Photopolarimetric studies of comets C/2023 H5 and 333P/LINEAR

ABSTRACT We report the first R-band ($\lambda = 0.630~\mu$m, $\Delta \lambda = 0.120~\mu$m) photopolarimetric observations of comet C/2023 H5 (Lemmon) at low phase angles (9.9$^\circ$ and 10.4$^\circ$) and 333P/LINEAR at a medium phase angle (62$^\circ$) using the 1.04-m Sampurnanand Telescope of Nainital on 2024 December 1, 2025 February 23, and 2025 March 4. For C/2023 H5, radial intensity profiles (following $I = kd^{-m}$) reveal three distinct spatial zones: steep sunward slopes (m = 1.28 to 1.29) indicating enhanced dust concentration due to weak gas drag, contrasting with shallow antisunward slopes (m = 0.60 to 0.65) in the inner coma, transitioning to shallower slopes ($m\, \lt\, 1$) in both directions at intermediate and outer regions where radiation pressure becomes influential. Aperture polarization measurements show negative polarization ($-1.5~{{\ \rm per\ cent}}$ to $-2.7~{{\ \rm per\ cent}}$, uncertainties $\sim$1 per cent). For 333P/LINEAR, intensity slopes exhibit asymmetric spatial variation with steep sunward slopes ($m = 1.12 \pm 0.06$) and shallower antisunward slopes ($m = 0.76 \pm 0.03$) in the inner coma, flattening outwards, with aperture polarization reaching $\sim 16~{{\ \rm per\ cent}}$, typical of the positive polarization branch at medium phase angles. The observation at $\alpha \approx 62^\circ$ represents the first reported R-band polarimetric measurement at this specific phase angle, wavelength, and bandwidth. Polarization maps reveal spatial variations in polarization, with C/2023 H5 showing the strongest negative polarization near the photocentre and 333P/LINEAR displaying a sunward–antisunward gradient. Image enhancement techniques reveal jet-like features in both comets. The intensity slopes with polarization measurements indicate weak to moderate activity levels, with dust behaviour governed by weak gas drag near the nucleus and radiation pressure in the outer coma.