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Abstract We present long-term photometric and spectroscopic studies of circumstellar material (CSM)–ejecta interacting supernova (SN) ASASSN-14il in the galaxy PGC 3093694. The SN reaches a peakr-band magnitude of ∼−20.3 ± 0.2 mag, rivaling SN 2006tf and SN 2010jl. The multiband and the pseudo-bolometric lightcurves show a plateau lasting ∼50 days. Semi-analytical CSM interaction models can match the high luminosity and decline rates of the lightcurves but fail to faithfully represent the plateau region and the bumps in the lightcurves. The spectral evolution resembles a typical Type IIn SN dominated by CSM interaction, showing blue continuum and narrow Balmer lines. The lines are dominated by electron scattering at early epochs. The signatures of the underlying ejecta are visible as the broad component in the Hαprofile from as early as day 50, hinting at asymmetry in the CSM. A narrow component is persistent throughout the evolution. The SN shows remarkable photometric and spectroscopic similarity with SN 2015da. However, the different polarization in ASASSN-14il compared to SN 2015da suggests an alternative viewing angle. The late-time blueshift in the Hαprofile supports dust formation in the post-shock CSM or ejecta. The mass-loss rate of 2–7M_⊙yr⁻¹suggests a luminous blue variable progenitor in an eruptive phase for ASASSN-14il. 

We present an optical photometric and spectroscopic analysis of the fast-declining hydrogen-rich Type II supernova (SN) 2019nyk. The light curve properties of SN 2019nyk align well with those of other fast-declining Type II SNe, such as SNe 2013by and 2014G. SN 2019nyk exhibits a peak absolute magnitude of −18.09 ± 0.17 mag in theVband, followed by a rapid decline at 2.84  ±  0.03 mag (100 d)⁻¹during the recombination phase. The early spectra of SN 2019nyk exhibit high-ionisation emission features as well as narrow H Balmer lines, persisting until 4.1 d since explosion, indicating the presence of circumstellar material (CSM) in close proximity. A comparison of these features with other Type II SNe displaying an early interaction reveals similarities between these features and those observed in SNe 2014G and 2023ixf. We also compared the early spectra to literature models, estimating a mass-loss rate of the order of 10⁻³M_⊙yr⁻¹. Radiation hydrodynamical modelling of the light curve also suggests the mass loss from the progenitor within a short period prior to explosion, totalling 0.16M_⊙of material within 2900R_⊙of the progenitor. Furthermore, light curve modelling infers a zero-age main sequence mass of 15M_⊙for the progenitor, a progenitor radius of 1031R_⊙, and an explosion energy of 1.1 × 10⁵¹erg.