Photometry of GD 428 in the uvbyβ system has been secured and analyzed. An average effective gravity of log g = 4.18 ± 0.15 and average effective temperature of 8050 are found. A spectrogram of the variable secured with the 5-meter telescope indicates the variable has an average radial velocity of —52 km s⁻¹ and a total range of ∼ 30 km s⁻¹. The m₁ index and spectrum indicate GD 428 is extremely metal poor. The effective surface gravities of 15 dwarf cepheids are used in conjunction with the pulsation equation to derive an expression for the dependence of the radii of the variables on period. The radii and temperatures are utilized to calculate the bolometric magnitudes which range from Mbol = +3.1 for GD 428 to Mbol= 0.0 for SS Psc. Pulsation models are employed to calculate the masses and pulsation constants Q. The masses of the variables are found to vary from 0.95 𝕸⊙ for the shortest period metal-poor stars to 2.2 𝕸⊙ for the longest period metal-rich variables. The Q values are found to lie in the range Q = 0.0325 to Q = 0.0335. The variables appear to be post-main-sequence stars in the hydrogen shell-burning stage of evolution. Isochrones (based on models) calculated by Ciardullo and Demarque are used to calculate Mbol values, masses, and ages. The masses and values calculated from the models are in good agreement with those calculated from the pulsation theory. If the metal-poor variables evolve from a ZAMS displaced below the Population I main sequence the restriction of the metal-rich variables to only the longer periods is easily accounted for. Ages of the variables are found to vary from 3 X 10⁹ yrs for the shortest period variables to 4 X 10⁸ yrs for the longest period variables. It appears that metal-poor stars have been formed in the Galaxy as recently as 2 X 10⁹ years ago unless some mechanism can be found that would delay their evolution.

Photometric (uvbyβ) observations of the strong-line RR Lyrae variable SW And are described. The photometry suggests that the star is reddened by E(b—y) = 0ṃ.036. Intrinsic (b-y) and c₁ values are used to derive the variations in Teff and logg. The mean values are ‹Teff› = 6680 K and ‹log g› = 2.9. Wesselink's method is used to derive a radius of R/R⊙ = 4.45. The radius, ‹Teff›, and ‹log g› values lead to ‹Mv› = 0ṃ9 and 𝕸 = 0.6 𝕸⊙. Some peculiarities in the behavior of the m₁ index are discussed. The mean m₁ value at light minimum indicates that SW And has a near solar abundance of heavy elements. Bibliographic Information(back to top)

Single-trail spectra of SX Phe have been obtained covering many cycles of this short-period dwarfcepheid variable at a dispersion of 18 Å mm⁻¹. The rapid changes in line intensities and the line doubling reported by Stock and Tapia (1971a) from 40 Å mm⁻¹ plates are not evident in our spectra.

Photometric (uvbyfi) observations of the RRc variable SS Psc suggest that it is more closely related to dwarf cepheids (RRs stars) than to the RRc variables. Intrinsic (b — y) and c₁ values are employed to derive the variations in surface gravity and temperature. The mean values are (log g eff) = 3.29 and (T eff ) = 7300° K. The mi index, ((mi) 0 ) = 0.178, and spectrum indicate it is a metal-strong star.

The geometric and photometric elements of the eclipsing star U Sge have been derived from uvby observations secured in 1973-74. The "best" elements are r₁ = 0.296, r₂ = 0.225, i = 90°; and L₁ = 0.130, L₂ = 0.870 in yellow light where the subscript 1 refers to the G2 IV-III component and the subscript 2 refers to the B8 V component. Radii and masses of the two stars can be derived by assuming that the larger star fills its Roche lobe. This assumption yields r₁ = 3.32 R⊙, r₂ = 2.52 ⊙, 𝕸₁ = 1.4⊙, and 𝕸₁ = 3.5⊙. The absolute magnitudes are found by two different methods and yield Mv = —0ṃ4 for the B star and Mv = +1ṃ8 for the G star. If corrections for radiative interactions are made, the absolute magnitude of the G star is Mv ≃+2ṃ2. Observational data secured in the u filter suggest that Balmer continuum emission can be detected from an emitting gas stream or disk. The gas must be concentrated near the following hemisphere of the B Star. The mi measurements of the secondary component suggest a metal deficiency of [Fe/H] = —0.6.