Journal Article

Evolution of spin direction of accreting magnetic protostars and spin–orbit misalignment in exoplanetary systems

Dong Lai, Francois Foucart and Douglas N. C. Lin

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 4, pages 2790-2798
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.18127.x
Evolution of spin direction of accreting magnetic protostars and spin–orbit misalignment in exoplanetary systems

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Recent observations have shown that in many exoplanetary systems the spin axis of the parent star is misaligned with the planet’s orbital axis. These have been used to argue against the scenario that short-period planets migrated to their present-day locations due to tidal interactions with their natal discs. However, this interpretation is based on the assumption that the spins of young stars are parallel to the rotation axes of protostellar discs around them. We show that the interaction between a magnetic star and its circumstellar disc can (although not always) have the effect of pushing the stellar spin axis away from the disc angular momentum axis towards the perpendicular state and even the retrograde state. Planets formed in the disc may therefore have their orbital axes misaligned with the stellar spin axis, even before any additional planet–planet scatterings or Kozai interactions take place. In general, magnetosphere–disc interactions lead to a broad distribution of the spin–orbit angles, with some systems aligned and other systems misaligned.

Keywords: accretion, accretion discs; protoplanetary discs; stars: magnetic field

Journal Article.  7502 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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