Absolute and Relative Amplitudes of Variations in Radius of Classical Cepheids

Abstract

On the basis of observational data for the absolute ΔR and relative ΔR/R amplitudes of variations in radius of galactic classical cepheids (55 stars from Balona and Stobie (1979) and 30 stars from Sollazzoet al. (1981)), four kinds of empirical linear relations are obtained: log(P ΔV)−logΔR, logP−logΔR, log(P ΔV)−log(ΔR/R), and logP−log(ΔR/R);P, R, and ΔV are the pulsation periods, the mean stellar radii, and the amplitudes of light variations, respectively. Three groups of stars are considered: short-period cepheids (SPC)-with logP≤1.1; long-period cepheids (LPC)-with logP>1.1; and s-cepheids (sC). Both the ΔR values and the ΔR/R values increase withP andP ΔV, for a given group of variables. A comparison is performed with our results obtained from data in other sources (Kurochkin, 1966; Gieren, 1982; etc.). The investigated relations can be applied for determining ΔR and ΔR/R of galactic classical cepheids, by using their observedP and ΔV. All studied galactic classical cepheids have ΔR/R<0.35, ΔR<10R ⊙ for SPC and 10R ⊙<ΔR≲60R ⊙ for LPC. The sC have smaller ΔR and ΔR/R values than other classical cepheids, at the same periods (the difference is about 2 times for ΔR and 1.4–2.8 times for ΔR/R); the studied sC have ΔR/R in the range 0.025–0.075 and ΔR in the range 1–3R ⊙ (only Y Oph has ΔR≃8R ⊙).