# The two magnetic components in the Herbig Ae SB2 system HD 104237

## TL;DR

This study measures and compares magnetic fields of the Herbig Ae primary and T Tauri secondary in the HD 104237 system, revealing weak and strong magnetic components respectively, with the primary's rotation period also estimated.

## Contribution

First detailed magnetic field measurements of both components in the HD 104237 system, highlighting their magnetic differences and primary's rotation period.

## Key findings

- Primary's magnetic field is weak, 47-72 G.
- Secondary's magnetic field is stronger, up to 600 G.
- Primary's rotation period is approximately 4.34 days.

## Abstract

We present longitudinal magnetic field measurements $\langle B_z \rangle$ for the Herbig Ae primary and the T Tauri secondary in the SB2 system HD 104237. These measurements were carried out using high spectral resolution observations obtained with the High Accuracy Radial velocity Planet Searcher in polarimetric mode, installed at the ESO La Silla 3.6 m telescope. In agreement with previous studies of Herbig Ae stars, the longitudinal magnetic field in the primary is rather weak, ranging from 47 G to 72 G. The secondary component possesses a variable, much stronger magnetic field, up to 600 G, as expected for a magnetically active T Tauri star. We estimated the rotation period of the primary, $P_{\mathrm{rot}}=4.33717\pm0.00316$ d ($=104\pm0.08$ h), from metal line equivalent width variations.