Rediscussion of eclipsing binaries. Paper XXVIII. The metallic-lined system DV Bootes

DV Boo is a detached eclipsing binary containing a metallic-lined A-star and a chemically normal late-F star, in an orbit with a period of 3.783 d and a possible slight eccentricity. We use a light curve from the Transiting Exoplanet Survey Satellite (TESS) and published spectroscopic results to determine the physical properties of the system to high precision. We find masses of 1.617 +/- 0.003 Msun and 1.207 +/- 0.004 Msun, and radii of 1.948 +/- 0.008 Rsun and 1.195 +/- 0.022 Rsun. The precision of the radius measurements is limited by the shallow partial eclipses and the unavailability of a spectroscopic light ratio due to the chemical peculiarity of the primary star. We measure a distance to the system of 125.0 +/- 1.5 pc, in good agreement with the Gaia DR3 parallax, and an age of 1.3 Gyr. A comparison with theoretical models suggests the system has a modestly sub-solar metallicity, in conflict with the slightly super-solar photospheric abundances of the secondary star.

💡 Research Summary

This paper presents a comprehensive re‑analysis of the detached eclipsing binary DV Bootis (DV Boo), which consists of a metallic‑lined (Am) A‑type primary and a chemically normal late‑F secondary. The authors combine a high‑cadence TESS light curve from sector 50 (120‑second sampling) with previously published spectroscopic data, notably radial velocities (RVs) from ÉLODIE and CAOS instruments, to derive the system’s fundamental parameters with unprecedented precision.

Using the JKTEBOP code (version 44), the authors performed a simultaneous fit of the TESS photometry, the RV curves of both components, and nine published times of minimum light spanning 32.4 years. The fit included the sum of the fractional radii, the ratio of the radii, the central surface‑brightness ratio, third light, orbital inclination, period, reference epoch, linear limb‑darkening coefficients (with non‑linear coefficients fixed to theoretical values), and, importantly, the eccentricity vector components e cos ω and e sin ω. While a circular orbit was initially assumed, the inclusion of a small e cos ω term significantly improved the χ², indicating a marginal but detectable eccentricity.

The resulting physical parameters are:

• Masses: M_A = 1.617 ± 0.003 M_⊙, M_B = 1.207 ± 0.004 M_⊙.
• Radii: R_A = 1.948 ± 0.008 R_⊙, R_B = 1.195 ± 0.022 R_⊙.
• Orbital inclination: i = 83.53 ± 0.17°.
• Fractional radii: (r_A + r_B) = 0.2177 ± 0.0015, k = r_B/r_A = 0.613 ± 0.011.
• Light ratio (ℓ_B/ℓ_A) = 0.255 ± 0.01, third light = 0.025 ± 0.01.
• Eccentricity: e ≈ 0.0036 ± 0.0036, with ω ≈ 89° ± 90°, indicating a very slight deviation from circularity that is statistically significant only in the Monte‑Carlo error analysis.
• Velocity semi‑amplitudes: K_A = 82.01 ± 0.12 km s⁻¹, K_B = 109.91 ± 0.08 km s⁻¹.
• Systemic velocities: γ_A = −28.15 ± 0.10 km s⁻¹, γ_B = −28.82 ± 0.06 km s⁻¹.

The authors note that the precision of the radii is limited by the shallow, partial eclipses (depths of 0.22 mag and 0.15 mag) and by the inability to obtain a reliable spectroscopic light ratio because the primary’s Am peculiarity alters line strengths. Nonetheless, the mass uncertainties are at the 0.2 % level, and the radius uncertainties are 0.4 % for the primary and 1.8 % for the secondary.

A distance of 125.0 ± 1.5 pc was derived using the effective temperatures (T_eff = 7370 ± 80 K for the primary, 6410 ± 80 K for the secondary), BV photometry, and 2MASS JHK_s magnitudes, applying surface‑brightness calibrations and a modest reddening of E(B−V) = 0.04 ± 0.02 mag. This distance is in excellent agreement with the Gaia DR3 parallax‑based distance of 125.8 ± 0.4 pc.

To assess the evolutionary status, the authors compared the measured masses, radii, effective temperatures, and luminosities with PARSEC 1.2 stellar evolution models for a range of metallicities (Z = 0.010–0.030). The radii of both stars constrain the age to ≈1.28 ± 0.05 Gyr, while the effective temperatures are best reproduced by models with Z ≈ 0.014, i.e., mildly sub‑solar metallicity. This finding conflicts with previous abundance analyses of the secondary star, which reported near‑solar abundances for 12 elements and modestly super‑solar values for five elements. The discrepancy likely arises because the primary’s Am nature makes its photospheric composition an unreliable proxy for the bulk metallicity of the system.

The paper concludes that DV Boo is a valuable benchmark system for testing stellar evolution models, especially because it contains an evolved Am primary and a near‑ZAMS F‑type secondary. However, the chemical peculiarity of the primary limits the ability to infer the system’s overall metallicity from spectroscopy alone. The authors recommend a new, high‑resolution, high‑signal‑to‑noise spectroscopic campaign focused on the secondary component to obtain a definitive metallicity measurement, and suggest that additional precise photometric or RV observations would help to confirm the marginal eccentricity.

In summary, this work delivers the most precise masses and radii to date for DV Boo, validates the Gaia distance, refines the orbital parameters, and highlights a tension between model‑predicted sub‑solar metallicity and spectroscopic indications of near‑solar or slightly super‑solar abundances. Resolving this tension will improve our understanding of Am star formation, binary evolution, and the reliability of eclipsing binaries as calibrators for stellar physics.