Magnetic field detections in massive systems at different stages of interaction

TL;DR

This study investigates magnetic fields in interacting massive binaries across different evolutionary stages using 53 HARPS-pol spectropolarimetric observations of 14 systems and the Least-Squares Deconvolution method to recover Stokes V and the mean longitudinal field $<B_z>$. Detections are obtained in all targets except SV Cen, with field strengths ranging from tens of Gauss to several kiloGauss; MY Ser shows extreme fields up to ~8.6 kG in one component, with other systems like V1294 Sco and V606 Cen also reaching the kiloGauss level. The results support the scenario that binary interaction drives magnetic-field generation in massive stars, and they highlight that the stronger fields can occur in multi-component or contact configurations. This work provides the first occurrence-rate assessment of magnetism in a representative sample of interacting binaries and has implications for massive-star evolution, the end states of binaries, and potential gravitational-wave progenitors.

Abstract

Despite the importance of magnetic fields in massive stars, their origin is widely debated and still not well understood. With the mounting evidence for the importance of studying magnetic fields in interacting massive binary and multiple systems, it appears necessary to investigate the presence of magnetic fields in semi-detached systems with ongoing mass transfer, and in contact systems where mass is actively being exchanged. We present an analysis of 53 high-resolution HARPSpol spectropolarimetric observations of a sample of 14 massive binary and multiple systems using the least-squares deconvolution technique. The majority of the studied systems are classified as semi-detached or contact binaries. Definite detections of the presence of a magnetic field are achieved in all studied systems apart from the rather faint system SV Cen, for which only a marginal detection was obtained. The fact that the presence of magnetic fields is detected in all but one of the studied systems strongly suggests that interaction between the system components plays a definite role in the generation of magnetic fields in massive stars. The measured mean longitudinal magnetic field strength for all targets is of the order of a few hundred Gauss to a few kiloGauss. The strongest longitudinal magnetic fields of 4 to 5kG are discovered in the massive O-type triple system MY Ser in both components of the contact binary. kiloGauss-order magnetic fields are also detected in two other systems, V1294 Sco and V606 Cen. It is possible that there is an implication of some system characteristics, such as multiplicity, the mass ratio between the components, and a large fillout factor, on the measured magnetic field strength. Our results for the magnetic field measurements in interacting binaries present the first assessment of the occurrence rate of magnetic fields in a representative sample of such systems.

Figures (15)

• Figure 1: LSD Stokes profiles of the standard star $\gamma$ Equ. Left: LSD Stokes $V$ profiles for the HARPS-pol observations of $\gamma$ Equ from 2011 to 2025. Right: Intensities of the LSD Stokes $I$ profiles of $\gamma$ Equ at different observational epochs.
• Figure 2: Results of our LSD analysis of 29 CMa. Stokes $I$, Stokes $V$, and diagnostic null $N$ spectra obtained for different line masks using one archival ESPaDOnS observation and six HARPS-pol observations are shown. The identified Zeeman signatures are presented in blue colour.
• Figure 3: As Figure \ref{['fig:29CMa']}, but for V402 Pup.
• Figure 4: As Figure \ref{['fig:29CMa']}, but for TU Mus.
• Figure 5: As Figure \ref{['fig:29CMa']}, but for SV Cen.