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, C$_2$, and C$_3$, while no significant NH$_2$ signal is identified. In our dataset, CN became detectable at 3.48 au, and C$_3$ and C$_2$ at 2.80 au. The mean ratios $\log\mathrm{C}_2/\mathrm{CN} = 0.00 \pm 0.07$ and $\log\mathrm{C}_3/\mathrm{CN} = -1.03 \pm 0.09$ 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 $\sim -3.5$, and particle sizes ranging from 1~$\mu$m to 4~mm. The inferred initial ejection velocities span from $\sim$20$ m $s$^{-1}$ to $\sim$100$ 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 $r_{\rm{h}} \lesssim 3$ au, where water sublimation is expected to dominate the activity regime. The dust-to-gas mass ratio remains consistently above unity, ranging from $\sim$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.