THE PERIOD OF ETA AQUILAE AND THE BEHAVIOR OF ITS HYDROGEN LINES

New radial-velocity measurements for the seven-day Cepheid η Aql concentrated during rising light have been made in 1984-85. This allows a redetermination of the period which is continuing to increase but somewhat more slowly than previously reported. The hydrogen lines show an increasing velocity of infall after the metallic lines have passed maximum velocity and then show a greater velocity of expansion at maximum light than do the metallic lines. The behavior of the hydrogen lines is more like ä Cep, whose period is five days, than like the ten-day Cepheids ζ Gem and β Dor.