Confirming the Magnetic Field Detection at the Surface of $\chi$ Cyg

TL;DR

This study reports the detection of a magnetic field at the surface of the star $\\chi$ Cyg during a specific pulsation phase, using spectropolarimetric observations, indicating a phase-dependent magnetic activity.

Contribution

First detection of surface magnetic field in $\\chi$ Cyg with phase-dependent characteristics using spectropolarimetry.

Findings

Detected a 3.4 G magnetic field near maximum light.

No magnetic detection outside the maximum light phase.

Magnetic field detection correlates with shock conditions during pulsation.

Abstract

We present spectropolarimetric observations of $\chi$ Cygni obtained with Neo-Narval at T\'elescope Bernard Lyot in 2025. We obtained observations across three epochs (2025 Jul, Aug, and Oct) near maximum light to search for magnetic field signatures at the stellar photosphere. We detected a clear circular polarization signal in the 2025 Aug observations (pulsation phases $0.99$ to $0.01$). We measure a mean longitudinal magnetic field of $B_l = 3.4 \pm 0.6$ G. No detections were obtained for the 2025 Jul and Oct epochs. The pulsation-phase dependence suggests that field detection is tied to specific shock conditions near maximum light.