Description of the POLARIMETRY OF ASTEROID ITOKAWA bundle V1.0 ============================================================== Bundle Generation Date: 2020-02-28 Peer Review: 2007 Asteroid Review, 2007-05-24 Discipline node: Small Bodies Node Content description based on the data set catalog file description for the PDS3 version, EAR-A-I0066-3-ITOKAWAPOL-V1.0 ====================================================================================================================== Note: for PDS3 data sets migrated to PDS4, the following text is taken verbatim from the data set description and confidence level note of the PDS3 data set catalog file. In these cases, some details may not be correct as a description of the PDS4 bundle. This data set contains the polarimetry of asteroid 25143 Itokawa published in Cellino et al. (2005). The observations were made from June 26 through July 3, 2004 with the Torino photopolarimeter at the 2.15 m telescope of the El Leoncito Observatory in Argentina. On June 26 and July 1 and 2, weather prevented any useful observations of Itokawa, so the data presented here are from the other nights of the run. The degree of linear polarization in five filters (Johnson-Cousins UBVRI) was measured over a wide range of phase angles, between 40 and 80 degrees. The data obtained are sufficient to derive an estimate of the asteroid's geometric albedo of 0.24 +/- 0.01. The single entries in the table correspond to averages over time spans of about one hour each. Some averaging was done because in polarimetry single measurements have usually fairly large error bars. During one hour the phase angle did not change by more than one degree, as can be seen from the difference in the phase angle listed in each entry of the table for the same night. Single polarization measurements consisted of eight photometric measurements corresponding to a cycle of eight different positions of the half-wave plate in front of the polarimeter. A single cycle takes about 3.5 minutes. For Itokawa it was decided that the usual procedure of computing the average nightly polarization, by making an average over all the single measurements taken during the night, was clearly not appropriate. The reason for not doing so was that the object was moving fast and the phase angle was changing. On the other hand, the phase change was fairly small over intervals of some tens of minutes. The average over the cycles continuously executed during time spans of about one hour was adopted as a compromise between the need of documenting the change in polarization for changing phase angle, and the need of having fairly good error bars in the corresponding polarization measurements. 25143 Itokawa is an S-type asteroid, an NEO, and was the target of the Hayabusa mission. Cellino, A., F. Yoshido, E. Anderlucci, P. Bendjoya, M. DiMartino, M. Ishiguro, A.M. Nakamura, and J. Saito, A polarimetric study of asteroid 25143 Itokawa, Icarus 179, 297-303, 2005. Known issues or problems with the data ====================================== Uncertainties for the measurements are given in the table. Note that albedo was determined by linear extrapolation of the polarization obtained within the phase angles 40-80 degrees, rather than near the inversion point (20-30 degrees). For further information about the measurements and analysis, see Cellino et al. (2005). PDS3 Source =========== Version 1.0 of this bundle was migrated from version 1.0 of the PDS3 data set EAR-A-I0066-3-ITOKAWAPOL-V1.0.