We review the local determination of the Hubble constant, H0, focusing on recent measurements of a distance ladder constructed from geometry, Cepheid variables and Type Ia supernovae (SNe Ia). We explain in some detail the components of the ladder: (1) geometry from Milky Way parallaxes, masers in NGC 4258 and detached eclipsing binaries in the Large Magellanic Cloud; (2) measurements of Cepheids with the Hubble Space Telescope (HST) in these anchors and in the hosts of 42 SNe Ia; and (3) SNe Ia in the Hubble flow. Great attention to negating systematic uncertainties through the use of differential measurements is reviewed. A wide array of tests are discussed. The measurements provide a strong indication of a discrepancy between the local measure of H0 and its value predicted by Λ Cold Dark Matter theory, calibrated by the cosmic microwave background (Planck), a decade-long challenge known as the ‘Hubble Tension’. We present new measurements with the James Webb Space Telescope of >320 Cepheids on both rungs of the distance ladder, in a SN Ia host and the geometric calibrator NGC 4258, showing good agreement with the same as measured with HST. This provides strong evidence that systematic errors in HST Cepheid photometry do not play a significant role in the present Hubble Tension. Future measurements are expected to refine the local determination of the Hubble constant.

We report the results of a 7-year monitoring program using the Australia Telescope Compact Array (ATCA) for the 9.9 GHz class I methanol maser in G331.13-0.24 where a periodic class II methanol maser is present. The great deal of the project was to control systematics at an unprecedented level. Although no periodic flux variation was found, the maser shows a very stable decline of 166±7 μJy/day. The radial velocity of the maser is stable down to 1 m/s level. We also report a marginal periodic signal in radial velocity (comparable to the level of systematics) of about 20±7 cm/s with the period of 475±22 days, close to that of the 6.7-GHz maser in the source. No hyperfine split was detected which suggests preferential excitation of a single hyperfine transition.

In the context of a project aimed to provide an updated theoretical scenario for various classes of radially pulsating stars, we present the first results obtained for anomalous Cepheids. By adopting reliable and updated evolutionary prescriptions concerning the luminosity levels for various core He-burning stellar models with masses suitable for entering the instability strip, we have computed nonlinear convective pulsation models for both fundamental and first-overtone mode anomalous Cepheids by exploring the impact of varying the metal abundance as well as the efficiency of super-adiabatic convection. These numerical simulations have allowed us to retrieve the boundaries of the instability strip and all relevant pulsation properties, namely period, amplitude, bolometric light and radial velocity curves. This theoretical scenario has been transformed into the Gaia photometric system to derive the first theoretical Period–Luminosity–Colour and Period–Wesenheit relations in the Gaia bands.

Like our Moon, the large icy satellites of Jupiter are thought to be in a Cassini State, an equilibrium rotation state characterized by a synchronous rotation rate and a precession rate of the rotation axis equal to that of the normal to the orbit. In these equilibrium states (up to four Cassini States are possible for a solid and rigid satellite), the spin axis of the satellite, the normal to its orbit and the normal to the inertial plane remain coplanar with an obliquity that remains theoretically constant. However, as the gravitational torque exerted on the satellite shows small periodic variations, the orientation of the rotation axis will also vary with time and nutations in obliquity will appear.

Here we present a dynamical model for the study of the Cassini States. This model includes the coupling between the polar motion and the spin axis precession/nutation which is neglected in the classical studies. We study the influence of the triaxiality of Ganymede on its four possible Cassini States, use a Toy model of the Moon to illustrate the nutations in obliquity obtained with the dynamical model, and investigate the influence of the presence of a subsurface ocean on the Cassini State I of Europa.

Rare systems with multiple sources strongly lensed by a single galaxy provide the most robust way to explore the geometry of the Universe and to study the inner mass structure of lens galaxies. We present here a study of the SDSS J0100+1818 deflector, analyzing its total and baryonic mass distributions. The system comprises an ultra-massive early-type galaxy, surrounded by ten multiple images of three background sources. Exploiting high-resolution HST photometry and VLT/X-shooter spectroscopy we conduct a strong lensing analysis with the software GLEE to reconstruct the complex surface brightness distributions of the background sources over approximately 7200 HST pixels. These results are presented in our recent paper, Bolamperti et al. (2023). Finally, we present some preliminary results from new VLT/MUSE observations, that will allow us to build a new strong lensing+dynamics joint model and measure the values of the total matter density and of the cosmological constant parameters, Ωm and ΩΛ.

In 2015, the high-mass star-forming region NGC6334I-MM1 underwent an accretion burst. Using VERA, we monitored 22 GHz water masers before and during the accretion burst to observe the changes in the maser spatial and velocity distributions in the region. The masers in CM2-W2 and MM1-W1 displayed variability that could be attributed to the accretion burst. The bright masers in CM2-W2 were found to better trace the shock structure as the epochs progressed. The mean 3D speeds derived from the proper motions were 50 km/s and 54 km/s for the pre-burst and burst epochs respectively. High-velocity proper motions were found at the southern edges of the N-S (∼80 km s−1) and NW-SE (∼150 km s−1) bipolar outflows. The precise mechanism of the flaring of the water masers due to the accretion burst has yet to be investigated.

OH megamasers (OHMs) are luminous masers found in (ultra-)luminous infrared galaxies ([U]LIRGs). OHMs are signposts of major gas-rich mergers associated with some of the most extreme star forming regions in our universe. The dominant OH masing line, occurring at 1667 MHz, can spoof the 1420 MHz neutral hydrogen (HI) line in untargeted HI emission line surveys. While only ∼120 OHMs are currently known, HI surveys on next-generation radio telescopes, such as the Square Kilometre Array (SKA) and its precursors, will detect unprecedented numbers of OHMs. This surge in detections will not only fundamentally change what we know about the OHM population, but will also unlock our ability to implement OHMs as tracers of major mergers and extreme star formation on cosmic scales. Here we present predictions for the number of OHMs that will be detected by these surveys. We also present our novel methods for identifying these interlopers using a k-Nearest Neighbors machine learning algorithm. Preliminary data from HI surveys on precursor SKA telescopes is being used to vet and strengthen these methods as well as give us a first look at a new era in OHM science. From a detection of one of the most luminous OHMs to the discovery of a megamaser at a record-shattering redshift, these new sources are glimpses into how our understanding of the known OHM population will soon be expanding and shifting rapidly and how they will influence our understanding of galaxy evolution.

The Bulge Asymmetries and Dynamic Evolution (BAaDE) project attempts to improve our knowledge about the structure and dynamics of the inner Milky Way galaxy by sampling tens of thousands of infrared color-selected evolved stars with circumstellar envelopes (CSEs). The SiO masers in these CSEs yield the object’s line-of-sight velocity instantly and accurately, and together provide a sample of point-mass particles that are complementary to high-mass star formation masers typically found in the Galactic Disk as well as to optical samples that cannot reach into the Galactic Plane and Bulge due to extremely high visual extinction. This presentation introduces the BAaDE survey and highlights current results.

This is a study about the dynamical stability of the GJ 876 exoplanetary system. The phase space of initial conditions (ICs) is characterized using the MEGNO indicator of chaos and the Shannon entropy approach for estimations of diffusivity. The results are compared to analyze correlations between the chaotic layers and the instability timescales. The long-term dynamical behavior of the system is reminiscent of the stable chaos, at least within the system’s lifetime.

We present our past and current long-term monitoring program of water masers in the circumstellar envelopes of evolved stars, augmented by occasional interferometric observations. Using as example the Mira-variable U Her, we identify three types of variability: periodic (following the optical variation), long-term (years-decades) and short-term irregular (weeks-months). We show there are regions in the maser shell where excitation conditions are favourable, which remain stable for many years. Lifetimes of maser clouds in the wind-acceleration zone are of the order of up to a few years. Much longer lifetimes are found for the peculiar case of a maser cloud outside that zone (as in RT Vir), or in some cases where the motion of spectral features can be followed for the entire 2 decade monitoring period (as in red supergiant VX Sgr).

Context: Theoretical scenarios describe the phenomenon of mass accumulation by high-mass young stellar objects (HMYSOs) through disk accretion. Aims: To find out whether the rotation of the core around hyper-compact (HC) HII regions is common Methods: The molecular core G301.1364-00.2249A was selected as the subject of investigation. Observations were carried out on CH3CN, SO2, H29α radio recombination line and continuum emission. Analysis involved the “Moment 0, 1, 2" and “Population-diagram” methods. Result: The structures of G301.1364-00.2249A exhibited clear definition. CH3CN moment 0 images revealed multiple enhanced emission regions and an absorption area. The moment 1 image depicted a velocity gradient from southeast to northwest. Conclusion: The molecular gas has a rotational motion in the direction from the southeast to northwest. The rotational temperature was measured at 293 K.

We present GECKOS (Generalising Edge-on galaxies and their Chemical bimodalities, Kinematics, and Outflows out to Solar environments), a new ESO VLT/MUSE large program. The main aim of GECKOS is to reveal the variation in key physical processes of disk formation by connecting Galactic Archaeology with integral field spectroscopic observations of nearby galaxies. Edge-on galaxies are ideal for this task: they allow us to disentangle the assembly history imprinted in thick disks and provide the greatest insights into outflows. The GECKOS sample of 35 nearby edge-on disk galaxies is designed to trace the assembly histories and properties of galaxies across a large range of star formation rates, bulge-to-total ratios, and boxy and non-boxy bulges. GECKOS will deliver spatially resolved measurements of stellar abundances, ages, and kinematics, as well as ionised gas metallicities, ionisation param- eters, pressure, and inflow and outflow kinematics; all key parameters for building a complete chemodynamical picture of disk galaxies. With these data, we aim to extend Galactic analysis methods to the wider galaxy population, reaping the benefits of detailed Milky Way studies, while probing the diverse mechanisms of galaxy evolution.

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.

We compare detailed observations of multiple H2O maser transitions around the red supergiant star VY CMa with models to constrain the physical conditions in the complex outflows. The temperature profile is consistent with a variable mass loss rate but the masers are mostly concentrated in dense clumps. High-excitation lines trace localised outflows near the star.

The OH/IR stars evolving on the Asymptotic Giant Branch are large-amplitude variable stars with periods in the range of ~400 to 2500 days, significantly longer than those of the related Mira variables. We use preliminary results from a monitoring program of the 1612-MHz OH maser variations of a sample of > 70 OH/IR stars to study a possible extension of Mira Period-Luminosity Relations to longer periods. The period distribution of the sample is split around P ~ 1100 days. Using WISE W3 absolute magnitudes as proxies for the luminosity and the best available distances, we found no convincing relation between periods and absolute magnitudes. A cause could be rapid evolution of the ‘extreme OH/IR stars’ (the group with P >1100 days) close to the tip of the AGB, where no increase of luminosity is expected on the short time-scales involved.

Galaxy-galaxy strong lensing (SL) systems provide a unique opportunity to test modified gravity theories. Deviations from General Relativity are encoded in the post-Newtonian parameter (γ). As a preparation for the upcoming data from the Vera Rubin Observatory Legacy Survey of Space and Time (LSST), our research group collected imaging data of SL systems from ground-based telescopes and conducted spectroscopic observations of 21 systems on the Southern Astrophysical Research (SOAR) Telescope to measure the lens velocity dispersions, σv. We briefly describe the semi-automated SL modelling of the systems in this sample and combine the results with σv from SOAR to derive an estimate for γ. Our preliminary results yield a value of $$\gamma= 1.17_{ - 0.33}^{ + 0.29}$$, which is consistent with General Relativity. Although the error bars are limited by the sample size, this result represents the first constraint on modified gravity obtained purely from ground-based data, with a sample completely independent from previous studies, and which allows for a self consistent end-to-end analysis.

The Impact Monitoring (IM) of Near Earth Objects (NEOs) is a fundamental part of the planetary defense strategy. Current NEO IM systems (Aegis, NEODyS and Sentry) scan the Confidence Region (CR) of each observed object looking for Virtual Impactors (VIs) with a time horizon of about 100 years. This procedure is performed regardless of the uncertainty with which the orbit of the object is known, and without considering whether a scattering encounter is present in the propagation time span. In view of the likely future increase of the IM workload due to higher future NEO discovery rates, it might be more reasonable to adapt the predictability horizon of the impacts to each object, taking into account the orbit uncertainty and the close encounters experienced. In this paper we discuss the problem of estimating a reasonable predictability horizon when multiple close encounters are present and start to address the problem proposing a formal mathematical definition of scattering encounter.

Early cosmic epochs are characterized by low metallicity and high specific star-formation rates. These conditions are dominated by massive-star feedback that may be dramatically different than the traditional model dominated by hot, thermal superwinds driven by supernova explosions. Instead, metal-poor feedback from massive stars may be radiation-dominated, with weak mechanical feedback, possibly aiding the escape of Lyα and Lyman continuum radiation. I will describe our understanding that is emerging from observations of starburst galaxies in the local universe.

Red supergiants (RSGs) are the brightest stars in the near-infrared. The existence of their period-luminosity relation (PLR) will be very helpful in determining cosmological distances. This review discusses the development in identification of RSGs, calculation of their light variation period, determination of the PLR, and the uncertainties associated. It is found that the PLR of RSGs exhibits the smallest scatter in the near-infrared, in particular within the P – MK relation. The PLRs in the LMC, SMC, M31, and M33 show no obvious dependence on the galactic metallicity, which follows approximately the relation as MK ≈ −3.1 log P – 1.9.