The results of new low-resolution spectroscopic observations of the short-period system WR 141 (WN5o + O5V–III, P ≈21.7^d ), as well as the results of their comparison with the material of previous studies in order to search for an evolutionary change in the orbital period, are presented. A secular increase in the orbital period of WR 141 with a rate Ṗ = 1.6 ± 0.9 s/yr, corresponding to a mass loss rate Ṁ_WR = (3.1 ± 1.9) ×10^ - 5 M_⊙ /yr with the masses of the stars in the system M_WR = 39 ± 10 M_⊙ and M_O = 37 ± 10 M_⊙ , is reported. A correlation between the mass loss rate of WR stars and their mass is discussed.

Aims. We aim to determine the secular evolution of the orbital period of the short-period binary system WR 127 (WN3b+O9.5V, P ≈ 9.555d). Methods. We performed new low-resolution spectroscopic observations of WR 127 with the 2.5 m CMO SAI telescope to construct the radial velocity curves of the components. Our results suggest component masses of MWRsin3(i) = 11.8 ± 1.4 M⊙ and MOsin3(i) = 17.2 ± 1.4 M⊙. By comparing these values with archival radial velocity curves we were able to create an (O − C) plot with an accuracy sufficient to search for the orbital period change in WR 127. Results. We report 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, which corresponds to a dynamical mass-loss rate from the Wolf-Rayet (WR) star of ĖWR = (2.6 ± 0.5) × 10−5 M⊙ yr−1. Conclusions. The mass-loss rate from WR stars in three Wolf-Rayet+OB binaries (WR 127, CX Cep, and V444 Cyg) as inferred from spectroscopic and photometric measurements suggests a preliminary empirical correlation between a WR star’s mass and its dynamical mass-loss rate of ṀWR ∼ MWR1.8. This relation is important for the understanding of the evolution of massive close binaries that include WR stars as such an evolution is a precursor of gravitational-wave binary merging events with neutron stars and black holes.

An analysis of the high-resolution ( R∼ 48000 ) optical spectrum of hot (B1Ibe) post-AGB star LS 4331 (IRAS 17381−1616) is presented. The detailed identification of the observed absorption and emission features in the wavelength range 3700–9200 Å is carried out for the first time. The atmospheric parameters and chemical composition of the star are derived from the non-LTE analysis of absorption lines. We estimated T_eff=20900± 500 K, log g=2.57 ± 0.08 , V_r=-51.7 ± 0.8 km s ^-1 , ξ _t=24 ± 4 km s ^-1 and v sin i=30 ± 5 km s ^-1 . An abundance analysis for C, N, O, Mg, Al, S, and Si reveals that the N and O abundance is close to solar while metal underabundances relative to the solar value (i.e., [Mg/H] = -1.04 dex, [Al/H] = -1.20 dex, [Si/H] = -0.46 dex) are found. LS 4331 is a high galactic latitude metal-poor and carbon-deficient hot post-AGB star. The underabundance of carbon ( [C/H]=-0.64 dex) is similar to that found in other hot post-AGB stars and indicates that the star’s AGB phase of evolution was terminated before the third dredge-up. Plasma diagnostics are derived from the nebular emission lines. The presence of nebular emission lines in the spectrum of LS 4331 indicates that the photoionization of the circumstellar envelope has already started. The nebular parameters and expansion velocity of the nebula are derived. Using the Gaia DR3 distance, the absolute luminosity of the star is derived, and the star’s position on the post-AGB evolutionary tracks suggests that its initial main sequence mass is about 1.2 M_⊙ . It is also reported that fast irregular brightness variations with an amplitude of up to 0.3 mag in the V band have been found in the star, typical of hot post-AGB objects.

We present the results of spectroscopic observations of two eclipsing WR + OB-type systems - CQ Cep and CX Cep - performed in 2020-2023 with a low-resolution slit spectrograph TDS (lambda lambda = 3660-7410 angstrom, R = 1300-2500) on 2.5-m telescope of the SAI MSU Caucasian Mountain Observatory. For CQ Cep, the radial velocity curves of a WN6 star are constructed, the problem of visibility of spectroscopic traces of an OB star is discussed, and the components' mass ratio q similar to 0.6 is estimated. For CX Cep, the radial velocity curves are constructed for both the WN5 and O5 components enabling their masses and circular orbit elements to be refined. The comparison of the radial velocity curves of these systems obtained in different epochs allowed us to derive the orbital period change rate (P) over dot by the spectroscopic method, which is found to be in good agreement with estimates obtained by comparing the moments of primary eclipse minima: (P) over dot = -0.0151 +/- 0. 0013 s yr(-1) for CQ Cep and (P) over dot = 0.054 +/- 0.009 s yr(-1) for CX Cep. The prospects of applicability of the spectroscopic dynamical method for studying the orbital evolution of Galactic WR + OB binaries and related objects are considered. We also discuss the effect of finite sizes of stars with stellar wind mass-loss in close binary systems on their orbital evolution.

ABSTRACT We present the results of new photometric and spectroscopic observations of the WN5+O6 binary V444 Cyg and a detailed analysis of extant spectroscopy and photometry. Using elements of the spectroscopic orbit and assuming e ≈ 0, i ≈ 78° we determined the masses and orbit sizes of the components of V444 Cyg as MO6 ≈ 26.4 M⊙, MWN5 ≈ 10.7 M⊙, aO6 ≈ 10.6 R⊙, aWN5 ≈ 26.1 R⊙. Based on new and archival light curves and using the Hertzsprung method, we improved the photometric estimate of the secular increase rate of the orbital period in V444 Cyg, obtaining $\dot{P}_{\mathrm{ph}} = 0.119\pm 0.003$ s yr−1. From a comparison of the new and archival radial velocity curves of V444 Cyg, we independently derived the secular orbital period change rate as $\dot{P}_{\mathrm{sp}} = 0.147\pm 0.032$ s yr−1, in agreement with the photometric $\dot{P}_{\mathrm{ph}}$. The obtained secular increase rate of the binary orbital period $\dot{P}$ and the mean radii of the components enabled us to estimate the stellar wind mass-loss rate from the WR star as $\dot{M}_{\mathrm{WN5}} = -(6.0\pm 0.4)\times 10^{-6}~{\rm M}_{\odot }\mbox{ yr}^{-1}$.