The Triple Protostellar System L1551 IRS5: Molecular Core to Circumstellar Disks
          Jeremy Lim, Institute of Astronomy & Astrophysics, Academia Sinica, Taiwan
          Shigehisa Takakuwa, Smithsonian Astrophysical Observatory, USA

          We present dust and ionized-gas images of L1551 IRS5 at angular resolutions as high as ~30 mas, corresponding to a spatial resolution of ~5 AU.  These are the most detailed such images ever made of a protostellar system.  We confirm the two known circumstellar dust disks with sizes of ~15 AU and a projected separation of ~45 AU, close to the average separation of binary systems.  We also report a previously unknown third dust disk of size ~10 AU at a projected separation of only ~11 AU from the primary, thus making L1551 IRS5 a triple system.  The brightness temperatures of all three dust disks are a few hundred Kelvins, indicating that they are actively accreting.  The two main components each exhibit a highly collimated bipolar ionized outflow that emerges perpendicular to the disk, although no such outflow was detected from the third component.  Neither outflows are resolved at their base, implying that they originate from a radial distance of <2.5 AU from their central protostars.   The major axes of the three circumstellar dust disks are closely, but not precisely, aligned with each other and the major axis of the surrounding molecular core; the orbital motion of the primary and secondary components is in the same sense as the rotational motion of this core.  These properties suggest that the three protostellar components formed as a result of fragmentation in the central region of their parent molecular core.  At intermediate spatial scales we find no clear evidence for a circumtriple dust disk, but instead protrusions from opposite sides of the primary and secondary components that may trace accreting matter streams from the surrounding core.