Issue |
A&A
Volume 452, Number 2, June III 2006
|
|
---|---|---|
Page(s) | 657 - 668 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:20053273 | |
Published online | 22 May 2006 |
Limb polarization of Uranus and Neptune
I. Imaging polarimetry and comparison with analytic models
1
Institut für Astronomie, ETH Zürich, 8092 Zürich, Switzerland e-mail: schmid@astro.phys.ethz.ch
2
Alte Kantonsschule Aarau, Bahnhofstrasse 91, 5001 Aarau, Switzerland
Received:
20
April
2005
Accepted:
10
January
2006
Imaging polarimetry of Uranus and Neptune in the R, i, and z bands
are presented. In all observations a radial limb polarization on the order
of 1% was detected with a position angle perpendicular to the
limb. The polarization is higher in both planets for the shorter
wavelength bands. As a first approximation, the polarization seems
to be equally strong along the entire limb. This is unlike Jupiter and
Saturn, where significant limb polarization is only observed at the poles.
We determined flux-weighted averages of the limb polarization and
radial limb polarization profiles, and investigated the degradation and
cancellation effects in the polarization signal due to the seeing-limited
spatial resolution of our observations. Taking this into
account we derived corrected values for the limb polarization in
Uranus and Neptune. The results are compared with analytic models
for Rayleigh scattering atmospheres for the semi-infinite case and
finite layers with ground albedo. The comparison shows that the
detected polarization is compatible with expectations. This indicates
that limb-polarization measurements offer a powerful diagnostic
tool for investigating the properties of scattering particles in the upper
atmospheres of Uranus and Neptune, in particular if more sophisticated
numerical modeling of the limb polarization becomes available.
It is also
concluded from the overall strength of the limb polarization that
the disk-integrated polarization of Uranus and Neptune for large
phase angles is high (%). This is of interest for
future polarimetric detections of extra-solar planets with atmospheric
properties similar to Uranus and Neptune.
Key words: planets and satellites: individual: Uranus / planets and satellites: individual: Neptune / polarization / scattering
© ESO, 2006
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