Evidence for an MHD disk wind via optical forbidden line\n spectro-astrometry
E. T. Whelan, Ilaria Pascucci, Uma Gorti, Suzan Edwards, Richard D. Alexander, M. Sterzik, C. Melo
Abstract
Spectro-astrometry is used to investigate the low velocity component (LVC) of\nthe optical forbidden emission from the T Tauri stars RU Lupi and AS 205 N.\nBoth stars also have high velocity forbidden emission (HVC) which is tracing a\njet. For AS 205 N, analysis reveals a complicated outflow system. For RU Lupi,\nthe [O I] 6300 and [S II] 6716, 6731 LV narrow component (NC) is offset along\nthe same position angle (PA) as the HVC but with a different velocity gradient\nthan the jet, in that displacement from the stellar position along the rotation\naxis is decreasing with increasing velocity. From the LVC NC PA and velocity\ngradient, it is inferred that the NC is tracing a wide angled MHD disk wind. A\nphotoevaporative wind is ruled out. This is supported by a comparison with a\nprevious spectro-astrometric study of the CO fundamental line. The decrease in\noffset with increasing velocity is interpreted as tracing an increase in the\nheight of the wind with increasing disk radius. This is one of the first\nmeasurements of the spatial extent of the forbidden emission line LVC NC (~ 40\nau, 8 au for RU~Lupi in the [S II] 6731 and [O I] 6300 lines) and the first\ndirect confirmation that the LVC narrow component can trace an MHD disk wind.