Dust and coma radicals in C/2024 E1 (Wierzchos): evolution of the activity

Abstract We present multi-epoch R-band imaging and long-slit spectroscopy of the dynamically new comet C/2024 E1 (Wierzchos) during its pre-perihelion phase, spanning heliocentric distances from 4.5 to 2.3 au. The most prominent fluorescence emissions in the visible wavelength range are detected. We measure production rates of CN, C2, and C3, while no significant NH2 signal is identified. In our dataset, CN became detectable at 3.48 au, and C3 and C2 at 2.80 au. The mean ratios log C2/CN = 0.00 ± 0.07 and log C3/CN = −1.03 ± 0.09 place the comet in an intermediate taxonomic regime between typical and carbon-depleted populations. Dust production rates, ejection velocities, and particle size distributions are constrained using a Monte Carlo dust tail model that reproduces the observed coma morphology. The dust population is characterized by a power-law size distribution with an exponent of ~−3.5, and particle sizes ranging from 1 μm to 4 mm. The inferred initial ejection velocities span from ~20 m s−1 to ~100 m s−1. We use the empirical relation between CN and OH to estimate the water production rate and derive the dust-to-gas mass ratio for heliocentric distances rh ≲ 3 au, where water sublimation is expected to dominate the activity regime. The dust-to-gas mass ratio remains consistently above unity, ranging from ~1 to 3 depending on the choice of scale lengths and the CN–OH conversion factor. This result characterizes C/2024 E1 as a “dust-rich” comet, where the mass loss is dominated by the refractory component rather than volatiles.