Abstract Intensive photometric and spectral observations of the variable star V2551 Cyg are presented. The light curve shape reveals that the target is a pulsating star, contrary to its previous classification as an eclipsing binary. The period and amplitude of the light curve, the amplitudes of color changes and the radial velocity curve of V2551 Cyg are similar to those of a high-amplitude δ Scuti variable. The target seems to pulsate with the fundamental mode. However, V2551 Cyg exhibits several important peculiarities: (i) the decreasing branch of its light curve is steeper than the increasing one; (ii) the radial velocity curve has a flat section in the phase range 0.7–1.2 and short increase of the negative radial velocity at phase 0.7; (iii) the rotational velocity is quite big for a HADS star; (iv) the Fourier coefficients of V2551 Cyg are quite different from those of HADS stars. The target classification is difficult due to these peculiarities.
Keywords stars: variables: delta Scuti — stars: variables: RR Lyrae — stars: individual (V2551 Cyg)
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