Análise espectroscópica de estrelas com variabilidade dominada pelo processo de acreção em NGC 2264

Abstract

Classical T Tauri stars (CTTS) are low-mass young stars (M⋆ < 2 M⊙ ), with estimated ages between 10^6 - 107 years, still in the process of formation, and variable. In this work, we analyzed time series spectral data of 54 CTTS with photometric variability dominated by hot spots, in the young cluster NGC 2264 (∼ 3 Myr). Our goal was to investigate whether stars with accretion-dominated variability could be responsible for the observed spread of ∼ 1 − 2 dex in the mass accretion rate vs. stellar mass relation, which remains unexplained in the literature. First, we removed all nebular contamination from the stellar spectra. We then normalized the spectra and calculated the mass accretion rate using the Hα emission line flux. For our calculations, we adopted the most up-to-date average distance to the cluster (722 ± 2 pc), obtained from Gaia satellite data. Our results revealed an average mass accretion rate variability of 0.4 dex on day timescales, with only 7.4% of our stars exhibiting day-scale variability greater than 1 dex, within the range of the mass-dependent accretion rate dispersion reported in the literature. When comparing our results from a sample of accretion-dominated CTTS, with literature samples where variability arises from different processes (accretion, occultation by dust, cold spots), we found that our sample had a higher percentage of stars with strong variability. This suggests that while accretion variability alone cannot fully explain all the observed mass-dependent dispersion in accretion rates, it plays a significant role in contributing to this dispersion.