Astronomy Letters

, Volume 39, Issue 5, pp 315–335 | Cite as

Non-LTE modeling of narrow emission components of He and Ca lines in optical spectra of classical T Tauri stars

Article

Abstract

Using LTE calculations of the structure of T Tauri stellar atmospheres heated by radiation from an accretion shock (Dodin and Lamzin 2012), we have calculated the spectrum of the hot spot emerging on the stellar surface by taking into account non-LTE effects for He I, He II, Ca I, and Ca II. 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 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 in all of the investigated stars except DK Tau has been found to be N0 > 1012 cm−3. We have managed to choose the parameters for eight stars at a calcium abundance in the accreted gas ξCa equal to the solar one, but we have been able to achieve agreement between the calculations and observations for TW Hya only by assuming ξCa to be approximately a factor of 3 lower than the solar one. The estimated parameters do not depend on interstellar extinction, because they have been determined from the spectra normalized to the continuum level. The calculated intensity of Ca II lines has turned out to be lower than the observed one, but this contradiction can be eliminated by assuming that, in addition to the accreted gas with a high density N0, a more rarefied gas also falls onto the star. The theoretical equivalent widths and relative intensities of the subordinate He I lines disagree significantly with the observations. This is apparently because non-LTE effects should be taken into account when calculating the structure of the upper layers of the hot spot, the accuracy of the cross sections for collisional processes from upper levels is insufficient, and the spot inhomogeneity should probably be taken into account.

Keywords

stars-individual: GM Aur BP Tau DK Tau DN Tau GI Tau GK Tau V836 Tau DI Cep TW Hya-T Tauri stars-stellar atmospheres-radiative transfer-spectra 

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Copyright information

© Pleiades Publishing, Ltd. 2013

Authors and Affiliations

  • A. V. Dodin
    • 1
    • 2
  • S. A. Lamzin
    • 1
    • 2
  • T. M. Sitnova
    • 1
    • 2
  1. 1.Sternberg Astronomical InstituteMoscowRussia
  2. 2.Faculty of PhysicsMoscow State UniversityMoscowRussia

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