A Study Of Magnetic Activities For Stars In Open Clusters

It is common knowledge that open clusters are dynamically associated sys-tems of stars, in which the stars have formed together within the same molecularcloud. Therefore, apart from the coeval nature of the stars, they have the samechemical composition, and usually are assumed to be at the same distance fromus and hence sufer from the same interstellar reddening. Particularly, open clus-ters are found mostly in the disk and especially the spiral arms, where many newstars are being formed. Hence it is a perfect place to study theories of stellar for-mation and evolution, and furthermore an ideal place to study stellar magneticactivities, taking into account that there are lots of low mass stars with rapidrotations in open clusters.Nearly2000open clusters have been detected in Galaxy, however, the mag-netic activities are not understood well for the low mass stars in open clusters.Our aim is to search for magnetically active stars in open clusters, and study theirmagnetic activities. During2008-2013, We carried out photometric observation-s of three young open clusters (NGC1348, ASCC5and NGC1960) with thepurpose of searching for variable stars with magnetic activities; we also obtainedspectroscopic observations for several stars in NGC1960and Pleiades to studytheir chromospheric activities. Based on these observations, we have obtainedmany interesting results, as follows.We carried out multi-color time-series photometric observations of the y-oung, poorly studied open cluster NGC1348, and discovered one contact binarystar: GSC2.3NCB0032066. The well known O’Connell efect (e.g., B0.03mag) was found in November2008, which indicates that this object is an activebinary star. We compared the light curves derived in diferent observing runs,and found that there existed a slight change from November to December,2008,which indicates the evolution of spot activity on at least one component in a time scale of about one month.We carried out Rc-band time-series photometric observations of the youngopen cluster ASCC5, and discovered four eclipsing binaries:2MASS J00570305+5541588,2MASS J00572555+5546091,2MASS J00580602+5541451and2MASSJ00583140+5539042(hereafter2MJ5703,2MJ5725,2MJ5806and2MJ5831re-spectively). We analyzed their light curves using the Wilson-Devinney light curvemodeling technique and derived their basic physical parameters.–2MJ5703is a typical A subtype contact binary system (mass ratio q(?)0.5,the degree of contact f(?)0.13) with a late F spectral type, having an orbitalperiod of0.44days.–2MJ5725is more likely a W subtype contact binary with a very low vari-ation amplitude of about0.07mag. It has an orbital period of about0.302days.There are asymmetric distortions in its light curves, suggesting the presence ofstarspots on the components.–2MJ5806is an H subtype contact binary system with a high mass ratioaround0.9and a small degree of contact of about0.1, and it has a short orbitalperiod of about0.274days.–2MJ5831is probably a W subtype contact binary with a low light vari-ation amplitude around0.m11and a short orbital period of0.273days. Thepresence of remarkable O’Connell efect and rapid variations of light curves in-dicate presence of strong magnetically activities on the components of this binary.We undertook photometric observations of the open cluster NGC1960in2012November, December and in2013February, and discovered nearly10vari-able stars in this feld. Among these variables, several ones are variable B stars,one is a δ Scuti Star, the others may be the magnetically active stars.We made photometric and spectroscopic observations of three member starsof Pleiades (PELS72, DH679and PELS75). Our observations indicate that allof them are magnetically active stars, being in very active states. –PELS72: There are at least two spots on the surface of this star in greatpart of observing runs, and the longitude separation between the two spots variesquickly. Furthermore, they are moving oppositely with respect to longitude,which gives us a clue of the presence of the meridian circulation.–DH679: It shows no rapid variation in its light curve shapes on a shorttime scale, however, it seems that there are two active longitudes180degrees a-part, based on longer data baselines, which usually relates to so-called“fip-fop”activity phenomenon.–PELS75: There are rapid variations in its light curve amplitudes, and theprimary spot shifts along longitude on a short time scale. More interestingly,spots in all datasets concentrate in a longitude range of about180degrees, indi-cating that the spots are inclined to emerge on the same hemisphere.It should be pointed out that further observations are needed to understandbetter their basic physical parameters and magnetic activities for these starsmentioned above.