Disk and outflow in Cepheus A-HW2: Interferometric SiO and HCO+ observations

Abstract

j\3.4 mm toward the Cepheus A East star-forming region. The HCO` line shows emission up to velocities of D50 km s~1 relative to the ambient cloud velocity. The spatial distribution of the highvelocity gas is bipolar, centered on HW2, and extends for D1@ along P.A.\55¡È60¡. The orientation of this molecular outÑow is very similar to that of the radio jet and CO emission associated with HW2. This conÐrms that current mass loss from HW2 takes place in the northeast-southwest direction. The momentum rate of the HCO` outÑow is 1.3]10~2 M km s~1 yr~1, 20 times larger than that of the _ ionized jet from HW2, suggesting that the jet could be largely neutral. Peaks of HCO` emission coincide with some of the radio-continuum sources in the region, consistent with outÑowÈambient gas interaction. Multiple episodes of outÑow activity from either one precessing source or a number of powering sources would explain the detection of moderate-velocity HCO` emission toward the HW7 chain of sources. The continuum emission at 3.4 mm is strongly peaked toward HW2, conÐrming that this is the most likely powering source for the outÑow. The SiO emission is barely elongated along P.A.\[33¡, i.e., almost perpendicular to the HCO` outÑow. A velocity trend consistent with a gradient of D31 km s~1 over 2A is detected along the major axis of the SiO structure ; these motions could be bound by 200 M_. Published H and CS observations support our suggestion that this represents the outer, D750 AU 2O radius, part of a circumstellar disk, although further observations are needed to conÐrm this interpretation.