Ramkrishna Nagar College

We report the first R -band ( lambda = 0 . 630 mu m, lambda = 0 . 120 mu m) photopolarimetric observations of comet C/2023 H5 (Lemmon) at low phase angles (9.9 degrees and 10.4 degrees) and 333P/LINEAR at a medium phase angle (62 degrees) 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 dr ag, contr asting with shallow antisunward slopes ( m = 0.60 to 0.65) in the inner coma, transitioning to shallower slopes ( m < 1 ) in both directions at int ermediat e and outer r egions wher e radiation pr essur e becomes influential. Aperture polarization measurements show negative polarization ( -1 . 5 per cent to -2 . 7 per cent , uncertainties similar to 1 per cent). For 333P/LINEAR, intensity slopes exhibit asymmetric spatial variation with steep sunward slopes ( m = 1 . 12 +/- 0 . 06 ) and shallower antisunward slopes ( m = 0 . 76 +/- 0 . 03 ) in the inner coma, flattening outwards, with aperture polarization reaching similar to 16 per cent , typical of the positive polarization branch at medium phase angles. The observation at alpha approximate to 62 degrees r epr esents 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 str ongest neg ative polarization near the photocentre and 333P/LINEAR displaying a sun ward-antisun ward gradient. Im- age enhancement techniques reveal jet -lik e 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

Magnetic fields play an important role in star formation but are often difficult to observationally probe in small star-forming molecular clouds. We study two such clouds, L1604 (towards the Galactic anticentre) and L121 (towards the Galactic centre), using R-band polarimetry to investigate their envelope magnetic field ( theta(B) (env) ) morphology, physical structure, and internal energetics. We find a key distinction: theta(env)(B) in L1604 is effectively parallel to the Galactic plane, while it is offset by similar to 70 degrees +/- 1 degrees in L121. Additionally, theta(env)(B) is misaligned with the core minor axes (derived from sub-millimeter data) by similar to 47 degrees +/- 1 degrees for L1604 and similar to 74 degrees +/- 1 degrees for L121. However, for L121, a much smaller offset of similar to 17 degrees +/- 1 degrees is found when compared with its minor axis obtained from optical data in the literature, suggesting scale-dependent variations in magnetic field geometry. The distances are calculated with using the near-infrared (NIR) photometry technique (which uses Two Micron All Sky Survey and Gaia DR3) are found to be 816 +/- 11 pc for L1604 and 124 +/- 1 pc for L121. We use the PNICER technique to create extinction maps and derived physical parameters using Herschel Spectral and Photometric Imaging Receiver (SPIRE) data. The mean column densities are similar to (2 . 2 +/- 1 . 1) x 10(21) cm(-2) for L1604 and similar to (1 . 3 +/- 0 . 6) x 10(21) cm(-2) for L121. The plane-of-sky magnetic field strengths (B-pos), estimate using the Davis-Chandrasekhar-Fermi method, are similar to (47 +/- 17) mu G for L1604 and similar to (72 +/- 23) mu G for L121. Both clouds exhibit sub-critical mass-to-flux ratios and sub-Alfvenic conditions, indicating magnetic dominance over gravity and turbulence. Our results highlight that envelopes are magnetically supported, while cores may become supercritical, demanding high-resolution data to trace the envelope-to-core magnetic influence.

The relative importance of magnetic fields, turbulence, and gravity during the early stages of star formation remains uncertain. We present a multiscale polarimetric investigation of L1287, a clustered low-mass star-forming region hosting a bipolar molecular outflow and a protostar. Our study combines new R-band optical polarimetric observations obtained with AIMPOL, tracing the magnetic field on envelope scales, with archival 850 mu m SCUPOL polarization data probing the dense molecular clump. The clump-scale magnetic field morphology is offset by similar to 59 degrees from the envelope field, and the polarization fraction decreases systematically toward higher-density regions, indicating depolarization. This trend is primarily attributed to reduced grain-alignment efficiency, with possible contributions from radiative torque disruption, while magnetic field tangling is unlikely to be the dominant factor. The density structure is derived using extinction map and Herschel SPIRE data. Combining Two Micron All Sky Survey (2MASS) photometry with Gaia parallaxes yields a distance of 920 +/- 76 pc. Using the Davis-Chandrasekhar-Fermi method, we estimate magnetic field strengths of similar to 111 +/- 27 mu G in the envelope and similar to 195 +/- 70 mu G in the dense clump. The envelope is magnetically subcritical, whereas the clump is supercritical. The Alfv & eacute;n Mach number indicates sub-Alfv & eacute;nic conditions in the envelope and a transition toward trans-Alfv & eacute;nic conditions in the dense gas. Virial analysis further shows that magnetic support dominates the envelope, while gravity dominates the clump. The alignment of the clump magnetic field with both the minor axis and the molecular outflow supports a magnetically regulated evolutionary scenario that transitions toward gravitational collapse at higher densities. These results provide observational evidence that magnetic criticality evolves significantly across spatial scales in star-forming clouds.

We present a multiwavelength study of three molecular clouds, L1346, L1388, and L1598, combining R -band polarimetric and archival photometric data to investigate their magnetic field morphology, physical characteristics, and dust grain alignment properties. Using a Near Infrared Photometric Technique, we estimate distances of 687 ± 26 pc (L1346), 414 ± 42 pc (L1388), and 642 ± 34 pc (L1598). Extinction mapping via the PNICER approach yields mean visual extinctions of 1.7, 1.4, and 2.0 mag, corresponding to column densities of 1.61, 1.33, and 1.92 × 10 ^21 cm ^−2 . Complementary Herschel SPIRE observations provide mean dust temperatures of 13.35 K (L1346) and 14.48 K (L1598), with clump masses of ∼16 M _⊙ and ∼11 M _⊙ . The virial parameter of L1598 ( α _vir = 0.86–1.04) confirms it as a gravitationally bound structure. Polarimetric observations, primarily probing the envelope regions, reveal mean polarization degrees of 4.46% (L1346), 3.34% (L1388), and 2.64% (L1598), with polarization angles closely aligned with the Galactic plane. Unlike L1598, the optical polarization vectors in L1346 and L1388 qualitatively agree with the large-scale Planck magnetic-field morphology. Applying the classical Davis-Chandrasekhar-Fermi (DCF) method, we derive approximate plane-of-sky (POS) magnetic field strength of ≈73 μ G (L1346), ≈17 μ G (L1388), and ≈23 μ G (L1598). A monotonic decrease in polarization rate with distance and a declining polarization efficiency with increasing extinction are observed in L1346 and L1388. Critical grain sizes of ≈0.069–0.102 μ m across L1346 and L1388, smaller than typical diffuse interstellar medium (ISM) values, indicate that alignment may be constrained by radiation field attenuation within the clouds. Taken together, these findings are compatible with the radiative torque alignment (RAT-A) theory.

We present a comprehensive polarimetric analysis of the main-belt asteroids 13 Egeria and 511 Davida, based on new R-band observations combined with previously published data in the R, V, and G bands. The new observations have been conducted using the 1.04 m Sampurnanand Optical Telescope at phase angles of α = 5.52^∘ for Egeria and α = 2.21 ° for Davida, covering a previously unexplored region of the phase–polarization curve for both objects. At these low phase angles, we have detected significant negative polarization: P_r = - 1.72 ± 0.06 for Egeria and P_r = - 0.91 ± 0.10 for Davida. These measurements provide valuable constraints within the negative polarization branch and significantly improve the overall phase–polarization profiles of the two asteroids. The inclusion of these new data enables more accurate determinations of key polarimetric parameters, including minimum polarization (P_min) , inversion angle α_inv , and polarimetric slope ( h ) . To maintain internal consistency, our analysis focuses on R-band observations supplemented by multi-band archival data. A comparative study with other well-characterized C-type asteroids reveals both shared features and subtle differences, potentially indicative of variations in surface texture or composition. These findings enhance our understanding of the surface scattering properties of Egeria and Davida and contribute to the broader characterization of C-type asteroid diversity, highlighting the importance of polarimetric studies for understanding surface properties and regolith characteristics within taxonomic groups, offering new insights into the nature of primitive bodies in the solar system.