Near opposition photometry of comet C/2007 N3 (Lulin)

TL;DR

This study presents photometric observations of comet C/2007 N3 (Lulin) near opposition, revealing a linear brightness increase with decreasing phase angle, consistent across wavelengths, with no non-linear opposition surge observed.

Contribution

It provides detailed photometric measurements of comet Lulin near opposition, demonstrating a wavelength-independent phase coefficient and absence of opposition surge above 1.7°.

Findings

Brightness increases linearly with decreasing phase angle.

Phase coefficient is wavelength-independent.

No non-linear opposition surge observed above 1.7°.

Abstract

Observations on comet C/2007 N3 (Lulin) were made at phase angles close to opposition ($1.7^{\circ}$ - $10^{\circ}$). Photometric observations were carried out during 2009 February 24-28, in the IHW blue and red continuum and $R$ broad band using photo-polarimeter mounted on the 1.2m telescope at Mt Abu IR Observatory. In all the bands, a significant linear increase in brightness with decreasing phase angle is detected for the above phase angle range. The phase coefficient ($\beta = 0.040\pm 0.001$ mag deg$^{-1}$ estimated in IHW red (6840\AA) filter band) is found to be independent of wavelength. No non-linear opposition surge is observed for phase angle $>1.7^{\circ}$. The linear increase in brightness with decreasing phase angle in the range mentioned earlier can be explained using the shadow hiding model. The colour of the comet is found to be similar to the solar colour indicating the dominance of grains larger than $0.1\mu m$. A dip in the brightness of about 0.20 mag is seen at the phase angle $\sim 6.5^\circ$.