Abstract.A multicolour photometric data basis is compiled for SU Dra from 356 Johnson UBV and 228 UBV (RI)C observations reported in this paper, in addition to 483 BV , 289 UBV , and 85 UBV RI observations found in the literature. Mean period, period change (4.40 ± .14) × 10 −10 day/day, and phase noise are derived from the V light curves by a variational procedure minimizing the length of the folded light curve (string length minimization, SLM). From variation of string length in the neighbourhood of minimum, observational error of photometry, observed amplitude, number of observations formulae are derived for the error of period and phase noise by statistical and analytical considerations. Secondary periodic variations are excluded to a few mmag level, indication of amplitude variation (Blazhko-effect) has not been found, however, systematic segregation of light curve segments is reported from different epochs in the descending branch before the brightness rise. Mean light and colour curves are derived from photometry and they are compared with those from integration of spectrophotometric observations. The period change is interpreted in terms of mixing events in the stellar interior.

Aims. The first U-band and new BV(RI) C photometry of the RRd star V372 Ser is presented to determine some parameters of the star.

No abstract

Abstract. For determining distance and mass of pulsating stars a new, purely photometric method is described in which radial velocity observations are not needed. From multicolour photometry the variation of angular diameter is determined in a conventional way by using the surface brightness of the theoretical atmospheric models ATLAS of Kurucz (1997). As a function of phase the following two parameters are introduced in the Navier-Stokes equation: gravity (of the appropriate static ATLAS model), and angular diameter. Distance and mass are derived from phases of standstill. Conclusions are drawn on the hydrodynamic behaviour of the atmosphere. The new method is compared with the Baade-Wesselink (BW) method. As an example the RR Lyrae variable SU Dra is given: using UBVR C photometry, a distance of 647 ± 16 pc, and a mass of 0.66 ± .03 M were found. In addition to the radius change (4.58−5.51) R radius undulations have been found with amplitude ≈0.2 R and period P/5, which are synchronized with the main period P = 0. d 66042. The present method has confirmed the distance value from the BW method; thus, in the problem of different distance scales from BW and other methods the short extragalactic distance scale has been bolstered by an independent argument. The mass is some 30 percent larger than the value from the equation of pulsation of van Albada & Baker (1971).