Nucleosynthesis by accelerated particles to account for the surface composition of HD 101065

Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium e-mail: sgoriely@astro.ulb.ac.be

Received: 17 October 2006
Accepted: 2 January 2007

Abstract

Context. Recent observations have suggested the presence of radioactive elements, such as Tc, Pm, and 84 99 elements at the surface of the chemically-peculiar magnetic star HD 101065, also known as Przybylski's star. The peculiar abundance pattern of HD 101065 has been explained so far by diffusion processes in the stellar envelope. However, those processes cannot be called on to explain the origin of short-lived radioelements.

Aims. The large magnetic field observed in Ap stars can be at the origin of a significant acceleration of charged particles, mainly protons and α-particles, that in turn can modify the surface content by interaction with the stellar material. This paper explores to what extent an irradiation process resulting from the interaction of the stellar material with energetic particles can by itself account for both the abundances determined by observation on the surface of the chemically peculiar star HD 101065 and the presence of unstable elements.

Methods.Due to the unknown characteristics of the accelerated particles that could be held responsible for this nuclear process, a purely parametric approach is followed, with the proton and α-particle flux amplitude and energy distribution taken as free parameters, as well as the total fluence

Results. This kind of irradiation process, at least for high fluences, can lead to a rich nucleosynthesis, including a significant production of heavy elements, as well as radioelements like Tc and Pm, and even transuranium. In this respect, the energy spectrum of the accelerated particles plays a crucial role. Many observational aspects of HD 101065's composition can be explained quantitatively.

Conclusions.The possible existence of high-fluence irradiation events need to be confirmed by hydrodynamics simulations but, most of all, by spectroscopic observations through detecting short-lived unstable elements on the surface of chemically peculiar stars.