2005/02/23 by Kevin R. Covey, Thomas P. Greene, Greg W. Doppmann +3 · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/429736
13 pages, 6 figures. Accepted for publication in the Astronomical Journal (tentatively for June 2005 edition)
arxiv created 2005/02/23 · openalex publication_date 2005/05/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
We report on the angular momentum content of heavily embedded protostars on the basis of our analysis of the projected rotation velocities ( v sin i ) of 38 Class I/flat-spectrum young stellar objects recently presented by Doppmann and others. After correcting for projection effects, we find that infrared-selected Class I/flat-spectrum objects rotate significantly more quickly (median equatorial rotation velocity ∼38 km s -1 ) than classical T Tauri stars (CTTSs; median equatorial rotation velocity ∼18 km s -1 ) in the ρ Ophiuchi and Taurus-Aurigae regions. Projected rotation velocity ( v sin i ) is weakly correlated with T eff in our sample but does not seem to correlate with Brγ emission (a common accretion tracer), the amount of excess continuum veiling ( r k ), or the slope of the spectral energy distribution between the near- and mid-IR (α). The detected difference in rotation speeds between Class I/flat-spectrum sources and CTTSs proves difficult to explain without some mechanism that transfers angular momentum out of the protostar between the two phases. Assuming that Class I/flat-spectrum sources possess physical characteristics ( M * , R * , and B * ) typical of pre–main-sequence stars, fully disk-locked Class I objects should have corotation radii within their protostellar disks that match well (within 30%) with predicted magnetic coupling radii. The factor of 2 difference in rotation rates between Class I/flat-spectrum and CTTS sources when interpreted in the context of disk-locking models also implies a factor of 5 or greater difference in mass accretion rate between the two phases. A lower limit of ∼ 10 -8 M ⊙ yr -1 for objects transitioning from the Class I/flat-spectrum stage to CTTSs is required to account for the difference in rotation rates of the two classes by angular momentum extraction through a viscous disk via magnetic coupling.