2005AJ....129.2765C -
Astron. J., 129, 2765-2776 (2005/June-0)
The angular momentum content and evolution of class I and flat-spectrum protostars.
COVEY K.R., GREENE T.P., DOPPMANN G.W. and LADA C.J.
Abstract (from CDS):
We report on the angular momentum content of heavily embedded protostars on the basis of our analysis of the projected rotation velocities (vsini) 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) than classical T Tauri stars (CTTSs; median equatorial rotation velocity ∼18 km/s) in the ρ Ophiuchi and Taurus-Aurigae regions. Projected rotation velocity (vsini) is weakly correlated with Teffin our sample but does not seem to correlate with Brγ emission (a common accretion tracer), the amount of excess continuum veiling (rk), 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 M{dot}∼10–8 M☉/yr 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.
Abstract Copyright:
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Journal keyword(s):
Accretion, Accretion Disks - Infrared: Stars - Stars: Formation - Stars: Pre-Main-Sequence - Stars: Rotation
Simbad objects:
19
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