Seminars and Colloquia at ESO Garching and on the campus

Classical Cepheids are fundamental calibrators of the cosmic distance scale and powerful tracers of stellar populations. In this talk, I present a new grid of nonlinear, convective pulsation models computed with the Stellingwerf hydrodynamical code.

The models are computed by simultaneously varying the mass–luminosity relation and the efficiency of superadiabatic convection, enabling a systematic exploration of key physical uncertainties. In the Gaia passbands, they provide the first homogeneous theoretical atlas of light curves, together with new metallicity-dependent Period–Luminosity–Color and Period–Wesenheitrelations. When applied to Galactic Cepheids with measured metallicities, these relations allow the derivation of theoretical parallaxes that can be directly compared with Gaia astrometry, offering an independent assessment of the Gaia parallax zero-point in view of Gaia DR4.

The same framework is extended to the near-infrared by transforming bolometric light curves into the JWST and Roman photometric systems. I will briefly present the first theoretical Period–Luminosity–Color and Period–Wesenheit relations in these bands, currently in preparation, along with initial predictions for the distance scale and a comparison with recent results based on JWST Cepheid samples from the literature.

By combining pulsation models with updated BaSTI evolutionary tracks, new metallicity-dependent Period–Age and Period–Age–Color relations are also derived in both Gaia and JWST passbands, enabling precise age estimates for Galactic Cepheids and providing new constraints on the recent star-formation history of nearby galaxies.

These results define a unified theoretical framework bridging Gaia, JWST, and Roman observations, providing essential tools for next-generation high-precision measurements of the Hubble constant and for the study of stellar populations in the Local Universe. Implications for ongoing efforts within the SPECTRUM project will also be briefly discussed.

The large amount and diversity of documentation available for users of the European Southern Observatory (ESO) — including Phase 1, Phase 2, and Phase 3 guidelines, instrument manuals, data-reduction pipeline documentation, and archive interfaces — makes it increasingly challenging for the astronomical community to efficiently find relevant information. To address this, we have developed ESOFinder, an in-house chatbot powered by Large Language Models (LLMs) and Retrieval-Augmented Generation (RAG). ESOFinder integrates public information from instrument manuals, phase 1/2/3 documentation, data reduction pipeline manuals, the ESO Knowledge Base, and key web resources to provide concise, context-aware, and reference-linked answers to user queries about proposal/observation preparation, data retrieval, and data processing. Built on open-source European LLMs (Mistral AI models), ESOFinder ensures data privacy, transparency, and complete control over the knowledge base. Its multi-step architecture allows verification of retrieved documents and generated answers, reducing the risk of hallucinations and improving the reliability of responses compared to generic tools like ChatGPT or Gemini. The current version of ESOFinder is being tested internally at ESO/DMO to evaluate its performance, assess its integration with internal workflows, and identify limitations in coverage and accuracy. These tests will guide further improvements, including the incorporation of additional documentation, and enhanced retrieval strategies. Ultimately, ESOFinder aims to become an interface for users to navigate ESO’s complex observing documentation ecosystem and to support both staff and community astronomers in their daily tasks. In this talk, I will introduce ESOFinder, describe its design—including the RAG pipeline and answer-generation strategy—and present the quality assessment of the tool based on feedback collected from ESO staff. I will finalize with a tutorial on how to use the tool so ESO staff, students, and fellows can help us test it.