The asymmetric wind of R127

R. E. Schulte-Ladbeck, University of Pittsburgh
Leitherer, Space Telescope Science Institute
G. C. Clayton, University of Colorado Boulder
C. Robert, Space Telescope Science Institute
M. R. Meade, University of Wisconsin-Madison
L. Drissen, Space Telescope Science Institute
A. Nota, Space Telescope Science Institute
W. Schmutz, ETH Zürich


We present optical, linear polarimetry in broad-band UBVRI filters plus narrow-band filters centered on the emission lines of Hα and the red [N II] and spectropolarimetry in the wavelength range from 4120 Å to 6770 Å of the luminous blue variable R127 in the Large Magellanic Cloud. Both observations display a decrease of the percentage polarization across the Hα emission line with respect to the continuum. We assume that Hα is recombination-line dominated and thus intrinsically unpolarized, and we use the continuum-subtracted line polarization to estimate the interstellar foreground polarization. The resulting amount of intrinsic continuum polarization of R127 is very large, of order 1%-1.5%, implying both the presence of copious free electrons and a considerable asphericity in their distribution. The two data sets, taken 2 months apart, display significant variations in the continuum polarization, which confirms that the stellar-wind properties of R127 are time-dependent in the maximum state. We discuss several possible wind geometries and present arguments favoring a clumpy, axisymmetric outflow.