Analysis of 70 Ophiuchi AB including seismic constraints

TL;DR

This study models the binary star system 70 Ophiuchi AB using seismic data to determine stellar parameters, test modeling tools, and assess the impact of physical assumptions, providing insights into stellar physics and evolution.

Contribution

It presents a comprehensive seismic analysis of 70 Ophiuchi AB, including multiple modeling approaches and physical assumptions, to accurately determine stellar properties and test stellar evolution codes.

Findings

Determined stellar age of 6.2 ± 1.0 Gyr for 70 Ophiuchi AB.

Found the mixing-length parameter for 70 Oph A is likely lower or equal to the solar value.

Confirmed consistency across different stellar evolution codes and calibration methods.

Abstract

The analysis of solar-like oscillations for stars belonging to a binary system provides a unique opportunity to probe the internal stellar structure and to test our knowledge of stellar physics. Such oscillations have been recently observed and characterized for the A component of the 70 Ophiuchi system. A model of 70 Ophiuchi AB that correctly reproduces all observational constraints available for both stars is determined. An age of 6.2 +- 1.0 Gyr is found with an initial helium mass fraction Y_i=0.266 +- 0.015 and an initial metallicity (Z/X)_i=0.0300 +- 0.0025 when atomic diffusion is included and a solar value of the mixing-length parameter assumed. A precise and independent determination of the value of the mixing-length parameter needed to model 70 Oph A requires accurate measurement of the mean small separation, which is not available yet. Current asteroseismic observations, however, suggest that the value of the mixing-length parameter of 70 Oph A is lower or equal to the solar calibrated value. The effects of atomic diffusion and of the choice of the adopted solar mixture were also studied. We also tested and compared the theoretical tools used for the modeling of stars for which p-modes frequencies are detected by performing this analysis with three different stellar evolution codes and two different calibration methods. We found that the different evolution codes and calibration methods we used led to perfectly coherent results.