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We present non-linear hydrodynamic pulsation models for OGLE-BLG-RRLYR-02792- a 0.26M_sun pulsator, component of the eclipsing binary system, analysedrecently by Pietrzynski et al. The star's light and radial velocity curvesmimic that of classical RR Lyrae stars, except for the bump in the middle ofthe ascending branch of the radial velocity curve. We show that the bump iscaused by the 2:1 resonance between the fundamental mode and the secondovertone - the same mechanism that causes the Hertzsprung bump progression inclassical Cepheids. The models allow to constrain the parameters of the star,in particular to estimate its absolute luminosity (approx 33L_sun) andeffective temperature (approx 6970K, close to the blue edge of the instabilitystrip).  We conduct a model survey for the new class of low mass pulsators similar toOGLE-BLG-RRLYR-02792 - products of evolution in the binary systems. We computea grid of models with masses corresponding to half (and less) of the typicalmass of RR Lyrae variable, 0.20M_sun<=M<=0.30M_sun, and discuss the propertiesof the resulting light and radial velocity curves. Resonant bump progression isclear and may be used to distinguish such stars from classical RR Lyrae stars.We present the Fourier decomposition parameters for the modelled light andradial velocity curves. The expected values of the phi_31 Fourier phase for thelight curves differ significantly from that observed in RR Lyrae stars, whichis another discriminant of the new class.

Pulsation models for the 0.26M_sun star mimicking RR Lyrae pulsator. Model survey for the new class of variable stars