The multicolour light curves and radial velocities for TYC 1031 1262 1 have been obtained and analysed. TYC 1031 1262 1 includes a Cepheid with a period of 4.15270 ± 0.00061 d. The orbital period of the system is about 51.2857 ± 0.0174 d. The pulsation period indicates that the secular period is increasing at a rate of of 2.46 ± 0.54 min yr −1 . The observed B, V and R magnitudes have been cleaned of the intrinsic variations of the primary star. The remaining light curves that have been obtained consist of eclipses and proximity effects, and these have been analysed to obtain the orbital parameters. The system consists of two evolved stars, F8 II + G6 II, with masses of M 1 = 1.640 ± 0.151 M and M 2 = 0.934 ± 0.109 M and radii of R 1 = 26.9 ± 0.9 R and R 2 = 15.0 ± 0.7 R , respectively. The pulsating star almost fills its corresponding Roche lobe, which indicates the possibility that mass loss or transfer has taken place. We find an average distance of d = 5070 ± 250 pc, using the BVR and JHK magnitudes, and also the V-band extinction. The kinematic properties and the distance to the Galactic plane (i.e. 970 pc) indicate that it belongs to the thick-disc population. Most of the observed and calculated parameters of TYC 1031 1262 1 lead to its classification as an anomalous Cepheid.Key words: binaries: eclipsing -binaries: spectroscopic -stars: fundamental parametersstars: variables: Cepheids.
I N T RO D U C T I O NPulsatingx variables are located in a restricted region, the so-called Cepheid instability strip (IS) in the Hertzsprung-Russell (HR) diagram. This region includes δ Scuti, RR Lyrae and Population I and II Cepheids. These can be used as an important basis for testing theories on stellar structure and evolution, as well as pulsation mechanisms. These variables have very different masses, effective temperatures and chemical abundances. The stars in the IS are found not only in a wide range of masses but also among very young Population I type stars to very old Population II type stars. These stars in the IS reveal many properties of the stellar interiors.At the beginning of the 20th century, Miss Leavitt made the great discovery that there is a relation between the period and the absolute magnitude of Cepheid variables in the Small Magellanic Cloud. Three decades later, Baade (1953) called attention to the difference in the period-luminosity (hereafter P-L) relations of the Cepheids in globular clusters and the classical Cepheids. Thus, the Cepheids are divided into two groups: Population I (usually called Type I) Cepheids and Population II (or Type II) Cepheids.Based on data obtained at the TÜBİTAK National Observatory. † E-mail: esin.sipahi@mail.ege.edu.tr Population I Cepheids are about 1.5 mag brighter than Population II Cepheids for the same pulsation periods. Taking into account this difference, Blaauw & Morgan (1954) made a revision of the P-L relation for the classical Cepheids. These variables are still used as distance indicators not only for our galaxy but also for nearby spiral and ir...