TY - JOUR

T1 - Light scattering by moving dust grains in the immediate vicinity of young stars

AU - Grinin, V. P.

AU - Mitskevich, A. S.

AU - Tambovtseva, L. V.

N1 - Funding Information: We wish to thank J.M. Dlugach, who calculated the reflectance for the Henyey–Greenstein phase function, and P.P. Petrov and D.I. Nagirner for helpful discussions and advice. We are also grateful to the referee N.N. Chugai for carefully reading the manuscript of this paper and the remarks. This work was supported by grant no. 12 from the Presidium of the Russian Academy of Sciences and INTAS grant no. 03-51-6311.

PY - 2006/1

Y1 - 2006/1

N2 - We consider the problem of the distortion of the photospheric spectrum for a young star as its light is scattered in the inner accretion disk in the dust grain evaporation region. In T Tauri stars, this region is at a distance of the order of several stellar radii and is involved in the large-scale motions of matter with velocities of ∼100 km s-1 or higher. The light scattering in such a medium causes the frequency of the scattered radiation to be shifted due to the Doppler effect. We analyze the influence of this effect on the absorption line profiles in the spectra of T Tauri stars using classical results of the theory of radiative transfer. We consider two models of a scattering medium: (i) a homogeneous cylindrical surface and (ii) a cylindrical surface with an azimuth-dependent height (such conditions take place during the accretion of matter onto a star with an oblique magnetic dipole). We show that in the first case, the scattering of the photospheric radiation causes the absorption lines to broaden. If the motion of the circumstellar matter in the dust evaporation region is characterized by two velocity components, then the line profile of the scattered radiation is asymmetric, with the pattern of the asymmetry depending on the direction of the radial velocity. In the second case, the scattered radiation can cause periodic shifts of the absorption line centroid, which can be perceived by an observer as periodic radial-velocity variations in the star. We suggest that precisely this effect is responsible for the low-amplitude radial-velocity variations with periods close to the stellar rotation periods that have recently been found in some of the T Tauri stars.

AB - We consider the problem of the distortion of the photospheric spectrum for a young star as its light is scattered in the inner accretion disk in the dust grain evaporation region. In T Tauri stars, this region is at a distance of the order of several stellar radii and is involved in the large-scale motions of matter with velocities of ∼100 km s-1 or higher. The light scattering in such a medium causes the frequency of the scattered radiation to be shifted due to the Doppler effect. We analyze the influence of this effect on the absorption line profiles in the spectra of T Tauri stars using classical results of the theory of radiative transfer. We consider two models of a scattering medium: (i) a homogeneous cylindrical surface and (ii) a cylindrical surface with an azimuth-dependent height (such conditions take place during the accretion of matter onto a star with an oblique magnetic dipole). We show that in the first case, the scattering of the photospheric radiation causes the absorption lines to broaden. If the motion of the circumstellar matter in the dust evaporation region is characterized by two velocity components, then the line profile of the scattered radiation is asymmetric, with the pattern of the asymmetry depending on the direction of the radial velocity. In the second case, the scattered radiation can cause periodic shifts of the absorption line centroid, which can be perceived by an observer as periodic radial-velocity variations in the star. We suggest that precisely this effect is responsible for the low-amplitude radial-velocity variations with periods close to the stellar rotation periods that have recently been found in some of the T Tauri stars.

KW - Scattered radiation

KW - Stars - variable and peculiar

KW - T Tauri stars

UR - http://www.scopus.com/inward/record.url?scp=33644984018&partnerID=8YFLogxK

U2 - 10.1134/S1063773706020058

DO - 10.1134/S1063773706020058

M3 - Article

AN - SCOPUS:33644984018

VL - 32

SP - 110

EP - 119

JO - Astronomy Letters

JF - Astronomy Letters

SN - 1063-7737

IS - 2

ER -