Episodic accretion, protostellar radiative feedback, and their role in low-mass star formation

Stamatellos, Dimitris; Whitworth, Anthony Peter; Hubber, D. A.

doi:10.1111/j.1365-2966.2012.22038.x

Cited by 81 publications

(105 citation statements)

References 103 publications

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“…This could result in varying protostellar luminosities, which in turn was shown to have an effect on the properties and stability of protostellar discs (Stamatellos et al 2012). A detailed analysis of episodic accretion and varying luminosities, however, is deferred to a subsequent paper.…”

Section: Open Questions and Uncertaintiesmentioning

confidence: 99%

Accretion and magnetic field morphology around Class 0 stage protostellar discs

Seifried

Banerjee

Pudritz

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We analyse simulations of turbulent, magnetised molecular cloud cores focussing on the formation of Class 0 stage protostellar discs and the physical conditions in their surroundings. We show that for a wide range of initial conditions Keplerian discs are formed in the Class 0 stage already. In particular, we show that even subsonic turbulent motions reduce the magnetic braking efficiency sufficiently in order to allow rotationally supported discs to form. We therefore suggest that already during the Class 0 stage the fraction of Keplerian discs is significantly higher than 50%, consistent with recent observational trends but significantly higher than predictions based on simulations with misaligned magnetic fields, demonstrating the importance of turbulent motions for the formation of Keplerian discs. We show that the accretion of mass and angular momentum in the surroundings of protostellar discs occurs in a highly anisotropic manner, by means of a few narrow accretion channels. The magnetic field structure in the vicinity of the discs is highly disordered, revealing field reversals up to distances of 1000 AU. These findings demonstrate that as soon as even mild turbulent motions are included, the classical disc formation scenario of a coherently rotating environment and a well-ordered magnetic field breaks down. Hence, it is highly questionable to assess the magnetic braking efficiency based on non-turbulent collapse simulation. We strongly suggest that, in addition to the global magnetic field properties, the small-scale accretion flow and detailed magnetic field structure have to be considered in order to assess the likelihood of Keplerian discs to be present.

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Section: Open Questions and Uncertaintiesmentioning

confidence: 99%

Accretion and magnetic field morphology around Class 0 stage protostellar discs

Seifried

Banerjee

Pudritz

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…That is, while the time-averaged accretion rate is still high, the actual accretion onto the protostar happens in long quiescent phases and short burst phases triggered by some physical instabilities within the disk (e.g. Zhu et al 2010;Stamatellos et al 2012;Dunham & Vorobyov 2012). Considering this, we adopṫ M = 8 × 10 −8 M ⊙ yr −1 to calculate the accretion luminosity based on the observation of Elias 2-27 (Najita et al 2015), which gives L acc = 0.379 L ⊙ .…”

Section: Protostar Evolutionmentioning

confidence: 99%

Grand-design Spiral Arms in a Young Forming Circumstellar Disk

Tomida

Machida

Hosokawa

et al. 2017

ApJL

103

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We study formation and long-term evolution of a circumstellar disk in a collapsing molecular cloud core using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues and its radius becomes as large as 200 AUs toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum in the highly resistive disk. Although the spiral arms disappear in a few rotations as expected in a classical theory, new spiral arms form recurrently as the disk soon becomes unstable again by gas accretion. Such recurrent spiral arms persist throughout the Class-0 and I phase. We then perform synthetic observations and compare our model with a recent high-resolution observation of a young stellar object Elias 2-27, whose circumstellar disk has grand design spiral arms. We find good agreement between our theoretical model and the observation. Our model suggests that the grand design spiral arms around Elias 2-27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.

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“…Episodic accretion can also affect processes such as disk fragmentation (Stamatellos et al 2011(Stamatellos et al , 2012 and lithium depletion (Baraffe & Chabrier 2010). It is therefore important to understand the magnitude-frequency distribution and determine how often bursts of a certain intensity occur.…”

Section: And For Fuormentioning

confidence: 99%

Chemical tracers of episodic accretion in low-mass protostars

Visser

Bergin

Jørgensen

2015

A&A

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Aims. Accretion rates in low-mass protostars can be highly variable in time. Each accretion burst is accompanied by a temporary increase in luminosity, heating up the circumstellar envelope and altering the chemical composition of the gas and dust. This paper aims to study such chemical effects and discusses the feasibility of using molecular spectroscopy as a tracer of episodic accretion rates and timescales. Methods. We simulate a strong accretion burst in a diverse sample of 25 spherical envelope models by increasing the luminosity to 100 times the observed value. Using a comprehensive gas-grain network, we follow the chemical evolution during the burst and for up to 10 5 yr after the system returns to quiescence. The resulting abundance profiles are fed into a line radiative transfer code to simulate rotational spectra of C 18 O, HCO + , H 13 CO + , and N 2 H + at a series of time steps. We compare these spectra to observations taken from the literature and to previously unpublished data of HCO + and N 2 H + 6−5 from the Herschel Space Observatory. Results. The bursts are strong enough to evaporate CO throughout the envelope, which in turn enhances the abundance of HCO + and reduces that of N 2 H + . After the burst, it takes 10 3 -10 4 yr for CO to refreeze and for HCO + and N 2 H + to return to normal. The H 2 O snowline expands outwards by a factor of ∼10 during the burst; afterwards, it contracts again on a timescale of 10 2 -10 3 yr. The chemical effects of the burst remain visible in the rotational spectra for as long as 10 5 yr after the burst has ended, highlighting the importance of considering luminosity variations when analyzing molecular line observations in protostars. The spherical models are currently not accurate enough to derive robust timescales from single-dish observations. As follow-up work, we suggest that the models be calibrated against spatially resolved observations in order to identify the best tracers to be used for statistically significant source samples.

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Episodic accretion, protostellar radiative feedback, and their role in low-mass star formation

Cited by 81 publications

References 103 publications

Accretion and magnetic field morphology around Class 0 stage protostellar discs

Accretion and magnetic field morphology around Class 0 stage protostellar discs

Grand-design Spiral Arms in a Young Forming Circumstellar Disk

Chemical tracers of episodic accretion in low-mass protostars

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