Polarimetric CCD imaging of comet 47P/Ashbrook-Jackson and variability of polarization in the inner coma of comets.
Polarimetric observations of comet 47P/Ashbrook-Jackson at low phase angle have been performed between 20 and 22 August 1993 from Pic du Midi Observatory by using the CCD-polarimetry method. The polarization maps, as compared with the brightness maps, enhance some details and asymmetry in the inner coma, i.e. a circumnucleus halo and jet structure. Values of polarization, obtained for various fields of view centered on the nucleus, are compared to results from previous observations performed in 1977 on the same comet by Kiselev and Chernova (1981Icar...48..473K). The detected evolution of polarization with increasing distance from the nucleus could be due to the presence of dust jets, as is suggested on the polarimetric map obtained on the 21 August 1993. These results are similar to those obtained by the same method on comet Levy C/1990 K1 for the same phase angle domain. The variability of the polarization around the nucleus is compared with the results obtained for others comets observed by remote sensing, and through in- situ measurements performed on comet 26P/Grigg-Skjellerup by the OPE instrument onboard the Giotto spacecraft. The nature of grains that fill the regions respectively of high and low polarization, detected in the inner coma of several comets for distances to the nucleus typically smaller than 3000km, are then tentatively discussed.
Astronomy and Astrophysics
- Pub Date:
- December 1996
- TECHNIQUES: POLARIMETRIC;
- COMETS: GENERAL;
- COMETS: INDIVIDUAL: 47P/ASHBROOK-JACKSON