Solar Spectral Irradiance (SSI) provides information about various properties of the solar atmosphere, including physical, chemical, thermal, and dynamic aspects. However, its importance extends beyond this, as solar emission in EUV wavelengths is the primary source of energy input to planetary atmospheres, significantly impacting their structure, composition, and dynamics, particularly in the Ionosphere-Thermosphere-Mesosphere (ITM) system. To study the impact of SSI on planetary atmospheres, it is important to provide long and continuous SSI time series. In the case of Earth, this can be used in ITM models to understand their impact. Since the photospheric magnetic flux drives the solar irradiance variability, it is possible to use the magnetic field to model the Solar Spectral Irradiance (SSI), e.g., the COronal DEnsity and Temperature (CODET) model. It is a physics-based model that uses the relationship between the magnetic field, density, temperature, and EUV emission. This work shows the most recent results and applications, e.g., new SSI time series in Earth’s exosphere and at Mars’ distances. New perspectives and improvements are also discussed.

Machine Learning applications have gained significant interest in the solar physics community for solving previously intractable problems and accelerating computationally demanding tasks that could otherwise require years to complete. This work presents a novel approach for spectropolarimetric inversions using machine learning models, specifically neural networks, trained with classical supervised methodology enhanced by a physical constraint in the loss function based on the WFA approximation. The results show that a weight of w=0.01 for the physical constraint term yields superior performance in some cases compared to unconstrained models when evaluating metrics such as RRMSE and correlation across different atmospheric depths on synthetic test data. When applied to observational data, although the model struggles with thermodynamic and velocity parameters, the magnetic field generation in the line-of-sight—which relates to the WFA constraint—shows improved generalization when the constraint is applied. These results suggest a promising new approach for developing supervised machine learning models that incorporate physical constraints, guiding them toward a deeper “understanding” of the underlying physics in the analyzed phenomena.

Observations at (sub-)millimeter wavelengths provide a valuable complementary perspective on the Sun and other stars, particularly regarding the thermal and magnetic structure, as well as the dynamics of their chromospheres and the resulting activity. While significant progress has been made in (sub-)millimeter solar observations, certain critical aspects still require diagnostic capabilities beyond those available with current observatories. In particular, simultaneous observations of the radiation continuum across an extended frequency range would enable the mapping of different atmospheric layers and, ultimately, the three-dimensional structure of the solar atmosphere. Capturing large regions of the Sun–or even the entire solar disk–with high temporal cadence would be essential for systematically identifying and tracking the temporal evolution of solar flares. Synoptic observations at higher angular resolution, such as daily maps spanning multiple years, would offer an unprecedented perspective on the solar activity cycle in this wavelength regime. Given that the Sun serves as a fundamental reference for investigating the atmospheres of active main sequence stars, utilizing the same instrument to observe both the Sun and other stars would unlock significant diagnostic potential for studying stellar activity and its implications for exoplanet habitability. The proposed Atacama Large Aperture Submillimeter Telescope (AtLAST), when equipped with a large array of detector elements to probe the radiation continuum across a broad frequency range, would be well-suited to deliver these essential observational capabilities. We present an overview of key science cases for AtLAST and considerations for the design of an instrument in comparison to potential upgrades of the Atacama Large Millimeter/submillimeter Array (ALMA), highlighting future scientific opportunities for studying solar and stellar activity.

In this work, we studied the relationship between photospheric proper motions and the magnetic field in four sunspots. We used continuum images and magnetic field data from the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager (SDO/HMI) that show the passage of each sunspot across the solar disk. Before processing the data, we employed advanced image processing techniques to coalign and correct limb darkening, projection, and p-mode effects. The horizontal proper motions and velocities were obtained by applying Local Correlation Tracking techniques to the continuum images. We present the maps of intensity continuum, magnetic field strength, and the radial profiles of the velocities obtained with LCT, as well as the vertical and horizontal components of the magnetic field. We found the first correlations between the velocities, the sizes of the sunspots, and the magnetic fields in the sunspots and the surrounding regions.

We present a preliminary variability analysis of space-based photometry for 2,500 candidate pulsating stars, with physical parameters derived from Strömgren–Crawford photometry. Using an automatic classification pipeline, we identified and characterized different variability types and detected $\delta$ Scuti / $\gamma$ Doradus hybrid candidates, which will be further analyzed through detailed asteroseismic modeling of their frequency and period-spacing patterns.

This project presents a spectroscopic study of the eclipsing binary star BUL-SC16 335, aiming to determine its physical properties and dynamical behavior. First, we review the different types of binary systems and the experimental methods used for their detection, as well as the processes applied to obtain the spectral lines of BUL-SC16 335. The analyzed data, recorded at La Silla Astronomical Observatory (Chile) by Alfred Tillich in October 2008, include more than 35 observations. These were reduced using several packages and tasks of the IRAF software, while also considering the instrumental effects of CCD cameras and the spectroscopic techniques applied in observational astronomy. Subsequently, specific scripts were implemented for the efficient determination of radial velocity and Julian date. Finally, the use of gnuplot allowed us to construct the radial velocity curve of BUL-SC16 335, contributing to the characterization of its eclipsing nature.

Finding low-mass planets around solar-type stars requires understanding the physical variability of the host star, which greatly exceeds the planet-induced radial-velocity modulation. This project aims to analyze – observationally and theoretically – the character and physical origins of fluctuations in solar photospheric absorption lines.

Observationally, photospheric equivalent-width variations were measured in 1000 selected spectra from three years of HARPS-N data of the Sun-as-a-star, showing changes that largely shadow the chromospheric Ca II H&K activity-cycle signal, but with much smaller amplitudes on sub-percent levels. Among iron lines, the greatest are for Fe II in the blue, while the trends change sign among lines in the green Mg I triplet and between Balmer lines. No variation was seen in the semi-forbidden Mg I 457.1 nm.

Theoretically, hydrodynamic 3D modeling of solar surface convection produces time sequences of synthetic high-resolution spectral atlases. Radial velocities averaged over small simulation areas jitter by some $\pm$150 m s$^{-1}$, scaling to $\sim$$\pm$2 m s$^{-1}$ for the full solar disk on timescales of granular convection. Among different lines, jittering is in phase, but the amplitudes differ by about one tenth of their values: greater for stronger and ionized lines, decreasing at longer wavelengths

Helio- and asteroseismic observations show that stellar cores rotate much more slowly than predicted by hydrodynamical standard rotating models, revealing the need for additional angular momentum transport processes. Internal gravity waves (IGWs) are a strong candidate for this transport. We extend their classical treatment by including the effect of the Coriolis acceleration in the damping of waves, entering the gravito-inertial regime. The new formalism, implemented in the STAREVOL code, is tested on a $1M_{\odot}$ pre-main and main-sequence model. Rotation modifies the spatial distribution of wave dissipation, moving the damping region closer to the excitation zone. This represents a first step toward a consistent treatment of gravito-inertial waves (GIWs) and an understanding of their role in the rotational evolution of low-mass stars.

The National Autonomous University of Honduras (UNAH) has initiated the establishment of the country’s first magnetic observatory, a landmark effort for geophysics and space weather research in Central America. This initiative, known as the Honduran Magnetic Observatory (MAGHO), forms part of a broader strategy to integrate Honduras into international scientific networks. In partnership with leading institutions, UNAH has advanced programmes in geomagnetic field monitoring, ionospheric scintillation and total electron content (TEC) studies, and cosmic ray detection. The observatory site was selected after extensive geophysical surveys, and international collaborations have provided essential instrumentation. MAGHO represents both a major step in strengthening regional scientific capacity and a contribution to global monitoring systems such as INTERMAGNET, NASA’s EZIE-Mag project, the ScintPi network, and the EL-BONGÓ astroparticle consortium. Its establishment underscores the importance of collaborative frameworks in expanding global coverage of space weather observations and promoting resilience against the growing impacts of solar–terrestrial disturbances.

A central question of stellar astrophysics is what determines the magnetic activity level of low-mass stars (defined here as stars with outer convection zones)? Numerous studies have addressed this question by studying how magnetic activity levels vary as a function of different stellar properties. It has long been known that rapidly rotating stars are more active than slowly rotating stars, and less massive stars are more active than more massive stars. However, until recently, it was unclear how magnetic activity depended on a star’s chemical composition. In this contribution, we discuss a series of recent works that investigate how stellar metallicity affects magnetic activity levels, as well as the knock on repercussions for stellar rotation evolution and exoplanet evolution.

We combine global coronal models, in-situ observations of the solar wind, and remote observations of the solar atmosphere to trace and study the source region characteristics associated with highly Alfvénic solar wind observed through the inner heliosphere. We discuss a case study combining modeling and multipoint in-situ composition measurements to trace wind sources, finding that the Alfvénic streams of interest emerged from coronal hole boundaries. The slow Alfvénic wind stream of interest showed mixed elemental composition metrics, pointing to additional work being necessary to fully understand the source and emergence of these streams. Through studying additional near-Sun wind streams observed by Parker Solar Probe, we find that the majority of slow Alfvénic wind streams emerge from overexpanded boundaries of coronal hole structures. This wind is characterized by low magnetic field strength at the estimated footpoint, low mass flux, and large expansion factors consistent with coronal hole type structures. A second class of slow Alfvénic wind streams is found to emerge from regions with high footpoint field strength, high mass flux, and large expansion factors indicating large heating below the critical point in a hot structure. We discuss the necessity for full-Sun coverage of the solar magnetic field coupled with heavy ion diagnostics to fully close our understanding of solar wind sources and emergence mechanisms.

This study examines the connection between far-side Active Regions (ARs), detected via helioseismic holography, and their subsequent emergence on the visible solar disk. Using Doppler data from SDO, we analyzed acoustic maps generated by NWRA and Stanford University from 2010 to 2023, comparing the far-side magnetic strength with NOAA- reported ARs on the near side. Our results show a weak but statistically significant correlation, suggesting that additional factors influence AR emergence. This work is a first step toward using far-side acoustic properties to predict solar flares.

The globular cluster $\omega$ Centauri, likely the remnant core of an accreted dwarf galaxy, is massive with complex stellar populations. Recent work has shown disagreement between the expected and actual number of binaries with long orbital periods in $\omega$ Centari. The cluster likely contains a large population of stellar-mass black holes, but so far none have been detected. In this work, we utilize data from a new astrophotometric catalog of stars in $\omega$ Centauri to perform an astrometric search for binaries, especially those with potential black hole companions. Using synthetic observations of simulated binaries, we measure the detection efficiency of our approach. We report a high detection efficiency for our approach which increases with increasing companion mass. We also report on the ongoing work to characterize these candidate binaries and the tentative detection of a binary with a $\sim 5\,\text{M}_\odot$ black hole companion.

We present multiwavelength evidence that the globular cluster X-ray source GCU7 is a young ultracompact X-ray binary in its initial, high-luminosity phase. Chandra observations from 1999–2023 show a persistently stable X-ray luminosity of $L_X \approx 1.2 \times 10^{39} \text{ erg s}^{-1}$, ruling out a transient nature such as a tidal disruption event. Correspondingly, long-term optical spectra consistently feature a unique signature of [N II] and [O III] emission, with a clear absence of hydrogen and helium. This combination of features strongly identifies GCU7 as a system with a helium white dwarf donor that is supplying material to a neutron star or black hole at a sustained super-Eddington rate. GCU7 thus serves as a key example of the early stages of UCXB evolution.

Neutron star-black hole mergers (NSBH) are still very rare in the list of gravitational wave (GW) sources, but together with binary neutron star mergers (BNS), they may play a crucial role in GW astronomy, producing not only GWs but also electromagnetic radiation, as well as neutrinos and high-energy particles. In the Open Gravitational-wave Catalog (4-OGC), out of 94 recorded observation events, 90 are BBH, 2 are NSBH mergers, and 2 are BNS mergers (Nitz et al. 2023). Therefore, despite the very limited number of NSBH and BNS mergers, their study is currently a very significant area of research. In this article, we will review the existing observational data of the events GW 200115 (S200115j) and GW 200105 (S200105ae), which are confirmed to be NSBH mergers. The GRANDMA project played an important role in observing these objects by ensuring coordination between telescopes in different countries and implementing advanced tracking strategies through joint observations.

The birth of globular clusters remains one of the most challenging open questions in computational astrophysics. Galaxy evolution codes can nowadays combine models for the non-equilibrium thermo-chemical evolution of the interstellar medium, stellar evolution and small-scale gravitational dynamics, enabling star-by-star models of small dwarf galaxies. In the griffin project we have modelled star formation in quiescent and starburst low-metallicity galaxies using a smoothed particle hydrodynamics method combined with methods for stellar evolution and accurate gravitational dynamics. We have shown that rotating globular cluster-like massive star clusters can form rapidly in starburst conditions. Stellar collisions lead to the mass growth of very massive stars in the cores of the clusters, providing a source of chemical enrichment and intermediate mass black holes. Expanding this framework with models for exotic objects such as supermassive stars will provide a setting for future studies of the origin of multiple populations in globular clusters.

Intermediate-mass black holes (IMBHs) occupy the $10^2$–$10^5\,M_\odot$ range, but their existence remains poorly constrained. Only a few candidates have been suggested in dwarf galaxies, globular clusters, and LIGO-Virgo-Kagra detections. To investigate their formation and demographics, we adopt two complementary approaches. We first analyze the dragonii direct N-body simulations, which follow clusters with up to $10^6$ stars, capture IMBHs growth. We then employ the semi-analytic code bpop, calibrated on dragonii, to explore a broad range of cluster and cosmological conditions.

Our models reproduce merger rates consistent with GWTC-3, with $\sim30$–60% of BBHs forming dynamically, mainly in globular and nuclear clusters. About 2–3% of mergers involve an IMBH, producing intermediate-mass ratio inspirals. The IMBH mass distribution spans $2.5\times10^2$–$4\times10^4\,M_\odot$, with rare growth beyond $10^6\,M_\odot$. Formation efficiency rises with initial binary fraction but declines in metal-rich environments. IMBHs thus emerge as a distinct population bridging stellar and supermassive black holes.

Globular clusters are a prototype of old, dense stellar systems that host diverse compact objects and binaries, including black holes and neutron stars. There are about 200 globular clusters in the Milky Way Galaxy, but many more beyond the Milky Way. They are divided into two groups according to their location: galactic globular clusters and intracluster globular clusters. On the small scale the globular clusters are an excellent laboratory to study 1) the nature of compact objects and binaries, 2) the dynamics of dense stellar systems, and 3) stellar evolution. On the larger scale, they are an efficient tool to investigate formation and evolution of galaxies and galaxy clusters. I present an overview of the current understanding of globular clusters in the universe: from the globular clusters in the Milky Way Galaxy to the young massive star clusters in high-redshift galaxies, and from galactic globular clusters to intracluster globular clusters.

Black holes (BHs) play a major role in the structural and dynamical evolutions of Globular Clusters (GCs). Several recent works searched for BHs in Galactic GCs using scaling relations derived from numerical simulations. However, the conclusions drawn by such approaches are strongly dependent on the specific prescriptions adopted in numerical simulations. Therefore, we analyzed a survey of 101 Monte Carlo simulations to identify some observable parameters that allow us to probe the present-day BH population in GCs reliably. We thoroughly show that a single observable is not suited to infer the BH mass fraction in real GCs: similar values could be attained by systems with different BH mass fractions, depending on the specific dynamical evolution of the system. Finally, we present a combination of observable parameters that efficiently breaks this degeneracy. We also compare values from numerical simulations with a sample of Galactic GCs.

Omega Centauri ($\omega$ Cen) is the most massive globular cluster in the Galaxy, providing the ideal environment for a large number of potential stellar mass black holes to be initially formed, as well as being retained due to the large escape velocity and extended relaxation time. However, $\omega$ Cen has been the focus of a long debate over whether there is a sub-population of stellar mass black holes or an intermediate mass black hole. In this work, we use roughly 14 years of archival Hubble Space Telescope observations to search for potential microlensing events caused by stellar mass black holes. We create synthetic data from simulations of $\omega$ Cen, which allows us to optimize our regression model and provides an idea of what real microlensing event statistics will reflect. We also report our detection completeness of the regression model and detail ongoing candidate follow-up.