Limb polarization of Uranus and Neptune ⋆ II. Spectropolarimetricobservations

• Main Authors: F. Joos, H. M. Schmid
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2006
• Subjects: South Pole; South pole
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.337.4742; http://arxiv.org/pdf/astro-ph/0612213v1.pdf

Aims. We have detected a strong limb polarization for Uranus and Neptune. With spectropolarimetric observations we characterize the spectral dependence of this limb polarization and explore the diagnostic potential for investigating the distribution and properties of the scattering particles. Methods. We present disk resolved spectropolarimetry of Uranus and Neptune covering the wavelength range from 5300 Å to 9300 Å and compare the spectropolarimetric signal for different limb sections and the center of the planetary disk. As an additional benefit we obtained center-to-limb disk profiles for the intensity and polarization for various wavelengths. Results. Our data show for both planets a strong linear limb polarization oriented perpendicular to the limb. The polarization at the center of the planetary disks is essentially zero. Overall the limb polarization increases towards shorter wavelengths, and it is further enhanced in the methane absorption bands when compared to adjacent inter band regions. Qualitatively, the polarization signal is very similar for Uranus and Neptune. For Uranus the peak limb polarization of the methane absorption bands reaches a maximum of 3 % whereas in the nearby higher albedo regions it peaks at about 2 %. The measured polarization for Neptune is significantly lower because the signal is averaged down by the limited spatial resolution of our Neptune data. The disk profiles for Uranus (center to limb profiles) show for the intensity a strong asymmetry between the bright South pole