The origin of tail-like structures around protoplanetary disks

Abstract

Aims. We study the origin of tail-like structures recently detected around the disk of SU Aurigae and several FU Orionis type stars. Methods. Dynamic protostellar disks featuring ejections of gaseous clumps and quiescent protoplanetary disks experiencing a close encounter with an intruder star were modelled using the numerical hydrodynamics code FEOSAD. Both the gas and dust dynamics were taken into account, including dust growth and mutual friction between the gas and dust components. Only plane-of-the-disk encounters were considered. Results. Ejected clumps produce a unique type of tails that are characterized by a bow-shock shape. These tails owe its origin to the supersonic motion of the ejected clumps through the dense envelope, which often surrounds young gravitationally unstable protostellar disks. The ejected clumps either sit at the head of the tail-like structure or disperse if their mass is insufficient to withstand the head wind of the envelope. On the other hand, close encounters with quiescent protoplanetary disks produce three types of the tail-like structures, which we defined as pre-collisional, post-collisional, and spiral tails. These tails can in principle be distinguished by peculiar features of the gas and dust flow in and around them. We found that the brown-dwarf-mass intruders do not capture circumintruder disks during the encounter, while the sub-solar-mass intruders can acquire appreciable circumintruder disks with elevated dust-to-gas ratios, which can ease their observational detection. However, this is true only for prograde collisions; the retrograde intruders fail to collect an appreciable gas and dust from the disk of the target. The masses of gas in the tails vary in the 0.85-11.8 M Jup limits, while the total mass of dust lies in the 1.75-30.1 M ⊕ range, with the spiral tails featuring the highest masses. The predicted mass of dust in the model tail-like structures is therefore higher than what was inferred for similar structures in SU Aur, FU Ori, and Z CMa, making their observational detection feasible. Conclusions. Tail-like structures around protostellar and protoplanetary disks can act as a smoking gun to infer interesting phenomena, such as clump ejection or close encounters. particular, the bow-shock morphology of the tails could point to clump ejections as a possible formation mechanism. Further numerical and observational studies are needed to better understand the detectability and properties of the tails.

Kinematic Structures in Planet-Forming Disks

“…Additional multiple systems show signs of stellar interactions, such as tidal streams: FU Ori ( Tobin et al 2016;Alves et al 2019). The observed features are consistent with numerical predictions (Dai et al 2015a;Bate 2018;Cuello et al 2019;Vorobyov et al 2020) and offer laboratories to better understand the disk dynamics by quantifying their response to gravitational torques. In particular, the synergy of gas dynamics in spirals, and the distribution of small and large dust grains as traced by IR scattered light images and mm thermal emission, can lead to constraints on the coupling between gas and dust in disks, and on the thermal structure of the disk itself (Juhász and Rosotti 2018;Rosotti et al 2020a).…”

Distinguishing between different mechanisms of FU-Orionis-type luminosity outbursts

“…All three burst mechanisms were simulated using the same numerical hydrodynamics code FEOSAD 1 . A detailed description of the code is presented in Vorobyov & Elbakyan (2018), with modifications relevant for modeling the MRI bursts and close encounters in Kadam et al (2020) and Vorobyov et al (2020c), respectively. Here, we review only the key aspects of burst modeling.…”

“…To study the bursts caused by close encounters, we use the model recently presented in Vorobyov et al (2020c). In this collision model, a diskless star is set on an encounter trajectory with a protoplanetary disk around a sub-solar mass star.…”

Molecules with ALMA at Planet-forming Scales (MAPS) XIX. Spiral Arms, a Tail, and Diffuse Structures Traced by CO around the GM Aur Disk

“…Gravitational instabilities (GI), potentially precipitated by infalling material, may drive spiral arm formation as well as the formation of tail-like structures through gas clumps ejected when the disk fragments (e.g., Boss 1997;Gammie 2001;Vorobyov & Basu 2005;Kratter et al 2008;Harsono et al 2011;Vorobyov et al 2020). It is ambiguous from Toomre Q parameter estimates whether GM Aur is in fact unstable.…”

“…Simulations have shown that close stellar encounters can create spiral and tail structures in disks (e.g., Clarke & Pringle 1993;Pfalzner 2003;Cuello et al 2019;Vorobyov et al 2020). Gas structures reminiscent of the GM Aur system have also been detected in several systems with stars separated by projected distances of a few hundred au, including RW Aur A and B (Rodriguez et al 2018), AS 205 N andS (Kurtovic et al 2018), and UX Tau A and C (Zapata et al 2020).…”