Observational signatures of linear warps in circumbinary discs

Abstract

In recent years an increasing number of observational studies have hinted at the presence of warps in protoplanetary discs, however a general comprehensive description of observational diagnostics of warped discs was missing. We performed a series of 3D SPH hydrodynamic simulations and combined them with 3D radiative transfer calculations to study the observability of warps in circumbinary discs, whose plane is misaligned with respect to the orbital plane of the central binary. Our numerical hydrodynamic simulations confirm previous analytical results on the dependence of the warp structure on the viscosity and the initial misalignment between the binary and the disc. To study the observational signatures of warps we calculate images in the continuum at near-infrared and sub-millimetre wavelengths and in the pure rotational transition of CO in the sub-millimetre. Warped circumbinary discs show surface brightness asymmetry in near-infrared scattered light images as well as in optically thick gas lines at sub-millimetre wavelengths. The asymmetry is caused by self-shadowing of the disc by the inner warped regions, thus the strength of the asymmetry depends on the strength of the warp. The projected velocity field, derived from line observations, shows characteristic deviations, twists and a change in the slope of the rotation curve, from that of an unperturbed disc. In extreme cases even the direction of rotation appears to change in the disc inwards of a characteristic radius. The strength of the kinematical signatures of warps decreases with increasing inclination. The strength of all warp signatures decreases with decreasing viscosity.

Flybys in protoplanetary discs: I. Gas and dust dynamics

“…An inner binary can generate similar signatures in the disc. See for example figures 9 and 10 in Juhász & Facchini (2017). The warped discs presented in that study have negative velocities on one side and positive velocities on the diametrically-opposite side (as in Figure 9).…”

Multi-epoch monitoring of the AA Tauri-like star V 354 Mon

“…Better characterizing the properties of inner disk warps is also relevant in view of recent discoveries of shadows seen in very high spatial resolution scattered light images (e.g., Marino et al 2015;Stolker et al 2016;Juhász & Facchini 2017, for disks around HAeBe stars) or as rotating structures observed with HST, for example, for the nearby CTTSs TW Hya (Debes et al 2017). An improved height model of the inner disk warp could address whether shadows seen in images of stellar light reflected at the disk surface might be related to the same disk warps that we studied in this paper.…”

Inferring giant planets from ALMA millimeter continuum and line observations in (transition) disks

“…We note that this problem arises no matter what is causing the gas depletion, unless material is rapidly infalling onto the star with radial supersonic velocities from the outer disk (Rosenfeld et al 2014;Owen 2016;Zhu & Stone 2017). Indeed some observations are now tracing hints of non-Keplerian motions within the central (sub-)mm cavity (Rosenfeld et al 2012;Casassus et al 2015;van der Plas et al 2017;Loomis et al 2017), but higher angular and spectral resolution observations are still needed to test this scenario (see Casassus 2016) and distinguish it from warped inner disks (e.g., Juhász & Facchini 2017;Facchini et al 2018). In this paper, we explore whether the CO cavities observed in most large transitions disks might be explained by a single massive planet.…”