GW Orionis: Inner disk readjustments in a triple system^⋆

¹ Departamento de Física TeóricaUniversidad Autónoma de Madrid, 28049 Cantoblanco Madrid, Spain
e-mail: mfang.cn@gmail.com
² SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
³ Universitäts-Sternwarte München, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany
⁴ Max-Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁵ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001 Vitacura, Santiago, Chile

Received: 6 May 2014
Accepted: 3 July 2014

Abstract

Context. Disks are expected to dissipate quickly in binary or multiple systems. Investigating such systems can improve our knowledge of the disk dispersal. The triple system GW Ori, still harboring a massive disk, is an excellent target.

Aims. We study the young stellar system GW Ori, concentrating on its accretion, wind activity and disk properties.

Methods. We use high-resolution optical spectra of GW Ori to do spectral classification and derive the radial velocities (RV). We analyze the wind and accretion activity using the emission lines in the spectra. We also use U-band photometry, which has been collected from the literature, to study the accretion variability of GW Ori. We characterize the disk properties of GW Ori by modeling its spectral energy distribution (SED).

Results.By comparing our data to the synthetical spectra, we classify GW Ori as a G8 star. Based on the RVs derived from the optical spectra, we confirm the previous result as a close companion in GW Ori with a period of ~242 days and an orbital semi-major axis of ~1 AU. The RV residuals after the subtraction of the orbital solution with the equivalent widths (EW) of accretion-related emission lines vary with periods of 5−6.7 days during short-time intervals, which are caused by the rotational modulation. The Hα and Hβ line profiles of GW Ori can be decomposed in two central-peaked emission components and one blue-shifted absorption component. The blue-shifted absorption components are due to a disk wind modulated by the orbital motion of the close companion. Therefore, the systems like GW Ori can be used to study the extent of disk winds. We find that the accretion rates of GW Ori are rather constant but can occasionally be enhanced by a factor of 2−3. We reproduce the SED of GW Ori by using disk models with gaps ~25−55 AU in size. A small population of tiny dust particles within the gap produces the excess emission at near-infrared bands and the strong and sharp silicate feature at 10 μm. The SED of GW Ori exhibits dramatic changes on timescales of ~20 yr in the near-infrared bands, which can be explained as the change in the amount and distribution of small dust grains in the gap. We collect a sample of binary/multiple systems with disks in the literature and find a strong positive correlation between their gap sizes and separations from the primaries to companions, which is generally consistent with the prediction from the theory.