Spectroscopic Searches for Evolutionary Orbital Period Changes in WR+OB Binaries: the Case of WR 127 (Hen 3-1772)

We aim at searching for secular evolution of the orbital period in the short-period binary system WR 127 (WN3b+O9.5V, P = 9.555ᵈ). We performed new low-resolution spectroscopic observations of WR 127 on 2.5-m CMO SAI telescope to construct the radial velocity curves of the components suggesting the component masses MWRsin³(i) = 11.8±1.4 M_, MOsin³(i)=17.2±1.4 M_. The comparison with archival radial velocity curves enabled us to calculate the $(O-C)$ plot with accuracy sufficient to search for the orbital period change in WR 127. We report on the reliable detection of a secular increase in the orbital period of WR 127 at a rate of Ṗ = 0.83±0.14~s~yr⁻¹ corresponding to the dynamical mass-loss rate from the WR star ṀWR = (2.6±0.5)× 10⁻⁵ M_ yr⁻¹. The mass-loss rate from WR stars in three WR+OB binaries (WR 127, CX Cep and V444 Cyg) as inferred from spectroscopic and photometric measurements suggests a preliminary empirical correlation between the WR star mass and the dynamical mass-loss rate MWR~ MWR1.8. This relation is important for the understanding of the evolution of massive close binaries with WR stars -- precursors of gravitational-wave binary merging events with neutron stars and black holes.