TY - JOUR

T1 - A short and sudden increase of the magnetic field strength and the accompanying spectral variability in the O9.7 V star HD 54879

AU - Hubrig, S.

AU - Küker , M.

AU - Järvinen , S.P.

AU - Kholtygin, A.F.

AU - Schöller, M.

AU - Ryspaeva, E.B.

AU - Sokoloff, D.D.

PY - 2019/4/21

Y1 - 2019/4/21

N2 - Only 11 O-type stars have been confirmed to possess large-scale organized magnetic fields. The presence of a '600 G longitudinal magnetic field in the O9.7 V star HD 54879 with a lower limit of the dipole strength of 1/42 kG was discovered a few years ago in the framework of the ESO large program 'B-fields in OB stars'. Our FORS 2 spectropolarimetric observations from 2017 October 4 to 2018 February 21 reveal the presence of short- and long-term spectral variability and a gradual magnetic field decrease from about '300 G down to about '90 G. Surprisingly, we discover on the night of 2018 February 17 a sudden, short-term increase of the magnetic field strength and measure a longitudinal magnetic field of '833 G. The inspection of the FORS 2 spectrum acquired during the observed magnetic field increase indicates a very strong change in spectral appearance with a significantly lower photospheric temperature and a decrease of the radial velocity by several 10 km s '1. Different scenarios are discussed in an attempt to interpret our observations. Our FORS 2 radial velocity measurements indicate that HD 54879 is a member of a long-period binary.

AB - Only 11 O-type stars have been confirmed to possess large-scale organized magnetic fields. The presence of a '600 G longitudinal magnetic field in the O9.7 V star HD 54879 with a lower limit of the dipole strength of 1/42 kG was discovered a few years ago in the framework of the ESO large program 'B-fields in OB stars'. Our FORS 2 spectropolarimetric observations from 2017 October 4 to 2018 February 21 reveal the presence of short- and long-term spectral variability and a gradual magnetic field decrease from about '300 G down to about '90 G. Surprisingly, we discover on the night of 2018 February 17 a sudden, short-term increase of the magnetic field strength and measure a longitudinal magnetic field of '833 G. The inspection of the FORS 2 spectrum acquired during the observed magnetic field increase indicates a very strong change in spectral appearance with a significantly lower photospheric temperature and a decrease of the radial velocity by several 10 km s '1. Different scenarios are discussed in an attempt to interpret our observations. Our FORS 2 radial velocity measurements indicate that HD 54879 is a member of a long-period binary.

KW - MHD

KW - stars: atmospheres

KW - stars: early-type

KW - stars: individual: HD 54879

KW - stars: magnetic field

KW - stars: variables: general

UR - http://www.scopus.com/inward/record.url?scp=85062286866&partnerID=8YFLogxK

U2 - 10.1093/mnras/stz198

DO - 10.1093/mnras/stz198

M3 - Article

VL - 484

SP - 4495

EP - 4506

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 4

ER -