IRAS-08159-3543 - OPTICAL-DETECTION OF THE DUSTY, NEUTRAL BIPOLAR WIND OF A LUMINOUS YOUNG STELLAR OBJECT

We have detected by optical means the neutral bipolar wind from IRAS 0 8159-3543, a deeply embedded, luminous young stellar object (YSO) (L s imilar to 2.4 x 10(4) L., A(V) greater than or similar to 43 mag). The wind is observable, because it carries huge amounts of dust flowing o utward in the bright lobes at upsilon(f) similar to 570 km s(-1). The velocity held of the neutral how was determined by long-slit spectrosc opy of the broad Her line emitted by the ionized envelope near the uns een YSO and scattered by the moving dust. The velocity of the neutral flow far out in the lobes is nearly the same as the outflow velocity r eached in the ionized envelope. Therefore, most of the outflowing mate rial in the lobes must have been accelerated by the primary mechanism at work near the YSO. The ionized envelope is bisected in its equatori al plane by an optically thick layer; also, in the scattered spectrum of the YSO several chromospheric Fe II emission lines are observed. Th ese findings can be taken as evidence for an active accretion disk sur rounding the YSO and driving the wind seen in the ionized envelope. Th e outflowing dust observed in the lobes may be carried along by a neut ral wind leaving the outer (cooler) parts of the disk. We estimate the spectral type of the YSO (F-K) from the brightness and color of the s cattered continuum: in the H-R diagram the YSO is located far above th e zero-age main sequence and the theoretical stellar birthline. The to tal mass loss in the wind is M similar to 6 x 10(-5)-2 x 10(-4) M. yr( -1). The corresponding ratio M/L lies within the range derived from CO outflows (Levreault 1988). Thus, relative to the luminosity of the so urce, the wind carries as much momentum as is observed in molecular ou tflows driven by YSOs of low and intermediate luminosity. Within a vol ume whose total extent is about 0.5 pc, the neutral outflow in the lob es is interspersed with shock-ionized material (filling factor similar to 0.04), which moves outward at about one-fourth of the speed of the neutral flow.