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Pulsating stars in binary systems are ideal laboratories to test stellarevolution and pulsation theory, since a direct, model-independent determinationof component masses is possible. The high-precision CoRoT photometry allows adetailed view of the frequency content of pulsating stars, enabling detectionof patterns in their distribution. The object HD 51844 is such a case showingperiastron brightening instead of eclipses. We present a comprehensive study ofthe HD 51844 system, where we derive physical parameters of both components,the pulsation content and frequency patterns. Additionally, we obtain theorbital elements, including masses, and the chemical composition of the stars.Time series analysis using standard tools was mployed to extract the pulsationfrequencies. Photospheric abundances of 21 chemical elements were derived bymeans of spectrum synthesis. We derived orbital elements both by fitting theobserved radial velocities and the light curves, and we did asteroseismicmodelling as well. We found that HD 51844 is a double lined spectroscopicbinary. The determined abundances are consistent with delta Delphiniclassification. We determined the orbital period (33.498 +- 0.002 d), theeccentricity (0.484 +- 0.020), the mass ratio (0.988 +- 0.02), and the massesto 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 frequencymodulation, frequency differences connected to the orbital period, andunexpected resonances (3:2, 3:5, and 3:4), which is a new discovery for a deltaScuti star.

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