show a large amount of extension and strike-slip that require balancing, which is not fulfilled by the paucity of compression recognized at present. Several approaches have been proposed to unravel the tectonics of the icy satellites from remote sensing of data acquired by the past missions to the support of terrestrial analogs. We show tectonic models that allow to explore multi-scale investigations of the deformation structures of the icy satellites, and in particular of Ganymede, which is the main target of the JUICE mission.
|
|