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The radial velocity of lambda Andromedae from the CA II emission lines.

1948; Institute of Physics; Volume: 54; Linguagem: Inglês

10.1086/106183

1538-3881

L. Gratton,

Astronomy and Astrophysical Research

The spectroscopic binary N Andromedae (mag. = 4.0, Sp. = G8 III-IV) was found to have very strong and rather sharp emission lines of Ca 11.1.2 The radial velocity from these emission lines and from the absorption lines was measured on 5 Merate and 30 McDonald spectrograms. The velocities from the absorption lines agree well with Luyten's orbital elements,3 but those from the emission lines show deviations which in some cases are several times larger than the probable error of the measurements. No simple relation can be found between the observed deviations and phase; when the deviations are large the lines usually appear sharp. If it is supposed that the emission lines origin- ate in the two bulges of the tidally distorted star, as was suggested by Hiltuer4 in the case df some eclipsing binaries of late spectral type, the observed deviations may be explained by irregular variations of the intensity ratio of the lines from the two bulges. In this case the spectral observations are consistent with a radius of the same order as the radius of the orbit. N Andromedae is a subgiant of visual absolute magnitude 1.9; its mass is then 1.8 O,from the mass-luminosity relation. From the orbital elements, assuming the radius of the orbit and that of the star to be equal, one finds 0.15 as the ratio of the masses of the smaller and of the larger star; the distance of the companion is about 32 X 106 km. The computed tidal distortion is very small and the variation of the gravity from the poles to the bulges is only 1.3 per cent. This variation, however, should be large enough to cause macroscopic currents of appreciable amount. It is probable that the emission lines originate at the bulges because of the deviation from normal equilibrium due to these currents. There are six binaries of spectral types G5-Ko with rather well known parallaxes, which show emission lines of Ca II; it is shown that for these stars there is a correlation between absolute magnitude and period. It is probable that this relation corresponds actually to a relation between density and radius of the relative orbit. I.Contr. Oss. Astr. Alilano-Merate, n.s. No. 17, 1944. 2.Pub. A. A. S. 10, 312, 1943. 3.Pub. Astr. Obs. Univ. Minnesota 2, No. I, 1934. 4.Ap. J. io6, 481, 1947. McDonald Observatory, Fort Davis, Tex.