Asteroseismology and Variability of Young Stars

F. J. G. Pinheiro

Abstract. Stellar parameters such as the mass, luminosity and effective temperature are essential to test Pre-Main Sequence (PMS) evolutionary models. The main objective behind this work is to show that the study of the pulsational behaviour of PMS stars can be used to test these models.

For achieving that goal, the inner structure and pulsational properties of PMS stars have been examined. In particular, were analysed the pulsation periods and amplitudes of the solar-type oscillations that could be displayed by T Tauri stars (TTS). This study concluded that Christensen-Dalsgaard diagrams allow to infer the mass and evolutionary status of young stars with mass less than 1.5 solar masses.

Herbig Ae stars which lie inside the Instability Strip display δ-Scuti type of pulsations. In this way, the properties of these objects can be constrained by comparing the observed oscillations with linear non-adiabatic radial pulsation models. A study of V346 Ori is presented here.

Nevertheless, it is not enough to prove that asteroseismology allows to derive the physical properties of TTS. It is fundamental to determine the conditions under which such oscillations can be detected. Yet, no reliable analysis can be performed without a knowledge on the variability intrinsic to these objects.

For this reason, it was monitored the continuum and line (Hα & Hβ) emission of some TTS: namely DI Cep, GI Tau, GK Tau, GM Aur and LkHα264. By keeping track of the flux variations over a time interval longer than the rotation period of these objects, it is possible to disentangle the effects due to different sources of variability. For DI Cep it has been possible to associate a periodicity found in the data with the presence of a hot stellar spot.

Numerical simulations were used in an attempt to determine the length of a run, the sampling interval, the frequency and amplitude of the oscillations that are required to detect solar-type oscillations in TTS. In these simulations a periodic signal previously added to data simulating a set of observations from TTS, is retrieved. It has been concluded that using a 3 month run, the amplitude of the smallest oscillation which could be detected is about 3% of the amplitude associated with other sources of variability.

Ph.D. in Astronomy
Faculdade de Ciências da Universidade do Porto
Supervisor(s): M. J. P. F. G. Monteiro, D. F. M. Folha
2006