The determination of the rotation period and magnetic field geometry of the strongly magnetic roAp star HD154708

TL;DR

This study determines the rotation period and magnetic field geometry of the strongly magnetic roAp star HD154708 using spectropolarimetric observations, revealing a nearly pole-on orientation and a dipolar magnetic field with a surface strength around 27 kG.

Contribution

First detailed magnetic field geometry and rotation period measurement for HD154708 based on spectropolarimetric data.

Findings

Rotation period of 5.3666 days accurately determined.

Magnetic field modeled as a centered dipole with ~27 kG surface strength.

Star observed nearly pole-on with magnetic axis inclined 22.5° to 35.5°.

Abstract

We obtained thirteen spectropolarimetric observations of the strongly magnetic rapidly oscillating Ap star HD154708 over three months with the multi-mode instrument FORS1, installed at the 8-m Kueyen telescope of the VLT. These observations have been used for the determination of the rotation period of P=5.3666+-0.0007d. Using stellar fundamental parameters and the longitudinal magnetic field phase curve, we briefly discuss the magnetic field geometry. The star is observed nearly pole-on and the magnetic field geometry can be described by a centred dipole with a surface polar magnetic field strength B_d between 26.1 and 28.8kG and an inclination of the magnetic axis to the rotation axis in the range 22.5deg to 35.5deg.