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TOPIC: HD 92207

Blobrana

L

Posts: 131433

Date: Feb 3 08:22 2015

HD92207	Permalink

Title: New spectroscopic and polarimetric observations of the A0 supergiant HD92207 Author: S. Hubrig, A.F. Kholtygin, M. Schöller, R.I. Anderson, S. Saesen, J.F. Gonzalez, I. Ilyin, M. Briquet Our recent search for the presence of a magnetic field in the bright early A-type supergiant HD92207 using FORS2 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 polarised spectra. We present new magnetic field measurements of HD92207 obtained on three different epochs in 2013 and 2014 using FORS2 in spectropolarimetric mode. A 3sigma detection of the mean longitudinal magnetic field using the entire spectrum, <B_z>_all=104±34G, 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 polarised light, i.e. in light with opposite sense of rotation, reveals that line profiles in the light polarised in a certain direction appear slightly split. The mechanism causing such a behaviour in the circularly polarised 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 8-10min using HARPS polarimetric spectra and on a time scale of 3-4min using time series obtained with the CORALIE spectrograph. No significant variability was detected on these time scales during the epochs studied. Read more (2844kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Dec 3 00:54 2008

HD 92207	Permalink

Title: Spectropolarimetric Variability and Co-Rotating Structure in HD 92207 Authors: R Ignace, S Hubrig, M Scholler We report on low resolution (R~3000) spectropolarimetry of the A0 supergiant star HD 92207. This star is well-known for significant spectral variability. The source was observed on seven different nights spanning approximately 3 months in time. With a rotation period of approximately 1 year, our data covers approximately a quarter of the star's rotational phase. Variability in the continuum polarisation level is observed over this period of time. The polarisation across the Halpha line on any given night is typically different from the degree and position angle of the polarisation in the continuum. Interestingly, Hbeta is not in emission and does not show polarimetric variability. We associate the changes at Halpha as arising in the wind, which is in accord with the observed changes in the profile shape and equivalent width of Halpha along with the polarimetric variability. For the continuum polarisation, we explore a spiral shaped wind density enhancement in the equatorial plane of the star, in keeping with the suggestion of Kaufer etal (1997). Variable polarisation signatures across Halpha are too complex to be explained by this simple model and will require a more intensive polarimetric follow-up study to interpret properly. Read more (51kb, PDF) __________________

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