Journal Article

Dead zones around young stellar objects: FU Orionis outbursts and transition discs

Rebecca G. Martin, Stephen H. Lubow, Mario Livio and J. E. Pringle

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 3, pages 2718-2725
Published in print July 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21076.x
Dead zones around young stellar objects: FU Orionis outbursts and transition discs

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We perform global time-dependent simulations of an accretion disc around a young stellar object with a dead zone (a region where the magneto-rotational instability cannot drive turbulence because the material is not sufficiently ionized). For infall accretion rates on to the disc of around 10−7 M yr−1, dead zones occur if the critical magnetic Reynolds number is larger than about 104. We model the collapse of a molecular gas cloud. At early times when the infall accretion rate is high, the disc is thermally ionized and fully turbulent. However, as the infall accretion rate drops, a dead zone may form if the critical magnetic Reynolds number is sufficiently large; otherwise the disc remains fully turbulent. With a dead zone the disc can become unstable to the gravo-magneto instability. The mass of the star grows in large accretion outbursts that may explain FU Orionis events. At late times there is not sufficient mass in the disc for outbursts to occur but the dead zone becomes even more prominent as the disc cools. Large inner dead zones in the later stages of disc evolution may help to explain observations of transition discs with an inner hole.

Keywords: accretion, accretion discs; protoplanetary discs; circumstellar matter; stars: pre-main-sequence

Journal Article.  5820 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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