Moderately luminous Type II supernovae ^⋆,⋆⋆

¹ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN, UK
e-mail: c.inserra@qub.ac.uk
² Dipartimento di Fisica ed Astronomia, Università di Catania, Sezione Astrofisica, via S. Sofia 78, 95123 Catania, Italy
³ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁴ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁵ Bonino-Pulejo Foundation, via Uberto Bonino 15/C, 98124 Messina, Italy
⁶ Università di Padova, Dipartimento di Fisica ed Astronomia G. Galilei, Vicolo dellOsservatorio, 3, 35122 Padova, Italy
⁷ INAF – Osservatorio astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁸ Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, Chile
⁹ Institut de Ciències de l’Espai (IEEC-CSIC), Facultat de Ciències, Campus UAB, 08193 Bellaterra, Spain
¹⁰ Fundación Galileo Galilei-INAF, Telescopio Nazionale Galileo, Rambla José Ana Fernández Pérez 7, 38712 Breña Baja, Spain
¹¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany

Received: 4 October 2012
Accepted: 17 May 2013

Abstract

Context. Core-collapse Supernovae (CC-SNe) descend from progenitors more massive than about 8 M_⊙. Because of the young age of the progenitors, the ejecta may eventually interact with the circumstellar medium (CSM) via highly energetic processes detectable in the radio, X-ray, ultraviolet (UV) and, sometimes, in the optical domains.

Aims. In this paper we present ultraviolet, optical and near infrared observations of five Type II SNe, namely SNe 2009dd, 2007pk, 2010aj, 1995ad, and 1996W. Together with few other SNe they form a group of moderately luminous Type II events. We investigate the photometric similarities and differences among these bright objects. We also attempt to characterise them by analysing the spectral evolutions, in order to find some traces of CSM-ejecta interaction.

Methods. We collected photometry and spectroscopy with several telescopes in order to construct well-sampled light curves and spectral evolutions from the photospheric to the nebular phases. Both photometry and spectroscopy indicate a degree of heterogeneity in this sample. Modelling the data of SNe 2009dd, 2010aj and 1995ad allows us to constrain the explosion parameters and the properties of the progenitor stars.

Results. The light curves have luminous peak magnitudes (−16.95 < M_B < −18.70). The ejected masses of ⁵⁶Ni for three SNe span a wide range of values (2.8 × 10^-2  M_⊙ < M(⁵⁶Ni)< 1.4 × 10^-1  M_⊙), while for a fourth (SN 2010aj) we could determine a stringent upper limit (7 × 10^-3  M_⊙). Clues of interaction, such as the presence of high velocity (HV) features of the Balmer lines, are visible in the photospheric spectra of SNe 2009dd and 1996W. For SN 2007pk we observe a spectral transition from a Type IIn to a standard Type II SN. Modelling the observations of SNe 2009dd, 2010aj and 1995ad with radiation hydrodynamics codes, we infer kinetic plus thermal energies of about 0.2–0.5 foe, initial radii of 2–5 × 10¹³ cm and ejected masses of ~5.0–9.5 M_⊙.

Conclusions. These values suggest moderate-mass, super-asymptotic giant branch (SAGB) or red super-giants (RSG) stars as SN precursors, in analogy with other luminous Type IIP SNe 2007od and 2009bw.