Outflow

In chapter 1, we mentioned `outflows' ejected from the protostars and pre-main-sequence stars. L1551 IRS5 is a typical example which shows a number of outflows are ejected in the course of star formation. One is molecular outflow, whose lobes extends $L \sim 0.5 (D/160{\rm pc}){\rm pc}$ in two opposite directions from the IRS-5 (Snell et al 1980). This is traced by CO $J=1\rightarrow 0$ emission line. They estimated an expansion velocity of the CO gas of $V_{\rm CO} \sim 15 {\rm km s^{-1}}$, a mass of 0.3 $M_\odot$. The dynamical age is equal to $\tau_{dyn}=L/V_{\rm CO}\sim 3\times 10^4{\rm yr}$. Inside the CO outflow lobe, several Herbig-Haro objects are found, which are emission-line nebulosities. Proper motion studies have revealed the motion of such H-H objects. Cudworth & Herbig (1979) reported HH28 and 29 have $0.15-0.20 {\rm arcsec yr^{-1}}$, which corresponds to $150 - 200{\rm km s^{-1}}$. In a neighbor of the IR source a stellar jet is found (Mundt & Fried 1983) by optical emission lines. Its size is equal to $17 {\rm arcsec} =4\times 10^{16}{\rm cm}(D/160{\rm pc})$ and the jet indicates rather well-collimated shape (the opening angle $\simeq 10^\circ$). The relationship between these two outflows (massive molecular outflow and less massive optical jet) are not clear yet.