The earliest O-type eclipsing binary in the Small Magellanic Cloud, AzV 476: A comprehensive analysis reveals surprisingly low stellar masses

Abstract

Massive stars at low metallicity are among the main feedback agents in the early Universe and in present-day star forming galaxies. When in binaries, these stars are potential progenitors of gravitational-wave events. Knowledge of stellar masses is a prerequisite to understanding evolution and feedback of low-metallicity massive stars. Using abundant spectroscopic and photometric measurements of an outstandingly bright eclipsing binary, we compare its dynamic, spectroscopic, and evolutionary mass estimates and develop a binary evolution scenario. We comprehensively studied the eclipsing binary system, AzV 476, in the Small Magellanic Cloud. The light curve and radial velocities were analyzed to obtain the orbital parameters. The photometric and spectroscopic data in the UV and optical were analyzed using the Potsdam Wolf-Rayet model atmospheres. The obtained results are interpreted using binary-evolution tracks. AzV 476 consists of an O4IV-III((f))p primary and an O9.5:Vn secondary. Both components have similar current masses (~20 M${}_{\odot }$) obtained from both the orbital and spectroscopic analysis. The wind mass-loss rate of log($\dot{M}$/(M${}_{\odot }$/yr))=-6.2 of the primary is a factor of ten higher than a recent empirical prescription for single O stars in the SMC. Only close-binary evolution with mass transfer can reproduce the current stellar and orbital parameters. The binary evolutionary model reveals that the primary has lost about half of its initial mass and is already core helium burning. Our comprehensive analysis of AzV 476 yields a consistent set of parameters and suggests previous case B mass transfer. The derived stellar masses agree within their uncertainties. The moderate masses of AzV 476 underline the scarcity of bright massive stars in the SMC. The core helium burning nature of the primary indicates that stripped stars might be hidden among OB-type populations.

18 pages + 5 pages appendix, 17 figures, 8 tables. Accepted for publication in A&A

References in corpus (25)

• The Gaia mission
• Physics Of Eclipsing Binaries. II. Towards the Increased Model Fidelity
• The VLT-FLAMES survey of massive stars: Evolution of surface N abundances and effective temperature scales in the Galaxy and Magellanic Clouds
• Barycentric Corrections at 1 cm/s for precise Doppler velocities
• BONNSAI: a Bayesian tool for comparing stars with stellar evolution models
• Spitzer SAGE-SMC Infrared Photometry of Massive Stars in the Small Magellanic Cloud
• On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
• Observational Evidence for Tidal Interaction in Close Binary Systems
• Wolf-Rayet stars in the Small Magellanic Cloud: I. Analysis of the single WN stars
• Testing massive star evolution, star-formation history and feedback at low metallicity : Spectroscopic analysis of OB stars in the SMC Wing
• Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity
• Metallicity-dependent wind parameter predictions for OB stars
• Massive donors in interacting binaries: effect of metallicity
• A FUSE Survey of the Rotation Rates of Very Massive Stars in the Small and Large Magellanic Clouds
• Testing eccentricity pumping mechanisms to model eccentric long period sdB binaries with MESA
• The IACOB project. VI. On the elusive detection of massive O-type stars close to the ZAMS
• The HD5980 multiple system: Masses and evolutionary status
• The Tarantula Massive Binary Monitoring. IV. Double-lined photometric binaries
• The excess of cool supergiants from contemporary stellar evolution models defies the metallicity-independent Humphreys-Davidson limit
• The rapid evolution of the exciting star of the Stingray Nebula
• A dearth of young and bright massive stars in the Small Magellanic Cloud
• ALMA observations of N83C in the early stage of star formation in the Small Magellanic Cloud
• Spectroscopic evolution of massive stars near the main sequence at low metallicity
• Mass loss rates from mid-IR excesses in LMC and SMC O stars
• The spin rates of O stars in WR + O Magellanic Cloud binaries