Talk

The past and future of the Sun: What solar twins can tell us about the solar magnetic and rotational evolution?

Diego Lorenzo-Oliveira, Universidade de Sao Paulo

Rotation-based ages of old Sun-like stars are rooted in a complex and intricate dependence on age, rotation, turbulent convection, structural variations and mass-loss due to magnetized winds. Classically, the age-dating method that relies on this phenomenon assumes that the rotational periods can be expressed in well-defined functions of the age and mass, the so-called gyrochronology relations. These relations had successfully confirmed the paradigm of rotation-activity-age coupling that powers the global dynamo evolution along the main-sequence and reproduced the main features observed in open clusters spanning a wide range of ages. However, in the light of Kepler data, the presence of apparently old and fast rotators that do not obey the usual gyrochronology relations led to the hypothesis of weakened magnetic breaking in some stars. We approached this problem by using a selected sample of solar twins and building a grid of rotational tracks as function of age, mass and metallicity over a large range of possible critical Rossby number to account for the magnetic weakened braking phenomena observed in the Kepler sample. Strong statistical evidence favoring the smooth rotation evolution (critical Rossby number solution ~2.6, or ages greater than ~8 Gyr) was found. The lower limit of critical Rossby number estimated is greater than 2.3 or older than 5.3 Gyr (at 95% confidence level) for a solar mass/metallicity star. These limits intercept an age range somewhat older than the Sun and the end of the main-sequence. This study highlights the difficulty to statistically discern both scenarios with the current sample of solar twins.