Stellar Astrophysics

POCTI/1999/FIS/34549

Principal investigator
João J. G. Lima

The main subject is the study of low-mass stars in the wider context of stellar evolution. We propose to characterize their internal structures, atmospheres and their interaction with the interstellar medium. Always bearing in mind how the characteristics evolve in time during the life of the star.

Therefore, the various components of the project, that constitute a coherent whole for tackling the problem, include:

- The study of the internal structure of the Sun and solar-type stars, for which seismic techniques are used. These techniques allow us to study convective zones in terms of their location, characteristics of overshoot, asphericity and variations with the magnetic cycle using observations (SOHO, GONG, etc.). We also try to extend these techniques to the detection of oscillations in young stars in order to study their internal structure.

- The study of atmospheres and winds, including various components:
(i) Multi-wavelength observations (infrared, optical, ultraviolet and X-rays) making use of several ground-base telescopes: ESO (La Silla and Paranal), La Palma (ING and NOT) and Mauna Kea; space-based telescopes such as XMM; and data-bases (IUE, ROSAT, HST).
(ii) Use of diagnostic techniques in photometry, high resolution spectroscopy and others, for example, emission measure, differential emission measure and Doppler tomography techniques.

The objective is, in any case, to improve the models of the atmospheres of stars similar to the sun but much younger, such T Tauri stars. In particular, the development of magnetic wind models constrained by the observations (those of ULYSSES and SOHO) and extended to recently formed stars, for which the magnetic field has an important role accelerating and collimating the wind. We wish to explore the validity of models and sample the parameter space that describes the phenomena under study; for example density, rotation, temperature, etc.

Special emphasis is given to recently formed stars, since this is a phase of the star when the level of activity is particularly strong both in terms of the variability and the associated time-scales, and also in comparison with the Sun. There is also an effort continuing to identify the mechanisms responsible for their activity and variability and also the consequences for the stellar wind of the interaction with the interstellar medium. In this regard we are trying to model the energy transfer mechanisms between these young stars and the interstellar medium. In this way we study both the morphology as well as the physical parameters of the objects that result from that interaction.

Funding institution
Fundação para a Ciência e a Tecnologia

Start: 7 August 2000
End: 29 April 2004