Extremely high-velocity co flows in young stellar objects

Very sensitive, wideband CO J = 1-0 and HCO + J = 1-0 line spectra axe obtained using the 12 m telescope at Kitt Peak for several young stellar objects: GL 490, HH7-11 (see also Lizano et al. 1987), S140, and MWC 1080. Very weak and "extremely high-velocity" (EHV) CO wings are found in all objects. Velocity widths of the EHV wings are substantially larger than those of the associated classical high-velocity outflows (e.g., Bally and Lada 1983). Broad wings are also found in HCO + spectra, but they are not as broad as CO wings in most cases. The observed parameters of the spectra are summarized in Table 1 and the spectra axe shown in Figure 1. The maximum velocity width AVm~x in Table 1 is measured at 2 mK level. All CO spectra are flat at least at one extreme velocity, i.e., either at maximum blueshifted velocity or at maximum redshifted velocity, and increase slowly at intermediate velocities before they finally increase steeply at low velocities. The line profiles suggest that some of the EHV CO emission is emitted from the neutral stellar wind (Lizano et al. 1987) which has not experienced much interaction with the surrounding medium, and some from both a decelerating neutral stellar wind and an ambient material entrained by a stellar wind. This interpretation is consistent with HCO + observations which show enhancement of HCO + emission compared to CO emission at high velocities.