Balachandran, Suchitra

Contact Email: suchitra@astro.umd.edu
Institute: Department of Astronomy, University of Maryland
Subject Area: Other (Please Specify Below)
Waveband: Optical
Technique: Spectroscopy
Other: Sun & Stellar Atmospheres (would fit into Sami Solanki's topic)
Presentation: Poster Display
Title: Rotational Braking, Angular Momentum Transport and the Light Element Abundances
Abstract: The observed depletion of lithium in the Sun, which requires non-standard mixing below the surface convective zone, has puzzled astronomers for many decades. In recent years, turbulence-based models have linked this mixing process to another fundamental, ubiquitous and yet poorly understood process: the transport and dissipation of angular momentum. In these models, the transport of angular momentum via turbulence leaves the star in a state of differential rotation and results in slow, deep mixing which leads to the destruction of the light elements, the extent of the depletion depending upon the magnitude of the rotational spin-down. Three pieces of observational evidence strongly contradict the predictions of the models making it increasingly clear that these models are not viable. First, helioseismology has revealed that the present-day Sun does not have a rapidly rotating core; angular momentum transport was therefore more rapid than predicted by the turbulence models. Second, a re-analysis of the Be II lines in Sun have shown that the solar beryllium abundance equals the meteoritic value, indicating that mixing below the solar convective zone has only been superficial. Third, short-period, tidally-locked binary stars have lithium abundances similar to the single stars at the same age and temperature in contradiction to previous assertions. This combination of observational evidence will be discussed in the context of lithium depletion data and alternate models for the transport of angular momentum.