Atomic Data Needs in Astrophysics: The Galactic Center “Scandium Mystery”

Brian Thorsbro

doi:10.3390/atoms8010004

Abstract

Investigating the Galactic center offers unique insights into the buildup and history of our Galaxy and is a stepping stone to understand galaxies in a larger context. It is reasonable to expect that the stars found in the Galactic center might have a different composition compared to stars found in the local neighborhood around the Sun. It is therefore quite exciting when recently there were reports of unusual neutral scandium, yttrium, and vanadium abundances found in the Galactic center stars, compared to local neighborhood stars. To explain the scandium abundances in the Galactic center, we turn to recent laboratory measurements and theoretical calculations done on the atomic oscillator strengths of neutral scandium lines in the near infrared. We combine these with measurements of the hyper fine splitting of neutral scandium. We show how these results can be used to explain the reported unusual scandium abundances and conclude that in this respect, the environment of the Galactic center is not that different from the environment in the local neighborhood around the sun.

Highlights

Understanding the formation and evolution of galaxies is one of the important questions in astrophysics today [1]
We focus on the Galactic center, which is interesting as it is an environment that is unique to the Galaxy, because of the presence of the super massive black hole
A unique scandium abundance in the Galactic center would suggest that the center is a site for a new channel of nucleosynthesis of neutral scandium and possibly other elements

Summary

Introduction

Understanding the formation and evolution of galaxies is one of the important questions in astrophysics today [1]. We focus on the Galactic center, which is interesting as it is an environment that is unique to the Galaxy, because of the presence of the super massive black hole This could lead to a different evolution of stars compared to the environment in the vicinity of our Sun. In order to be able to observe stars in the Galactic center, one has to turn to very bright giant stars and observe them in the infrared wavelength regions. A unique scandium abundance in the Galactic center would suggest that the center is a site for a new channel of nucleosynthesis of neutral scandium and possibly other elements Such a trend is important to understand, especially when observing the centers of far away galaxies, which would be a natural choice to observe first, as the center is the most luminous part of a galaxy. We summarize our findings first reported in Thorsbro et al [6] and discuss the atomic data needs in astrophysics on the basis of this

Observations

Analyzing the Hyperfine Structure

Other Important Physical Effects

Conclusions