[Paper Review] Rediscussion of eclipsing binaries. Paper III. The interferometric, spectroscopic and eclipsing binary V1022 Cassiopeiae

J. Southworth|arXiv (Cornell University)|Dec 10, 2020

Stellar, planetary, and galactic studies4 references4 citations

TL;DR

This paper presents the first high-precision measurement of the masses and radii of the eclipsing binary V1022 Cassiopeiae using TESS photometry and high-resolution spectroscopic radial velocities, yielding masses of 1.626±0.001 M☉ and 1.609±0.001 M☉, radii of 2.591±0.026 R☉ and 2.472±0.027 R☉, and a consistent distance of ~63.4–64.0 pc from four independent methods, all matching solar-metallicity evolutionary models at ~2 Gyr age.

ABSTRACT

V1022 Cas has been known as a spectroscopic binary for a century. It was found to be eclipsing based on photometry from the Hipparcos satellite, and an astrometric orbit was recently obtained from near-infrared interferometry. We present the first high-precision measurement of the radii of the stars based on light curves obtained by the TESS satellite. Combined with published radial velocities from high-resolution spectra, we measure the masses of the stars to be 1.626 +/- 0.001 Msun and 1.609 +/- 0.001 Msun, and the radii to be 2.591 +/- 0.026 Rsun and 2.472 +/- 0.027 Rsun. The 12.16-d orbit is eccentric and the stars rotate sub-synchronously, so the system is tidally unevolved. A good match to these masses and radii, and published temperatures of the stars, is found for several sets of theoretical stellar evolutionary models, for a solar metallicity and an age of approximately 2 Gyr. Four separate distance determinations to the system are available, and are in good agreement. The distances are based on surface brightness calibrations, theoretical bolometric corrections, the Gaia parallax, and the angular size of the astrometric orbit. A detailed spectroscopic analysis of the system to measure chemical abundances and more precise temperatures would be helpful.

Motivation & Objective

• To measure the masses and radii of the spectroscopic-astrometric-eclipsing binary V1022 Cassiopeiae with high precision for inclusion in the DEBCat database.
• To test the consistency of multiple independent distance measurements derived from surface brightness, bolometric corrections, Gaia parallax, and interferometric orbit size.
• To compare the observed stellar parameters with theoretical evolutionary models to infer age, metallicity, and evolutionary state.
• To identify the need for improved spectroscopic analysis of photospheric abundances and effective temperatures for future refinement.

Proposed method

• High-precision light curves from TESS Sector 17 and 24 were used to model the partial eclipses and derive fractional radii.
• Radial velocities from high-resolution spectroscopy (Fekel et al. 2005) were combined with orbital solutions to determine individual stellar masses.
• Astrometric orbit from K-band interferometry (CHARA array) provided a geometric distance and confirmed the orbital inclination.
• The surface brightness–temperature relation and bolometric corrections were applied to derive distance estimates from photometry and effective temperatures.
• Theoretical stellar evolution models (PARSEC, Dartmouth, Yonsei-Yale) were compared to observed masses, radii, and temperatures to infer age and metallicity.
• Four independent distance estimates were cross-validated: surface brightness, bolometric corrections, Gaia DR2 parallax, and interferometric angular semimajor axis.

Experimental results

Research questions

• RQ1 What are the precise masses and radii of the two F6 V stars in V1022 Cassiopeiae, derived from TESS photometry and spectroscopic radial velocities?
• RQ2 How consistent are the four independent distance estimates—surface brightness, bolometric corrections, Gaia parallax, and interferometric orbit size—for this system?
• RQ3 What is the best-fitting age and metallicity for V1022 Cassiopeiae when compared to theoretical stellar evolution models?
• RQ4 To what extent do the observed masses, radii, and temperatures match predictions from solar-metallicity models at ~2 Gyr?
• RQ5 What improvements in precision could be achieved with higher-accuracy spectroscopic measurements of effective temperature and chemical abundances?

Key findings

• The masses of the two stars in V1022 Cassiopeiae were measured with 0.1% precision: 1.626±0.001 M☉ and 1.609±0.001 M☉.
• The radii were determined to 1% precision: 2.591±0.026 R☉ and 2.472±0.027 R☉, limited by partial eclipse depth and light ratio accuracy.
• Four independent distance estimates—63.2±1.1 pc (surface brightness), 62.7±1.0 pc (bolometric corrections), 64.02±0.27 pc (interferometry), and 63.42±0.35 pc (Gaia DR2)—agree within 1.4σ.
• The system is consistent with a solar metallicity and an age of approximately 2 Gyr, as confirmed by PARSEC, Dartmouth, and Yonsei-Yale evolutionary models.
• The stars are tidally unevolved and rotate sub-synchronously in an eccentric 12.16-day orbit, indicating they are not in synchronised tidal equilibrium.
• A more precise spectroscopic analysis of effective temperatures and chemical abundances is needed to further discriminate between model sets and reduce uncertainties.