Emission Line Variability of the Accreting Young Brown Dwarf 2MASSW J1207334-393254: From Hours to Years

We have obtained a series of high-resolution optical spectra for 2MASSW J1207334-393254 (2M1207). Two consecutive observing nights at the ESO Very Large Telescope with the UVES spectrograph yielded a timeseries with a resolution of ∼ 12min. Additional high-resolution optical spectra were obtained months apart at the Magellan Clay telescope using the MIKE instrument. Combined with previously published results, these data allow us to investigate changes in the emission line spectrum of 2M1207 on timescales of hours to years. Most of the emission line profiles of 2M1207 are broad, in particular that of Hα, indicating that the dominant fraction of the emission must be attributed to disk accretion rather than to magnetic activity. From the Hα 10% width we deduce a relatively stable accretion rate between 10M⊙/yr for two nights of consecutive observations. Therefore, either the accretion stream is nearly homogeneous over