| 其他摘要 | It is common knowledge that open clusters are dynamically associated systems of stars, in which the stars have formed together within the same molecular cloud. Therefore, apart from the coeval nature of the stars, they have the same chemical composition, and usually are assumed to be at the same distance from us and hence suffer from the same interstellar reddening. Particularly, open clusters are found mostly in the disk and especially the spiral arms, where many new stars are being formed. Hence it is a perfect place to study theories of stellar formation and evolution, and furthermore an ideal place to study stellar magnetic activities, taking into account that there are lots of low mass stars with rapid rotations in open clusters. Nearly 2000 open clusters have been detected in Galaxy, however, the magnetic 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 their magnetic activities. During 2008-2013, We carried out photometric observations of three young open clusters (NGC 1348, ASCC 5 and NGC 1960) with the purpose of searching for variable stars with magnetic activities; we also obtained spectroscopic observations for several stars in NGC 1960 and Pleiades to study their chromospheric activities. Based on these observations, we have obtained many interesting results, as follows. We carried out multi-color time-series photometric observations of the young, poorly studied open cluster NGC 1348, and discovered one contact binary star: GSC2.3 NCB0032066. The well known O’Connell effect (e.g., ?B?0.03 mag) was found in November 2008, which indicates that this object is an active binary star. We compared the light curves derived in different 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 young open cluster ASCC 5, and discovered four eclipsing binaries: 2MASS J00570305+5541588, 2MASS J00572555+5546091, 2MASS J00580602+5541451 and 2MASS J00583140+5539042 (hereafter 2MJ5703, 2MJ5725, 2MJ5806 and 2MJ5831 respectively). We analyzed their light curves using the Wilson-Devinney light curve modeling technique and derived their basic physical parameters. –2MJ5703 is 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 orbital period of 0.44 days. –2MJ5725 is more likely a W subtype contact binary with a very low variation amplitude of about 0.07 mag. It has an orbital period of about 0.302 days. There are asymmetric distortions in its light curves, suggesting the presence of starspots on the components. –2MJ5806 is an H subtype contact binary system with a high mass ratio around 0.9 and a small degree of contact of about 0.1, and it has a short orbital period of about 0.274 days. –2MJ5831 is probably a W subtype contact binary with a low light variation amplitude around 0.11 mag and a short orbital period of 0.273 days. The presence of remarkable O’Connell effect and rapid variations of light curves indicate presence of strong magnetically activities on the components of this binary. We undertook photometric observations of the open cluster NGC 1960 in 2012 November, December and in 2013 February, and discovered nearly 10 variable stars in this field. 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 stars of Pleiades (PELS 72, DH 679 and PELS 75). Our observations indicate that all of them are magnetically active stars, being in very active states –PELS 72: There are at least two spots on the surface of this star in great part of observing runs, and the longitude separation between the two spots varies quickly. Furthermore, they are moving oppositely with respect to longitude, which gives us a clue of the presence of the meridian circulation. –DH 679: It shows no rapid variation in its light curve shapes on a short time scale, however, it seems that there are two active longitudes 180 degrees apart, based on longer data baselines, which usually relates to so-called“flip-flop”activity phenomenon. –PELS 75: There are rapid variations in its light curve amplitudes, and the primary spot shifts along longitude on a short time scale. More interestingly, spots in all datasets concentrate in a longitude range of about 180 degrees, indicating that the spots are inclined to emerge on the same hemisphere. It should be pointed out that further observations are needed to understand better their basic physical parameters and magnetic activities for these stars mentioned above. |
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