A 0.2 solar mass protostar with a Keplerian disk in the very young L1527 IRS system

摘要

In their earliest stages, protostars accrete mass from their surroundingenvelopes through circumstellar disks. Until now, the smallest observedprotostar/envelope mass ratio was ~2.1. The protostar L1527 IRS is thought tobe in the earliest stages of star formation. Its envelope contains ~1 solarmass of material within a ~0.05 pc radius, and earlier observations suggestedthe presence of an edge-on disk. Here we report observations of dust continuumemission and 13CO (J=2-1) line emission from the disk around L1527, from whichwe determine a protostellar mass of M = 0.19 +/- 0.04 solar masses and aprotostar/envelope mass ratio of ~0.2. We conclude that most of the luminosityis generated through the accretion process, with an accretion rate of ~6.6 x10^-7 solar masses per year. If it has been accreting at that rate through muchof its life, its age is ~300,000 yr, though theory suggests larger accretionrates earlier, so it may be younger. The presence of a rotationally--supporteddisk is confirmed and significantly more mass may be added to itsplanet-forming region as well as the protostar itself.