Protostars and Planets VI, Heidelberg, July 15-20, 2013
Veiling by lines: the new approach to interpretation of CTTS spectra.
Lamzin, Sergei (Sternberg Astronomical Institute, Moscow, Russia)
Dodin, Alexandr (Sternberg Astronomical Institute, Moscow, Russia)
We have calculated the structure and emergent spectrum of a hot spot that appear on CTTS surface due to heating by radiation from an accretion shock. For the first time not only continuum but also line emission of the hot spot was taken into account. Our calculations confirmed hypotheis of Petrov et al. (2001), Gahm et al. (2008) and Petrov et al. (2011) that the strongest of these lines manifest themselves as narrow components of helium and metal emission lines, while the weaker ones decrease significantly the depth of photospheric absorption lines, although until now, this effect has been thought to be due to the emission continuum alone. It appeared that the relative contribution of lines to the veiling increases with decreasing accretion flux, i.e. veiling by lines is the most important for CTTSs with moderate veiled spectra. We found that neglecting the contribution of lines to the veiling can produce an appreciable errors in determining the effective temperature, interstellar extinction,radial velocity, and v sin i for CTTS.
Assuming the pre-shock gas density N0 and velocity V0 to be the same at all points of the accretion stream cross section, we have calculated the spectrum of the star+circular spot system at various N0, V0, and parameters characterizing the star and the spot. Using nine stars as an example, we show that the theoretical optical spectra reproduce well the observed veiling of photospheric absorption lines in 0.4-1.2 mkm spectral band, as well as the profiles and intensities of the so-called narrow components of He II and Ca I emission lines with an appropriate choice of parameters. The accreted gas density N0 in all of the investigated stars except DK Tau has been found to be > 1e+12.
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