Abstract
ABSTRACT Results are reported for a narrow- and intermediate-band uvby-beta photometric study of the dwarf Cepheid GD 428, which was performed to determine the star's temperature variation, color excess, reddening-free color indices, and surface gravity. A spectrum trailed synchronously through four cycles of the star was also obtained in an attempt to ascertain the spectral type and radial-velocity variations. An average radial velocity of -52 km/s is determined along with a total velocity amplitude of about 30 km/s, an average approximate (b-y) color excess of +0.238, an average log g of about 4.18, and an average effective temperature of 8050 K. It is found that GD 428 is extremely metal-poor and has an absolute magnitude of at least 2.6. The physical properties of 16 dwarf Cepheids are examined, a period-radius relation is obtained, and bolometric magnitudes, masses, pulsation constants, and ages are calculated for the 16 stars. It is concluded that dwarf Cepheids are post-main-sequence stars in the hydrogen shell-burning stage of evolution and that metal-poor stars must have formed in the Galaxy as recently as 2 billion years ago.
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