HD 51844: An Am delta Scuti in a binary showing periastron brightening

TL;DR

This study analyzes the binary star HD 51844, revealing its pulsation characteristics, orbital parameters, and chemical composition, with novel findings on resonances and tidal excitations in a delta Scuti star using high-precision CoRoT data.

Contribution

First detailed analysis of HD 51844 combining spectroscopy, photometry, and asteroseismology, discovering new resonance phenomena and tidal excitations in a delta Scuti binary system.

Findings

HD 51844 is a double-lined spectroscopic binary with a 33.5-day orbit.

Detected 115 pulsation frequencies, including resonances and tidally excited modes.

Identified unexpected frequency resonances (3:2, 3:5, 3:4) in a delta Scuti star.

Abstract

Pulsating stars in binary systems are ideal laboratories to test stellar evolution and pulsation theory, since a direct, model-independent determination of component masses is possible. The high-precision CoRoT photometry allows a detailed view of the frequency content of pulsating stars, enabling detection of patterns in their distribution. The object HD 51844 is such a case showing periastron brightening instead of eclipses. We present a comprehensive study of the HD 51844 system, where we derive physical parameters of both components, the pulsation content and frequency patterns. Additionally, we obtain the orbital elements, including masses, and the chemical composition of the stars. Time series analysis using standard tools was mployed to extract the pulsation frequencies. Photospheric abundances of 21 chemical elements were derived by means of spectrum synthesis. We derived orbital elements both by fitting the observed radial velocities and the light curves, and we did asteroseismic modelling as well. We found that HD 51844 is a double lined spectroscopic binary. The determined abundances are consistent with delta Delphini classification. We determined the orbital period (33.498 +- 0.002 d), the eccentricity (0.484 +- 0.020), the mass ratio (0.988 +- 0.02), and the masses to 2.0 +- 0.2 M_sun for both components. Only one component showed pulsation. Two p modes (f_22 and f_36) and one g mode (f_orb) may be tidally excited. Among the 115 frequencies, we detected triplets due to the frequency modulation, frequency differences connected to the orbital period, and unexpected resonances (3:2, 3:5, and 3:4), which is a new discovery for a delta Scuti star.