Towards the global magnetic field of the planet-hosting red giant eps Tau

TL;DR

This study investigates the magnetic field of the red giant epsilon Tau using spectropolarimetric data, revealing potential inhomogeneity and instrumental effects affecting measurements.

Contribution

The paper identifies a new instrumental polarization effect and suggests magnetic field inhomogeneity in epsilon Tau based on spectropolarimetric observations.

Findings

Magnetic field detected on one observation exceeding 3σ

Instrumental polarization outliers identified in ESPaDOnS spectra

Magnetic field distribution suggests possible inhomogeneity

Abstract

We present the results of a search for the magnetic field inhomogeneity for the red giant $\epsilon$ Tau. This research is based on observations obtained over 10 nights in 2008-2010 with the ESPaDOnS CFHT spectropolarimeter. We found a previously undescribed instrumental effect in the ESPaDOnS spectra, consisting of random polarization outliers. Therefore, to measure the magnetic field from the unblended individual lines, we preliminarily cleared the initial array of spectral lines from the lines distorted by polarization outliers. On only one date from ten, the magnetic field of $\epsilon$ Tau was found to exceed 3$\sigma$. We also revealed that during two nights the time series of the magnetic field values shows a distribution that is different from the normal distribution. A hypothesis was put forward that this may be due to the inhomogeneity of the magnetic field of this star.