We present a clear evidence for the motion of the companion star in the Low Mass X-Ray Binary ( LMXB ) X1822-371 .
We detect NIII \lambda 4640 emission moving in antiphase with the radial velocity curve of the neutron star and produced on the X-ray heated hemisphere of the donor star .
From the motion of this feature we derive a lower limit to the radial velocity semi-amplitude of the companion star K _ { 2 } \geq 300 \pm 8 km s ^ { -1 } , which , combined with a previous determination of the inclination angle and the pulsar ’ s radial velocity curve , yield M _ { 2 } \geq 0.36 ( 2 ) M _ { \odot } and M _ { 1 } \geq 1.14 ( 6 ) M _ { \odot } .
The HeI \lambda 4471 absorption line moves at lower velocities ( \simeq 225 km s ^ { -1 } ) and with a -0.05 phase shift , suggests a likely origin on the gas stream near the L _ { 1 } point .
In addition , we detect an S-wave emission of OVI \lambda 3811 produced by illumination of the hot-spot bulge by the central source .
The Balmer lines are dominated by broad absorptions probably due to obscuration of the accretion disc by vertically extended cool material from the splash region and overflowing stream .
We also derive a more accurate , and significantly different ( compared to earlier work ) systemic velocity of \gamma = -44 \pm 5 km s ^ { -1 } based on the motion of the HeII \lambda 4686 wings and Doppler tomography .
This work confirms the power of imaging the companion stars in LMXBs and outbursting transients using the Bowen fluorescence transitions .