Abstract We present photometric and spectroscopic studies of two core-collapse supernovae (SNe) 2008aq and 2019gaf in the optical wavelengths. Light curve and spectral sequence of both the SNe are similar to those of other Type IIb SNe. The pre-maximum spectrum of SN 2008aq showed prominent H α lines, the He lines started appearing in the near maximum spectrum. The near maximum spectrum of SN 2019gaf shows shallow H α absorption and He lines with almost similar strength. Both the SNe show transition from hydrogen-dominated spectra to helium-dominated spectra within a month after maximum brightness. The velocity evolution of SN 2008aq matches well with those of other well-studied Type IIb SNe, while SN 2019gaf shows higher velocities. Close to maximum light, the H α and He I line velocities of SN 2019gaf are ∼ 2000 km sec−1 and ∼ 4000 km sec−1 higher than other well-studied Type IIb SNe. Semi-analytical modeling indicates SN 2019gaf to be a more energetic explosion with a smaller ejecta mass than SN 2008aq. The zero-age main-sequence (ZAMS) mass of the progenitor estimated using the nebular spectra of SN 2008aq ranges between 13 to 20 M⊙, while for SN 2019gaf, the inferred ZAMS mass is between 13 to 25 M⊙. The O i to Ca ii lines flux ratio favors a less massive progenitor star in a binary system for both the SNe.
Singh et al. (2026) studied this question.