Over the last two decades, strong gravitational lensing has emerged as a potential method for studying the nature and distribution of dark matter on sub-galactic scales. In addition to the main lens substructure, line-of-sight dark matter haloes contribute greatly to the subtle perturbations of lensed images. Line-of-sight haloes, unlike dark matter subhaloes, imprint distinct anisotropic and quadrupole signatures in the maps that depict the divergence and curl of the effective deflection field, respectively, giving rise to quadrupole moments of the image-plane averaged two-point correlation function of these maps. In terms of central density evolution and dark matter halo distribution, the shapes and amplitudes of the two-point function multipoles alter dramatically in the presence of warm dark matter and self-interacting dark matter. This method, in conjunction with upcoming large-scale surveys, provides the prospect of improving the constraints on dark matter at a critical time in strong gravitational lensing research.

Solar flares are an explosive manifestation of the complex magnetic structuring of active regions in the solar atmosphere. The photospheric magnetic field is found to change rapidly, abruptly, and significantly during flaring events. Previous studies are mainly based on line-of-sight or low-cadence data. In this work, we focus on the temporal and spatial evolution of the permanent changes in the magnetic field of solar flares from high-cadence vector data (135 seconds) of the imaging system (dopplergrams and magnetograms) of the SDO/HMI instrument. The highly energetic events under analysis occurred during the solar cycle 24, covering low and high energy ranges, according to GOES classification. This investigation also stands as a crucial input for the characterization and understanding of sunquakes.

Solar-like stars evolve through the Asymptotic Giant Branch (AGB) phase. This phase is characterized by increased radii, high luminosities, and significant mass loss. In order to understand the survival of companions during this phase, and explain the presence of planets orbiting white dwarfs, it is essential to examine the orbital evolution of these systems. Several physical mechanisms come into play for AGB stars, including stellar mass loss and tidal interactions between the star and its companion. Assessing mass-loss rates and accretion to the companion requires complex radiation-hydro-chemical simulations. Furthermore, comprehending the full history of tidal dissipation in low-mass stars during their late evolutionary stages, which strongly depends on their internal structure, requires dedicated analytical and numerical studies.

Nebular Heii emission implies the presence of energetic photons (E≽54 eV). Despite the great deal of effort dedicated to understanding Heii ionization, its origin has remained mysterious, particularly in metal-deficient star-forming galaxies. Unfolding Heii-emitting, metal-poor starbursts at z∼0 can yield insight into the powerful ionization processes occurring in the primordial universe. Here we present a study on the origin of the extended nebular Heii emission in SBS 0335-052E, one of the most metal-poor (Z ∼ 3% Z⊙ Heii-emitter starbursts known locally. Based on optical VLT/MUSE spectroscopic and Chandra X-ray observations, and current stellar models we found that the Heii-ionization budget of SBS 0335-052E can only be produced by peculiar, nearly metal-free ionizing stars (called here “PopIII-like” stars) with a top-heavy initial mass function. This result is in line with recent simulations for PopIII star formation down to z=0.

We present a progress report of our project aiming to increase the number of known Cepheids in double-lined binary (SB2) systems from six to 100 or more. This will allow us, among other goals, to accurately measure masses for a large sample of Cepheids. Currently, only six accurate Cepheid masses are available, which hinders our understanding of their physical properties and renders the Cepheid mass–luminosity relation poorly constrained. At the same time, Cepheids are widely used for essential measurements (e.g., extragalactic distances, the Hubble constant). To examine Cepheid period–luminosity relations, we selected as binary candidates Cepheids that are too bright for their periods. To date, we have confirmed 56 SB2 systems, including the detection of significant orbital motions of the components for 32. We identified systems with orbital periods up to five times shorter than the shortest reported period to date, as well as systems with mass ratios significantly different from unity (suggesting past merger events). Both features are essential to understand how multiplicity affects the formation and destruction of Cepheid progenitors and what effect this has on global Cepheid properties. We also present eight new systems composed of two Cepheids (only one such system was known before). Among confirmed SB2 Cepheids, there are also several wide-orbit systems. In the future, these may facilitate independent accurate geometric distance measurements to the Large and Small Magellanic Clouds.

We present dual-frequency VLBI observations of a nearby radio galaxy NGC 4261 at 22 and 43 GHz using the East Asia VLBI Network. In particular, the first sub-pc scale image of the 22 GHz water megamaser line in the circumnuclear region of NGC 4261 is shown. Our results suggest that the megamaser emission in NGC 4261 can be associated with the inner radius of the obscuring disk, as it is proposed for the nearest radio-loud megamaser source NGC 1052. An alternative hypothesis on the megamaser association is the shock region of the interaction between the jet and ambient molecular clouds.

I present the first evidence of multiple populations in the globular cluster (GCs) 47 Tucanae based on images collected with the near-infrared camera (NIRCam) on board the James Webb Space Telescope (JWST). While NIRCam photometry is poorly sensitive to multiple populations among stars brighter than the main-sequence (MS) knee, the M-dwarfs more-massive than ∼0.1 define a wide color range due to multiple populations. The star-to-star color differences are mostly due to the different amounts of water vapor (hence oxygen) that affect the spectra of M-dwarfs. The chromosome map unveils an extended first population (1P) composed of M-dwarfs with different metallicities and three main groups of second-population (2P) stars that are depleted in oxygen with respect to the 1P. I present the discovery of an MS of very-low-mass stars and tentatively associated it with a sequence composed of O-rich stars alone.

Astrometric very long baseline interferometry (VLBI) observations of stellar masers are an excellent method to determine distances and proper motions in our Galaxy. Large maser astrometry surveys, the Bar and Spiral Structure Legacy survey and the VLBI Exploration for Radio Astrometry, allowed astronomers to determine fundamental Galactic parameters, such as the rotation curve and the distance to the Galactic centre, as well as to trace the spiral arms. In this review, the results of these surveys will be summarised and compared with astrometric measurements using other methods.

In the interstellar medium, inelastic collisions are so rare that they cannot maintain a local thermodynamical equilibrium (LTE). Atomic and molecular populations therefore do not follow a simple Boltzmann distribution and non-LTE spectra are the rule rather than the exception. In such conditions, accurate state-to-state collisional data are crucial for a quantitative interpretation of spectra. In recent years, considerable progress has been made in quantum calculations of inelastic cross sections for a variety of targets, types of transitions and projectiles. For a few benchmark species, detailed comparisons between theory and experiment were also carried out at the state-to-state level and in the quantum regime. In this article, we highlight such comparisons for three important molecules: CO, H2O and CH+. We also describe current computational efforts to extend these advances to ever larger targets, new transition types, and new environments (e.g. stellar envelopes or cometary atmospheres).

Old stellar populations in our Galaxy provide fossil records of the metal enrichment in the first few billion years of the cosmic history. Growing elemental abundance data of individual stars combined with stellar ages and kinematics allow us to make constraints on characteristic properties of the metal-enrichment sources in the early Universe, such as the first stars. In order to interpret observed chemical abundances in the oldest stellar populations in terms of metal-enrichment sources, stellar and supernova yield models are crucial. In this article, we review how we can interpret observed chemical abundances in old stars in terms of the nature of metal enrichment sources. We discuss the limitations and the prospects of empirically constraining supernova yield models based on a large sample of extremely metal-poor stars. At the same time, we emphasize the importance of hunting old stars beyond the Solar neighborhood, which can be achieved with the next-generation multi-object spectrographs at large telescopes.

The butterfly diagram of the solar cycle is the equatorward migration of sunspot’s emergence latitudes as the solar cycle evolves, which was attributed to the equatorward flow at the base of the convection zone. However, helioseismological studies indicate controversial forms of the flow, and even present poleward flow at the base, which poses a big challenge to the wide-accepted mechanism. So we aim to propose a new mechanism, that is the latitude-dependent radial flux transport.

We present astrometric very long baseline interferometry (VLBI) studies of AGB stars. To understand the properties and evolution of AGB stars, distances are an important parameter. The distribution and kinematics of their circumstellar matter are also revealed with the VLBI method. We used the VERA array to observe 22 GHz H2O masers in various subclasses of AGB stars. Parallaxes of the three OH/IR stars NSV17351, OH39.7+1.5, IRC−30363, and the Mira-type variable star AW Tau were newly obtained. We present the circumstellar distribution and kinematics of H2O masers around NSV17351. The absolute magnitudes in mid-infrared bands of OH/IR stars with very long pulsation periods were investigated and a period-magnitude relation in the WISE W3 band, MW3 = (−7.21 ± 1.18) log P + (9.25 ± 3.09), was found for the Galactic AGB stars. The VLBI is still a powerful tool for parallax measurements of the Galactic AGB stars surrounded by thick dust shells.

The Gaia-ESO Survey (GES) is a large public spectroscopic survey that has collected spectra of about 100,000 stars. The survey provides not only the reduced spectra, but also the radial velocities, stellar parameters and surface abundances resulting from the analysis of the spectra. We present the work of the groups that analysed the spectra of the hottest stars in that Survey. The large temperature range that is covered (Teff = 7,000 to 50,000 K) requires the use of different analysis codes by the different groups. Eight groups each analysed part of the data, with significant overlap that allowed cross-checks. In total 17,693 spectra of 6,462 stars were analysed, most of them in 37 open star clusters. The homogenisation of all this information led to stellar parameters for 5,584 stars. Abundances for at least one of the elements He, C, N, O, Ne, Mg, Al, Si and Sc were determined for 292 stars. The GES hot star data, as well as the Survey data in general, will be of considerable use in future studies of stellar evolution and open clusters.

HD34445 is a system that consists of a star and six planets. In some previous work, we investigated the dynamical stability of the system by means of numerical simulations. Here, we explore the system further by carrying out additional numerical experiments. A total of 100000 simulations confirm previous findings of the stability status of the system at the 1σ and 99% c.i. level. We find that only 2.7% of the systems with parameters varied within 1σ from the mean were unstable, while that percentage rose to about 28% for systems with parameter values taken within the 99% c.i. These preliminary results are presented and discussed herein.

We present high-precision strong lensing models for the galaxy clusters MACS J0416.1–0403 at z=0.396 and Abell 2744 at z=0.307. The models are constrained by two of the largest data-sets of secure multiple images ever used in lensing. These are identified from the photometric images observed by the Hubble space telescope and JWST in combination with spectroscopic data obtained by the Multi-Unit Spectroscopic Explorer at the Very Large Telescope. The same spectro-photometric data are used to create pure and complete samples of cluster member galaxies. Our models allow an extremely precise estimation of the cluster total mass distribution and produce accurate magnification maps that are fundamental to study the physical properties (mass, size, luminosity, etc.) of the lensed high-redshift galaxies.

Gravitational lensing in clusters of galaxies is one of the most powerful methods to probe the dark matter mass distribution inside such systems, after mapping the baryonic component, and test the currently accepted ɅCDM cosmological paradigm. With the advent of new high-resolution facilities such as the JWST, strong lensing (SL) is capable of providing extremely accurate mass measurements in the densest regions of such structures. Weak lensing (WL) provides complementary information by measuring the total mass distribution in the outskirts of galaxy clusters, where no multiple images of background sources are produced.

In my talk, I will present updates on the WL mass reconstruction of the Frontier Fields galaxy cluster Abell 2744 (z = 0.308) based on Subaru, Magellan, and JWST data, and I will show how the results obtained, combined with accurate SL modeling of this lens, provide a consistent picture of the cluster total mass distribution. I will discuss the pipeline used for this work, the extensive checks performed on the different datasets and the scientific results obtained. Being composed of several substructures undergoing a merging process, the complex geometry of this cluster makes it an ideal laboratory to verify the consistency and reliability of the results obtained with the two methods. I will compare the predictions of the SL models extrapolated in the outer regions of the cluster with the non-parametric WL mass reconstruction to look for potential systematic effects affecting the SL analysis.

NGC3603 is one of the youngest massive clusters of the Milky Way which uniquely enables studying the interplay between massive star feedback and the surrounding interstellar medium. Yet, a deep infrared (IR) view of the cluster is missing. We present guaranteed time observations of NGC3603 consisting of near infrared spectroscopy taken with VLT-KMOS. This data set will provide a first, rather complete IR census.