演講資訊

摘要：

A classical paradox in high-mass star formation is that powerful radiation pressure can halt accretion, preventing further growth of a central star. Disk accretion has been proposed to solve this problem, but the disks and the accretion process in high-mass star formation are poorly understood. We executed high-resolution (R=35,000-70,000) iSHELL spectroscopy in K-band for eleven high-mass protostars. Br-γ emission was observed toward eight sources, and the line profiles for most of these sources are similar to those of low-mass PMS stars. Using an empirical relationship between the Br-γ and accretion luminosities, we tentatively estimate disk accretion rates ranging from .10−8 and ∼10−4 M yr−1 . These low-mass-accretion rates suggest that high-mass protostars gain more mass via episodic accretion as proposed for low-mass protostars. Given the detection limits, CO overtone emission (v=2-0 and 3-1), likely associated with the inner disk region (r 100 au), was found towards two sources. This low detection rate compared with Br-γ emission is consistent with previous observations. Ten out of the eleven sources show absorption at the v=0-2 R(7) − R(14) CO R-branch. Most of them are either blueshifted or redshifted, indicating that the absorption is associated with an outflow or an inflow with a velocity of up to ∼ 50 km s−1 . Our analysis indicates that the absorption layer is well thermalized (and therefore nH2 & 106 cm−3 ) at a single temperature of typically 100-200 K, and located within 200-600 au of the star.