Supernova progenitor stars in the initial range of 23 to 33 solar masses and their relation with the SNR Cassiopeia A

¹ Departamento de Investigación en Física, Universidad de Sonora, Apdo. Postal 5-088, Hermosillo, Sonora, México e-mail: brenda@cajeme.cifus.uson.mx
² Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada 22800, Baja Californa, México
³ Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands

Received: 5 April 2008
Accepted: 20 March 2009

Abstract

Context. Multi wavelength observations of Cassiopeia A (Cas A) have provided us with strong evidence of circumstellar material surrounding the progenitor star. It has been suggested that its progenitor was a massive star with strong mass loss. But, despite the large amount of observational data from optical, IR, radio, and x-ray observations, the identity of Cas A progenitor is still elusive.

Aims. In this work, we computed stellar and circumstellar numerical models to look for the progenitor of Cas A. The models are compared with the observational constraints that come from chemical observed abundances and dynamical information.

Methods. We first computed stellar evolution models to get time-dependent wind parameters and surface abundances using the code STERN. To explore the range of masses proposed by several previous works, we chose a set of probable progenitor stars with initial masses of 23, 28, 29, 30, and 33 , with initial solar composition (, ) and mass loss. The derived mass loss rates and wind terminal velocities are used as inner boundary conditions in the explicit, hydrodynamical code ZEUS-3D to simulate the evolution of the circumstellar medium. We simplified the calculations by using one-dimensional grids in the main sequence and red super-giant (RSG) stages, and two-dimensional grids for the post-RSG evolution and supernova (SN) blast wave.

Results. Our stellar set gives distinct SN progenitors: RSG, luminous blue super giants (LBSGs), and Wolf-Rayet (WR) stars. We named these type of stars “luminous blue super giant” (LBSGs) to distinguish them from normal blue super giants (BSGs) of much lower initial masses. The 23  star explodes as an RSG in a dense, free-streaming wind surrounded by a thin, compressed, RSG shell. The 28  star explodes as an LBSG, and the SN blast wave interacts with a low density, free streaming wind surrounded by an unstable and massive “RSG+LBSG” shell. Finally, the 30 and 33  stars explode as WR stars surrounded by fast WR winds that terminate in a highly fragmented “WR+RSG shell”. We compared the surface chemical abundances of our stellar models with the observational abundances in Cas A. The abundance analysis shows that the progenitor was a star with an initial mass of about 30 , while the hydrodynamical analysis favors progenitors with initial masses around 23.