Episodic Accretion in Young Stars

Author(s)

M. Audard, P. Ábrahám, M. M. Dunham, J. D. Green, N. Grosso, K. Hamaguchi, J. H. Kastner, Á. Kóspál, G. Lodato, M. M. Romanova, S. L. Skinner, E. I. Vorobyov, Z. Zhu

Abstract

In the last 20 years, the topic of episodic accretion has gained

significant interest in the star-formation community. It is now viewed

as a common, although still poorly understood, phenomenon in low-mass

star formation. The FU Orionis objects (FUors) are long-studied examples

of this phenomenon. FU Orionis objects are believed to undergo accretion

outbursts during which the accretion rate rapidly increases from

typically 10-7 to a few 10-4 M⊙ yr-1, and remains

elevated over several decades or more. EXors, a loosely defined class of

pre-main-sequence stars, exhibit shorter and repetitive outbursts,

associated with lower accretion rates. The relationship between the two

classes, and their connection to the standard pre-main-sequence

evolutionary sequence, is an open question: Do they represent two

distinct classes, are they triggered by the same physical mechanism, and

do they occur in the same evolutionary phases? Over the past couple of

decades, many theoretical and numerical models have been developed to

explain the origin of FUor and EXor outbursts. In parallel, such

accretion bursts have been detected at an increasing rate, and as

observing techniques improve, each individual outburst is studied in

increasing detail. We summarize key observations of pre-main-sequence

star outbursts, and review the latest thinking on outburst triggering

mechanisms, the propagation of outbursts from star/disk to disk/jet

systems, the relation between classical EXors and FUors, and newly

discovered outbursting sources — all of which shed new light on

episodic accretion. We finally highlight some of the most promising

directions for this field in the near- and long-term.

Organisation(s)

Department of Astrophysics

Pages

387-410

DOI

https://doi.org/10.2458/azu_uapress_9780816531240-ch017

Publication date

2014

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics

Portal url

https://ucrisportal.univie.ac.at/en/publications/d77152cd-85f6-445e-972b-013cd83c6a6d