The Axis Is Nearly Perpendicular to the Orbital Plane ; (2) the Sense Is the Same As That of the Revolution ; (3) the Period Is Longer Than That of the Revolution
No. 7.] 247 75. An Explanation of the Periodic Variable Stars. By Kiyotsugu HIRAYAMA, M.I.A. Astronomical Observatory, Azabu, Tokyo. (Comm. July 13, 1931.) The binary hypotheses, initially proposed to explain the periodic variable stars, were defective. The pulsation theory seemed more promising ; but even this is disappointing in explaining the varieties and the minor details, of the phenomena. The following explanation ,1) although qualitative, seems satisfactory for those. The hypothesis is based on the capture theory of the stars,2) recently proposed by the writer, and is inconsistent with the fission theory. Cepheid Variables. The Cepheid variable is supposed to be a contact system of a giant star and a dwarf star which is almost dark. The relative orbit is supposed to be nearly circular, in accordance with the general tendency of the binary stars. For the rotation of the primary, the following qualifications are made : (1) the axis is nearly perpendicular to the orbital plane ; (2) the sense is the same as that of the revolution ; (3) the period is longer than that of the revolution. No assumption is made for the rotation of the companion, although the libration is very probable. Taking as a model, the stars of spherical form of the masses 10 and 1 solar units, and the period of revolution, 0.02 year, the mean distance comes out as 0.16 astronomical unit, and the velocitiesrelative to the centre of gravity, as 22.3 and 223.5 km sec-1. As a consequence of the relative motion of the companion, a trail, or an abrasion, so to speak, is left on the surface of the primary, which may be recovered as the time goes on.
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