NLTE Spectral Modelling of the Nearby Stripped-Envelope Supernova 2024ehs

We present a detailed study of the Type IIb supernova 2024ehs, discovered in March 2024 in the nearby galaxy NGC 3443 at a distance of 23.8 plus or minus 0.9 Mpc. Using photometric and spectroscopic observations spanning 10 months, we analyse its light curve, spectral evolution, and physical properties with the SUMO radiative transfer code. SN 2024ehs exhibits a narrow light-curve peak, rapid decline, and weak helium lines, distinguishing it from typical Type IIb supernovae. Comparisons with other objects, including SNe 1993J and 2020acat, and modelling of nebular spectra suggest a low ejecta mass, high velocities (about 20,000), and a 56 Ni mass just below about0.1, M. Furthermore, the nebular spectral models indicate a progenitor with a helium core mass of about 6, M, consistent with a zero-age main-sequence mass of about 23, M. The composition of spectra is explored through photospheric modelling, finding a link between expansion velocity and the relative strength of different element lines. This work discusses further the diversity of stripped-envelope supernovae and the role of binary interactions for their progenitors, and demonstrates the need for further modelling to refine 56 Ni mass estimates and to understand the physical mechanisms driving their evolution.