A. C. S. Rei, P. P. Petrov, J. F. Gameiro
Aim. We analysed high-resolution photospheric spectra of accreting T Tauri stars LkHα 321, V1331 Cyg, and AS 353A with the aim of clarifying the nature of the line-dependent veiling. Each of these objects shows a strong emission line spectrum and powerful wind features indicating high rates of accretion and mass loss.
Methods. Equivalent widths of hundreds of weak photospheric lines were measured in the observed spectra of high quality and compared with those in synthetic spectra of appropriate models of stellar atmospheres.
Results. The photospheric spectra of the three T Tauri stars are highly veiled. We found that the veiling is strongly line-dependent: larger in stronger photospheric lines and weak or absent in the weakest ones. No dependence of veiling on excitation potential within 0 to 5 eV was found. Different physical processes responsible for these unusual veiling effects are discussed in the framework of the magnetospheric accretion model.
Conclusions. The observed veiling has two origins: (1) an abnormal structure of stellar atmosphere heated up by the accreting matter, and (2) a non-photospheric continuum radiated by a hot spot with temperature lower than 10 000 K. The true level of the veiling continuum can be derived by measuring the weakest photospheric lines with equivalent widths down to ≈10 mÅ. A limited spectral resolution and/or low signal-to-noise ratio results in overestimation of the veiling continuum. In the three very active stars, the veiling continuum is a minor contributor to the observed veiling, while the major contribution comes from the line-dependent veiling.
stars: activity; stars: pre-main sequence; stars: variables: T Tauri; Herbig Ae/Be; stars: individual: LkHα 321; stars: individual: V1331 Cyg; stars: individual: AS 353A
Astronomy and Astrophysics
Volume 610, Article Number A40, Number of pages 10