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Can We Predict the Global Magnetic Topology of a Pre-main-sequence Star from Its Position in the Hertzsprung–Russell Diagram?

Gregory, S. G. and Donati, J.-F and Morin, J. and Hussain, G. A. J. and Mayne, N. J. and Hillenbrand, L. A. and Jardine, M. (2012) Can We Predict the Global Magnetic Topology of a Pre-main-sequence Star from Its Position in the Hertzsprung–Russell Diagram? Astrophysical Journal, 755 (2). Art. No. 97. ISSN 0004-637X. doi:10.1088/0004-637X/755/2/97.

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Zeeman-Doppler imaging studies have shown that the magnetic fields of T Tauri stars can be significantly more complex than a simple dipole and can vary markedly between sources. We collect and summarize the magnetic field topology information obtained to date and present Hertzsprung-Russell (H-R) diagrams for the stars in the sample. Intriguingly, the large-scale field topology of a given pre-main-sequence (PMS) star is strongly dependent upon the stellar internal structure, with the strength of the dipole component of its multipolar magnetic field decaying rapidly with the development of a radiative core. Using the observational data as a basis, we argue that the general characteristics of the global magnetic field of a PMS star can be determined from its position in the H-R diagram. Moving from hotter and more luminous to cooler and less luminous stars across the PMS of the H-R diagram, we present evidence for four distinct magnetic topology regimes. Stars with large radiative cores, empirically estimated to be those with a core mass in excess of ~40% of the stellar mass, host highly complex and dominantly non-axisymmetric magnetic fields, while those with smaller radiative cores host axisymmetric fields with field modes of higher order than the dipole dominant (typically, but not always, the octupole). Fully convective stars above ≳ 0.5 M_☉ appear to host dominantly axisymmetric fields with strong (kilo-Gauss) dipole components. Based on similarities between the magnetic properties of PMS stars and main-sequence M-dwarfs with similar internal structures, we speculate that a bistable dynamo process operates for lower mass stars (≾ 0.5 M_☉ at an age of a few Myr) and that they will be found to host a variety of magnetic field topologies. If the magnetic topology trends across the H-R diagram are confirmed, they may provide a new method of constraining PMS stellar evolution models.

Item Type:Article
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Morin, J.0000-0002-4996-6901
Additional Information:© 2012 American Astronomical Society. Received 2012 January 30; accepted 2012 June 21; published 2012 August 1. The authors thank L. Siess, N. Baliber, and F. C. Adams for insightful discussions, E. Tognelli and P. G. Prada Moroni for sending stellar internal structure information from their PMS evolution models, Y.-C. Kim for sending convective turnover time estimates, and the referee for useful comments. S.G.G. is supported by NASA grant HST-GO-11616.07-A. J.M. is supported by a postdoctoral fellowship of the Alexander von Humboldt foundation. The “Magnetic Protostars and Planets” (MaPP) project is supported by the funding agencies of CFHT and TBL (through the allocation of telescope time) and by CNRS/INSU in particular, as well as by the French “Agence Nationale pour la Recherche” (ANR).
Funding AgencyGrant Number
Alexander von Humboldt FoundationUNSPECIFIED
Canada-France-Hawaii Telescope (CFHT)UNSPECIFIED
Centre National de la Recherche Scientifique/Institut national des sciences de l'Univers (CNRS/INSU)UNSPECIFIED
Agence Nationale pour la Recherche (ANR) (France)UNSPECIFIED
Subject Keywords:Hertzsprung-Russell and C-M diagrams; stars: evolution; stars: formation; stars: interiors; stars: magnetic field; stars: pre-main sequence
Issue or Number:2
Record Number:CaltechAUTHORS:20121102-072944939
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Official Citation:Can We Predict the Global Magnetic Topology of a Pre-main-sequence Star from Its Position in the Hertzsprung–Russell Diagram? S. G. Gregory et al. 2012 ApJ 755 97
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35251
Deposited By: Ruth Sustaita
Deposited On:02 Nov 2012 14:55
Last Modified:09 Nov 2021 23:13

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