2001/01/31 by Michiel R. Hogerheijde · 79 citations
Physics and Astronomy · #Accretion (finance) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Millimeter #Phase (matter) #RADIUS #Rotation (mathematics) #Star formation #Stars #Stellar, planetary, and galactic studies #T Tauri star #Young stellar object #astro-ph
paper · pdf · doi:10.1086/320972
published in The Astrophysical Journal 553(2), 618-632 (IOP Publishing) · Accepted ApJ. 33 pages, including 10 B/W figures and 1 color figure. Uses AASTeX
arxiv created 2001/01/31 · openalex publication_date 2001/06/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Evidence for a transitional stage in the formation of a low-mass star is reported, intermediate between the fully embedded and the T Tauri phases. Millimeter aperture synthesis observations in the HCO + J = 1-0 and 3-2, HCN 1-0, 13 CO 1-0, and C 18 O 1-0 transitions reveal distinctly different velocity fields around two embedded, low-mass young stellar objects. The 0.6 M ☉ of material around TMC 1 (IRAS 04381+2517) closely follows inside-out collapse in the presence of a small amount of rotation (~3 km s -1 pc -1 ), while L1489 IRS (IRAS 04016+2610) is surrounded by a 2000 AU radius, flared disk containing 0.02 M ☉ . This disk shows Keplerian rotation around a ~0.65 M ☉ star and infall at 1.3( r /100 AU) -0.5 km s -1 , or, equivalently, sub-Keplerian motions around a central object between 0.65 and 1.4 M ☉ . Its density is characterized by a radial power law and an exponential vertical scale height. The different relative importance of infall and rotation around these two objects suggests that rotationally supported structures grow from collapsing envelopes over a few times 10 5 yr to sizes of a few thousand AU, and then decrease over a few times 10 4 yr to several hundred AU typical for T Tauri disks. In this scenario, L1489 IRS represents a transitional phase between embedded young stellar objects and T Tauri stars with disks. The expected duration of this phase of ~5% of the embedded stage is consistent with the current lack of other known objects like L1489 IRS. Alternative explanations cannot explain L1489 IRS's large disk, such as formation from a cloud core with an unusually large velocity gradient or a binary companion that prevents mass accretion onto small scales. It follows that the transfer and dissipation of angular momentum is key to understanding the formation of disks from infalling envelopes.