Optical spectroscopic observations of GX 339-4 were carried out between 1998 May ( X-ray high state ) and 1999 May ( X-ray low state ) over 7 epochs .
The equivalent width of H \alpha increased during the high state then decreased during the low state .
The equivalent width of HeII \lambda 4686 decreased over both states .
The full-width half-maximum of H \alpha , H \beta , HeII \lambda 4686 and the Bowen blend increased from 1998 to 1999 indicating that the emission line regions moved closer to the compact object .
H \beta shows a redshifted absorption feature at \lambda 4880 at all epochs .
This line remains unidentified .
Analysis of individual spectra from 1998 May 28-31 show modulation of the radial velocities , equivalent width and V/R ratios of H \alpha on the 14.86 hour orbital period .
The equivalent width of HeII \lambda 4686 also varies on the orbital period .
This is the first time since the study of Callanan et al .
( 7 ) that spectroscopic data has confirmed the orbital period .
The semi-amplitude of the H \alpha radial velocities is K _ { 1 } = 14 km s ^ { -1 } .
Hence the mass function = 2 x 10 ^ { -4 } M _ { \odot } .