A 0.2 solar mass protostar with a Keplerian disk in the very young L1527 IRS system (1212.0861v1)

Abstract: In their earliest stages, protostars accrete mass from their surrounding envelopes through circumstellar disks. Until now, the smallest observed protostar/envelope mass ratio was ~2.1. The protostar L1527 IRS is thought to be in the earliest stages of star formation. Its envelope contains ~1 solar mass of material within a ~0.05 pc radius, and earlier observations suggested the presence of an edge-on disk. Here we report observations of dust continuum emission and 13CO (J=2-1) line emission from the disk around L1527, from which we determine a protostellar mass of M = 0.19 +/- 0.04 solar masses and a protostar/envelope mass ratio of ~0.2. We conclude that most of the luminosity is generated through the accretion process, with an accretion rate of ~6.6 x 10^-7 solar masses per year. If it has been accreting at that rate through much of its life, its age is ~300,000 yr, though theory suggests larger accretion rates earlier, so it may be younger. The presence of a rotationally--supported disk is confirmed and significantly more mass may be added to its planet-forming region as well as the protostar itself.

• The paper determines a protostellar mass of 0.19 ± 0.04 M☉ with a unique low protostar/envelope mass ratio of approximately 0.2.
• It confirms a rotationally supported 180 AU Keplerian disk, challenging existing models of magnetic braking in early disk formation.
• The study highlights dynamic accretion at ~6.6×10^-7 M☉/yr, indicating a very young system (~300,000 years) with evolving mass accretion processes.

Analysis of a 0.2 Solar Mass Protostar with a Keplerian Disk in the L1527 IRS System

This paper presents an in-depth paper of the protostar L1527 IRS located in the Taurus cloud, leveraging high-resolution observations to elucidate critical parameters of this young stellar object. The research uncovers substantial details about L1527, a protostar residing within a dense envelope of approximately 1 solar mass (M_☉) and identifies a Keplerian disk surrounding it, contributing significantly to our understanding of early star formation phases.

The authors employ dust continuum and $^{13}$CO ($J=2\rightarrow1$) line emission data collected through the Submillimeter Array (SMA) and the Combined Array for Research in Millimeter Astronomy (CARMA) to derive core properties of the L1527 system. A protostellar mass is determined to be approximately 0.19 ± 0.04 M_☉, with a remarkably low protostar/envelope mass ratio of roughly 0.2. This stands in contrast to previously observed protostellar systems, where protostars typically possess more than twice the mass of their envelopes.

A key finding is the confirmation of a rotationally supported disk with a diameter of approximately 180 AU, exhibiting Keplerian rotation, as evidenced by redshifted and blueshifted components situated on opposing sides of the protostellar core. This disk is of particular interest due to its substantial size during the early Class 0 evolutionary stage, challenging certain theoretical disk formation models that predict significant magnetic braking. The mass of this disk is estimated to be at least 0.007 M_☉, though acknowledged to be a lower bound given potential opacity effects.

The protostar's accretion dynamics also provide insightful implications. With the accretion rate posited at approximately 6.6 × 10^-7 M_☉ yr^-1, the system is inferred to be relatively young, potentially around 300,000 years old, contingent on known accretion history and theoretical models suggesting higher prior accretion rates. This dynamic accretion process is suggested to contribute predominantly to the system's luminosity output.

The research posits significant implications for the theoretical modeling of protostellar disk formation under varying magnetic field strengths and orientations, proposing that scenarios with weaker magnetic influences or non-aligned fields could account for such substantial disk structures. The paper further proposes that such a disk might accrete more mass, possessing potential to reach solar-mass scales and nurture planet formation processes akin to early solar system conditions.

The L1527 system exemplifies a well-characterized Class 0 protostar, benefiting from robust observational and modeling strategies. This research boosts current theoretical comprehension by elucidating both disk formation and early stellar mass accretion processes, while simultaneously highlighting the dynamic interplay of factors influencing star formation in embryonic protostellar systems. Future investigations may further refine these models, integrating additional parameters and broader observational datasets to enhance our understanding of star formation, particularly in the early evolutionary stages evidenced by L1527.