Colloquia

The inflow of accretion in active galactic nuclei (AGN) and subsequent outflow are ultimately related to the feedback processes that link galaxy and black hole growth. New capabilities, especially JWST and ALMA, probe the scales where feedback is initiated. They reveal the multi-phase AGN environment that produces emission and obscures the activity of the central engine. Even nearby samples show evolution, distinguishing a phase of building up the AGN from one where outflow dominates and dusty winds can appear. Numerical radiative transfer models that aim to account for the resulting observations must be augmented to include a wider range of physical properties in these environments.

Oscillations of solar-like stars are thought to be stochastically excited, and following Lighthill, the primary excitation mechanism is often assumed to be quadrupolar turbulent Reynolds stresses, though other models for excitation have been proposed. Recently, techniques have been developed to measure the near field wavefronts emitted by individual solar acoustic sources. These techniques have been successfully applied to radiative magnetohydrodynamic simulations of the upper solar convection zone and lower solar atmosphere, and direct waveform fitting has been used to invert for the source properties. Efforts to extend these measurements to high spatial resolution, high temporal cadence solar observations are underway. In this talk we will summarize what the global p-mode spectrum suggests about the stochastic excitation of the solar acoustic oscillations, describe what we have learned about the excitation of acoustic waves recently from the numerical simulations, and outline an observational path to similar success with the real Sun.

The ESAC Science Data Centre (ESDC) hosts the scientific  archives from the astronomy, planetary, heliophysics, and human and  robotic exploration missions from ESA. In particular, at the ESDC we host mirrors of the Hubble Space Telescope and the James Webb Space Telescope archives, as well as the main archives for many other astronomy missions such as Planck, Herschel, XMM-Newton and Euclid. These archives represent more than three decades of space‑based astronomy and their science archives offer tremendous potential for new discoveries. In addition to the archives, at the ESDC we have developed ESASky (sky.esa.int), a web application to discover astronomical data from ESA and other partner agencies and ground based observatories, and ESA Datalabs, a science platform that allow users to discover, access and analyze the data from these missions  on premises, without the need to download anything. In this presentation I will show how users of the eHST, eJWST and Euclid Data Space can take advantage of ESASky and ESA Datalabs science platform to implement and execute end‑to‑end research workflows. This is possible thanks to two very intuitive user interfaces that combine search tools to discover the  data from HST, JWST and Euclid,  analysis and calibration software for the case of JWST, and the necessary computational resources, all in the same data centre.

Scientific coffee will be served in the cafeteria at 12:30 BEFORE THE SEMINAR

Dozens of gravitationally self-bound stellar groupings are known to orbit the halo of the Milky Way. At the faint end, some of these satellites are globular clusters: compact (few pc size), chemically homogeneous systems whose internal dynamics show no evidence for dark matter. Others, on the other hand, are dwarf galaxies: typically larger (~kpc size) systems with varied stellar populations and internal kinematics suggestive of the presence of large amounts of dark matter.  More recently, a number of satellites with properties straddling these two categories have been identified: they are compact in size, but fainter than traditional globular clusters or dwarf galaxies, and with velocity dispersions so low that only upper limits can be placed on their dark matter content. I will discuss the cosmological significance of these systems for the clustering of dark matter in the smallest scales, and for our understanding of the formation of the faintest galaxy systems in the Universe.

Asteroids preserve key records of the Solar System’s history, providing insights into collisional and surface evolution as well as the origins of water and life on Earth. Among them, Near-Earth Asteroids (NEAs), with perihelion distances smaller than 1.3 au, represent a unique population that enables detailed investigations of the secular evolution of their orbits and spin states. They are also crucial targets for future spacecraft exploration, planetary defense, and potential space resource utilization. In this talk, I will introduce recent observational studies of NEAs conducted during close approaches to Earth within a few lunar distances, where otherwise impossible observations become feasible. These include simultaneous tricolor video photometry of sub-minute rotators, as well as archival-data studies of an asteroid that will soon approach Earth closely enough to become a spatially resolved target.

B-type stars have temperatures ranging from 10000 to 30000 Kelvin and masses between 3 and 20 Mo. They exhibit radiation-driven stellar winds that lead to significant mass loss throughout their evolution, influencing the chemical enrichment of the interstellar medium. A key feature of this stellar group is its high degree of heterogeneity, including a wide variety of peculiar objects such as stars with high rotational velocities, circumstellar envelopes, or chemical anomalies (e.g., Be, B[e], HAeBe, and LBVs). In these cases, determining fundamental parameters like effective temperature (Teff)  and surface gravity (logg) is particularly challenging, as both line intensities and profiles can be strongly affected by circumstellar material or rotation.

An alternative and robust methodology for estimating these parameters is the BCD (Barbier-Chalonge-Divan) Spectrophotometric Classification System. Based on the analysis of the Balmer discontinuity (or Balmer jump) at 3700 Å, this method was developed as a quantitative equivalent to the MK and Yerkes systems using measurable observable parameters. The BCD system offers a straightforward approach to determining Teff and logg, even in stars with prominent emission lines, while also providing independent estimates of color excess and distance.

In this seminar, I will discuss the application of the BCD method to a diverse sample of objects, ranging from B-type stars in open clusters to emission-line stars and objects in transitional evolutionary phases, such as sgB[e], LBV, and HAeBe stars.

The implementation of Adaptive Optics at the GTC, combined with the science instrument FRIDA -- an imager and integral field spectrograph operating in the near-infrared —- represents a factor of 10 to 15 improvement in angular resolution compared to current or planned GTC instruments. These resolutions are still a factor of 1.5 to 4 better than those achieved by the finest space telescopes, JWST and HST. This presentation highlights the imminent realisation of these capabilities at the GTC and the unique scientific opportunities enabled by the GTC+AO+FRIDA combination. To this end, I will outline possible science pathways that are uniquely possible with GTC+AO+FRIDA, ranging from stellar surface mapping to studies of the Local Group at the finest spatial scales and the high-redshift Universe.