Search For And Study Of Variable Stars In The Open Clusters

Study of variable stars in open clusters is particularly important since the sameage, chemical abundance, reddening and distance can be assumed for stars that be-long 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 stellarevolution theories, and provide significant clues to the dynamical evolution of the par-ent star clusters. We conducted photometric surveys for some particular open clustersand studied special variable stars in open clusters in detailed.First of all, we carried out time-series BV CCD photometric observations of theopen cluster NGC7654to probe the nature of B-type main sequence pulsators. Eigh-teen slowly pulsating B (SPB) stars have been detected, among which fourteen candi-dates 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 clustermembers based on membership analysis. Observationally, this makes NGC7654be-come the richest galactic open cluster in terms of SPB star content. It is also a newdiscovery that NGC7654hosts three γ Dor star candidates. We found that all thesestars (eighteen SPBs and three γ Dor stars) have periods longer than their correspond-ing fundamental radial mode. It is very interesting that these eighteen SPBs show arough period-luminosity relation that also covers the γ Dor stars at the low luminosityextension. We found for the first time that there may be a single period-luminosityrelation applicable to all g-mode main sequence pulsators.Secondly, the first time-series CCD photometric survey of eclipsing binaries inthe cluster NGC2141was conducted to confirm the efect of binary on the wide mainsequence 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 lightcurve, period and location in the color-magnitude diagram, the sample was catego-rized 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 eclipsingbinaries is also a probable blue straggler belonged to the cluster. It is shown that thewide main sequence of the cluster NGC2141probably results from the presence ofa rich population of binary stars in the cluster itself. In addition, we presented BVRIphotometry for the cluster and determined the cluster age as2.5Gyr, the reddeningE(B V) as0.35and the distance modulus (m M) as14.15. The cluster reddeningand distance modulus derived by us are for the first time strongly supported by theanalysis 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 stragglereclipsing binary system in the old open cluster NGC2141to understand the forma-tion mechanism and evolution of blue stragglers in the open clusters. The ephemeriswas derived and the orbital period of the system was redetermined to be0.6227days.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 sec-ondary component filling its Roche lobe. The photometric mass ratio M2/M1is deter-mined to be round0.190±0.002and the ratio of V-band luminosity L2/L1(V) is about0.033±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.