Rotationally modulated variations and the mean longitudinal magnetic field of the Herbig Ae star HD 101412

TL;DR

This study measures the magnetic field variations of the Herbig Ae star HD 101412 over its rotation cycle, revealing a nearly edge-on view and a predominantly dipolar magnetic topology.

Contribution

First detailed measurement of magnetic field variation over a rotation cycle for HD 101412, determining its rotation period and magnetic geometry.

Findings

Rotation period of 42.076 days was determined.

Magnetic field shows a single-wave variation, indicating a dipolar magnetic topology.

Star is observed nearly edge-on, influencing magnetic field observations.

Abstract

Despite of the importance of magnetic fields for the full understanding of the properties of accreting Herbig Ae/Be stars, these fields have scarcely been studied over the rotation cycle until now. One reason for the paucity of such observations is the lack of knowledge of their rotation periods. The sharp-lined young Herbig Ae star HD101412 with a strong surface magnetic field became in the last years one of the most studied targets among the Herbig Ae/Be stars. A few months ago we obtained multi-epoch polarimetric spectra of this star with FORS2 to search for a rotation period and to constrain the geometry of the magnetic field. We measured longitudinal magnetic fields on 13 different epochs distributed over 62 days. These new measurements together with our previous measurements of the magnetic field in this star were combined with available photometric observations to determine the rotation period. The search of the rotation period resulted in P=42.076+-0.01d. According to near-infrared imaging studies the star is observed nearly edge-on. The star exhibits a single-wave variation of the longitudinal magnetic field during the stellar rotation cycle. These observations are usually considered as evidence for a dominant dipolar contribution to the magnetic field topology.