GW Orionis: Inner disk readjustments in a triple system

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.

The Architecture of the GW Ori Young Triple-star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses

“…The residuals from our initial fit indicated that our formal velocity uncertainties are underestimated, and so the uncertainties on each measurement are scaled to achieve a reduced χ 2 ν = 1 for our final solution. The period of the inner orbit is consistent with that of Mathieu et al (1991) and Fang et al (2014); however, due to the SB2 nature of the system, most other orbital parameters are significantly different. We find a larger semi-amplitude for the primary, K A = 8.36 ± 0.14 km s −1 , a mass ratio of q ≡ M B /M A = 0.60 ± 0.02, and a statistically significant eccentricity e in = 0.13 ± 0.02.…”

“…However, they found the disk has an intermediate inclination to the line of sight (i disk ≈ 35 • ), in apparent conflict with the eclipse model. Indeed, this adds to a collection of indirect evidence for a more complicated geometry in the inner disk, including mid-infrared fluxes that vary on ∼year timescales (Fang et al 2014), and CO rovi-brational emission lines with multi-component profiles (which requires a complicated geometry and/or temperature structure in the inner disk; Najita et al 2003).…”

TheHerschel/PACS view of the Cep OB2 region: Global protoplanetary disk evolution and clumpy star formation

“…Nevertheless, this depends on the ability of the planet to block the gas flow (and not only dust) through the gap, which is uncertain (Müller & Kley 2013;Zhu & Stone 2014) and inconsistent with some of the accreting binary systems known to date (e.g. Fang et al 2014), including cases such as 82-272 in Tr 37, which is an accreting spectroscopic binary (Sicilia-Aguilar et al 2006b).…”

A study of dust properties in the inner sub-au region of the Herbig Ae star HD 169142 with VLTI/PIONIER

“…Such replenishing can be occasionally enhanced by a collision between the largest parental bodies or by gravitational stirring from a nearby planet (Krivov 2010). Small amounts of dust from the outer disk passing through the planet-induced gap region (Pinilla et al 2016) can also be an unsteady supply of inner NIR-emitting dust and cause NIR variations on timescale of several decades (e.g., in the case of GW Ori, Fang et al 2014). …”