New spectroscopic and polarimetric observations of the A0 supergiant HD 92207

Our recent search for the presence of a magnetic field in the bright early A-type supergiant HD 92207 using FORS 2 in spectropolarimetric mode revealed the presence of a longitudinal magnetic field of the order of a few hundred Gauss. However, the definite confirmation of the magnetic nature of this object remained pending due to the detection of short-term spectral variability probably affecting the position of line profiles in left- and right-hand polarized spectra. We present new magnetic field measurements of HD 92207 obtained on three different epochs in 2013 and 2014 using FORS 2 in spectropolarimetric mode. A 3σ detection of the mean longitudinal magnetic field using the entire spectrum, <B_z>_all=104±34 G, was achieved in observations obtained in 2014 January. At this epoch, the position of the spectral lines appeared stable. Our analysis of spectral line shapes recorded in opposite circularly polarized light, i.e. in light with opposite sense of rotation, reveals that line profiles in the light polarized in a certain direction appear slightly split. The mechanism causing such a behaviour in the circularly polarized light is currently unknown. Trying to settle the issue of short-term variability, we searched for changes in the spectral line profiles on a time scale of 8-10 min using HARPS polarimetric spectra and on a time scale of 3-4 min using time series obtained with the CORALIE spectrograph. No significant variability was detected on these time scales during the epochs studied. Based on observations collected with the CORALIE echelle spectrograph mounted on the 1.2-m Swiss telescope at La Silla Observatory, data obtained at the European Southern Observatory (ESO Prg. 092.D-0209(A), and data obtained from the ESO Science Archive Facility under request MSCHOELLER 102067).