At the end of the eighties, it has been noted that the photospheric absorption lines of Classical T Tauri Stars (CTTS) were not as deep as the corresponding lines of "normal" stars with the same spectral type. The veiling, a quantitative measure of this effect, was rapidly interpreted as due to the line filling by a smooth blue continuum presumably related to the accretion process. This continuum excess has apparently several spectral components which may indicate that there are actually several sources of veiling (Costa et al. 1999). It is assumed to be additive, however simultaneous photometric and spectroscopic data is required to definitively show it (Chelli et al. 1999).
Hartigan et al. (1989, HHKHS hereinafter) were the first to propose a simple algorithm to extract the veiling from high to very high resolution spectra of T Tauri stars. Recently, Chelli (1999, CH99 hereinafter) investigated further the method proposed by HHKHS, making a detailed balance of its astronomical performances and a rigorous analysis of the sources of bias. An important theoretical conclusion of this study stated that, in principle, it is possible to extract the veiling from the large scale structures of low resolution spectra of CTTS. The present work aims to demonstrate the validity of this statement reporting a practical application to quasi-simultaneous high (10000) and low (300) resolution spectra of the CTTS BP Tau.
© European Southern Observatory (ESO) 1999
Online publication: September 13, 1999