The Spectrographic Problem of U Cephei.
Abstract
The velocity-curve of this eclipsing binary was redetermined from measures of 115 McDonald Observatory spectrograms. If this curve is interpreted in the usual way, the elements are: P = 2.493 days, = -5 km/sec, K = 120 km/sec, e = 0.20, = 400, and T = phase 2.16 days after minimum light. AJthough the eccentricity is much smaller than that obtained by Carpenter from plates taken nearly 20 years ago, the asymmetry of my velocity-curve does resemble his and confirms the discrepancy between spectrographic and photometric observations. In the partial phases of the eclipse the lines of the B8 star show a large rotation effect which suggests that the equatorial velocity of rotation of the brighter B8 star is 200 km/sec. That of the fainter, G2, star is less than 50 km/sec, in spite of the greater size of this star. The rapid angular velocity of the B8 star, which is far in excess of the angular velocity in the orbit, constitutes a particularly interesting cosmogonical problem. During the partial phases there appear sharp lines of H and Ca `I which are displaced from those of the limbs of the B8 star and which give ye- locities of about +100 km/sec before totality and -150 km/sec after totality. These lines are not pro- duced by the G2 star but must originate in `a tenuous stream of gas which may circle around the G2 star in a manner similar to that of the streams in fi Lyrae and SX Cassiopeiae. The spectrum of the B8 star shows systematically weaker lines in the first partial phase than in the second. Similarly, the lines of the receding stream (before totality) are weaker than the lines of the approaching stream (after totality). The lines of He i confirm Redman's conclusion that lines broadened by Stark effect must be weaker at the limb of the B8 star than in the center. On the other hand, CaII does not appreciably change in equivalent width and therefore becomes more conspicuous (narrower and deeper) as totality is ap- proached. This constitutes an argument against the hypothesis that "pure absorption" is predomi- nantly responsible for the formation of lines in the B8 star. It is suggested that the asymmetry of the velocity-curve may be caused by the same stream which gives rise to sharp H lines in the partial phases
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1944
- DOI:
- 10.1086/144610
- Bibcode:
- 1944ApJ....99..222S