Yunfei Yang

AD Cancri: A shallow contact solar-type eclipsing binary and evidence for a dwarf third component and a 16 year magnetic cycle

CCD photometric observations of AD Cancri obtained from 2000 March 7 to 2004 December 20 are presented. Variations of the light levels at the primary minimum and both maxima are found. Uniform solutions of four sets of photometric data were derived by using the Wilson-Devinney method. The solutions suggest that AD Cancri is a shallow W-type contact binary (f 8.3% +/- 1.3%) with a highmass ratio of 1/q = 0.770 +/- 0.002. The long-term variation of the light curve is explained by variable dark-spot models of the more massive component star with a possible 17 yr cycle. Our 13 times of light minimum over 5 years, including others collected from the literature, have been used for the period study. The complex period changes can be sorted into a long-term period increase at rate of dP/dt +(4.94 +/- 0.16) x 10(-7) days yr(-1), a 16.2 yr periodic component (A(3) = 0.0155 days), and a very small amplitude period oscillation (A(4) = 0.0051 days, P-4 = 6.6 yr). The existence of third light may indicate that there is a tertiary component in the binary system. Solving the four-band light curves of Samec & Bookmyer, it is found that the contribution of the tertiary component to the total light of the triple system increases with wavelength, which suggests that it is very cool and may be a very red main-sequence star. The small-amplitude period oscillation may be caused by the light-time effect of the cool tertiary component (M-3 similar to 0.41 M-circle dot). The 16.2 yr periodic component in the orbital period and the 17 yr cyclic activity of the dark spot on the more massive component both may reveal that the more massive component displays solar-type magnetic activity with a cycle length of about 16 yr.

DEEP, LOW-MASS RATIO OVERCONTACT BINARY SYSTEMS. XII. CK BOOTIS WITH POSSIBLE CYCLIC MAGNETIC ACTIVITY AND ADDITIONAL COMPANION

We present precision CCD photometry, a period study, and a two-color simultaneous Wilson code solution of the short-period contact binary CK Bootis. The asymmetric light curves were modeled by a dark spot on the primary component. The result identifies that CK Boo is an A-type W UMa binary with a high fillout of f = 71.7(+/- 4.4)%. From the O-C curve, it is found that the orbital period changes in a complicated mode, i.e., a long-term increase with two sinusoidal variations. One cyclic oscillation with a period of 10.67(+/- 0.20) yr may result from magnetic activity cycles, which are identified by the variability of Max. I - Max. II. Another sinusoidal variation (i.e., A = 0.0131 days(+/- 0.0009 days) and P-3 = 24.16(+/- 0.64) yr) may be attributed to the light-time effect due to a third body. This kind of additional companion can extract angular momentum from the central binary system. The orbital period secularly increases at a rate of dP/dt = +9.79(+/- 0.80) x 10(-8) days yr(-1), which may be interpreted by conservative mass transfer from the secondary to the primary. This kind of deep, low-mass ratio overcontact binaries may evolve into a rapid-rotating single star, only if the contact configuration do not break down at J(spin) > (1/3)J(orb).

DISPERSAL OF G-BAND BRIGHT POINTS AT DIFFERENT LONGITUDINAL MAGNETIC FIELD STRENGTHS

G-band bright points (GBPs) are thought to be the foot-points of magnetic flux tubes. The aim of this paper is to investigate the relation between the diffusion regimes of GBPs and the associated longitudinal magnetic field strengths. Two high resolution observations of different magnetized environments were acquired with the Hinode/ Solar Optical Telescope. Each observation was recorded simultaneously with G-band filtergrams and Narrow-band Filter Imager (NFI) Stokes I and V images. GBPs are identified and tracked automatically, and then categorized into several groups by their longitudinal magnetic field strengths, which are extracted from the calibrated NFI magnetograms using a point-by-point method. The Lagrangian approach and the distribution of diffusion indices approach are adopted separately to explore the diffusion regime of GBPs for each group. It is found that the values of diffusion index and diffusion coefficient both decrease exponentially with the increasing longitudinal magnetic field strengths whichever approach is used. The empirical formulas deduced from the fitting equations are proposed to describe these relations. Stronger elements tend to diffuse more slowly than weak elements, independently of the magnetic flux of the surrounding medium. This may be because the magnetic energy of stronger elements is not negligible compared with the kinetic energy of the gas, and therefore the flows cannot perturb them so easily.

Characterizing motion types of G-band bright points in the quiet Sun

We study the motion of G-band bright points (GBPs) in the quiet Sun to obtain the characteristics of different motion types. A high resolution image sequence taken with the Hinode/Solar Optical Telescope (SOT) is used, and GBPs are automatically tracked by segmenting 3D evolutional structures in a space-time cube. After putting the GBPs that do not move during their lifetimes aside, the non-stationary GBPs are categorized into three types based on an index of their motion type. Most GBPs that move in straight or nearly straight lines are categorized as a straight motion type, a few moving in rotary paths into rotary motion, and the others fall into a motion type we called erratic. The mean horizontal velocities are 2.18 +/- 0.08 k m s(-1), 1.63 +/- 0.09 k m s(-1) and 1.33 +/- 0.07 k m s(-1) for straight, erratic and rotary motion types, respectively. We find that a GBP drifts at a higher and constant velocity during its whole life if it moves in a straight line. However, it has a lower and variational velocity if it moves on a rotary path. The diffusive process is ballistic-, super-and sub-diffusion for straight, erratic and rotary motion types, respectively. The corresponding diffusion index (gamma) and coefficients (K) are 2.13 +/- 0.09 and 850 +/- 37 k m(2) s(-1), 1.82 +/- 0.07 and 331 +/- 24 k m(2) s(-1), and 0.73 +/- 0.19 and 13 +/- 9 k m(2) s(-1). In terms of direction of motion, it is homogeneous and isotropic, and usually persists between neighboring frames, no matter what motion type a GBP is classified as.

DEEP, LOW MASS RATIO OVERCONTACT BINARY SYSTEMS. XIII. DZ PISCIUM WITH INTRINSIC LIGHT VARIABILITY

New multi-color photometry for the eclipsing binary DZ Psc was performed in 2011 and 2012 using the 85 cm telescope at the Xinglong Station of the National Astronomical Observatories of China. Using the updated Wilson-Devinney (W-D) code, we deduced two sets of photometric solutions. The overcontact degree is f = 89.7(+/- 1.0)%, identifying DZ Psc as a deep, low mass ratio overcontact binary. The asymmetric light curves (i.e., LC2 in 2012) were modeled by a hot spot on the primary star. Based on all of the available light minimum times, we discovered that the orbital period of DZ Psc may be undergoing a secular period increase with a cyclic variation. The modulated period and semi-amplitude of this oscillation are P-mod = 11.89(+/- 0.19) yr and A = 0.0064(+/- 0.0006) days, which may be possibly attributed to either cyclic magnetic activity or light-time effect due to the third body. The long-term period increases at a rate of dP/dt = +7.43(+/- 0.17) x 10(-7) days yr(-1), which may be interpreted as conserved mass transfer from the less massive component to the more massive one. With mass transferring, DZ Psc will finally merge into a rapid-rotation single star when J(spin)/J(orb) > 1/3.

Cosmological time dilation in short gamma-ray bursts

Using the parameter V [ ≡ (64)max/(1024)max], the ratio of expected peak counts in 64 ms and 1024 ms, proposed by Che et al. recently, we find the cosmological time dilation in short gamma-ray bursts (t90 < 1.5 s) directly from the Burst and Transient Source Experiment catalog. The parameter V of short bursts shows a good correlation with the brightness B when we use (64)max as a measure of brightness B rather than (1024)max, introduced by Lamb et al. in 1993. In a Friedmann universe with Ω = 1 and Λ = 0, the estimated redshift is about 2 and the time dilation factor (TDF) with the energy correction is about 1.8. The fact that these results generally agree with those found in long bursts supports the same origin of long and short gamma-ray bursts.

Investigation of Umbral Dots with the New Vacuum Solar Telescope

Umbral dots (UDs) are small isolated brightenings observed in sunspot umbrae. They are convective phenomena existing inside umbrae. UDs are usually divided into central UDs (CUDs) and peripheral UDs (PUDs) according to their positions inside an umbra. Our purpose is to investigate UD properties and analyze their relationships, and further to find whether or not the properties depend on umbral magnetic field strengths. Thus, we selected high-resolution TiO images of four active regions (ARs) taken under the best seeing conditions with the New Vacuum Solar Telescope in the Fuxian Solar Observatory of the Yunnan Astronomical Observatory, China. The four ARs (NOAA 11598, 11801, 12158, and 12178) include six sunspots. A total of 1220 CUDs and 603 PUDs were identified. Meanwhile, the radial component of the vector magnetic field of the sunspots taken with the Helioseismic and Magnetic Imager on-board the Solar Dynamics Observatory was used to analyze relationships between UD properties and umbral magnetic field strengths. We find that diameters and lifetimes of UDs exhibit an increasing trend with the brightness, but velocities do not. Moreover, diameters, intensities, lifetimes and velocities depend on the surrounding magnetic field. A CUD diameter was found larger, the CUD brighter, its lifetime longer, and its motion slower in a weak umbral magnetic field environment than in a strong one.

On the Relationship Between G-Band Bright Point Dynamics and Their Magnetic Field Strengths

G-band bright points (GBPs) are regarded as good manifestations of magnetic flux concentrations. We aim to investigate the relation between the dynamic properties of GBPs and their longitudinal magnetic field strengths. High spatial and temporal resolution observations were recorded simultaneously with G-band filtergrams and Narrow-band Filter Imager (NFI) Stokes I

Evolution of isolated G-band bright points: size, intensity and velocity

I

Midterm Periodicity Analysis of the Mount Wilson Magnetic Indices Using the Synchrosqueezing Transform

and V