Progress report on solar age calibration

TL;DR

This paper presents a seismic calibration method for estimating the Sun's age and chemical composition, using low-degree modes and separating contributions from background and glitch effects, resulting in a main-sequence age estimate of 4.68 billion years.

Contribution

It introduces a robust seismic calibration technique that isolates contributions from different stellar structures, improving age and composition estimates over previous methods.

Findings

Estimated solar main-sequence age: 4.68 Gyr

Derived initial heavy-element abundance: Z=0.0169

Method shows consistency with BiSON data

Abstract

We report on an ongoing investigation into a seismic calibration of solar models designed for estimating the main-sequence age and a measure of the chemical abundances of the Sun. Only modes of low degree are employed, so that with appropriate modification the procedure could be applied to other stars. We have found that, as has been anticipated, a separation of the contributions to the seismic frequencies arising from the relatively smooth, glitch-free, background structure of the star and from glitches produced by helium ionization and the abrupt gradient change at the base of the convection zone renders the procedure more robust than earlier calibrations that fitted only raw frequencies to glitch-free asymptotics. As in the past, we use asymptotic analysis to design seismic signatures that are, to the best of our ability, contaminated as little as possible by those uncertain properties of the star that are not directly associated with age and chemical composition. The calibration itself, however, employs only numerically computed eigenfrequencies. It is based on a linear perturbation from a reference model. Two reference models have been used, one somewhat younger, the other somewhat older than the Sun. The two calibrations, which use BiSON data, are more-or-less consistent, and yield a main-sequence age $t_\odot=4.68\pm0.02 $Gy, coupled with a formal initial heavy-element abundance $Z=0.0169\pm0.0005$. The error analysis has not yet been completed, so the estimated precision must be taken with a pinch of salt.