Multiplicity of northern bright O-type stars with optical long baseline interferometry

Abstract

Context. The study of the multiplicity of massive stars gives hints on their formation processes and their evolutionary paths, which are still not fully understood. Large separation binaries (>50 milliseconds of arc, mas) can be probed by adaptive-optics-assisted direct imaging and sparse aperture masking, while close binaries can be resolved by photometry and spectroscopy. However, optical long baseline interferometry is mandatory to establish the multiplicity of Galactic massive stars at the separation gap between 1 and 50 mas. Aims. In this paper, we aim to demonstrate the capability of the new interferometric instrument MIRC-X, located at the CHARA Array, to study the multiplicity of O-type stars and therefore probe the full range of separation for more than 120 massive stars (H < 7.5 mag). Methods. We initiated a pilot survey of bright O-type stars (H < 6.5 mag) observable with MIRC-X. We observed 29 O-type stars, including two systems in average atmospheric conditions around a magnitude of H = 7.5 mag. We systematically reduced the obtained data with the public reduction pipeline of the instrument. We analyzed the reduced data using the dedicated python software CANDID to detect companions. Results. Out of these 29 systems, we resolved 19 companions in 17 different systems with angular separations between ∼ 0.5 and 50 mas. This results in a multiplicity fraction f m = 17/29 = 0.59 ± 0.09, and an average number of companions f c = 19/29 = 0.66 ± 0.13. Those results are in agreement with the results of the SMASH+ survey in the Southern Hemisphere. Thirteen of these companions have been resolved for the first time, including the companion responsible for the nonthermal emission in Cyg OB2-5 A and the confirmation of the candidate companion of HD 47129 suggested by SMASH+. Conclusions. A large survey on more than 120 northern O-type stars (H < 7.5) is possible with MIRC-X and will be fruitful.

The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions

“…In terms of detecting binary companions, CHARA/MIRC (-X) routinely reaches a contrast ratio of 1% or lower (corresponding to a magnitude difference of more than 5 mag; e.g., De Furio et al 2022;Klement et al 2022b;Lanthermann et al 2023), with the best-performance limit being ∼0.3% (Δmag ∼ 6.4; Gallenne et al 2015). Thanks to the six telescopes and the resulting dense coverage of the (u, v) plane, CHARA is capable of detecting faint companions with snapshot observations, i.e., 10-20 minute integrations of fringes on the science target.…”

Vortex Fiber Nulling for Exoplanet Observations: First Direct Detection of M Dwarf Companions around HIP 21543, HIP 94666, and HIP 50319

“…The three companions covered here were previously known only from RV and/or astrometric observations, such that our results represent their first direct detections and provide the first spectra for the companions. Though KPIC VFN alone can provide a detection, in this Letter we complement the VFN observations with CHARA observations using the MIRC-X and MYSTIC beam combiners (Anugu et al 2020;Setterholm et al 2023), which have a demonstrated history of success at these angular separations (e.g., Roettenbacher et al 2015aRoettenbacher et al , 2015bThomas et al 2021;De Furio et al 2022;Lanthermann et al 2023). This allows us to validate the VFN performance in this first demonstration against CHARA's well-established performance.…”

Seven-year periodic variations in the methanol maser line displayed by the massive protostar IRAS 20216+4104

“…Spectroscopic and imaging optical observations have shown that 70% to 90% massive stars have at least one companion (Sana et al 2014;Lanthermann et al 2023). A survey of radial velocities of 16 embedded high-mass stars revealed that at least 20% of the targets are close binaries (Apai et al 2007).…”