Search for the magnetic field of the O7.5 III star xi Persei

TL;DR

This study aimed to detect a magnetic field in the star xi Persei using high-resolution spectropolarimetry, but only upper limits were established, suggesting any magnetic field present is weaker than 300 G, which could influence stellar wind behavior.

Contribution

First spectropolarimetric attempt to measure magnetic fields in xi Persei, providing upper limits and insights into its pulsation amplitude changes.

Findings

No definitive magnetic field detected, upper limit ~300 G.

Pulsation amplitude changed within a year.

Star's magnetic influence on wind remains uncertain.

Abstract

Cyclical wind variability is an ubiquitous but as yet unexplained feature among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest representative of this class on the Northern hemisphere. As its prominent cyclical wind properties vary on a rotational time scale (2 or 4 days) the star has been already for a long time a serious magnetic candidate. As the cause of this enigmatic behavior non-radial pulsations and/or a surface magnetic field are suggested. We present a preliminary report on our attempts to detect a magnetic field in this star with high-resolution measurements obtained with the spectropolarimeter Narval at TBL, France during 2 observing runs of 5 nights in 2006 and 5 nights in 2007. Only upper limits could be obtained, even with the longest possible exposure times. If the star hosts a magnetic field, its surface strength should be less than about 300 G. This would still be enough to disturb the stellar wind significantly. From our new data it seems that the amplitude of the known non-radial pulsations has changed within less than a year, which needs further investigation.