L.-J. Li

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (30)120.17 Total impact

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    ABSTRACT: V2051 Oph is a deeply eclipsing dwarf nova with an orbital period below the period gap of cataclysmic variables (CVs). It has been photometrically monitored since 2008 June and 24 mid-eclipse times of the white dwarf have been obtained. The changes in the orbital period are investigated using all of the available mid-eclipse times. A continuous period decrease with a rate of P =-5.93 10-10 days yr-1 was discovered to be superimposed on a periodic variation with a small amplitude of 0d000329 and a period of 21.64 years. The standard theory predicted that the evolution of CVs below the period gap is driven by gravitational radiation. However, angular momentum loss (AML) via gravitational radiation is insufficient to explain this decrease, and additional AML via magnetic braking that is about five times the gravitational radiation rate is required. This is consistent with the theoretical requirement indicating that magnetic braking of the fully convective star is not completely stopped. The cyclic oscillation was interpreted as the variation of the arriving eclipse time via the presence of a third body because the required energy for the Applegate mechanism is much larger than that radiated from the secondary in 10 years. Its mass is derived asM i sin 7.3 (±0.7) F= .,b Jupiter mass. For orbital inclinations i 30° .3,F .,a it would be a planetary object. The giant circumbinary planet is orbiting around V2051 Oph at an orbital separation of about 9.0 astronomical units (AU) in an eccentric orbit (e = 0.37). These conclusions support the ideas that some planets could survive stellar late evolution and that dwarf novae are also planetary hosting stars. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Nov 2015 · The Astrophysical Journal Supplement Series
  • L. Liu · S.B. Qian · J.J. He · L.J. Li · E.G. Zhao · L.Q. Jiang · Z.T. Han
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    ABSTRACT: The first complete VRcIc light curves of V608 Cas are presented and analyzed by using the 2010 version of the W-D code. The photometric results show that V608 Cas is a moderate mass-ratio (q= 0.373±0.005), shallow contact (f= 19.7±4.9%) binary. A cool spot is present on the massive component. The orbital period of V608 Cas may increase continuously according to the (O-C) diagram, with a rate of dP/dt= +6.49×10-7 days/year. The fundamental parameters of V608 Cas are estimated as: M1= 0.95±0.15M⊙,M2= 0.35±0.08M⊙,R1= 0.78±0.12R⊙,R2= 0.50±0.10R⊙,L1= 0.563±0.112L⊙,L2= 0.233±0.086L⊙, where the uncertainties mainly come from the uncertainty of the primary's effective temperature.
    No preview · Article · Jul 2015 · New Astronomy
  • W.-P. Liao · S.-B. Qian · E.-G. Zhao · L.-J. Li
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    ABSTRACT: We observed the well-known unusual deep over-contact binary in 2012 and 2013. A new set of light curves and eight new observed times of light minima were derived. A total of 130 available CCD times of light minima were analyzed. The highest rate of long-term period increase in W UMa stars (+10.21 s century−1) was confirmed. The rapid period increase implies that the primary is accreting mass from the secondary at a high rate of $\skew4\dot{M} = 5.3 \times 10^{-6}\,M_{\odot }\:$yr−1. The asymmetric light curves (i.e., the O'Connell effect) were analyzed with the Wilson-Devinney Code. It was found that the spotted photometric solution with the third light is the best one for fitting the light curves. The main photometric results confirmed that LP UMa is an unusual W UMa system with a high mass ratio (q = 0.823 ± 0.003), deep-contact configuration (f = 66.6% ± 3.1%), and a temperature difference of Δ T = 700 K. The period increase in LP UMa may be a part of a long-period cyclic change because of the large third light contributions to the total system (61.52% in V, 61.39% in R, and 61.36% in I). All of these quite different properties make LP UMa a very interesting system to study. The possible evolutionary stage is also discussed.
    No preview · Article · Jun 2015 · Publications- Astronomical Society of Japan
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    ABSTRACT: DW Psc is a high-amplitude SX Phe-type variable with a period of pulsation of 0.05875 days. Using a few newly determined times of maximum light together with those collected from the literature, the changes in the observedcalculated (O-C) diagram are analyzed. It is discovered that the O-C curve of DW Psc shows a cyclic variation with a period of 6.08 years and a semi-amplitude of 0.0066 days. The periodic variation is analyzed for the light travel time effect, which is due to the presence of a stellar companion (M2 sin i ∼ 0.45(±0.03) M⊙). The twocomponent stars in the binary system are orbiting each other in an eccentric orbit (e ∼ 0.4) at an orbital separation of about 2.7(±0.3) AU. The detection of a close stellar companion to an SX Phe-type star supports the idea that SX Phe-type pulsating stars are blue stragglers that were formed from the merging of close binaries. The stellar companion has played an important role in the merging of the original binary by removing angular momentum from the central binary during early dynamical interaction or/and late dynamical evolution. After the more massive component in DW Psc evolves into a red giant, the cool close companion should help to remove the giant envelope via possible critical Roche-lobe overflow, and the system may be a progenitor of a cataclysmic variable. The detection of a close stellar companion to DW Psc makes it a very interesting system to study in the future. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Jan 2015 · The Astronomical Journal
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    J. J. Wang · S. B. Qian · J. J. He · L. J. Li · E. G. Zhao
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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.
    Preview · Article · Oct 2014 · The Astronomical Journal
  • L.-J. Li · S.-B. Qian
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    ABSTRACT: Long-cadence-corrected pre-search data conditioning (PDC) fluxes of FN Lyr (KIC 6936115) and V894 Cyg (KIC 9591503), observed continuously by the Kepler mission, spanning over 1470 d, are used to determine hundreds of times of maximum and minimum for the analysis of O − C residuals. The interpretation of the clear variations in the O − C diagrams is that these are caused by the light-travel-time effect as a result of additional companions. The mass functions of the companions are f (M) = (3.94 ± 0.82) × 10−6 and (2.01 ± 0.22) × 10−4 M⊙. Assuming that the orbital plane inclination follows a random distribution, the companions to both stars can be constrained to be substellar objects (brown dwarf or giant planet), with 89.4 and 59.4 per cent probability, respectively. Under the assumption that the orbital inclination equals 90°, the distances between the companions and the central RR Lyrae stars at periastron should be 1.03 and 0.50 au, respectively. In addition, the orbital periods are 794.8 and 1084.4 d for FN Lyr and V894 Cyg, respectively. By comparing these orbital parameters with those of B subdwarf stars in binary systems, there are strong hints that horizontal branch stars might have different evolution histories. The long-term pulsation period changes are also discussed. Based on our studies, RR Lyrae stars in binary systems are not rare, at least among binary systems with wider separations.
    No preview · Article · Aug 2014 · Monthly Notices of the Royal Astronomical Society
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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.
    No preview · Article · Jan 2014 · New Astronomy
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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 $_{.}^{\circ}$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.
    No preview · Article · Dec 2013 · Monthly Notices of the Royal Astronomical Society
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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.
    No preview · Article · Nov 2013 · The Astrophysical Journal Supplement Series
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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.
    No preview · Article · Jul 2013 · The Astrophysical Journal Supplement Series
  • L.-Y. Zhu · S.-B. Qian · X. Zhou · L.-J. Li · E.-G. Zhao · L. Liu · N.-P. Liu
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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.
    No preview · Article · Jul 2013 · The Astronomical Journal
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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.
    Full-text · Article · Jul 2013 · The Astrophysical Journal Letters
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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.
    No preview · Article · Oct 2012 · Journal of Magnetism and Magnetic Materials
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    ABSTRACT: Composite samples (1−x)La0.7Ca0.2Sr0.1MnO3(LCSMO)+x(ZnO) with different ZnO doping level x prepared through liquid phase method have been systematically investigated and compared with the samples prepared through solid state reaction. For both methods, the results of X-ray diffraction and scanning electron microscopy indicate that no reaction occurred between LCSMO and ZnO grains. The incorporation of ZnO in the LCSMO matrix lowers the metal-insulator transition temperature (TP) and increases the resistivity of the composites. The results also show that an enhanced magnetoresistance (MR) effect of the composites is observed at an applied magnetic field of 3k Oe, which is quite different from the samples through solid state reaction, where only one transition temperature and one peak appeared in the MR of the liquid phase method. Our results revealed that the liquid phase method is suitable for volume-production of ZnO with smaller grain size. The admixture of LCSMO and ZnO is very uniform and it is possible to get fully extended enhancement of grain boundary magnetoresistance.
    No preview · Article · Oct 2012 · Journal of Superconductivity and Novel Magnetism
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    ABSTRACT: The (La0.7Ca0.3MnO3)1−x /(Er2O3)x composites with x=0, 1, 2, 3, 4, 7, 9, 15, 17, and 20% were prepared by a solid state reaction process. The magnetic and electrical transport properties of the composites were investigated. The X-ray diffraction (XRD), scanning electronic microscopy (SEM), and the calculation of lattice parameters of La0.7Ca0.3MnO3 (LCMO) indicated that there is no reaction between La0.7Ca0.3MnO3 and Er2O3; especially, compared with pure LCMO, a new metal-insulator transition temperature (T P2) was observed at a lower temperature in some composites with x=1,2,3,4, and 7%, which may result from the existence of a new phase related to Er2O3 dopant at grain boundaries or surfaces of LCMO grains. An enhancement of low field magnetoresistance (LFMR) is obtained at temperature below 130 K for the composites with higher Er2O3 content, but the intrinsic CMR at T P1 decreased monotonously with increasing Er2O3 content. The increased LFMR results from the spin-dependent scattering and spin-polarized tunneling at the grain boundaries and the decreased intrinsic CMR due to the Double Exchange (DE) interaction between Mn3+ and Mn4+ ions.
    No preview · Article · Jul 2012 · Journal of Superconductivity and Novel Magnetism
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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.
    Full-text · Article · Apr 2012 · Monthly Notices of the Royal Astronomical Society
  • L. Zhu · S. Qian · L. Liu · W. P. Liao · J. J. He · L. J. Li · E. G. Zhao · Z. B. Dai · J. Zhang · K. Li
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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.
    No preview · Article · Dec 2011
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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
    No preview · Article · Jul 2011 · Astrophysics and Space Science
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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.
    Preview · Article · Jun 2011 · Monthly Notices of the Royal Astronomical Society
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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 4.5MJup. Their respective distances from the polar are 3.6 and 5.4 au with periods of 6.54 and 11.96 yr, respectively. The observed rate of decrease of period derived from the downward parabolic change in the observed — calculated (O — C) curve is a factor of 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 yr of observations will reveal the presence of the predicted third planet.
    Full-text · Article · Mar 2011 · Monthly Notices of the Royal Astronomical Society

Publication Stats

238 Citations
120.17 Total Impact Points


  • 2008-2015
    • Chinese Academy of Sciences
      • • Yunnan Observatories
      • • Graduate School
      Peping, Beijing, China
  • 2014
    • China Academy of Chinese Medical Sciences
      Peping, Beijing, China
  • 2008-2012
    • Huazhong University of Science and Technology
      • School of Physics
      Wu-han-shih, Hubei, China
  • 2009-2011
    • China University of Mining & Technology Beijing Graduate School
      Peping, Beijing, China