SS 433 is an X-ray binary and the source of sub-relativistic , precessing , baryonic jets .
We present high-resolution spectrograms of SS 433 in the infrared H and K bands .
The spectrum is dominated by hydrogen and helium emission lines .
The precession phase of the emission lines from the jet continues to be described by a constant period , P _ { jet } = 162.375 d. The limit on any secularly changing period is | \dot { P } | \lesssim 10 ^ { -5 } .
The He I \lambda 2.0587 \mu m line has complex and variable P-Cygni absorption features produced by an inhomogeneous wind with a maximum outflow velocity near 900 km s ^ { -1 } .
The He II emission lines in the spectrum also arise in this wind .
The higher members of the hydrogen Brackett lines show a double-peaked profile with symmetric wings extending more than \pm 1500 km s ^ { -1 } from the line center .
The lines display radial velocity variations in phase with the radial velocity variation expected of the compact star , and they show a distortion during disk eclipse that we interpret as a rotational distortion .
We fit the line profiles with a model in which the emission comes from the surface of a symmetric , Keplerian accretion disk around the compact object .
The outer edge of the disk has velocities that vary from 110 to 190 km s ^ { -1 } .
These comparatively low velocities place an important constraint on the mass of the compact star : Its mass must be less than 2.2 M _ { \odot } and is probably less than 1.6 M _ { \odot } .