Seminars and Colloquia at ESO Santiago

Cosmic noon represents the peak of cosmic star formation activity and marks the global transition of star-forming galaxies. Great achievements have been made in the past two decades in understanding the clumpy UV structures, high gas fractions, and highly turbulent disks in these cosmic noon galaxies. However, a detailed understanding of their star formation complexities, stellar substructures, gas transport, and star-formation quenching is still under debates. In this talk, I will share our recent efforts with VLT/ERIS, ALMA, NOEMA, as well as JWST in resolving the substructures and the multi-phase gas content in typical main-sequence galaxies at cosmic noon. I will discuss how these resolved properties provide insights into the internal processes driving the evolution of massive disk galaxies at cosmic noon.

Cataclysmic variables (CVs) — short-period interacting binaries where a white dwarf accretes matter from a Roche-lobe-filling companion — are key laboratories for studying accretion physics, nova eruptions, and binary evolution. Yet, their population census remains incomplete. Gaia Data Release 3 (DR3), with its all-sky time-domain photometry and low-resolution spectroscopy, offers an unprecedented dataset to advance CV discovery and classification.

We are developing a new Gaia-based CV catalogue that integrates variability metrics from light curves with spectral diagnostics to improve candidate selection and reduce contamination. This work is in progress: we are currently exploring optimal feature extraction methods, testing classification strategies, and benchmarking against existing compilations (e.g. Pala et al. 2020). We aim to identify previously unrecognised CVs and assess the completeness and biases of the resulting sample.

This project will serve as a foundation for targeted follow-up observations with ESO facilities. Medium-resolution spectroscopy with instruments such as 4MOST, X-shooter, and FORS2 can confirm and characterise candidates, while high-speed photometry with ULTRACAM can probe accretion dynamics. We will also explore synergies with future Gaia data releases and large surveys like the Vera C. Rubin Observatory LSST, ensuring that the catalogue remains a dynamic, evolving resource for the community.

The twin 6.5-m Magellan telescopes at Las Campanas Observatory (LCO) continue to offer a versatile suite of instruments that enable a wide range of astrophysical research. Six instruments (IMACS, MAGE, FIRE, FOURSTAR, LDSS3, and LLAMAS) are mounted permanently and available on a nightly basis, while additional instruments (MIKE, PFS, M2FS, IFUM, PISCO, MagAO-X, Megacam, WINERED) rotate at the Clay telescope depending on semester demand. This model has supported diverse investigations and sustains Magellan’s role as a flexible scientific facility.

In this presentation we will review the current instrumentation status, operational challenges, and recent upgrades that ensure reliability and efficiency. I will show one example of a long-term program enabled by Magellan’s broad coverage and sensitivity. We will then look to future developments, including new instruments and planned enhancements that will expand Magellan’s capabilities in the coming decade. These advances are designed to keep Magellan at the forefront of optical and infrared astronomy, complementing the next generation of large-aperture facilities.

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Less than 30 years ago, we did not know whether planets exist outside our solar system. Fast forward to 2024, astronomers have discovered well over 7000 planets orbiting other stars similar to our Sun, including some that may have the right conditions to host life. As we learned that the formation of planets seems to go hand-in-hand with the birth of stars, we begin to wonder:

• What happens to planetary systems when their host stars run out of fuel, and turn into Earth-sized white dwarfs?
• Are those systems, if they exist, detectable?
• What will happen to our solar system, and to the Earth?
• And what are the possible implications for life?

I will discuss the final fate of planetary systems, the observational fingerprints of planets and their debris orbiting white dwarfs, and how studying these exotic systems help us to improve our general understanding of the formation of planets.

Fundamental questions remain about the accretion and outflow physics of cataclysmic variable stars, and their counterparts, AM CVn systems. In an AM CVn system, both the accretor and donor are white dwarf stars. To date, only one AM CVn system has been detected in the radio spectrum and the mechanism for this is yet to be determined. Using observations from the Karl J. Jansky Very Large Array (VLA), I have obtained the deepest radio constraints to date, for two AM CVn systems: AM CVn and HP Lib. I have cross-matched these data and catalogue data, with large scale surveys such as LOFAR, RACS and VLASS to constrain the radio properties of the population of AM CVns for the first time ever. With this, we can investigate the radio emission mechanisms in accreting white dwarf binaries. Additionally, this study aims to contribute to ongoing efforts in understanding whether the radio emissions observed in CVs are due to flares in the atmosphere of the donor star, versus transient jets originating from the accretion disk. In this talk, I will discuss how understanding outflows and radio emissions from accreting white dwarfs such as these may help constrain radio emission mechanisms in CVs and similar compact binaries undergoing accretion.

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The most compelling evidence for existence of cosmic black holes enshrouded by
their event horizons is presently provided by the LIGO/VIRGO detections of
gravitational waves, the GRAVITY tracking of relativistic stellar and
accretion disk motions in the Galactic Centre, and the EHT imaging of the
strong gravitational lensing on scales down to several gravitational radii in
M87 and Sgr A*.  All these observations however can be still reconciled also
with a range of hypothetical horizonless objects such as wormholes,
gravastars, and naked singularities. This poses a problem of identifying the
most efficient means and ways for discerning between the canonical black holes
and their exotic cousins. While this problem is currently being addressed from
a number of different directions, it can be argued that measurements of the
total strength and three-dimensional structure of magnetic field on scales
below about ten thousand of gravitational radii may turn out to be the most
effective tool for that. Exploration of this possibility has been the prime
focus of the M2FINDERS project which employs several approaches for making
magnet field estimates down to the event horizon scale. These include studies
of the synchrotron spectrum and opacity, brightness temperature, and Faraday
rotation made with the EHT, GMVA, VLBA, JVLA and, prospectively, also with
ALMA. A review of the M2FINDERS methodology, observations, and early results
will be presented here and further discussed in context of perspective
developments of this line of research.

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The Pyramid Wavefront Sensor (PWFS) is a leading candidate for current and next-generation adaptive optics (AO) systems due to its high sensitivity. However, it has non-linearities and a limited dynamic range. The classical solution of using modulation to increase the dynamic range comes at the cost of reduced sensitivity and also limits the speed at which the AO system can operate to less than 1 kHz. Therefore, we propose using an unmodulated PWFS in the near-infrared, as the dynamic range increases linearly with wavelength. This eliminates the need for modulation and removes the speed limitation. The classical PWFS design employs a 4-sided pyramid (4PWFS) which suffers from a roof defect at the tip – an important issue in the absence of modulation, where precision at the tip is essential. The 3-sided PWFS (3PWFS) does not have this defect, making it a preferable  alternative. Additionally, it requires fewer pixels, making it less sensitive to readout noise.

We have developed a prototype of a 3PWFS and set up an AO bench testbed at the Geneva Observatory to evaluate its performance. We conducted laboratory and simulation tests under simulated OHP/PAPYRUS observing conditions. The results from the laboratory tests are in close agreement with our simulations - the 3PWFS successfully closes the AO loop under varying turbulence conditions, achieving a Strehl ratio of ~70% for seeing up to 4 arcsecs. I will present the design, operation, and results from the AO testbed. I will also present results from the on-sky tests conducted at the PAPYRUS bench. The results obtained at PAPYRUS bench are representative of expected performance at the VLT, as both sites have similar D/r₀ values. These results highlight the potential of the 3PWFS-based AO system as a prototype for integration into future high-contrast VLT and ELT instruments like RISTRETTO and ANDES.

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