Abstract
Models of Delta Scuti stars are tested against radial pulsations in the four lowest modes, using a linear, nonadiabatic approximation. It is shown that the theoretical blue edge locations of the instability strip on the H-R diagram depend strongly (ΔlogT e≃0.03) on both opacity interpolation and variations of the envelope helium abundanceY. Several other factors have small effect (Δ logT e≲0.01): variations of the heavy element abundanceZ, the use of various opacity tables, the treatment of convection, and the number of envelope mass zones. A comparison with both results obtained by various authors and observations is performed. The locations of the observed blue edge and our theoretical third-harmonic ones are consistent. A nonlinear dependence of the theoretical blue edge locations on envelope helium abundanceY is derived. A star withY≃0.2 may pulsate within the instability strip, if it is not near the blue edge.
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