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 MWR³ (i) = 11. 81. 4 M_, MO³ (i) =17. 21. 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. 830. 14~s~yr^-1 corresponding to the dynamical mass-loss rate from the WR star ṀWR = (2. 60. 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 MWR^1. 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.