SPECTROPOLARIMETRIC VARIABILITY AND CO-ROTATING STRUCTURE IN HD92207
R Ignace$^1$, S Hubrig$^2$, M Scholler$^3$
$^1$ East Tennessee State University
$^2$ European Southern Observatory, Chile
$^3$ European Southern Observatory, Germany
We report on low resolution ($Rapprox 3000$) 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 cover approximately a quarter of the
star's rotational phase. Variability in the continuum polarization
level is observed over this period of time. The polarization across the
H$_alpha$ line on any given night is typically different from the degree
and position angle of the polarization in the continuum. Interestingly,
H$beta$ is not in emission and does not show polarimetric variability.
We associate the changes at H$_alpha$ as arising in the wind, which is in
accord with the observed changes in the profile shape and equivalent width
of H$_alpha$ along with the polarimetric variability. For the continuum
polarization, 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 polarization signatures across H$_alpha$
are too complex to be explained by this simple model and will require a
more intensive polarimetric follow-up study to interpret properly.
Reference: to appear in AJ
Status: Manuscript has been accepted
Weblink: http://lanl.arxiv.org/abs/0812.0310
Comments:
Email: ignace@etsu.edu