Surprisingly Weak Magnetism on Young Accreting Brown Dwarfs
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چکیده
We have measured the surface magnetic flux on four accreting young brown dwarfs and one non-accreting young very low-mass star utilizing high resolution spectra of absorption lines of the FeH molecule. A magnetic field of 1-2 kG had been proposed for one of the brown dwarfs, 2MASS J1207334−393254, because of its similarities to higher mass T Tauri stars as manifested in accretion and the presence of a jet. We do not find clear evidence for a kilo-Gauss field in any of our young brown dwarfs but do find a 2 kG field on the young VLM star. Our 3-σ upper limit for the magnetic flux in 2MASS J1207334−393254 just reaches 1 kG. We estimate the magnetic field required for accretion in young brown dwarfs given the observed rotations, and find that fields of only a few hundred Gauss are sufficient for magnetospheric accretion. This predicted value
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تاریخ انتشار 2009