No abstract

Differential photoelectric photometry in the V filter of the S Set star YZ Boo was carried out in 1982 and 1984. With a total time span of 16,398 days and 77 times of maximum light new ephemerides were found.

Abstract. uvby − β photometry of the large amplitude δ Scuti stars BP Peg, DY Peg, DY Her, CY Aqr and YZ Boo is presented. Since the data were obtained almost simultaneously in all filters, meaningful physical parameters have been derived for each star along their pulsation cycles using the calibrations from Nissen (1988) for A and F stars to determine the reddening and derive the unreddened photometric values. The utilization of the theoretical grids of Relyea & Kurucz (1978) has allowed temperature and gravity values to be determined. A comparison with previously reported values is presented.

Recently, new views of the current status of δ Scuti stars have been developed by Rodríguez & Breger (2001) who carried out an excellent review, listing 8 pre-main-sequence (PMS) δ Scuti candidates and examined the possibility of the existence of PMS δ Scuti variable stars. Here we discuss the nature of 4 stars from their list: 2 said to be members of NGC 2264 and 2 of NGC 6823.

This is part of a series which has the purpose of examining the nature of the stars belonging to open clusters. The aim of this series is, among others things, to study short period pulsating stars, mainly of the Delta Scuti type, by first establishing the membership of each star to the cluster, to determine the abundance of the Be and Ap phenomena and blue stragglers in open clusters for clusters of different ages and metalicities and, eventually, to study the chemical enrichment of the galaxy when age, dynamics and metalicity are known for a fair number of clusters.In the present study, an analysis of the open clusters NGC 1444, NGC 1662, NGC 2129, NGC 2169 and NGC 7209 is presented. These clusters were selected because they seem to have a relatively large number of early type stars. The observations were carried out at the National Astronomical Observatory of the UN AM. The 1.5 m telescope with a multichannel uvby-/? spectrophotometer was utilized for the acquisition of the data. A compilation of the observations and results are presented in Table 1.Since the aim of the present paper is to establish physical and geometric characteristics of the cluster stars, the first step was to determine membership of the observed stars to each of the clusters. Then we defined which stars were Main Sequence stars and the broad spectral regions to which they belonged by constructing a [mi] -[c\] diagram. It defines three main spectral regions: early type stars of class Β and early A; A and F stars, and late type stars. The distance for each group has been calculated separately.