First detection of a magnetic field in the fast rotating runaway Oe star $zeta$,Ophiuchi

S. Hubrig$^1$, L.M. Oskinova$^2$, M. Sch"oller$^3$

$^1$ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482~Potsdam, Germany
$^2$ Universit"at Potsdam, Institut f"ur Physik und Astronomie, 14476~Potsdam, Germany
$^3$ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748~Garching, Germany

The star $zeta$,Ophiuchi is one of the brightest massive stars in the northern hemisphere and
was intensively studied in various wavelength domains. The currently available observational material
suggests that certain observed phenomena are related to the presence of a magnetic field.
We acquired spectropolarimetric observations of $zeta$,Oph
with FORS,1 mounted on the 8-m Kueyen telescope of the VLT to investigate if a magnetic field
is indeed present in this star.
Using all available absorption lines, we detect a mean longitudinal magnetic field
$left< B_zright>_{rm all}= 141pm45$,G, confirming the magnetic nature of this star.
We review the X-ray properties of $zeta$,Oph with the aim to
understand whether the X-ray emission of $zeta$,Oph is dominated by magnetic
or by wind instability processes.

Reference: AN, in print
Status: Manuscript has been accepted