K-band High-resolution Spectroscopy of Embedded High-mass Protostars

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 process are poorly understood. We executed high-resolution ($R$=35,000-70,000) iSHELL spectroscopy $K$-band for eleven protostars. Br-$\gamma$ emission was observed toward eight sources, line profiles most these sources similar those low-mass PMS stars. Using an empirical relationship between luminosities, we tentatively estimate disk rates ranging from $\lesssim$10$^{-8}$ $\sim$10$^{-4}$ $M_\odot$ yr$^{-1}$. These low-mass-accretion suggest protostars gain more mass via episodic as Given detection limits, CO overtone ($v$=2-0 3-1), likely associated with inner region ($r \ll 100$ au), found towards two sources. This low-detection rate compared consistent previous observations. Ten out show absorption at $v$=0-2 ${\rm R(7)-R(14)}$ R-branch. Most them either blueshifted or redshifted, indicating outflow inflow velocity up $\sim50$ km s$^{-1}$. Our analysis indicates layer well thermalized (and therefore $n_{\mathrm H_2} \gtrsim 10^6$ cm$^{-3}$) single temperature typically 100-200 K, located within 200-600 au