Zhongmu Li

MAGNETIC ACTIVITY AND ORBITAL PERIOD VARIATION OF THE SHORT-PERIOD ECLIPSING BINARY DV Psc

We present six new BVRcIc CCD light curves of a short-period RS CVn binary DV Psc obtained in 2010-2012. The light curve distortions change on both short and long timescales, which is explained by two starspots on the primary component. Moreover, five new flare events were detected and the flare ratio of DV Psc is about 0.082 flares per hour. There is a possible relation between the phases (longitude) of the flares and starspots for all of the available data of late-type binaries, which implies a correlation of the stellar activity of the spots and flares. The cyclic oscillation, with a period of 4.9 +/- 0.4 yr, may result from the magnetic activity cycle, identified by the variability of Max. I-Max. II. Until now, there were no spectroscopic studies of chromospheric activity indicators of the H-beta and H-gamma lines for DV Psc. Our observations of these indicators show that DV Psc is active, with excess emissions. The updated O - C diagram with an observing time span of about 15 yr shows an upward parabola, which indicates a secular increase in the orbital period of DV Psc. The orbital period secularly increases at a rate of dP/dt = 2.0x10(-7) days yr(-1), which might be explained by the angular momentum exchanges or mass transfer from the secondary to primary component.

A SYSTEMATIC STUDY OF EFFECTS OF STELLAR ROTATION, AGE SPREAD, AND BINARIES ON COLOR–MAGNITUDE DIAGRAMS WITH EXTENDED MAIN-SEQUENCE TURNOFFS

Stellar rotation, age spread and binary stars are thought to be three most possible causes of the peculiar color-magnitude diagrams (CMDs) of some star clusters, which exhibit extended main-sequence turn-offs (eMSTOs). It is far from getting a clear answer. This paper studies the effects of three above causes on the CMDs of star clusters systematically. A rapid stellar evolutionary code and a recently published database of rotational effects of single stars have been used, via an advanced stellar population synthesis technique. As a result, we find a consistent result for rotation to recent works, which suggests that rotation is able to explain, at least partially, the eMSTOs of clusters, if clusters are not too old (

Combined Effects of Binaries and Stellar Rotation on the Color-Magnitude Diagrams of Intermediate-age Star Clusters

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Chromospheric activity of periodic variable stars (including eclipsing binaries) observed in DR2 LAMOST stellar spectral survey

2.0\,Gyr). In addition, an age spread of 200 to 500\,Myr reproduces extended turn-offs for all clusters younger than 2.5\,Gyr, in particular, for those younger than 2.2\,Gyr. Age spread also results in extended red clumps (eRCs) for clusters younger than 0.5\,Gyr. The younger the clusters, the clearer the eRC structures. Moreover, it is shown that binaries (including interactive binaries) affect the spread of MSTO slightly for old clusters, but they can contribute to the eMSTOs of clusters younger than 0.5\,Gyr. Our result suggests a possible way to disentangle the roles of stellar rotation and age spread, i.e., checking the existence of CMDs with both eMSTO and eRC in clusters younger than 0.5\,Gyr.