The angular momentum loss through Be star disks and its impact on the evolution of fast-rotating stars

• Grant number: 17/24629-6
• Support Opportunities: Scholarships abroad - Research
• Effective date (Start): September 06, 2018
• Effective date (End): September 23, 2018
• Field of knowledge: Physical Sciences and Mathematics - Astronomy - Stellar Astrophysics
• Valor Concedido/Desembolsado (R$): 22,039.80 / 22,039.80
• Principal Investigator: Alex Cavaliéri Carciofi
• Grantee: Alex Cavaliéri Carciofi
• Host Investigator: Georges Meynet
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Research place: Université de Genève, Switzerland

Abstract

My group in the Astronomy Department of IAG/USP specializes in Be stars. These stars, still in the main sequence, rotates very fast and, as a result, shed matter and angular momentum in their equatorial regions. This matter spreads out by means of viscous diffusion, thus forming a disk. Recently, we finished the first large-scale study of the dynamical evolution of a large sample of Be star disks. We studied 81 disk events (here understood as events of disk formation followed by a full disk dissipation) of 54 Be stars in the Small Magellanic Cloud (SMC), using a new method developed during the PhD thesis of Dr. Leandro R. Rímulo. This study allowed us to measure, for the first time, the rate of angular momentum (AM) loss through the disk. Since the source of AM is the central star, what was actually measured is how much AM the stars are losing.These results were compared with predictions from the Geneva stellar evolution models. It was found that the Be stars in the SMC are losing AM at a rate up to two orders of magnitude smaller than the rates predicted by the models. The goal of the visit to the Geneva Observatory is to work directly with the group of Prof. Georges Meynet, a co-author of the Geneva Stellar Evolution Code. Prof. Meynet's group was a pioneer in the study of the effects of rotation in stellar evolution. During the visit we plan to tackle two related problems: 1) What is the cause of the discrepancy between our measurements and the models and how the models must be modified in order to reproduce the observations; 2) To understand the impacts these modifications will have in the theoretical predictions of stellar evolution of fast-rotating stars, such as main sequence lifetimes, surface abundance enhancements, etc.