We present new spectra of WR 140 ( HD 193793 ) in the JHK bands with some covering the 1.083- \mu m He i emission line at higher resolution , observed between 2000 October and 2003 May to cover its 2001 periastron passage and maximum colliding-wind activity .
The WC7 + O4-5 spectroscopic binary WR 140 is the prototype of colliding-wind , episodic dust-making Wolf-Rayet systems which also show strong variations in radio and X-ray emission .
The JHK spectra showed changes in continuum and in the equivalent widths of the WC emission lines , consistent with formation of dust starting between 2001 January 3 and March 26 ( orbital phases 0.989 and 0.017 ) and its subsequent fading and cooling .
The 1.083- \mu m He i line has a P-Cygni profile which showed variations in both absorption and emission components as WR 140 went through periastron passage .
The variation of the absorption component of the profile yielded tight constraints on the geometry of the wind-collision region , giving \theta = 50 ^ { \circ } \pm 8 ^ { \circ } 
for the opening semi-angle of the interaction region ‘ cone ’ , indicating a wind-momentum ratio ( \dot { M } v _ { \infty } ) _ { O } / ( \dot { M } v _ { \infty } ) _ { WR } = 0.10 , about three times larger than previously believed .
As the system approached periastron , the normally flat-topped emission component of 1.083- \mu m line profile showed the appearance of a significant sub-peak .
The movement of the sub-peak across the profile was seen to be consistent with its formation in wind material flowing along the contact discontinuity between the WC7 and O4-5 stellar winds and the changing orientation of the colliding wind region as the stars moved in their orbits .
The flux carried in the sub-peak was significant , exceeding the X-ray fluxes measured at previous periastron passages .
This additional source of radiative cooling of the shock-heated gas probably causes it to depart from being adiabatic around periastron passage , thereby accounting for the departure of the X-ray flux from its previously expected 1 / d -dependency .