Millimeter observations of the disk around GW Orionis

Abstract

The GW Ori system is a pre-main sequence triple system (GW Ori A/B/C) with companions (GW Ori B/C) at ∼1 AU and ∼8 AU, respectively, from the primary (GW Ori A). The primary of the system has a mass of 3.9 M ⊙ , but shows a spectral type of G8. Thus, GW Ori A could be a precursor of a B star, but it is still at an earlier evolutionary stage than Herbig Be stars. GW Ori provides us an ideal target for experiments and observations (being a "blown-up" upscaled Solar System with a very massive "sun" and at least two "upscaled planets"). We present the first spatially-resolved millimeter interferometric observations of the disk around the triple pre-main-sequence system GW Ori, obtained with the the Submillimeter Array, both in continuum and in the 12 CO J = 2 − 1, 13 CO J = 2 − 1, and C 18 O J = 2 − 1 lines. These new data reveal a huge, massive, and bright disk in the GW Ori system. The dust continuum emission suggests a disk radius around 400 AU. But, the 12 CO J = 2 − 1 emission shows much more extended disk with a size around 1300 AU. Due to the spatial resolution (∼1 ′′ ), we cannot detect the gap in the disk which is inferred from spectral energy distribution (SED) modeling. We characterize the dust and gas properties in the disk by comparing the observations with the predictions from the disk models with various parameters calculated with a Monte Carlo radiative transfer code RADMC-3D. The disk mass is around 0.12 M ⊙ , and the disk inclination with respect to the line of sight is around ∼ 35• . The kinematics in the disk traced by the CO line emission strongly suggest that the circumstellar material in the disk is in Keplerian rotation around GW Ori. Tentatively substantial C 18 O depletion in gas phase is required to explain the characteristics of the line emission from the disk.

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

“…We estimated the total disk mass of GW Ori using the results from our 13 CO and C 18 O modeling in §3.1, which we emphasize are very indirect measurements that rely upon uncertain conversion factors between 12 CO and H 2 . We find somewhat larger disk masses when modeling C 18 O compared to 13 CO (0.095 M vs. 0.020 M , respectively), which is in conflict with the finding of Fang et al (2017) that C 18 O must be depleted relative to 13 CO. We attribute the differences in our disk masses to insufficiently complex models of disk structure and optical depth effects, and note that in general estimating disk masses from CO is notoriously difficult (Yu et al 2017), although in our case it is encouraging that they are roughly consistent with estimates based on the dust continuum emission (0.1 M ; Fang et al 2017). In the context of the large disk mass survey by Andrews et al (2013), GW Ori's disk mass is slightly larger than the mean predicted value for its stellar mass, although still consistent with the large 1σ envelope in this relationship at high stellar masses.…”

“…The disk material provided a natural explanation for the quasi-periodic optical dimming of GW Ori over ∼30 day durations: the suspicion was that a disk around the secondary was eclipsing the primary, presuming a nearly edge-on viewing angle (Shevchenko et al 1992(Shevchenko et al , 1998. Fang et al (2017) spatially resolved the disk material with Submillimeter Array (SMA) observations of the dust continuum and the line emission from CO isotopologues, demonstrating its large radial extent and therefore presumably circum-triple architecture. However, they found the disk has an intermediate inclination to the line of sight (i disk ≈ 35 • ), in apparent conflict with the eclipse model.…”

A triple-star system with a misaligned and warped circumstellar disk shaped by disk tearing

“…S1B) shows the intensity-weighted line-of-sight velocity of the Doppler-shifted CO gas. The velocity gradient seen on the largest scales (> 200 au) is broadly consistent with the one seen in the outer disk (15,45), with the Northern part of the disk receeding from the observer (red-shifted). In the inner 200 au we see a twist in the first-moment map, whose morphology is consistent with a pattern seen previously in a lower-resolution ALMA observation (83).…”

“…Given that polarized intensity images are typically dominated by forwardscattering from dust grains, this indicates that the Eastern side of the disk is facing towards the observer. This conclusion is also supported by CO rotation measurements (15,45) that show that the Northern part of the disk is receeding from the observer (red-shifted). If the disk rotates in retrograde motion (i.e.…”

“…For all rings we identify the southern node as the ascending node, which is consistent with the rings being in retrograde rotation (i.e. following the rotation direction of the stellar orbits) and the Northern part of the rings receeding from the observer, as derived from the CO rotation measurements (15,45).…”