Optical polarimetry and photometry of comet 17P/Holmes

TL;DR

This study presents optical polarimetry and photometry observations of comet 17P/Holmes, revealing typical dust characteristics, dust particle size variations, and changes in brightness distribution over two months.

Contribution

First detailed polarimetric and photometric analysis of comet 17P/Holmes during its 2007 outburst period.

Findings

Comet exhibited negative polarisation at a phase angle of 13°.

Radial brightness variation indicates an increase in smaller dust particles outward.

Presence of a shock region near the nucleus that gradually dissipated.

Abstract

Comet 17P/Holmes was observed for linear polarisation using the optical polarimeter mounted on the 1.2m telescope atop Gurushikhar peak near Mt. Abu during the period November-December 2007. Observations were conducted through the IHW narrow band (continuum) filters. During the observing run the phase angle was near $13^{\circ}$ at which the comet showed negative polarisation. On the basis of the observed polarisation 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 out ward. Radial brightness variation seen near the nucleus on November 6 is indicative of the presence of a blob or shocked region beyond 10" from the nucleus which has gradually smoothened by December 13. The brightness distribution is found steeper during November 5-7 as compared to on December 13.