50 Dra: Am-type twins with additional variability in a non-eclipsing system

¹ Astronomical Institute of the Czech Academy of Sciences, Fričova 298, CZ-25165 Ondřejov, Czech Republic
² Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
³ Instytut Astronomiczny, Uniwersytet Wrocławski, Kopernika 11, PL-51-622 Wrocław, Poland
⁴ Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic

^⋆ Corresponding author: skarka@asu.cas.cz

Received: 23 September 2024
Accepted: 8 April 2025

Abstract

Context. The interplay between radiative diffusion, rotation, convection, and magnetism in metallic-line chemically peculiar stars is not yet fully understood. Recently, evidence has emerged that these effects can work together.

Aims. Our goal was to study the bright binary system 50 Dra, describe its orbit and components, and study additional variability.

Methods. We conducted our analysis using TESS short-cadence data and new high-resolution spectroscopic observations. We disentangled the spectra using KOREL and performed spectral synthesis with ATLAS9 and SYNTHE codes. The system was modelled using KOREL and PHOEBE2.4. We also employed SED fitting in ARIADNE and isochrone fitting using PARAM1.5 codes.

Results.Our findings indicate that the non-eclipsing system 50 Dra (with an inclination of 49.9(8) deg), which displays ellipsoidal brightness variations, consists of two nearly equal A-type stars with masses of M₁ = 2.08(8) and M₂ = 1.97(8) M_⊙, and temperatures of 9800(100) and 9200(200) K, respectively. Our analysis also indicates that the system, with an orbital period of P_orb = 4.117719(2) days, is tidally relaxed with a circular orbit and synchronous rotation of the components. Furthermore, we discovered that both stars are metallic-line Am chemically peculiar stars with an underabundance of Sc and an overabundance of iron-peak and rare-earth elements. We identified additional variations with slightly higher frequency than the rotational frequency of the components that we interpret as prograde g-mode pulsations.

Conclusions. The system 50 Dra exhibits multiple co-existing phenomena and may have an impact on our understanding of chemical peculiarities and pulsations.