The Interpretation of ɛ Aurigae
Abstract
The light-curve of this eclipsing binary is rediscussed with the help of the spectro- graphic elements determined at the Yerkes Observatory. The ratio of the radii and the mass ratio are determined with the assumption that the visible component falls upon the empirical mass-luminosity-curve. The orbital inclination is found to be about 70°. The spectrum is formed by the smaller, F2 star. The larger component has a temperature of about i 2000_14000 and gives no appreciable light in the region covered by the spectroscopic observations. The spectroscopic and photometric observations duriiig the eclipse show that the infrared star is semitransparent and that its nonselective opacity for visual and photo- graphic light is concentrated in an outer shell. It is suggested that this effect is produced by photo-electric ionization from the F2 star. The spectral lines of the F2 star are visible throughout the total phase of the eclipse. In addition, there are lines produced in the ionized shell of the infrared star. The latter are displaced by the rotation of this component, and the displacements and intensities are in accord with the hypothesis. The close proximity, before mid-eclipse, of the ro- tationally displaced lines of the infrared star to the normal lines of the F2 star results in a relatively small increase of the equivalent breadth. After mid-eclipse, when the two lines are better separated, the increase in the equivalent breadth is more pronounced. The equatorial velocity of rotation of the infrared star is approximately ~o km/sec. The problem of the formation of an absorbing layer in the atmosphere of the infrared component by the radiation of the other component is investigated. Relations giving the extent of the region of the infrared star ionized by the outside radiation are derived. The optical thickness of the ionized region in visual and photographic light is calcu- lated as a function of the maximum density along the ray traversing the atmosphere. An approximately constant optical thickness is found for a r~nge of maximum density sufficiently wide to account for the observed constant minimum. A considerable excess of the amount of ionizing radiation over that calculated from Planck's law is required in order to give an optical thickness equal to that observed. The opacity of the non- ionized region of the infrared component between the ionized region considered and the observer is calculated. The effect of this opacity is found to be suficiently small, pro- vided the relative hydrogen content of the atmosphere of the infrared component is below a certain limit. Some aspects of the problem of line absorption in the atmosphere of the cool companion are considered. The results obtained are summarized, and the possible importance of a source of opacity other than the electron scattering and photo- electric transition opacity is briefly discussed
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1937
- DOI:
- 10.1086/143888
- Bibcode:
- 1937ApJ....86..570K