Variable Accretion and Outflow in Young Brown Dwarfs

We report on the first dedicated monitoring campaign of spectroscopicvariability in young brown dwarfs. High-resolution optical spectra of sixtargets in nearby star-forming regions were obtained over 11 nights between2005 January-March on the Magellan 6.5m telescope. We find significantvariability in Halpha and a number of other emission lines related to accretionand outflow processes on a variety of timescales ranging from hours to weeks toyears. The most dramatic changes are seen for 2M1207, 2M1101 and ChaI-ISO217.We observe possible accretion rate changes by about an order of magnitude intwo of these objects, over timescales of weeks (2M1207) or hours (2M1101). Theaccretion 'burst' seen in 2M1101 could be due to a 'clumpy' flow. We also seeindications for changes in the outflow rate in at least three objects. In onecase (ISO217), there appears to be a ~1-hour time lag between outflow andaccretion variations, consistent with a scenario in which the wind originatesfrom the inner disk edge. Our variability study supports a close to edge-oninclination for the brown dwarf LS-RCrA 1. The fact that all targets in oursample show variations in accretion and/or outflow indicators suggests thatstudies of young brown dwarf properties should be based either on large samplesor time series. As an example, we demonstrate that the large scatter in therecently found accretion rate vs. mass relationship can be explained primarilywith variability. The observed profile variations imply asymmetric accretionflows in brown dwarfs, which, in turn, is evidence for magnetic funneling bylarge-scale fields. We show that accreting sub-stellar objects may harbormagnetic fields with ~kG strength (abridged).