Study of variable stars in open clusters is particularly important since the same age, chemical abundance, reddening and distance can be assumed for stars that belong to the cluster and most kinds of variable stars are also presented in open clusters. These variable star systems are used to probe the stellar internal structure, test stellar evolution theories, and provide significant clues to the dynamical evolution of the parent star clusters. We conducted photometric surveys for some particular open clusters and studied special variable stars in open clusters in detailed. First of all, we carried out time-series BV CCD photometric observations of the open cluster NGC 7654 to probe the nature of B-type main sequence pulsators. Eighteen slowly pulsating B (SPB) stars have been detected, among which fourteen candidates are newly discovered, three known ones are confirmed, and a previously foundδ Scuti star is also identified as a SPB candidate. Twelve SPBs are probable cluster members based on membership analysis. Observationally, this makes NGC 7654 become the richest galactic open cluster in terms of SPB star content. It is also a new discovery that NGC7654 hosts three γ Dor star candidates. We found that all these stars (eighteen SPBs and three γ Dor stars) have periods longer than their corresponding fundamental radial mode. It is very interesting that these eighteen SPBs show a rough period-luminosity relation that also covers the γ Dor stars at the low luminosity extension. We found for the first time that there may be a single period-luminosity relation applicable to all g-mode main sequence pulsators. Secondly, the first time-series CCD photometric survey of eclipsing binaries in the cluster NGC 2141 was conducted to confirm the effect of binary on the wide main sequence of the cluster. Ten new variables were discovered, seven of which are prob able members of the cluster. With the method of phase-dispersion minimization , the periods for nine variables were determined. On the basis of the behavior of light curve, period and location in the color-magnitude diagram, the sample was categorized as follows: three EW-type eclipsing binaries, two EA-type eclipsing binaries, two EB-type eclipsing binaries, one RRd-type variable star, one RS CVn-type star and one unknown type variable star. It is very interesting that one of EB-type eclipsing binaries is also a probable blue straggler belonged to the cluster. It is shown that the wide main sequence of the cluster NGC 2141 probably results from the presence of a rich population of binary stars in the cluster itself. In addition, we presented BVRI photometry for the cluster and determined the cluster age as 2.5 Gyr, the reddening E(B -V) as 0.35 and the distance modulus (m-M) as 14.15. The cluster reddening and distance modulus derived by us are for the first time strongly supported by the analysis of an EW-type eclipsing binary that very likely belongs to the cluster. Finally, we presented for the first time the photometric analysis of a blue straggler eclipsing binary system in the old open cluster NGC 2141 to understand the formation mechanism and evolution of blue stragglers in the open clusters. The ephemeris was derived and the orbital period of the system was redetermined to be 0.6227 days. A photometric analysis for light curve was done with the Wilson-Devinney Code (2003). The best photometric solution reveals a semi-detached binary with the secondary component filling its Roche lobe. The photometric mass ratio M2/M1 is determined to be round 0.190±0.002 and the ratio of V-band luminosity L2/L1(V) is about 0.033±0.001, which indicates the secondary component is overluminous. As a result, we concluded that this blue straggler eclipsing binary system results from a substantialmass exchange between these two components.
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