T Sextantis, an RR Lyrae Star of Type "c."

Three-color photoelectric and spectroscopic observations establish the light, color, spectrum, and radial-velocity variations of T Sextantis, the first type c RR Lyrae star to be studied in detail Present and past observations fit the new elements: Max ,1 = JD 2427458 463 + 0 32468767E Different cycles of light-variation cannot be superimposed exactly; dispersion at a given phase is about 0 03 mag in V Ultraviolet colors show several times this dispersion, particularly toward maximum light. In the plot of B - V versus U - B colors, the progression of points through a full cycle describes a loop in the opposite sense to that of RR Lyrae. Radial-velocity and spectral-class amplitudes are small, 28 km/sec and 0 5 class (from hydrogen lines), respectively, commensurate with the relatively small light- amplitude of the star, 0 mag in V. The pronounced hump in the light-curve around phase 0.85, characteristic of type c RR Lyrae variables, may possibly result from collision between rising and falling atmospheric layers. If this is correct, then, at least for this star, the poor fit of the velocity-curve to the light- and color-curves which commonly afflicts pulsation models nnds its explanation in the partial irrelevance of the velocity-curve to changes in the principal radiating surfaces of the star.