* Astronomy

Title: The bipolar outflow and disk of the brown dwarf ISO217
Authors: V. Joergens, A. Pohl, A. Sicilia-Aguilar, Th. Henning (ITA/ZAH Heidelberg, MPIA Heidelberg, Universidad de Madrid)

We show that the very young brown dwarf candidate ISO217 (M6.25) is driving an intrinsically asymmetric bipolar outflow with a stronger and slightly faster red-shifted component based on spectro-astrometry of forbidden [SII] emission lines observed in UVES/VLT spectra taken in 2009. ISO217 is only one out of a handful of brown dwarfs and VLMS (M5-M8) for which the existence of an outflow has been detected and which show that the T Tauri phase continues at the substellar limit. We measure a spatial extension of the outflow of ±190mas (±30AU) and velocities of ±40-50kms/s. We show that the strong velocity asymmetry between both lobes of a factor of 2 found in 2007 by Whelan et al. might be smaller than originally anticipated and likely evolves over a period of a few years. We detect also forbidden [FeII]7155 emission, which could potentially originate at the hot inner region of the outflow. To understand the ISO217 system, we have determined the properties of its accretion disk based on radiative transfer modelling of the SED. Our disk model is in very good agreement with Herschel/PACS data at 70mu. We find that the disk is flared and intermediately inclined (~45deg). The total disk mass (4e-6 Solar masses) is small compared to the accretion and outflow rate of ISO217 (~1e-10 Solar masses/yr). We suggest to explain this discrepancy by either a larger disk mass than inferred from the model (strong undetected grain growth) and/or by an on average lower accretion and outflow rate than the determined values. We show that a disk inclination significantly exceeding 45deg, as suggested from Halpha modelling and from the fact that both lobes of the outflow are visible, is not consistent with the SED data. Thus, despite its intermediate inclination angle, the disk of this brown dwarf appears to not obscure the red outflow component in [SII], which is very rarely seen for T Tauri objects (only one other case).

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