28/11/2012 – 14h00 – Auditório IAG – IAG/USP
Observational effects of magnetism in massive stars: surface nitrogen abundances
Massive stars are hot and luminous objects able to strongly influence their environment. Their intense UV radiation ionize the surrounding hydrogen, creating HII regions; they synthesize heavy elements in their core, yield them to the surroundings and thus participate to the chemical enrichment of the interstellar medium. In addition, they are the progenitors of core-collapse supernovae and long-duration Gamma Ray Bursts, respectively the most luminous and energetic events met in the universe.
The evolution of massive stars is governed mainly by their rotation and their mass loss rate. This means that any physical process affecting these properties is likely a strong contributor to the final fate of a massive star. Since the pioneering work of Babel & Montmerle (1997), it is known that large-scale magnetic fields may strongly affect their winds. Their internal structure as well is expected to experience strong modifications, forcing the star to follow new evolutionary paths. Considering the large influence massive stars have in various domains of astrophysics, it is crucial to understand their magnetic properties and the way they affect their evolution.
In this presentation, I will describe a quantitative spectroscopic analysis -realized with the radiative transfer code CMFGEN- of the six magnetic O stars known to date. The main goal is to determine their nitrogen content, best indicator of their evolutionary status, and try to identify specific abundance patterns that could be attributed only to the presence of a magnetic field. Their surface enrichments will be compared to the ones measured for O stars without magnetic fields and to evolutionary models, providing an observational basis on which theoretical simulations could rely on to better understand how the evolution of massive stars is affected by magnetism.
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