Physical Parameter Determination for the δ Scuti Star HD 200925

Abstract

HD 200925 is an unusual star: the period is stable on a time scale of many years, yet it shows variations which are either large and irregular, or small, suggesting a possible Blazhko effect (Poretti 1984; Joner & Johnson 1985); it has larger values of Teff and log g derived from uvbyβ than those of dwarf Cepheids of similar period; and it has a somewhat higher metal abundance, [Fe/H], than the Hyades. Furthermore, in conflict to what Joner and McNamara (1983) determined – that m1 index shows no variation with temperature – HD 200925 shows a definite variation, unlike that predicted in Crawford (1979). No explanation of this has yet been found. Johnson & Joner (1986) also derived an unusual and unexpected value of [Fe/H]. Finally, with respect to the pulsation periods of this star, Mantegazza & Poretti (1986) determined the existence of two periods: one definite, 0.26730 d and a possible second one of 0.2138 d which yield a ratio of P2/P1 = 0.800, the theoretical ratio expected between the first and the second overtones, found in other pulsating variables. All of these facts make HD 200925 an interesting star, motivating the present study.