  We present the results of space-based photometric and ground-based
spectroscopic observing campaigns on the gamma-ray binary LS 5039. The new
orbital and physical parameters of the system are similar to former results,
except we found a lower eccentricity. Our MOST-data show that any broad-band
optical photometric variability at the orbital period is below the 2 mmag
level. Light curve simulations support the lower value of eccentricity and
imply that the mass of the compact object is higher than 1.8 solar masses.
