Research at the SAGA Team

The SAGA (Stellar Abundances and Galactic Archaeology) Team conducts research on the areas of stellar evolution and Galactic stellar populations from the observational astrophysics point of view. We use spectroscopy to determine the chemical composition of stars. The SAGA team is exploring novel methodologies to extract complete, precise, and accurate chemical abundances from large samples of stellar spectra. A set of high-quality stellar abundances is the missing piece of the Galactic chemical enrichment puzzle that our team aims to provide.

Below, you can find brief descriptions of the large projects that we are currently working on.

Playing CHESS with stars

Project funded by a Sonata Bis grant from NCN (2020-2025)

Project members: R. Smiljanic (P.I.); Sergen Ozdemir and John E. Martínez Fernández (PhD students); Former members: Maria Luiza L. Dantas and Hélio D. Perottoni (Post-docs)

This project is going to provide multi-elemental stellar chemical abundances of unprecedented quality for a sample of more than 10 000 F-, G-, or K-type stars observed with the UVES spectrograph (Ultraviolet and Visual Echelle Spectrograph). The project aims to reveal the sequence of events that describe the chemical evolution of the Galaxy from the early stages to the present.

To achieve our ambitious goal, we will develop a new and innovative system for the large scale analysis of stellar spectroscopic data. This new CHEmical Survey analysis System, CHESS, will enable the extraction of complete, precise, and accurate chemical abundances from large samples of stellar spectra.

An important innovation of this analysis system is the combination of the physical modelling of stellar spectra, done using radiative transfer codes, with data-driven and machine learning methods.

By playing (running) CHESS with (a large sample of) stars, a quality jump in the determination of stellar chemical abundances will be achieved and, as consequence, we will take the understanding of the Galactic chemical enrichment to whole new level.

The old Milky Way: a holistic approach to an accurate analysis of metal-poor stars

Project funded by an OPUS-LAP grant co-financed by NCN and the German DFG (2024-2026)

Project members: R. Smiljanic (Polish co-P.I.) and N. Christlieb (German co-P.I.); André Rodrigo da Silva (PhD student in a 1-year project); Deepak (post-doc based in Poland) and Susmitha Antony (post-doc based in Germany); One additional post-doc under recruitment (in Poland).

The project is a collaboration between groups at the Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences (CAMK, the acronym in Polish), the Centre for Astronomy of the University of Heidelberg (ZAH, the acronym in German). Researchers at the Italian National Institute for Astrophysics (INAF, the acronym in Italian) involved in the CUBES project are also important collaborators.

Our ambition in this project is to conduct an unprecedented, homogeneous analysis of a large set of spectra of very metal-poor stars (defined here as those with metallicity [Fe/H]) ≲ −2.0). The aim is to obtain an accurate and detailed view of their chemical abundances, which will enable a meticulous study of the properties of the first nucleosynthesis sources of stellar origin in the Universe, as well as reconstructing the early chemical evolution of our galaxy.

Furthermore, we propose an original and bold plan to prepare for optimal use of the data to be collected with two new spectrographs that will become available soon: 4MOST (4-metre Multi-Object Spectroscopic Telescope) and CUBES (Cassegrain U-Band Efficient Spectrograph). The work plan is comprehensive and ambitious, including tasks to address the problem from the observational, theoretical, computational, and experimental sides.

Near-UV stellar spectroscopy: uncovering the past and building the future

Project funded by an OPUS grant from NCN (2019-2022; extended to 2023)

Project status: final report in preparation; final publications in preparation!

Former project members: R. Smiljanic (P.I.), André Rodrigo da Silva (PhD student), Riano Giribaldi and Maria Luiza L. Dantas (Post-docs)

This project concentrates in exploring the near-ultraviolet (near-UV) region of the stellar spectra that is observable from the ground (mostly between ∼ 3000 and ∼ 4500 Å). This spectral region is of difficult analysis because of the large number of atomic and molecular lines that are present in the spectra of F-, G-, and K-type stars.

We are working on improving our capabilities of computing synthetic stellar spectra in the near-UV. This improved capability will then be used to investigate different astrophysical problems:

  • The evolution of abundances of beryllium in metal-poor halo stars;
  • Abundances of heavy neutron-capture elements in metal-poor stars;
  • The near-UV photometric colors of globular cluster stars within the multiple-populations framework.

Moreover, we are involved in the CUBES consortium, an international consortium developing a new near-UV spectrograph to be installed at the Very Large Telescope(VLT). Our capabilities of simulating near-UV stellar spectra are useful for defining the desired characteristics of this new instrument.

This project is giving our group improved resources to use near-UV stellar spectra not only to uncover some of the secrets of the past of our Galaxy (the nucleosynthesis of light and heavy elements; the accretion processes in the early Galaxy; and the formation of globular clusters) but also to be part of future developments of instrumentation in the ESO community.

Acknowledgement

The research done at the SAGA Team has been supported by several grants awarded by National Science Center (NCN) over the years.