A survey of optical and near-infrared jets in Taurus embedded sources

We describe optical ([S II], 6732 Angstrom) and near-infrared (H-2, 2.122 mu m) imaging observations of 22 embedded protostars in the Taurus-Auriga molecular cloud. Our survey identifies 4 new [S II] emission sources and 4 new H-2 sources. We detect three emission knots in both [S n] and H-2 one object with H-2 emission has no [S II] emission. These results increase the number of class I sources with optical or near-IR outflows to 13. We also detect [S II] emission in two additional class II sources, ZZ Tau IRS and IC 2087 IRS. When combined with previous results, the frequency of optical outflows among class II sources, similar to 10%, is much smaller than the frequency among class I sources, greater than or similar to 60%. The large difference in the frequency of optical and molecular outflows indicates that outflow activity decreases with age among pre-main-sequence stars. The jets in the Taurus-Auriga protostars are poorly collimated, with multiple knots indicative of large opening angles, similar to 10 degrees-40 degrees. The image morphologies are complex and suggest a time dependence in the direction of ejection. A simple precessing jet can account for the sinusoidal chain of [S II] knots-HH 31-associated with 04248+2612. The precessing jets, together with the good alignment between the axes of the jets, molecular outflows, and reflection nebulae, support current models where jets produce molecular outflows and bipolar cavities in the dense infalling cloud cores surrounding class I sources. (C) 1997 American Astronomical Society.