Seminar: Accretion and Magnetic Activity on the Young Brown Dwarf J0844-7833

We present HST-COS FUV and HST-STIS optical observations toward the young 52 M_Jup accreting brown dwarf 2MASS-J08440915-7833457 (J0844-7833). We analyse the hot FUV lines such C IV and Si IV, as well as the presence and origin of molecular hydrogen emission. The C IV line profiles are narrower than other classical T Tauri stars (CTTSs), resembling those of weak-lined T Tauri stars more closely. Despite other evidence for accretion such as an accretion disc and excess continuum emission, the C IV integrated line flux does not follow the level expected of an accreting object in the magnetically saturated regime. However, comparing J0844-7833 to more appropriate low mass analogs, it does show excess C IV emission characteristic of accretion, suggesting that the magnetic saturation level may need to be redefined for the lowest masses. The C IV/Si IV ratio is found to be significantly higher than most classical T Tauri stars, with a few exceptions (e.g. TW Hya). This indicates some silicate dust processing, though not as much as in TW Hya for example. We find that the L_CIV/L_acc ratio is higher for J0844-7833 than for other CTTS, which suggests a difference in the accretion structure at these masses. We discuss these results in the context of formation and accretion onto the lowest mass objects, including giant planets forming in the discs around other stars, a relatively unexplored mass regime in accretion studies.