Seminars and Colloquia at ESO Santiago

Cool dwarfs (Teff < 4700 K) are the most abundant stars in the Milky Way and preserve a primarily stable surface composition over their lifetimes.  As such, these stars can provide critical insights into Galactic chemical structure and evolution, with cool subdwarfs specifically tracing the oldest stellar populations.  On smaller star-planet scales, the chemical composition of cool-dwarf planet hosts offers fundamental constraints on planet formation pathways and bulk planetary composition. Despite their importance, the spectroscopic analysis of cool dwarfs remains challenging. Their low effective temperatures produce spectra dominated by dense and blended molecular absorption bands, resulting in a long-standing lack of accurate and homogeneous chemical abundance measurements for these stars. In this talk, I first review our previous work on the fundamental properties of a large sample (~3800) of M dwarfs and M subdwarfs based on low-resolution spectroscopy and discuss their role in probing the chemical enrichment history of the Milky Way. I then introduce AutoSpecFit, an automated, line-by-line spectral fitting pipeline for high-resolution spectroscopy, paired with AutoSpecNorm, a complementary code designed to achieve robust and consistent spectral normalization. Our technique allows for reliable abundance measurements of up to 15 key elements in cool dwarfs, including the main planet-building elements, i.e., C, O, Mg, Al, Si, Ca, and Fe.  As illustrative applications, I demonstrate results from high-resolution (R=45,000), NIR IGRINS spectra of cool-dwarf planet hosts, including stars having planets targeted by JWST programs, and highlight our exploration of star–planet compositional links for different types of planets. I also show results from a high-resolution (R=31,500) optical ARCES spectrum of a bright halo M subdwarf, presenting the applicability of the method at low metallicities. The advent of future facilities such as the Extremely Large Telescope will enable high-resolution, high-signal-to-noise-ratio spectroscopy of faint and distant cool dwarfs, extending these studies to currently inaccessible stellar populations. The methodology presented here opens a new vista for exploring Galactic archaeology as well as exoplanet formation and composition using future high-resolution surveys.

AB Aurigae is a class II young stellar object (YSO) located at a distance of 156 pc. With several candidate protoplanets identified or predicted within its very extended structure with multiple spiral arms, some of which having been attributed to late infall, it is a complex and interesting disk. In this talk, I present a newly detected candidate protoplanet first observed in near-infrared, which we now look at using ALMA line emission data from 12CO, 13CO and C18O. I will then discuss some masking techniques we will use to make a deeper search into our region of interest. Finally, I show and discuss the detection of well-defined regions of emission around the coordinates of the detected candidate, as well as velocity kinks in all of our tracers.

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Extreme day-night temperature contrasts in hot Jupiters drive strong winds that control their climate by transporting heat and material, yet the mechanisms that regulate wind speeds remain poorly understood. High resolution spectroscopy is sensitive to the line-of-sight velocity of the atmosphere and can hence provide key observational constraints on wind speeds. Recently, CRIRES+ observations of WASP-127 b have revealed the first direct evidence of an equatorial super-rotating jet, and allowed a precise measurement of the jet speed. This detection stands in contrast with observations of the similarly irradiated planet HD 209458 b, where CRIRES+ showed no sign of a jet-like circulation. This change in behavior, together with the precise wind speed measurements, provides a unique opportunity to both quantitatively and qualitatively test the dynamical predictions of general circulation models (GCMs). Here, we present a comprehensive modeling study of these two planets, and discuss potential origins of the different circulation patterns. We further discuss the data processing techniques used to extract the Doppler signature of atmospheric circulation from high resolution spectra, and show how common telluric removal methods significantly bias the retrieved signal. We propose a new, PCA-based method to overcome these biases, which will be particularly useful for future ELT observations.

Classical Wolf-Rayet (WR) stars represent the final evolutionary stage of the most massive stars and are immediate progenitors of stellar-mass black holes. They are hot, stripped, often core-He burning stars that have strong, optically thick winds. Their formation has long been a topic of debate, with two popular channels being self-stripping through strong stellar winds or stripping by a companion. The multiplicity properties of WR stars can provide important insights into their formation as well as their eventual fate. In this talk, I will present a VLTI/GRAVITY survey searching for wide companions in these stars that are often inaccessible with spectroscopy. The strong capabilities of GRAVITY combined with the strong stellar winds of WR stars also led to serendipitous discoveries deserving their own investigation. I will briefly discuss these new exciting science cases and how we can advance them.

How are the extended and low-surface brightness halos of early-type galaxies built up, and which role does their environment play in their evolution? Studying their halos provides essential insights into their accretion history as accretion and merging events leave behind long-lasting signatures. These accretion events also release stars into the intra-group light (IGL), whose assembly is closely linked with the morphological transformation of galaxies in groups and clusters.

In the first part of my talk, I will present our work charactering the haloes and surrounding IGL of nearby massive early-type galaxies in groups and clusters with planetary nebulae as discrete kinematic tracers in synergy with deep and wide-field imaging, resolved stellar population studies, and integral-field spectroscopy. In the second part of my talk, I will address the discovery space for simultaneously studying planetary nebulae and stellar populations with integral-field spectrographs such as MUSE at the VLT and SITELLE at the CFHT. I will present our pilot papers on planetary nebulae in early- and late-type galaxies and contrast our observational results with predictions from state-of-the-art simulations of post-asymptotic giant branch stellar evolution.

Many exoplanets have been found, but still no Earth-like planet in a one-year orbit around a solar-type star. Limitations no longer stem from observations but from the physical variability of the host star, which greatly exceeds the radial-velocity modulation by an Earth-like planet.  Current observational efforts are to find planets around our Sun, monitoring the Sun-as-a-star with extreme precision radial-velocity spectrometers.  Theoretical hydrodynamic simulations produce time-variable solar spectral atlases, where radial-velocity jittering is followed in different spectral features.  A step toward exoEarth detection will be to identify dissimilar spectral lines (strong or weak, neutral or ionized, high or low excitation, etc.) with disparate responses to stellar activity, to disentangle wavelength shifts induced by exoplanets from those originating in stellar atmospheres.

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The ESPRESSO spectrograph, mounted on the VLT, was designed to achieve a long-term radial velocity (RV) precision of 10 cm/s, enabling the detection of Earth-mass planets within the habitable zones (HZ) of their host stars.

I present results from the instrument’s Guaranteed Time Observations campaign on three low-activity G, K, and M stars. We characterize the precision achievable from the timescales of minutes and dominated by pulsations, to timescales of years as required for HZ planet detection. To achieve this, we employ different RV calculation methods and activity indicators, assessing the limiting factors of both instrumental precision and stellar RV stability. Using a comprehensive analysis, we reach a RV floor level of 40 cm/s over a timescale of several years.

Interestingly, the ESPRESSO data shows no evidence for several previously announced planetary signals; we discuss the population of planets that, while not directly observed, remain consistent with ESPRESSO data. 

Finally, I explore the stellar physical phenomena that can be studied to further improve RV precision and enhance our planet detection capabilities. This is key for the future precise RV campaigns as enabled by ESPRESSO and similar instruments.

fist - FITS Inspection Streamlined Tool

The most commonly used FITS display tools, such as RTD or DS9 are now more than 25 years old. They are extremely powerful but can at times lack flexibility, specially in what comes scripting and interfacing. I created ´fist´ as a simple browser-based FITS interface, programmed completely on python. The package already includes the most commonly used features and allows for including additional instruments or tools.

exoptima: an observability and radial precision interface for observing Exoplanets  

´exoptima´ is a web-based interface that computes observability for a given object, and evaluates this observability not only for a specific date but also over the whole year. It also estimates radial velocity precision for a given instrument/telescope using a simple scaling from the ESPRESSO ETC values. The tool can be a valuable aid at planning Exoplanet RV observations.

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