Multi-Generational Star Formation in L1551

Abstract

The L1551 molecular cloud contains two small clusters of Class 0 and I protostars, as well as a halo of more evolved Class II and III YSOs, indicating a current and at least one past burst of star formation. We present here new, sensitive maps of 850 and 450 um dust emission covering most of the L1551 cloud, new CO J=2-1 data of the molecular cloud, and a new, deep, optical image of [SII] emission. No new Class 0/I YSOs were detected. Compact sub-millimetre emitters are concentrated in two sub-clusters: IRS5 and L1551NE, and the HL~Tauri group. Both stellar groups show significant extended emission and outflow/jet activity. A jet, terminating at HH 265 and with a very weak associated molecular outflow, may originate from LkHa 358, or from a binary companion to another member of the HL Tauri group. Several Herbig Haro objects associated with IRS5/NE were clearly detected in the sub-mm, as were faint ridges of emission tracing outflow cavity walls. We confirm a large-scale molecular outflow originating from NE parallel to that from IRS5, and suggest that the "hollow shell" morphology is more likely due to two interacting outflows. We confirm the presence of a prestellar core (L1551-MC) of mass 2-3 Mo north-west of IRS5. The next generation cluster may be forming in this core. The L1551 cloud appears cometary in morphology, and appears to be illuminated and eroded from the direction of Orion, perhaps explaining the multiple episodes of star formation in this cloud. The full paper (including figures) can be downloaded at http://www.jach.hawaii.edu/~gms/l1551/l1551-apj641.pdf, or viewed at http://www.jach.hawaii.edu/~gms/l1551/.