2009 Annual Science Report
Arizona State University Reporting | JUL 2008 – AUG 2009
Astrophysical Controls on the Elements of Life, Task 6: Determine Which Elemental or Isotopic Ratios Correlate With Key Elements
In our “follow the elements” strategy we work to refine searches for planetary systems likely to host life by identifying systems with favorable elemental compositions. Because some relevant elements or isotopes (for example 26Al) are difficult or impossible to observe due to low abundances or short lifetimes, we wish to find easily observable indicators of their presence. In most cases this involves identifying elements or isotopes that are either produced primarily by the same process as the isotope of interest or produced in unique ratios to other isotopes by that process. This requires simulating the synthesis of isotopes in stars and supernovae and their ejection into space and incorporation into forming planetary systems.
Collaborating investigator Patrick Young and graduate student Carola Ellinger with support from outside collaborators at the University of Arizona and Los Alamos National Laboratory have published 3D simulations of a core collapse supernova of a massive star. These simulations combined with 1D models for a range of stars were used to identify the production sites of 26Al and its potential tracers. We find that the sulfur to silicon ratio in supernova ejecta correlates strongly with production of 26Al. Phosphorus is produced under the same conditions, so we have an indication that solar systems enriched by 26Al from supernovae will also be enriched in P. The total amount of S and Si injected into a protoplanetary system is likely to be small compared to the mass of the disk, so it will be difficult to identify candidate systems on the basis of the S/Si ratio alone, especially if there is substantial variation in abundances between stars already. We should, however, be able to identify ejecta in young supernova remnants that are rich in 26Al, and use those clumps of material as constraints on models of injection into protoplanetary disks.
Working with co-I Steven Desch we also find that comparison of oxygen isotopes in solar wind and model supernovae are compatible with injection of 26Al into the early solar system. Calculations of a 3D explosion of a 15 solar mass star are in progress. Our code has been updated with an improved nuclear reaction network and cooling to model formation of the dense clumps that may participate in element injection. Medium resolution (107 particles) simulations compare models with and without cooling. We plan to have a flagship 108 particle simulation completed by the end of the calendar year.
Young and student Mike Pagano with collaborators at the University of Rochester will measure and analyze the amount of enrichment by supernovae of triggered star formation regions in the Scorpius-Centaurus stellar association. The amount of enrichment will provide limits on the efficiency of incorporation of supernova material into forming planetary systems, and its spatial heterogeneity will constrain how uniformly supernovae enrich their local environment.
PROJECT INVESTIGATORS:Patrick Young
PROJECT MEMBERS:Francis Timmes
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Sources of prebiotic materials and catalysts