2014 Annual Science Report
Arizona State University Reporting | SEP 2013 – DEC 2014
Astrophysical Controls - Task 2 - Model the Chemical & Dynamical Evolution of Massive Stars
Stars create the chemical elements heavier than hydrogen and helium, with the majority arising from the lives and violent deaths of massive stars in supernova explosions. The starting chemical composition of stars also affects their evolution and that of their associated planets. We have performed computational simulations for a large range of stellar masses to provide predictions for important stellar characteristics (i.e., brightness, temperature, stellar winds, composition) over the stars’ lifetimes and made the data available to the public. We have also simulated the explosions of massive stars to predict the chemical abundances of material ejected from the dying stars and how that material is distributed in the surrounding universe. As a complement, we are modeling how the habitable zones and planets of stars with different abundances evolve.
The composition of stars strongly influences their evolution and properties of their planets. Patrick Young and Amanda Truitt (ASU) have created a grid of stellar models for 0.5 – 1.2 solar masses, 0.1 to 1.5 times solar metallicity, and O/Fe ratios of 0.5 to 2 times solar with the TYCHO stellar evolution code. These models include predicted habitable zone locations as a function of time for each stellar model for a range of assumptions. With Jeremy Dietrich (Harvard) they have created a web-based interface for accessing and visualizing simulations data and producing interpolated stellar and habitable zone evolutionary tracks for any arbitrary combination of mass, metallicity, and O/Fe ratio in the parameter space. The majority of stars in the solar neighborhood of interest to astrobiologists should fall in this range. A pilot project for characterizing individual stars and planetary systems with detailed compositional information was carried out for tau Ceti (see also task 7) by Young, Truitt, and Michael Pagano (ASU). The TYCHO stellar evolution code is updated to start production of massive star models using the compositional variations determined from task 7 and used here for low mass stars.