A short and sudden increase of the magnetic field strength and the accompanying spectral variability in the O9.7 V star HD 54879
Hubrig, S.; Schöller, M.; Järvinen, S. P.; Küker, M.; Kholtygin, A. F.; Ryspaeva, E. B.; Sokoloff, D. D.
Germany, Russia
Abstract
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 ∼2 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. 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.