L.-J. Li

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (24)105.51 Total impact

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    ABSTRACT: New CCD photometric observations of overcontact binary CW Cas were carried out in 2004 and 2011. In particular, the light curve obtained in 2004 shows a remarkable O'Connell effect. Compared with light curves in different observing seasons, variations were found. These variations can be explained by dark spot activities on the surface of at least one component. Using the Wilson-Devinney code with a spot model, we find that the photometric solutions confirm CW Cas is a shallow W-subtype overcontact binary with a spotted massive component. Our new determined times of minimum light together with the others published in the literature were analyzed to find a change of orbital period. From the O – C curves, the period of the system shows a cyclic period change (P 3 = 69.9 yr, A 3 = 0.03196 days) superposed on the linear increase. The cyclic variation, if explained as the light-travel time effect, reveals the presence of a tertiary companion.
    The Astronomical Journal 10/2014; 148(5):95. · 4.97 Impact Factor
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    ABSTRACT: GW UMa is a new high-amplitude δδ Scuti variable star with a period of 0d.203193670d.20319367. By using a few new determined times of light maximum together with those collected from the literature, the changes in Observed-Calculated (O-C) diagram were analyzed. It is discovered that the O-C curve of GW UMa shows a cyclic variation with a period of 13.2 years and a semi-amplitude of 0.0023 days. The periodic variation was analyzed for the light-travel time effect that may be due to the presence of a stellar companion. The mass of the stellar companion is determined to be M2sini=0.11(±0.01)M2sini=0.11(±0.01) M⊙M⊙ when a mass of 1.761.76 M⊙M⊙ for GW UMa is adopted. The two component stars in the binary system are orbiting each other at an orbital separation about 6.5(±0.8)6.5(±0.8) AU. For orbital inclinations i⩾22.6°i⩾22.6°, the mass of the companion star would be M2<0.3M2<0.3 M⊙M⊙ and it is a fully convective star. The detection suggests that hidden stellar companions to bright stars may be not unusual.
    New Astronomy. 01/2014;
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    ABSTRACT: By using 78 newly determined timings of light minima together with those collected from the literature, we analysed the changes in the observed minus calculated (O-C) diagram in HS 0705+6700, a short-period (2.3 h) eclipsing binary that consists of a very hot subdwarf B-type (sdB) star and a very cool fully convective red dwarf. We confirmed the cyclic variation in the O-C and refined the parameters of the circumbinary brown dwarf (reported to orbit the binary system in 2009) by analysing the changes for the light travel time effect that arises from the gravitational influence of the third body. Our results indicate the lower mass limit of the third body to be M3 sin i' = 33.7(±1.6) MJup. This companion would be a brown dwarf if its orbital inclination is larger than 27.7° and it is orbiting the central eclipsing binary with an eccentricity e ˜ 0.2 at a separation of about 3.7(±0.1) au.
    Monthly Notices of the Royal Astronomical Society 12/2013; 436(2):1408-1414. · 5.52 Impact Factor
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    ABSTRACT: BI Vul is a cool eclipsing binary star (Sp. = K3 V) with a short period of 0.2518 days. The first charge-coupled device (CCD) light curves of the binary in the BVRI obtained on 2012 August 21 are presented and are analyzed using the Wilson-Devinney code. It is discovered that BI Vul is a marginal contact binary system (f = 8.7%) that contains two very similar cool components (q = 1.037). Both the marginal contact configuration and the extremely high mass ratio suggest that it is presently evolving into contact with little mass transfer between the components and it is at the beginning stage of contact evolution. By using all available times of minimum light, the variations in the orbital period are investigated for the first time. We find that the observed – calculated (O – C) curve of BI Vul shows a cyclic change with a period of 10.8 yr and an amplitude of 0.0057 days, while it undergoes a downward parabolic variation. The cyclic oscillation is analyzed for the light-travel time effect that arises from the gravitational influence of a possible third stellar object. The mass and orbital separation of the third body are estimated as M 3 ~ 0.30 M ☉ and ~4.9 AU, respectively. The downward parabolic change reveals a long-term period decrease at a rate of \dot{P}=-9.5\times {10^{-8}} days yr–1. The period decrease may be caused by angular momentum loss via magnetic stellar wind and/or it is only a part of a long-period (longer than 32 yr) cyclic variation, which may reveal the presence of another stellar companion in a wider orbit. These observational properties indicate that the formation of the Siamese twin is driven by magnetic braking and the third stellar companion should play an important role by removing angular momentum from the central binary.
    The Astrophysical Journal Supplement Series 11/2013; 209(1):13-. · 16.24 Impact Factor
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    ABSTRACT: We discovered that the O–C curve of V753 Mon shows an upward parabolic change while undergoing a cyclic variation with a period of 13.5 yr. The upward parabolic change reveals a long-term period increase at a rate of days yr–1. Photometric solutions determined using the Wilson-Devinney method confirm that V753 Mon is a semi-detached binary system where the slightly less massive, hotter component star is transferring mass to the more massive one. This is in agreement with the long-term increase of the orbital period. The increase of the orbital period, the mass ratio very close to unity, and the semi-detached configuration with a less massive lobe-filling component all suggest that V753 Mon is on a key evolutionary stage just after the evolutionary stage with the shortest period during mass transfer. The results in this paper will shed light on the formation of massive contact binaries and the evolution of binary stars. The cyclic oscillation in the O–C diagram indicates that V753 Mon may be a triple system containing an extremely cool stellar companion that may play an important role for the formation and evolution in the binary system.
    The Astrophysical Journal Supplement Series 07/2013; 207(2):22. · 16.24 Impact Factor
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    ABSTRACT: V401 Cyg is a quadruple system in which the spectroscopic signature of a close-in tertiary and a distant visual companion star were reported. Orbital properties of the close-in companion should provide valuable information on the formation of close binaries and stellar dynamical interaction. By analyzing new times of minimum light together with those collected from the literature, we discovered that the observed–calculated (O – C) curve of V401 Cyg shows a cyclic change with a short period of 3.5 yr and a semi-amplitude of 0.00436 days while it undergoes an upward parabolic variation. Those photoelectric and CCD data covered more than two cycles and were analyzed for the light-travel time effect via the presence of the tertiary companion. The mass of the third body was determined to be M 3sin i' = 0.65(± 0.08) M ☉, which is close to the value estimated from the spectroscopic data (M 3 ~ 0.64 M ☉). This reveals that the orbital inclination of the tertiary was about i' ~ 90°, indicating that the contact components of V401 Cyg have the possibility of being eclipsed by the tertiary at an orbital distance of about 3.0 AU, and it may be a triply eclipsing hierarchical triple system. The upward parabolic change indicates a period increase at a rate of revealing a mass transfer from the secondary to the primary (M ☉ yr–1). This is consistent with the predictions of the theory of thermal relaxation oscillation (TRO) suggesting that V401 Cyg is undergoing an expanding-orbit stage in the TRO cycles.
    The Astronomical Journal 07/2013; 146(2):28. · 4.97 Impact Factor
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    ABSTRACT: WX Cen is one of a few compact binary supersoft X-ray sources (CBSS) in the Galaxy that is a possible Type Ia supernova (SN Ia) progenitor. The supersoft X-ray radiation is explained as hydrostatic nuclear burning on the surface of the white dwarf component that is accreting hydrogen from a stellar companion at a high rate. If the mass donor in this system has a low mass, as has been suggested in the literature, one would expect a high wind-driven mass transfer rate. In that case, the orbital period of the system should increase. To test this theoretical prediction, we have monitored the system photometrically since 2010. By using four newly determined eclipse timings together with those collected from the literature, we discovered that the orbital period is decreasing at a rate of dP/dt = –5.15 × 10–7 days yr–1. The long-term decrease in the orbital period is contrary to the prediction that the system is powered by wind-driven accretion. It therefore seems plausible that the mass donor could be more massive than the white dwarf, and that the mass transfer is driven by the thermal instability of the donor star. This finding suggests that WX Cen is a key object to check the physical mechanisms of mass accretion in CBSS. The corresponding timescale of the period change is about yr, indicating that WX Cen may evolve into an SNe Ia within one million years in the Galaxy.
    The Astrophysical Journal Letters 07/2013; 772(2):L18. · 6.35 Impact Factor
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    ABSTRACT: A series of bulk polycrystalline La0.7Ca0.2Sr0.1MnO3 (LCSMO)/Pd composites were prepared by chemical plating and structural, electrical, magnetic, and magnetoresistance (MR) properties were investigated. It is found that Pd additions are uniformly distributed on the grain boundaries of the LCSMO grains, which decrease the resistivity and the saturation magnetic moment of the matrix. An interesting phenomenon is observed that at a given field, when the plating time increases, the MR increases at low addition level (0>t (plating time)<40 min) and decreases at high addition level (t>40 min), indicating an optimal plating time of 40 min, at which the MR value is maximum. Our analysis suggests that the improvement of grain boundaries originating from Pd addition plays an important role in enhancing the MR.
    Journal of Magnetism and Magnetic Materials 10/2012; 324(20):3286–3290. · 2.00 Impact Factor
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    ABSTRACT: We report here the discovery of an optical flare observed in R band from the red-dwarf eclipsing binary CU Cnc whose component stars are at the upper boundary of full convection (M1=0.43 and M2=0.4M0, M0 is the solar mass). The amplitude of the flare is the largest among those detected in R band (~0.52mag) and the duration time is about 73 minutes. As those observed on the Sun, quasi-periodic oscillations were seen during and after the flare. Three more R-band flares were found by follow up monitoring. In total, this binary was monitored photometrically by using R filter for 79.9 hours, which reveals a R-band flare rate about 0.05 flares per hour. These detections together with other strong chromospheric and coronal activities, i.e., very strong H_alpha and H_beta emission features and an EUV and X-ray source, indicate that it has very strong magnetic activity. Therefore, the apparent faintness (~1.4 magnitude in V) of CU Cnc compared with other single red dwarfs of the same mass can be plausibly explained by the high coverage of the dark spots.
    Monthly Notices of the Royal Astronomical Society 04/2012; 423(4). · 5.52 Impact Factor
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    ABSTRACT: HW Vir-like eclipsing binaries are a group of detached binary systems that consists a very hot subdwarf B (sdB) type primary and a fully convective M-type secondary with periods shorter than 4 hours. Here we report the preliminary photometric study of the HW Vir-like binary NSVS14256825 based on our four years data. By analyzing the high precise BV(IR)c light curves of NSVS14256825 with the 2003 version of Wilson-Van Hamme code, we derived the mass ratio of this binary as q=0.22. Assuming the mass of the primary component of NS14256825 is 0.46 M⊙, the mass of its secondary component should be 0.1M⊙(105MJup) for the fully convective star. The O-C diagram of NS14256825 is shown here and the detail analysis is in progress.
    12/2011;
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    ABSTRACT: In a programme to understand the evolution of contact binaries, we have re-observed EQ Cep, ER Cep and V371 Cep, which are members of the old open cluster NGC 188, photometrically. Combining our photometric solutions with some known parameters of the cluster, we derived the mass and the radius for each component. Meanwhile, we investigated the period changes of the three systems, finding a long-term increase of period in every system and discovering two cyclic variations in ER Cep besides the long-term changes (T3= 5.40 ± 0.01 yr, A3= 0.0135 ± 0.0016 d; T4= 17.6 ± 0.1 yr). From the derived physical parameters and analysis of the orbital period, we conclude that (i) both components of V371 Cep have very possibly evolved off the main sequence, as a result of the derived accelerations of gravity log g1= 3.93 and log g2= 3.98, and (ii) ER Cep is at least a triple, or even quadruple, system, something suggested by the overmassive derived total mass (∼3.51 M⊙) and the 5.4-yr-cycle periodic oscillation.
    Monthly Notices of the Royal Astronomical Society 06/2011; 415(4):3006 - 3012. · 5.52 Impact Factor
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    ABSTRACT: Using the precise times of mid-egress of the eclipsing polar HU Aqr, we discovered that this polar is orbited by two or more giant planets. The two planets detected so far have masses of at least 5.9 and 4.5\,M_{Jup}. Their respective distances from the polar are 3.6 AU and 5.4 AU with periods of 6.54 and 11.96 years, respectively. The observed rate of period decrease derived from the downward parabolic change in O-C curve is a factor 15 larger than the value expected for gravitational radiation. This indicates that it may be only a part of a long-period cyclic variation, revealing the presence of one more planet. It is interesting to note that the two detected circumbinary planets follow the Titus-Bode law of solar planets with n=5 and 6. We estimate that another 10 years of observations will reveal the presence of the predicted third planet.
    Monthly Notices of the Royal Astronomical Society 03/2011; 414. · 5.52 Impact Factor
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    ABSTRACT: This paper analyzes the first obtained four-color light curves of V396 Mon using the 2003 version of the W-D code. It is confirmed that V396 Mon is a shallow W-type contact binary system with a mass ratio q = 2.554(±0.004) and a degree of contact factor f = 18.9%(±1.2%). A period investigation based on all available data shows that the period of the system includes a long-term decrease (dP/dt = –8.57 × 10–8 days yr–1) and an oscillation (A 3 = 0.0160 day, T 3 = 42.4 yr). They are caused by angular momentum loss and light-time effect, respectively. The suspect third body is possibly a small M-type star (about 0.31 solar mass). Though some observations indicate that this system has strong magnetic activity, by our analysis we found that the Applegate mechanism cannot explain the periodic changes. This binary is an especially important system according to Qian's statistics of contact binaries as its mass ratio lies near the proposed pivot point about which the physical structure of contact binaries supposedly oscillates.
    The Astronomical Journal 01/2011; 141(2):44. · 4.97 Impact Factor
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    ABSTRACT: We obtained several epochs of light minima and a complete R light curve of the W-type contact binary V1128 Tau in 2009. Two cool spots on the massive component are used to model the photometric light curve. Using all available data we find evidence for a long-term period variation with an amplitude of 0.0050±0.0012 days and a period of 16.7±0.9 years. Using parameters derived from a photometric model of the 2009 light curve we show that this period change could be explained by the Applegate mechanism on one of the components. KeywordsStars: binaries: close–Stars: binaries: eclipsing–Stars: individuals (V1128 Tau)–Stars: evolution
    Astrophysics and Space Science 01/2011; 334(1):131-137. · 2.06 Impact Factor
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    L.-J. Li, S.-B. Qian
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    ABSTRACT: We measure two new times of light maximum of the SX Phoenicis star DY Pegasi in 2008 December and collect 410 pe/CCD times of light maximum that had been published. These data could be modeled with a nonlinear fit including a continuously decreasing period change (dP/dt = –9.04 × 10–12 days day–1) and a periodic change with a period of 42.2 yr. If this periodic change is caused by the light traveling time effect of an orbital motion of DY Pegasi in a binary system, the deduced mass of the companion could be 0.028 M ☉ and it is probably a brown dwarf.
    The Astronomical Journal 05/2010; 139(6):2639. · 4.97 Impact Factor
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    ABSTRACT: Detections of Jupiter-like giant planets in orbit around short-period white dwarf binaries should provide insight into the formation and evolution of circumbinary planets (planets orbiting both components of short-period binaries), as well as into the ultimate fate of planets and the late evolutionary stage of binary stars (e.g. the evolution of the common envelope). However, to date no planets have been detected as companions to such close binaries. Here, we report the discovery of a giant planet orbiting the only known hibernating cataclysmic variable (CV), QS Vir, with a period of 7.86 yr. We analysed the variations of the orbital period of the eclipsing white dwarf–red dwarf binary, and a very small-amplitude cyclic change is found to be superimposed on a long-term period decrease. The period oscillation has the smallest amplitude among close binary stars and can be plausibly interpreted as the light-travel time effect via the presence of a third body. We found that the tertiary component is a giant planet with a mass of ∼6.4 MJupiter at a distance of ∼4.2 astronomical units (au) from the binary. The continuous decrease is explained as angular momentum loss via magnetic braking which is driving the evolution of the hibernating CV into a normal cataclysmic binary.
    Monthly Notices of the Royal Astronomical Society Letters 11/2009; 401(1):L34 - L38. · 5.52 Impact Factor
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    ABSTRACT: Orbital period variations of some eclipsing cataclysmic variable stars (e.g., SW Sex-type CVs) and pre-CVs (e.g., HW Vir-type binaries) were analyzed by including some new times of light minimum obtained with several small telescopes in the world. It is found that the orbital periods of most sample stars show a cyclic change while they undergo a long-term variation. The evidence of magnetic breaking (MB) for fully convective star was given. Our investigation indicates that the evolution of CVs with period shorter than 3 hours may be also governed by MB, which is in agreement with new period distribution of CVs and with the results that fully convective stars are very active, with strong and stable magnetic field. It is revealed that the treat of MB in the standard theory should be modified and in this way the "period minimum" problem can be solved. The long-term period changes and the relation between the orbital period and its rate of change (dP/dt) are discovered for SW Sex-type CVs. These results supported that SW Sex-type CVs have the highest luminosity among CVs and was the reason that results in the observed SW Sextantis phenomena. We show that the cyclic period variations can not be explained by the mechanism of magnetic activity cycles of the late type component because of the problem of energy. The light-travel time effect via the presence of a tertiary component is the most possible mechanism to interpret the periodic change. It is shown that the extremely low-mass objects (e.g., brown dwarf stars and huge planets) are usually encountered as a tertiary component in CVs and pre-CVs.
    07/2009; 404:248.
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    ABSTRACT: Composites with compositions La0.7Ca0.2Sr0.1MnO3 (LCSMO)/xCoFe2O4 (CFO) were prepared by a standard ceramic technique. The structure and morphology of the composites have been studied by the X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The XRD and SEM results indicate that no reaction occurs between LCSMO and CFO grains, and that CFO segregates mostly at the grain boundaries of LCSMO. The variation in resistivity with temperature has been studied and shows a semi-conducting behavior, furthermore the composites exhibit metallic percolation threshold at x = xP = 8%. The magnetic moment (σS) changed with the increase of CFO. Curie temperature (TC) is a dividing point; T < TC, σS decreases with CFO content increasing, while T >TC, σS changes contrarily with the addition of CFO. The magnetoresistance (MR) effect is enhanced at a wide temperature range in an applied magnetic field (3 kOe). The spin-polarized tunneling and the spin-dependent scattering may be attributed to the enhanced low-field magnetoresistance (LFMR) effect.
    Journal of Alloys and Compounds 04/2009; 474(s 1–2):316–320. · 2.73 Impact Factor
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    ABSTRACT: La0.7Ca0.3MnO3+x(ZnO) composites with x=0, 2, 3, 4, 6, 12, 20, 35 and 55% (the molar ratio of ZnO to LCMO matrix) were obtained by mixed LCMO and ZnO powders and sintered at 1000°C for 3h. The structure, morphologies, electro-magnetic transport behavior and magnetic properties of the composites were systematically studied. The results of X-ray diffraction and scanning electronic microscopy indicated no new phase appeared in the composites except LCMO and ZnO phases, and ZnO segregated mostly at the grain boundaries of LCMO. Compared with pure La0.7Ca0.3MnO3, we have observed two peaks in the curve of the temperature dependence on the resistivity. One is the insulator–metal (I–M) transition temperature (TP1), which kept almost the same for all the samples and was observed and reported generally at high temperature in LCMO. The other is a new I–M transition temperature (TP2), which occurred at low temperature for the doped samples (x≥3%) and decreased with increasing ZnO concentration. TP1 and TP2 of the composites are corresponding to the magnetic transition temperature TC1 and TC2, respectively. According to the magnetic properties of the composites, the magnetic transition temperature TC1 of the samples is the same. Enhanced low-field magnetoresistance was obtained in the composite. We have observed the max MR (43%) for the sample x=35% under the field 3000Oe at 110K. These phenomena can be explained using the double-exchange (DE) mechanism, the grain boundary effect and the intrinsic transport properties together.
    Journal of Alloys and Compounds 01/2009; 469(1):552-557. · 2.73 Impact Factor
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    ABSTRACT: Two CCD epochs of light minimum and a complete R light curve of SS Ari are presented. The light curve obtained in 2007 was analyzed with the 2003 version of the W-D code. It is shown that SS Ari is a shallow contact binary system with a mass ratio q=3.25 and a degree of contact factor f=9.4%(±0.8%). Aperiod investigation based on all available data shows that there may exist two distinct solutions about the assumed third body. One, assuming eccentric orbit of the third body and constant orbital period of the eclipsing pair, results in a massive third body with M 3=1.73M ⊙ and P 3=87.0 yr. On the contrary, assuming continuous period changes of the eclipsing pair the orbital period of tertiary is 37.75 yr and its mass is about 0.278M ⊙. Both of the cases suggest the presence of an unseen third component in the system.
    Astrophysics and Space Science 01/2009; 321(1):19-35. · 2.06 Impact Factor

Publication Stats

10 Citations
105.51 Total Impact Points

Institutions

  • 2010–2014
    • Chinese Academy of Sciences
      • Yunnan Observatories
      Peping, Beijing, China
  • 2008–2012
    • Huazhong University of Science and Technology
      • School of Physics
      Wuhan, Hubei, China
  • 2008–2009
    • Northeast Institute of Geography and Agroecology
      • Yunnan Observatories
      Peping, Beijing, China