Towards a comprehensive study of stars

Our research activity revolves around four main thematic lines: Star Formation, Stellar Physics, Stellar Populations and The Sun and the Heliosphere.

I. Star Formation

'Pillars of Creation'
‘Pillars of Creation’. Credit: NASA, ESA, Hubble Heritage Team (STScI/AURA).

Star formation is a fundamental process for the enrichment of the interstellar medium (ISM), having driven the evolution of matter from the primordial conditions to the complex and chemically diverse conditions essential for life. Understanding the physical processes that led cold molecular clouds in the ISM to fragment into cores and evolve towards main-sequence stars and planetary systems remains a challenging task in modern astrophysics.

The Star Formation thematic line currently focuses on two main areas of research:

  • Star formation in the context of the large Galactic scale of the ISM, focusing on the role of filamentary structures in generating the observed mass distribution from low- to high-mass stars, and the impact of feedback from massive stars;
  • A detailed study of the evolution of individual pre-main-sequence stars and their circumstellar disks.

We have expertise on analysing submillimetre dust emission observations (Herschel) of star forming regions in order to identify and derive physical properties of filaments, dense cores and protostars, with our own analytical tools. Moreover, we perform infrared and millimetre studies (VLT and ALMA) of massive star formation and study the impact of their feedback to trigger new generations of stars in the compressed layers of the cold molecular medium.

The characterization of pre-main-sequence stars (PMS) and their environments and, in particular, T Tauri stars (TTSs), is achieved using several strategies, namely, photometric analysis of circumstellar disks around Classical T Tauri stars (cTTSs), spectroscopic studies (UV and visible) of signatures of outflows and accretion rates, and spectropolarimetry observations using SPIRou of the complex magnetic field structures permeating TTSs. We are also involved in the modelling of the topology of the magnetospheric region surrounding these objects, in devising simulations for the connection between accretion and outflows that ultimately control their evolution, and in the determination of mass accretion rates and angular momentum losses.

II. Stellar Physics

The Stellar Physics thematic line focuses on understanding the physical processes that take place in stars, from the stellar interior to the surface.

The team has a large expertise in data analysis and stellar modelling, and vast experience in probing the physics of stars. We develop, test and apply seismic inference tools aimed at retrieving information on chemical mixing and segregation in order to test, improve, and validate new formulations being implemented in stellar evolution models.

The seismic analyses conducted by the team allow the measurement of the stellar mass, age, metallicity and helium abundance, the depths of the convective and helium ionization regions, as well as the properties of stellar cores. Furthermore, we also measure and study rotation and magnetic activity in stars, both through asteroseismology and low-frequency brightness variations, in order to characterize stellar magnetic cycles and their driving mechanisms. Our research in stellar physics has strong connections with the evolution of stellar systems and their interaction with the circumstellar environment, including planets.

PLATO Satellite
PLATO Satellite. Credit: OHB-System-AG.

In the context of asteroseismology, we actively participate in international consortia related to the NASA space missions Kepler/K2 and TESS. Furthermore, we are leading and participating in several PLATO (ESA) working groups. The team also contributes to the Ariel (ESA) consortium, where it is responsible for the determination of ages, masses, and radii of the stars in the mission’s Reference Sample.

III. Stellar Populations

The Stellar Populations thematic line focuses on the precise characterization of solar-type and red-giant stars, which provides precious information that can be readily applied to several areas of research, including Galactic archaeology and Galactic chemical evolution.

Milky Way
The bulging heart of the Milky Way as it hangs over the Chajnantor plateau (Atacama Desert, Chile). Credit: ESO/P. Horálek.

The team has a vast experience in using high-resolution spectroscopy to determine stellar atmospheric parameters (namely, effective temperature, surface gravity, and metallicity), as well as the chemical compositions of stars, which are then used to investigate the interstellar medium’s elemental enrichment history across different regions of the Milky Way (or Galaxy). The team further combines the chemical compositions of stars with accurate asteroseismic age estimates to study the formation and evolution of different stellar populations of the Galaxy and of the Milky Way as a whole.

Currently, we actively participate in several international consortia, including PLATO, Ariel, HIRES@ELT, the Maunakea Spectroscopic Explorer (MSE), ESPRESSO@VLT, NIRPS@ESO 3.6-m Telescope, SPIRou@CFHT, and the Gaia-ESO Survey (concluded), among others.

IV. The Sun and the Heliosphere

The Sun and the Heliosphere thematic line focuses on studying the solar atmosphere as well as the influence of solar activity on the heliosphere and the Earth’s atmosphere, also known as space weather.

Solar physics is a branch of astrophysics that focuses on the study of the solar atmosphere. The Sun is the most important celestial body to us. In combination with the unique properties of our planet, it provides the necessary conditions to sustain life on Earth. Although the Sun has been studied for centuries, many questions still remain unanswered, from the sudden increase in the temperature of its outermost layer, the corona, to the prediction of its activity cycles and eruptive events.

Space Weather
Artist’s concept of space weather, the factors that cause it, and the technology impacted by it. Credit: NASA.

Space weather describes the time-varying conditions in the near-Earth space environment, including the solar wind, the magnetosphere, the ionosphere, and the thermosphere. The scientific aims of space weather are to understand solar activity, the interplanetary/planetary environments and the solar- and non-solar-driven perturbations that affect them, and also to forecast and nowcast the potential impact of solar activity on biological and technological systems. Having their origin in the Sun, space weather disturbances affect modern technological infrastructures, the most vulnerable of which are satellites, GNSS (Global Navigation Satellite System) navigation, communications, air navigation, electric power, and pipeline operations.

The team has vast experience in image processing, radiative transfer inversion, magnetohydrodynamic wave detection and analysis, and machine learning. We apply these techniques to a variety of data sets, e.g., to solar spectropolarimetric observations in order to study the solar atmosphere, and to in situ observations of GNSS signal disturbances, the Earth’s magnetic field etc., to better understand how solar activity influences the Earth and near-Earth heliosphere.

Currently, we participate and collaborate in several national and international projects. Members of the team lead the Portuguese participation in the European projects SWATNet and SWAIR, contribute actively to the EST Preparatory Phase, are building the first Portuguese solar spectropolarimeter, and are also developing the first detailed regional model of the ionosphere. We also maintain collaborations in the context of the SUNRISE and Solar Orbiter missions.