7470 20250204104853.0 10.1051/0004-6361/202452352 DOI SCART-2025-0101 Deshmukh, K. Investigating 39 Galactic Wolf-Rayet stars with VLTI/GRAVITY: Uncovering a long-period binary desert 2024 Context. Wolf-Rayet stars (WRs) represent one of the final evolutionary stages of massive stars and are thought to be the immediate progenitors of stellar-mass black holes. Their multiplicity characteristics form an important anchor point in single and binary population models for predicting gravitational-wave progenitors. Recent spectroscopic campaigns have suggested incompatible multiplicity fractions and period distributions for N- and C-rich Galactic WRs (WNs and WCs) at both short and long orbital periods, in contradiction with evolutionary model predictions. Aims. In this work, we employed long-baseline infrared interferometry to investigate the multiplicity of WRs at long periods and explored the nature of their companions. We present a magnitude-limited (K < 9; V < 14) survey of 39 Galactic WRs, including 11 WN, 15 WC, and 13 H-rich WN (WNh) stars. Methods. We used the K-band instrument GRAVITY at the Very Large Telescope Interferometer (VLTI) in Chile. The sensitivity of GRAVITY at spatial scales of ∼1 to 200 milliarcseconds and flux contrast of 1% allowed an exploration of periods in the range 102 ‑ 105 d and companions down to ∼5 M⊙. We carried out a companion search for all our targets, with the aim of either finding wide companions or calculating detection limits. We also explored the rich GRAVITY dataset beyond a multiplicity search to look for other interesting properties of the WR sample. Results. We detected wide companions with VLTI/GRAVITY for only four stars in our sample: WR 48, WR 89, WR 93, and WR 115. Combining our results with spectroscopic studies, we arrived at observed multiplicity fractions of fobsWN = 0.55 ± 0.15, fobsWC = 0.40 ± 0.13, and fobsWNh = 0.23 ± 0.12. The multiplicity fractions and period distributions of WNs and WCs are consistent in our sample. For single WRs, we placed upper limits on the mass of potential companions down to ∼5 M⊙ for WNs and WCs, and ∼7 M⊙ for WNh stars. In addition, we also found other features in the GRAVITY dataset, such as (i) a diffuse extended component contributing significantly to the K-band flux in over half the WR sample; (ii) five known spectroscopic binaries resolved in differential phase data, which constitutes an alternative detection method for close binaries; and (iii) spatially resolved winds in four stars: WR 16, WR 31a, WR 78, and WR 110. Conclusions. Our survey reveals a lack of intermediate- (a few hundred days) and long- (a few years to decades) period WR systems. The 200d peak in the period distributions of WR+OB and BH+OB binaries predicted by Case B mass-transfer binary evolution models is not seen in our data. The rich companionship of their O-type progenitors in this separation range suggests that the WR progenitor stars expand and interact with their companions, most likely through unstable mass transfer, resulting in either a short-period system or a merger. NO Sana, H. Mérand, A. Bordier, E. Langer, N. Bodensteiner, J. Dsilva, K. Frost, A. J. Gosset, E. Le Bouquin, J. -B. Lefever, R. R. Mahy, L. Patrick, L. R. Reggiani, M. Sander, A. A. C. Shenar, T. Tramper, F. Villaseñor, J. I. Waisberg, I. Astronomy & Astrophysics 692 2024 A109 21 laurent.mahy@ksb-orb.be 22912621 http://publi2-as.oma.be/record/7470/files/Deshmukh_AA_2024.pdf 3240 http://publi2-as.oma.be/record/7470/files/Deshmukh_AA_2024.gif?subformat=icon icon 7517 http://publi2-as.oma.be/record/7470/files/Deshmukh_AA_2024.jpg?subformat=icon-180 icon-180 published in REFERD