(2014) provides a comprehensive review of these and other burst triggering mechanisms.ĭistinguishing between different outburst triggers is not an easy task. Global simulations of clustered star formation also indicate that gravitationally unstable protostellar disks with high rates of mass infall from the surrounding environment can drive accretion bursts ( Kuffmeier et al. 2017), planet-disk interaction and mass-exchange ( Lodato & Clarke 2004 Nayakshin & Lodato 2012), and a close encounter between a protoplanetary disk and an intruder star in young stellar clusters (e.g., Pfalzner 2008 Forgan & Rice 2010). 2020), infall of gaseous clumps formed through disk gravitational fragmentation (e.g., Vorobyov & Basu 2005, 2015 Machida et al. These mechanisms include the magnetorotational instability (MRI) in the innermost disk regions prompted by a sudden increase in the ionization fraction (e.g., Armitage et al. However, the mechanisms that trigger such an increase are uncertain. It is generally agreed that FUors are caused by a sudden increase in the mass accretion rate from the disk on the protostar.
2014 Connelley & Reipurth 2018) and several new candidates are routinely discovered every year. Dozens of such objects have been confirmed to date ( Audard et al. FU-Orionis-type luminosity outbursts (FUors) that are characterized by an increase in luminosity by some orders of magnitude are a prime example of accretion variability. Evidence is growing that protostellar accretion is not constant or steadily declining, but is highly variable (e.g., Contreras Peña et al. One aspect that is currently under debate is the behavior of protostellar accretion with time. Protostars grow in mass through accretion from a surrounding protostellar disk, but the details of protostellar accretion are not fully understood. Key words: protoplanetary disks / stars: protostars / hydrodynamics / instabilities Further studies including a wider model parameter space and the construction of synthetic disk images in thermal dust and molecular line emission are needed to constrain the mechanisms that lead to FU Orionis bursts. Burst-triggering mechanisms are associated with distinct kinematic features in the burst-hosting disks that may be used for their identification. The considered burst mechanisms produce a variety of light curves with the burst amplitudes varying in the Δ m = 2.5−3.7 limits, except for the clump-infall model where Δ m can reach 5.4, although the derived numbers may be affected by a small sample and boundary conditions.Ĭonclusions. The deviations of velocity channels in the burst-hosting disks from a symmetric pattern typical of Keplerian disks are strongest for the clump-infall and collision models, and carry individual features that may be useful for the identification of the corresponding burst mechanism. Velocity channel maps also show distinct kinks and wiggles, which are caused by gas disk flows that are particular to each considered burst mechanism. The disks in the stellar encounter and clump-infall models are characterized by deviations from the Keplerian rotation of tens of per cent, while the disks in the MRI models are characterized by deviations of only a few per cent, which is mostly caused by the gravitational instability that fuels the MRI bursts. We found that the circumstellar disks featuring accretion bursts can bear kinematic features that are distinct for different burst mechanisms, which can be useful when identifying the origin of a particular burst. Numerical hydrodynamics simulations in the thin-disk limit were employed to model the bursts in disk environments that are expected for each burst mechanism. We study all three of these burst mechanisms to determine the disk kinematic characteristics that can help to distinguish between them.
Accretion and luminosity bursts can be triggered by three distinct mechanisms: the magnetorotational instability (MRI) in the inner disk regions, clump infall in gravitationally fragmented disks, and close encounters with an intruder star. Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, No.1, Sec. Research Institute of Physics, Southern Federal University, Elbakyan 2 ,3, Hauyu Baobab Liu 4 and Michihiro Takami 4ĭepartment of Astrophysics, University of Vienna,Į-mail: of Physics, University of Leicester,
Astronomical objects: linking to databasesĮduard I.Including author names using non-Roman alphabets.Suggested resources for more tips on language editing in the sciences Punctuation and style concerns regarding equations, figures, tables, and footnotes
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