Optical polarimetry and photometry of comet 17P/Holmes

Comet 17P/Holmes was observed for linear polarization using the optical polarimeter mounted on the 1.2-m telescope atop Gurushikhar peak near Mt. Abu during the period 2007 November-December. Observations were conducted through the International Halley Watch narrow-band (continuum) filters. During the observing run, the phase angle was near 13 degrees at which the comet showed negative polarization. On the basis of the observed polarization data, we find comet 17P/Holmes to be a typical comet with usual dust characteristics. We note that radial rate of change of brightness in coma in red band is higher than that in blue band; it has decreased by a factor of 3.6 and 2.5, respectively, in red and blue bands during the November-December run, indicating relative increase in the abundance of smaller dust particles outward. Radial brightness variation seen near the nucleus on November 6 is indicative of the presence of a blob or shocked region beyond 10 arcsec from the nucleus which has gradually smoothened by December 13. The brightness distribution is found steeper during November 5-7 as compared to that on December 13.