The N Enrichment and Supernova Ejection of the Runaway Microquasar LS 5039

We present an investigation of new optical and ultraviolet spectra of themass donor star in the massive X-ray binary LS 5039. The optical band spectralline strengths indicate that the atmosphere is N-rich and C-poor, and weclassify the stellar spectrum as type ON6.5 V((f)). The N-strong and C-weakpattern is also found in the stellar wind P Cygni lines of N V 1240 and C IV1550. We suggest that the N-enrichment may result from internal mixing if theO-star was born as a rapid rotator, or the O-star may have accreted N-rich gasprior to a common-envelope interaction with the progenitor of the supernova. Were-evaluated the orbital elements to find an orbital period of P=4.4267 +/-0.0010 d. We compared the spectral line profiles with new non-LTE,line-blanketed model spectra, from which we derive an effective temperatureT_eff = 37.5 +/- 1.7 kK, gravity log g = 4.0 +/- 0.1, and projected rotationalvelocity V sin i = 140 +/- 8 km/s. We fit the UV, optical, and IR fluxdistribution using a model spectrum and extinction law with parameters E(B-V)=1.28 +/- 0.02 and R= 3.18 +/- 0.07. We confirm the co-variability of theobserved X-ray flux and stellar wind mass loss rate derived from the H-alphaprofile, which supports the wind accretion scenario for the X-ray production inLS 5039. Wind accretion models indicate that the compact companion has a massM_X/M_sun = 1.4 +/- 0.4, consistent with its identification as a neutron star.The observed eccentricity and runaway velocity of the binary can only bereconciled if the neutron star received a modest kick velocity due to a slightasymmetry in the supernova explosion (during which >5 solar masses wasejected).Comment: 38 pages, 9 figures; 2004, ApJ, 600, Jan. 10 issue, in press Discussion revised thanks to comments from P. Podsiadlowsk