Letter to the Editor

Effects of dust on light-curves of ϵ Aurigae-type stars

J. Budaj

Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranska Lomnica, Slovak Republic
e-mail: budaj@ta3.sk

Received: 23 May 2011
Accepted: 15 July 2011

Abstract

Context.ϵ Auriga is one of the most mysterious objects in the sky. Previous modeling of its light-curve assumed a dark, inclined, non-transparent or semi-transparent dusty disk with a central hole. The hole was necessary to explain the light-curve with a sharp mid-eclipse brightening.

Aims. The aim of the present paper is to study the effects of dust on the light-curves of eclipsing binary stars and to develop an alternative physical model for ϵ Aur-type objects that is based on the optical properties of dust grains.

Methods. The code Shellspec was modified to calculate the light-curves and spectra of these objects. The code solves the radiative transfer along the line of sight in interacting binaries. Dust and angle-dependent Mie scattering were included in the code for this purpose.

Results. Our model of ϵ Aur consists of two geometrically thick flared disks: an internal optically thick disk and an external optically thin disk, which absorbs and scatters radiation. Disks are in the orbital plane and are almost edge-on. We argue that there is no need for a highly inclined disk with a hole to explain the current eclipse of ϵ Aur even if there is a possible shallow mid-eclipse brightening. We demonstrate that phase-dependent light scattering and the optical properties of the dust can have a significant effect on the light-curves of these stars and can even produce a mid-eclipse brightening. This is a natural consequence of the strong forward scattering. We also demonstrate that shallow mid-eclipse brightening might result from eclipses by nearly edge-on flared (dusty or gaseous) disks.