view Abstract Citations (6) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of the Wolf-Rayet Eclipsing Binary HD 193576 = V 444 Cygni. Kopal, Zdenek Abstract An analysis of the Lick photoelectric 1ight~curve of HD 193576, coupled with available spectroscopic evidence, leads to the following conclusions regarding the structure and absolute dimensions of this re- markable eclipsing system: 1. The Woif-Rayet component of HD 193576 must possess an extended envelope capable of dimming light of the 0 star which passes through it at the time of primary minimum but whose own emission is so small a fraction of the total luminosity of the star that no appreciable loss of light results when the 0 star passes in front of it. This should explain the observed unequal durations of the alternate minima. 2. The radius of the effective core of the Woif-Rayet component (which emits at least 90 per cent of its total light) cannot exceed approximately one-fourth the radius of the whole star. The envelope sur- rounding this core must be partially transparent to blue light of the 0 star and cannot be of the nature of a thin absorbing shell. Whether or not the transition between the luminous core and surrounding en- velope is gradual or abrupt seems impossible to decide from the photometric evidence alone. 3. The bodily eclipses of the 0 component and of the effective core of the Woif-Rayet star are partial, the orbital inclination being in the neighborhood of 770 The radius of the 0 component is found to amount to approximately 27 per cent of the radius of the relative orbit, or about 10 ®, that of the opaque core of the Woif-Rayet star being less determinate but apparently much smaller. The masses of the 0 and W stars are 270 and 10.50, respectively. This model of HD 193576 is in agreement with the small variation of light observed between minima. 4. Practically the entire photometric effipticity of HD 193576 can be accounted for by the 0 compo- nent, leaving little or nothing to be explained by the W envelope. This shows again that this envelope must be relatively dark. Because of its great dimensions, its distortion is undoubtedly considerable; but, since it does not appear noticeably to affect the light-changes between minima, the contribution of the envelope to the combined light of the system must be insignificant. 5. The abnormal width of the primary minimum indicates that the envelope surrounding the W core extends to at least 14 solar radii in the direction of the line joining the centers of the two stars. An atmos- phere of such dimensions must be at the limit of dynamical stability and is likely to suffer a continuous loss of matter streaming out of the conical end of the critical equipotential with velocities smaller than the or- dinary velocity of escape. Atmospheric tides raised by the 0 component might explain the observed asym- metry of helium emission bands and its variation with the phase. This suggests, incidentally, that these bands are likely to originate in outer parts of the extended envelope rather than close to the photosphere of the W star, where tides are much less important. 6. Since, by hypothesis, even the uneclipsed part of the 0 component shines at mid-primary minimum through the whole extent of the W envelope, which may seriously reduce its light, the observed depth of the primary minimum, combined with that of the secondary, can yield oniy a lower limit for the surface brightness of the W star. On the basis of computations made in this paper--crude as they are-it appears certain that the true surface brightness, and consequently the effective temperature, of the W core is at least as high as that of the 0 component, and quite possibly higher. Our hypothesis removes, therefore, any conspicuous discrepancy between the effective and ionization temperature of the Woif-Rayet star Publication: The Astrophysical Journal Pub Date: September 1944 DOI: 10.1086/144659 Bibcode: 1944ApJ...100..204K full text sources ADS |