We infer the emission positions of twin kilohertz quasi-periodic oscillations ( kHz QPOs ) in neutron star low mass X-ray binaries ( NS-LMXBs ) based on the Alfvén wave oscillation model ( AWOM ) .
For most sources , the emission radii of kHz QPOs cluster around a region of 16 - 19 km with the assumed NS radii of 15 km .
Cir X-1 has the larger emission radii of 23 \sim 38 km than those of the other sources , which may be ascribed to its large magnetosphere-disk radius or strong NS surface magnetic field .
SAX J1808.4-3658 is also a particular source with the relative large emission radii of kHz QPOs of 20 \sim 23 km , which may be due to its large inferred NS radius of 18 \sim 19 km .
The emission radii of kHz QPOs for all the sources are larger than the NS radii , and the possible explanations of which are presented .
The similarity of the emission radii of kHz QPOs ( \sim 16 - 19 km ) for both the low/high luminosity Atoll/Z sources is found , which indicates that both sources share the similar magnetosphere-disk radii .