A spectroscopic multiplicity survey of Galactic Wolf-Rayet stars

Abstract

Context. Most massive stars reside in multiple systems that will interact over the course of their lifetime. This has important consequences on their future evolution and their end-of-life products. Classical Wolf-Rayet (WR) stars represent the final end stages of stellar evolution at the upper-mass end. While their observed multiplicity fraction is reported to be ∼0.4 in the Galaxy, their intrinsic multiplicity properties and the distributions of their orbital parameters remain insufficiently constrained to provide a reliable anchor to compare to evolutionary predictions. Aims. As part of a homogeneous, magnitude-limited (V ≤ 12) spectroscopic survey of northern Galactic WR stars, this paper aims to establish the observed and intrinsic multiplicity properties of the early-type nitrogen-rich WR population (WNE), including estimates of the multiplicity fraction and the shape of their orbital period distribution. Additionally, we compare these with the properties of the carbon-rich WR population (WC) stars obtained in the first paper of this series. Methods. We obtained high-resolution spectroscopic time series of the complete magnitude-limited sample of 16 WNE stars observable with the 1.2 m Mercator telescope at La Palma, typically providing a time base of about two to eight years. We measured relative radial velocities (RVs) using cross-correlation and used RV variations to flag binary candidates. Using an updated Monte Carlo method with a Bayesian framework, we calculated the three-dimensional likelihood for the intrinsic binary fraction ( f WNE int ), the maximum period (log P max ), and the power-law index for the period distribution (π) for the WNE population with P min fixed at 1 d. We also used this updated method to re-derive multiplicity parameters for the Galactic WC population. Results. Adopting a peak-to-peak RV variability threshold of 50 km s −1 as a criterion, we classify 7 of the 16 targets as binaries. This results in an observed multiplicity fraction ( f WNE obs ) of 0.44 ± 0.12. Assuming flat priors, we derive the best-fit multiplicity properties f WNE int = 0.56 +0.20 −0.15 , log P max = 4.60 +0.40 −0.77 , and π = −0.30 +0.55 −0.53 for the parent WNE population. We explored different mass-ratio distributions and note that they did not change our results significantly. For the Galactic WC population from Paper 1, we re-derive f WC int = 0.96 +0.04 −0.22 , log P min = 0.75 +0.26 −0.60 , log P max = 4.00 +0.42 −0.34 , and π = 1.90 +1.26 −1.25 . Conclusions. The derived multiplicity parameters for the WNE population are quite similar to those derived for main-sequence O binaries but differ from those of the WC population. The significant shift in the WC period distribution towards longer periods is too large to be explained via expansion of the orbit due to stellar winds, and we discuss possible implications of our results. Analysis of the WNL population and further investigation of various evolutionary scenarios is required to connect the different evolutionary phases of stars at the upper-ma...

Spectroscopic searches for evolutionary orbital period changes in WR+OB binaries: The case of WR 127 (Hen 3-1772)

“…In addition to improving the orbital system parameters, the authors also studied parameters of the interaction zone of the components' stellar winds. Dsilva et al (2022) conducted a spectroscopic survey of several known WR nitrogen stars to study their spectral binarity. Observations were carried out with the High-Efficiency and high-Resolution Mercator Echelle Spectrograph (HERMES).…”

“…In contrast, our comparison of radial velocity curves clearly indicates an increase in the orbital period: the parabolic arms in Fig.4are directed upwards. As in the case with V444 Cyg(Shaposhnikov et al 2023b), here we have almost exclusively used radial velocity curves in the N v 4603 Å line; the only exception is high-resolution measurements in the N v 4945 Å line taken fromDsilva et al (2022).…”

“…(b) Based on the optical eclipse depth.References. (H45)Hiltner (1945); (GB67)Ganesh & Bappu (1967); (M81)Massey (1981); (Ch11) de La Chevrotière et al (2011); (D22)Dsilva et al (2022).) = A E + B (O C) = A E 2 + B E + C WR 127, HJD = 2453220.1 + 9.555E ) = A E + B (O C) = A E 2 + B E + CWR 127, HJD = 2460187.81 + 9.55465E…”

The interplay between mass-loss and binarity

“…5. We refer to Dsilva et al (2022) for updated results, but the conclusions remain. WNE and WC stars seem to have different period distributions, with the first one being heavily tweaked towards short period systems and the latter is flatter and favours long-period systems.…”

Newly Discovered Wolf–Rayet Stars in M31

“…Once these massive stars end their stellar lives, they leave behind black holes. Around 30%-40% of WRs exist in short-period (<10 day) binary systems (Bartzakos et al 2001;Foellmi et al 2003;Schnurr et al 2008;Dsilva et al 2022) and are the progenitors to the black hole mergers being detected as gravitational-wave events (Abbott et al 2016). However, while constraints have been placed on the binary fraction of the short-period WR systems, the overall influence of binarity on the evolution of WRs, and massive stars in general, is still an open question.…”