Halpha spectropolarimetry of the B[e] supergiant GG Carinae

TL;DR

This study uses spectropolarimetry to analyze the circumstellar disk geometry of the B[e] supergiant GG Carinae, revealing a rotating disk with a well-defined symmetry axis through polarization measurements.

Contribution

First spectropolarimetric analysis of GG Car revealing disk geometry and rotation, enhancing understanding of B[e] supergiant circumstellar environments.

Findings

Intrinsic polarization confirms a non-spherical circumstellar environment.

Detected rotation of the disk indicated by PA variation along Halpha.

Consistent symmetry axis across epochs suggests a stable disk orientation.

Abstract

Aims. We study the geometry of the circumstellar environment of the B[e] supergiant star GG Car. Methods. We present observations acquired using the IAGPOL imaging polarimeter in combination with the Eucalyptus-IFU spectrograph to obtain spectropolarimetric measurements of GG Car across Halpha at two epochs. Polarization effects along the emission line are analysed using the Q-U diagram. In particular, the polarization position angle (PA) obtained using the line effect is able to constrain the symmetry axis of the disk/envelope. Results. By analysing the fluxes, GG Car shows an increase in its double-peaked Halpha line emission relative to the continuum within the interval of our measurements (~43 days). The depolarization line effect around Halpha is evident in the Q-U diagram for both epochs, confirming that light from the system is intrinsically polarized. A rotation of the PA along Halpha is also observed, indicating a counter-clockwise rotating disk. The intrinsic PA calculated using the line effect (~85deg) is consistent between our two epochs, suggesting a clearly defined symmetry axis of the disk.