Séminaire MHD (SEMHD)

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In this talk I will review the main theoretical aspects concerning the interaction between the magnetosphere of a young forming star and a surrounding accretion disk. Nowadays, it is clear that young stars are magnetically active, having large-scale magnetic fields of a few kG. Such a field is strong and extensive enough to control the accretion onto the star and to play a crucial role in the regulation of the stellar angular momentum. In fact, one of the most puzzling aspects of low-mass protostars (so called T Tauri stars) is that they exhibit slow and constant rotation periods (3–10 days, well below their break-up speed) despite the fact that they are still actively accreting and contracting.
Referring to analytical and numerical arguments, I will first analyze the mechanism which leads to the truncation of the disk and the formation of accretion funnels onto the surface of the star. I will then elucidate different solutions to balance the stellar spin-up due to the accretion torque and to contraction. In order to evaluate their efficiency, I will show results of numerical MHD simulations and describe different interaction regimes between the magnetosphere and the accretion disk.
Bibliographie :
• Analytical works
– Ghosh P., Lamb F.K., 1979, Astrophys. J., 232, 259.
– Koldoba A.V., Lovelace R.V.E., Ustyugova, G.V., Romanova M.M., 2002, Astron. J., 123, 2019.
– Li J., Wilson G., 1996, Astrophys. J., 527, 910.
– Matt S., Pudritz R.E., 2005a, Montly Notices Roy. Astron. Soc., 356, 167.
– Matt S., Pudritz R.E., 2005b, Astrophys. J., 632, L135.
– Mohanty S., Shu F.H., 2008, Astrophys. J., 687, 1323.
– Ostriker E.C., Shu F.H., 1995, Astrophys. J., 447, 813.
– Shu F., Najita J., Ostriker E., Wilkin F., Ruden S., Lizano S., 1994, Astrophys. J., 429, 781.
– Uzdensky D.A., Konigl A., Litwin C., 2002, Astrophys. J., 565, 1191.
• Numerical works
– Bessolaz N., Zanni C., Ferreira J., Keppens R., Bouvier J., 2008, Astron. Astrophys., 478, 155.
– Goodson A.P., Winglee R.M., 1999, Astrophys. J., 524, 159.
– Long M., Romanova M.M., Lovelace R.V.E., 2005, Astrophys. J., 634, 121.
– Long M., Romanova M.M., Lovelace R.V.E., 2008, Astrophys. J., 386, 1274.
– Miller K.A., Stone J.M., 1997, Astrophys. J., 489, 890.
– Romanova M.M., Ustyugova G.V., Koldoba A.V., Lovelace R.V.E., 2002, Astrophys. J., 578, 420.
– Romanova M.M., Ustyugova G.V., Koldoba A.V., Wick J.V., Lovelace R.V.E., 2003, Astrophys. J., 595, 1009.
– Romanova M.M., Ustyugova G.V., Koldoba A.V., Lovelace R.V.E., 2004, Astrophys. J., 610, 910.

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