EDP Sciences
Free access
Issue
A&A
Volume 440, Number 3, September IV 2005
Page(s) 1105 - 1118
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20052901


A&A 440, 1105-1118 (2005)
DOI: 10.1051/0004-6361:20052901

Spatially resolving the accretion shocks on the rapidly-rotating M0 T-Tauri star MN Lupi

K. G. Strassmeier1, J. B. Rice2, A. Ritter1, M. Küker1, G. A. J. Hussain3, S. Hubrig4 and R. Shobbrook5

1  Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: [KStrassmeier;ARitter;MKueker]@aip.de
2  Department of Physics, Brandon University, Brandon, Manitoba R7A 6A9, Canada
3  Harvard Smithsonian Center for Astrophysics, Cambridge, USA
4  European Southern Observatory, 19001 Santiago, Chile
5  Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 Australia

(Received 18 February 2005 / Accepted 9 June 2005)

Abstract
We obtained high-resolution, high-quality VLT/UVES spectra to reconstruct the two-dimensional surface structure of the rapidly-rotating classical T-Tauri star MN Lupi on two separate nights. Both surface maps show a structured warm (5000 K) band centered around the pole at a latitude of $\approx$65°. Located within the band are two hot spots with temperatures of approximately or possibly even in excess of 5800 K, i.e. 2000 K above the effective photospheric temperature. Both maps appear with an adjacent equatorial band of temperature 3400 K, some 400-500 K below the effective photospheric temperature. While we interpret the two hot spots and the warm high-latitude band to be the heating points from two accretion impacts at the time of our observations and their redistributed energy trailed due to the fast stellar rotation, respectively, the cool equatorial band may not be cool after all but due to obscuration of the stellar surface by the innermost region of the disk. The fact that the hot spots appear at high stellar latitude is in agreement with the magnetospheric accretion model that proposes material funnelling onto the star along a predominantly dipolar magnetic field at roughly 50° latitude. The evidence of ongoing disk accretion, together with the very fast rotation of MN Lupi of just 3-4 times below its break-up velocity, suggests that the accretion mechanism is the cause of its rapid surface rotation. We present a model of magnetic star-disk coupling for MN Lupi that predicts a polar surface magnetic field of $\approx$3 kG.


Key words: stars: activity -- starspots -- stars: imaging -- stars: individual: MN Lup -- stars: individual: T Tauri -- stars: pre-main sequence

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© ESO 2005