Seminars and Colloquia at ESO Santiago

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Matter ejection, in the form of either winds or jets, is ubiquitous in accreting X-ray binaries. Although it is clear that accretion and ejection are profoundly intertwined in these types of systems, the origin and the details of such an interconnection are yet to be unraveled. This is particularly true for systems where a low-magnetized neutron star (NS) accretes matter from a low-mass companion star (NS low-mass X-ray binaries, LMXBs). Indeed, unlike the case of accreting black holes, in NS LMXBs the already delicate interplay between accretion and ejection may be further complicated by the presence of, e.g., the NS magnetic field, the boundary layer and the emission from the NS surface. For instance, jets in NS LMXBs have been claimed to be more collimated than in BH LMXBs, their occurrence sometimes seems to be unrelated to the spectral state and their observed radio luminosity show a rather scattered distribution. X-ray winds on the other hand have been often detected in states where they were not expected, in particular in a class of NS LMXBs, the Accreting Millisecond X-ray Pulsars (AMXPs), where the channeling of the accretion flow along the magnetic field lines makes these systems visible as rapidly spinning X-ray pulsars. Finally, AMXPs typically drive more powerful jets than other (non-pulsating) NS LMXBs and their rapid orbital expansion can be explained by strong mass outflows. In this talk, I will review the emerging pattern of peculiar outflows in NS LMXBs, the possible implications for jet and wind-launching mechanisms in these systems and the key role that future multi-band observing campaigns will play in clarifying its physical origin.

The Bulge Asymmetries and Dynamic Evolution (BAaDE) project aims to significantly improve models of the structure and dynamics of the inner Galaxy. The goal is to probe into regions not reachable with optical and nIR sampling of the Galactic Bulge and Plane by performing an SiO maser survey in evolved AGB stars, observed with ALMA and the VLA. These CSE masers reveal the stellar line-of-sight kinematics and can be used as point-mass particles in dynamical modeling representing the older stellar populations. The survey will be complementary to many other surveys, either because of very limited overlap (e.g., sampling different types of objects) or by providing additional information (e.g., providing velocities). The project also includes novel studies to obtain relatively accurate stellar distances in order to derive general stellar properties like bolometric and maser luminosities. The BAaDE survey, by itself or in combination with approximate distances, will yield a wealth of data allowing many different studies and statistical analysis on AGB stars, CSEs and SiO maser modeling and occurrence. Here we will showcase our data and highlight some of the exciting results.

Since the 1980s, the discovery of the "Great Attractor" has led to the dynamics of the Galaxy, the Local Group and cluster, being considered as being subject to gravitational effects modifying the Hubble flow. Over the years, numerous studies have been conducted to locate and estimate the topology, mass, and nature of this enormous concentration of matter. At the turn of the 21st century, the results obtained have made it possible to approximate its characteristics which are located well beyond the Hydra-Centaurus Supercluster. 
We review the most recent results obtained, in particular through the analysis of surrounding galaxy clusters and by determining the properties of clusters close to the galactic plane. 

The weakness of the hyperfine 21cm line, the main tracer of the atomic gas content of galaxies, has meant that we know little about the HI mass of high-redshift galaxies and its evolution. This has long been one of the biggest lacunae in our understanding of galaxy evolution. ``Stacking'' of the 21cm emission signals from a large sample of high-redshift galaxies, with known optical positions and redshifs and observed simultaneously with a radio interferometer, can allow one to determine the atomic gas properties of the galaxy population. The advent of new or upgraded radio interferometers, with wideband spectral capabilities and modern correlators, has recently yielded dramatic progress in this field. In this talk, I will describe the state of the art in such 21cm stacking experiments from deep studies with the Giant Metrewave Radio Telescope that have yielded the first measurements of the atomic gas properties of star-forming galaxies during the era of cosmic noon.

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Gamma-ray bursts fascinate astronomers both for their astounding power and for their effectiveness as cosmological probes. Spectroscopy of their bright optical counterparts allows to dissect the interstellar and circumgalactic medium of high-redshift star-forming galaxies, testing their gas, metals, dust, and molecular content. At the same time, also thanks to a new suite of instruments, we have been discovering a richer diversity of progenitor systems - with the two main players being collapsing massive stars and binary compact object mergers. I will highlight the recent progress and surprises in the field achieved via the "Stargate" program at the VLT.

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