Luminous type II Supernovae

Context. In this paper we present spectroscopic and photometric observation of five type II supernovae (SNe), namely SNe 2009dd, 2007pk, 2010aj, 1995ad, and 1996W. Together with other few SNe they form a group of luminous type II events. Aims. We investigate the similarities and the di erences among these five SNe, that represent the bulk of the luminous type II so far. We also attempt to characterise this subgroup of core-collapse SNe by analysing their spectral evolution, in order to find evidences of interaction that are common to them. Methods. We collect data ranging from the ultraviolet (UV) to the near-infrared (NIR) with several telescopes in order to construct well-sampled light curves and spectral evolutions from the photospheric to the nebular phase. Both photometric and spectroscopic evolution indicate significant di erences among the objects and between them and other luminous type II SNe. Modelling the data of SNe 2009dd, 2010aj and 1995ad allows us to constrain the explosion parameters and the properties of the progenitor star, and compare the inferred estimates with those available for the similar SNe 2007od and 2009bw. Results. The light curves have luminous peak magnitudes 18:70 < MB < 17:18 and a wide range of 56 Ni masses 7 10 3 M photospheric spectra of SNe 2009dd, 1995ad and 1996W. Instead for SN 2007pk we observe a spectral transition from a type IIn to a standard type II. Modelling the observations with a radiation hydrodynamics code, we infer for SNe 2009dd, 2010aj and 1995ad a kinetic plus thermal energy of about 0.2‐0.5 foe, an initial radius of 2‐5 10 13 cm and an ejected mass of 5.0‐9.5 M . The results suggest a super-asymptotic giant branch (SAGB) progenitor or a RSG exploded as a weak Fe CC-SN for these SNe, similarly to the other luminous type II SNe 2007od and 2009bw. The SNe analysed share only the high luminosity and the short plateau duration suggesting a sample far from homogeneity, but consistent with the bright branch of type II SNe. Such events might represent the link in the distribution of physical properties between standard type II and strong interacting type IIn SNe.