Asteroseismology and interferometry of the F7V spectroscopic binary χ Draconis A in the TESS CVZ

Abstract

Asteroseismology provides precise stellar parameters, which are particularly useful for benchmark stars with accurate independent measurements. However, most benchmark solar-like oscillators are red giants. We present a detailed analysis of the asteroseismic main-sequence benchmark star ̧hi Dra A in the Transiting Exoplanet Survey Satellite (TESS) northern continuous viewing zone. We aim to derive its stellar mass and radius from asteroseismic modelling of individual mode frequencies and test these derived values against an independent dynamical mass and interferometric radius measurements. We determined the dynamical mass of ̧hi Dra using 618 radial velocity measurements obtained with the SONG telescope at Tenerife. Our results were derived via the spectral disentanglement method, and 53 relative astrometric measurements. From the disentangled spectra, we also determined the spectroscopic parameters of ̧hi Dra A. With the PAVO beam combiner at CHARA, we obtained the interferometric radius of ̧hi Dra A. We determined asteroseismic parameters from 16 sectors of 20 sec cadence TESS photometry. We determine T_ ̊m eff =6277 =-0.51 =0.08 =1.028 ± 0.004 ̊m M_⊙ for ̧hi Dra A and M_ K, ̊m Fe/H dex, and $ α/̊m Fe dex from the spectroscopic analysis. For the dynamical fit, we obtain a mass of M_ ̊m A ̊m B =0.735 ± 0.003 ̊m M_⊙ for ̧hi Dra B. Combining the derived interferometric angular diameter with dynamical parallax yields an interferometric radius of R_ ̊m A = 1.159^ +0.029 _ -0.028 ̊m R_⊙, the first interferometric radius of ̧hi Dra A. In the TESS power spectrum, we identify 38 individual oscillating modes. Using these modes, we modelled the star with nine independent pipelines to test the resulting model mass and radius against our independently calculated mass and radius. All models yield masses slightly lower than the dynamical mass. Using asteroseismic scaling relations, we find that scaling masses from corrected scaling relations best reproduce the dynamical mass. The combination of spectroscopy, interferometry, and asteroseismology yields precise results for the main component of the ̧hi Dra system, making it one of the best-characterised main-sequence solar-like oscillators.