New light curves and photometric solutions of FP Lyn,FV CVn and V354 UMa are presented.We found that these three systems are W-subtype shallow contact binaries.In addition,it is obvious that the light curves of FP Lyn...New light curves and photometric solutions of FP Lyn,FV CVn and V354 UMa are presented.We found that these three systems are W-subtype shallow contact binaries.In addition,it is obvious that the light curves of FP Lyn and V354 UMa are asymmetric.Therefore,a hot spot was added on the primary star of FP Lyn and a dark spot was added on the secondary star of V354 UMa.At the same time,we added a third light to the photometric solution of FP Lyn for the final result.The obtained mass ratios and fill-out factors are q = 1.153 and f = 13.4% for FP Lyn,q = 1.075 and f = 4.6% for FV CVn,and q = 3.623 and f = 10.7% for V354 UMa respectively.The investigations of orbital period for these three systems indicate that the periods are variable.FP Lyn and V354 UMa were discovered to have secularly increasing components with rates of dp/dt = 4.19 ×10^-7 dyr^-1 and dp/dt = 7.70 ×10^-7 dyr^-1 respectively,which are feasibly caused by conservative mass transfer from the less massive component to the more massive component.In addition,some variable components were discovered for FV CVn,including a rate of dp/dt =-1.13 ×10^-6 dyr^-1 accompanied by a cyclic oscillation with amplitude and period of 0.0069 d and 10.65 yr respectively.The most likely explanation for the long-term decrease is angular momentum loss.The existence of an additional star is the most plausible explanation for the periodic variation.展开更多
TZ Eri and TU Her are both classic Algol-type systems(Algols). By observing and collecting times of minimum light, we constructed the O-C curves for the two systems. The long-time upward and downward parabolas shown i...TZ Eri and TU Her are both classic Algol-type systems(Algols). By observing and collecting times of minimum light, we constructed the O-C curves for the two systems. The long-time upward and downward parabolas shown in these diagrams are considered to be the result of the combination of mass transfer and angular momentum loss. The secular orbital period change rates are d P/dt = 4.74(±0.12) ×10-7 d yr-1 and d P/dt =-2.33(±0.01) × 10-6 d yr-1, respectively. There are also cyclic variations in their O-C curves which might be caused by the light-travel time effect(LTTE). A circumbinary star may exist in the TZ Eri system with a mass of at least 1.34 M⊙, while there are possibly two celestial bodies that almost follow a 2 : 1 resonance orbit around the TU Her binary pair. Their masses are at least 2.43 M⊙and 1.27 M⊙.展开更多
We present eight sets of new light curves for binaries FG Sct,VZ Lib and VZ Psc,which are all contact eclipsing binaries with short orbital periods.We carried out our observations from 2016 to 2017 using the 60-cm tel...We present eight sets of new light curves for binaries FG Sct,VZ Lib and VZ Psc,which are all contact eclipsing binaries with short orbital periods.We carried out our observations from 2016 to 2017 using the 60-cm telescope administered by National Astronomical Observatories,Chinese Academy of Sciences,the Holcomb Observatory at Butler University and the SARA-CT telescope in Chile.We firstly determined the orbital parameters of FG Sct using the O-C method and obtained photometric solutions utilizing the updated W-D program.We also studied its period variation and discovered that its orbital period is decreasing at a rate of 6.39(±0.24)×10^-8 d yr-1,which was likely caused by mass transfer from the primary component to the secondary component or angular momentum interchange between the two components via magnetic interactions.For VZ Lib and VZ Psc,we simultaneously analyzed their BV RI light curves in conjunction with the published radial velocities.In order to obtain the orbital parameters of VZ Lib,we also analyzed its period variation and revised cyclic change,which could be attributed to either the light-time effect due to a tertiary companion or magnetic activity cycle mechanism.We derived the periods of the tertiary component of VZ Lib to be 48.7(±0.1) yr or magnetic cycle to be 46.9(±1.9) yr.Strong emission lines at Ca II H+K,Hα,Hβ,Hγ and Ca II IRT were detected in the LAMOST spectra of VZ Psc,which imply chromospheric activities in this binary system.展开更多
This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010-October 2017. The stars from our study are located in the star-forming HII r...This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010-October 2017. The stars from our study are located in the star-forming HII region IC 5070. These objects were previously detected as either emission line stars, flare stars, T Tauri variables or Herbig Ae/Be stars. Photometric observations, especially concerning the long-term behavior of the objects, are missing in the literature. We present the first photometric monitoring for all stars from our study. The analysis of the obtained BV RI photometric data allows us to draw the conclusion that all investigated objects are variable stars. In the case of LkHα 146,we identified previously unknown periodicity in its photometric variability.展开更多
Wavelet transform is applied to reanalyze the low amplitude δ Scuti star HD 52788, which exhibits complex light variations with uncertain frequency solutions. We gain an insight into the strong instability of pulsati...Wavelet transform is applied to reanalyze the low amplitude δ Scuti star HD 52788, which exhibits complex light variations with uncertain frequency solutions. We gain an insight into the strong instability of pulsation present in the star. Based on an estimate of the star's physical parameters, its evolutionary status is determined. An attempt of asteroseismic modelling failed to predict the observed dense frequencies. Because of its varying pulsation spectrum, HD 52788 is a distinctive and very interesting object among δ Sct stars for testing current models of stellar evolution and pulsation.展开更多
It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a doub...It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a double carbon-oxygen white dwarf(CO WD) merges. It has been recently found that the nucleus of the bipolar planetary nebula Henize 2–428 consists of a double CO WD system that has a total mass of^1.76 M⊙, a mass ratio of^1 and an orbital period of^4.2 h, which is the first and only discovered progenitor candidate for an SN Ia predicted by the violent merger scenario. In this work, we aim to reproduce the evolutionary history of the central double CO WD of Henize 2–428. We find that the planetary nebula Henize 2–428 may originate from a primordial binary that has a^5.4 M⊙primary and a^2.7 M⊙secondary with an initial orbital period of^15.9 d. The double CO WD was formed after the primordial binary experienced two Roche-lobe overflows and two common-envelope ejection processes.According to our calculations, it takes about^840 Myr for the double CO WD to merge and form an SN Ia driven by gravitational wave radiation after their birth. To produce the current status of Henize 2–428,a large common-envelope parameter is needed. We also estimate that the rate of SNe Ia from the violent merger scenario is at most 2.9 × 10^(-4) yr^(-1), and that the delay time is in the range of^90 Myr to the Hubble time.展开更多
The radiative mechanism of black hole X-ray transients （BHXTs） in their quiescent states （defined as the 2-10 keV X-ray luminosity ≤ 10^34 erg s-1） remains unclear. In this work, we investigate the quasi-simultan...The radiative mechanism of black hole X-ray transients （BHXTs） in their quiescent states （defined as the 2-10 keV X-ray luminosity ≤ 10^34 erg s-1） remains unclear. In this work, we investigate the quasi-simultaneous quiescent state spectrum （including radio, infrared, optical, ultraviolet and X-ray） of two BHXTs, A0620-00 and XTE J1118＋480. We find that these two sources can be well described by a coupled accretion - jet model. More specifically, most of the emission （radio up to infrared, and the X-ray waveband） comes from the collimated relativistic jet. Emission from hot accretion flow is totally insignificant, and it can only be observed in mid-infrared （the synchrotron peak）. Emission from the outer cold disk is only evident in the UV band. These results are consistent with our previous investigation on the quiescent state of V404 Cyg and confirm that the quiescent state is jet-dominated.展开更多
Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented.These stars are located in the association Cepheus OB3,in t...Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented.These stars are located in the association Cepheus OB3,in the field of the young star V733 Cephei.Photometric observations,especially concerning the long-term variability of the stars,are missing in the literature.We present the first longterm V(RI)c monitoring for them,that cover 13 years.Results from our study indicate that all of the investigated stars manifest strong photometric variability.The presented paper is a part of our program for the photometric study of pre-main-sequence stars located in active star-forming regions.展开更多
We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Ga...We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ)Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ)The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB)systems;(ⅲ)All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR)systems;(ⅳ)The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ)The sum 0.871 M⊙of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M⊙assumed for the known contact binary stars.展开更多
The first multi-color light curve analysis of the AH Mic binary system is presented.This system has very few past observations from the southern hemisphere.We extracted the minima times from the light curves based on ...The first multi-color light curve analysis of the AH Mic binary system is presented.This system has very few past observations from the southern hemisphere.We extracted the minima times from the light curves based on the Markov Chain Monte Carlo(MCMC)approach and obtained a new ephemeris.To provide modern photometric light curve solutions,we used the Physics of Eclipsing Binaries(PHOEBE)software package and the MCMC approach.Light curve solutions yielded a system temperature ratio of 0.950,and we assumed a cold starspot for the hotter star based on the O’Connell effect.This analysis reveals that AH Mic is a W-subtype W UMa contact system with a fill-out factor of 21.3%and a mass ratio of 2.32.The absolute physical parameters of the components are estimated by using the Gaia Early Data Release 3(EDR3)parallax method to be M_(h)(M_(⊙))=0.702(26),M_(c)(M_(⊙))=1.629(104),R_(h)(R_(⊙))=0.852(21),R_(c)(R_(⊙))=1.240(28),L_(h)(L_(⊙))=0.618(3)and L_(c)(L_(⊙))=1.067(7).The orbital angular momentum of the AH Mic binary system was found to be 51.866(35).The components’positions of this system are plotted in the Hertzsprung-Russell diagram.展开更多
The Van Hoof effect is a phase shift existing between the radial velocity curves of hydrogen and metallic lines within the atmosphere of pulsating stars.In this article,we present a study of this phenomenon through th...The Van Hoof effect is a phase shift existing between the radial velocity curves of hydrogen and metallic lines within the atmosphere of pulsating stars.In this article,we present a study of this phenomenon through the spectra of the brightest pulsating star RR Lyr of RR Lyrae stars recorded for 22 yr.We based ourselves,on the one hand,on 1268 spectra(41 nights of observation)recorded between the years 1994 and 1997 at the Observatory of Haute Provence(OHP,France)previously observed by Chadid and Gillet,and on the other hand on 1569 spectra(46nights of observation)recorded at our Oukaimeden Observatory(Morocco)between 2015 and 2016.Through this study,we have detected information on atmospheric dynamics that had not previously been detected.Indeed,the Van Hoof effect which results in a clear correlation between the radial velocities of hydrogen and those of the metallic lines has been observed and analyzed at different Blazhko phases.A correlation between the radial velocities of different metallic lines located in the lower atmosphere has been observed as well.For the first time,we were able to show that the amplitude of the radial velocity curves deduced from the lines of hydrogen and that of FeⅡ(λ4923.921?)increases toward the minimum of the Blazhko cycle and decreases toward the maximum of the same Blazhko cycle.Furthermore,we found that the Van Hoof effect is also modulated by the Blazhko effect.Thus,toward the minimum of the Blazhko cycle the Van Hoof effect is more visible and at the maximum of the Blazhko cycle,this effect is minimal.We also observed the temporal evolution of the amplitudes of the radial velocities of the lower and upper atmosphere.When observed over a long time,we can interpret it as a function of the Blazhko phases.展开更多
Rotating Radio Transients(RRATs)are a relatively new subclass of pulsars that emit detectable radio bursts sporadically.We analyzed 10 RRATs observed using the Parkes telescope,with eight of these observed via the ult...Rotating Radio Transients(RRATs)are a relatively new subclass of pulsars that emit detectable radio bursts sporadically.We analyzed 10 RRATs observed using the Parkes telescope,with eight of these observed via the ultra-wide-bandwidth low-frequency(UWL)receiver.We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs.We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs.All of their integrated pulses follow a simple power law,consistent with the known range of pulsar spectral indices.Their average spectral indices of single pulses are-0.9,-1.2,and-1.0 respectively,which are within the known range of pulsar spectral indices.Additionally,we find that the spreads of single-pulse spectral indices for these RRATs(ranging from-3.5 to+0.5)are narrower compared to what has been observed in other RRATs.Notably,the average spectral index and scatter of single pulses are both relatively small.For the remaining five RRATs observed at the UWL receiver,we also provide the upper limits on fluence and flux density.In addition,we obtain the timing solution of PSR J1709-43.Our analysis shows that PSRs J1919+1745,J1709-43,and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.展开更多
We present the complete set of physical and geometrical parameters of the visual close binary system GJ 9830 for the first time by applying Al-Wardat’s complex method.This method combines magnitude difference from sp...We present the complete set of physical and geometrical parameters of the visual close binary system GJ 9830 for the first time by applying Al-Wardat’s complex method.This method combines magnitude difference from speckle interferometry,synthetic spectral energy distributions of the binary components which are constructed based on grids of Kurucz blanketed models(ATLAS9),and the orbital solution using Tokovinin’s dynamical method to estimate the parameters of individual components.The analysis of the system by employing synthetic photometry resulted in the following set of parameters:Teff= 6220 ± 100 K,log g = 4.30 ± 0.12,R = 1.10 ± 0.08 R⊙for the primary component and Teff= 4870 ± 100 K,log g = 4.60 ± 0.11,R = 0.709 ± 0.07 R⊙for the secondary component.The recently published dynamical parallax from the Gaia space mission was used to calculate the total mass of the binary system as 1.75 ± 0.06 M⊙,which coincides with those estimated using Al-Wardat’s method as MA= 1.18 ± 0.10 M⊙,MB= 0.75 ± 0.08 M⊙.The analysis of the system reveals that both components are characteristic of main sequence stars and have an age of around 1.4 ± 0.50 Gyr.The evolutionary tracks and isochrones of the system’s components are discussed,and the fragmentation process is suggested as the most likely process for the formation of the system.展开更多
By using the Lunar-based Ultraviolet Telescope （LUT） from 2014 December 2 to December 4, the first near-UV light curve of the well-known Algol-type binary TW Dra is reported, which is analyzed with the 2013 version ...By using the Lunar-based Ultraviolet Telescope （LUT） from 2014 December 2 to December 4, the first near-UV light curve of the well-known Algol-type binary TW Dra is reported, which is analyzed with the 2013 version of the W-D code. Our solutions confirmed that TW Dra is a semi-detached binary system where the secondary component fills its Roche lobe. The mass ratio and a high inclination are obtained （q = 0.47, i = 86.68°）. Based on 589 available data spanning more than one century, the complex period changes are studied. Secular increase and three cyclical changes are found in the corresponding orbital period analysis. The secular increase changes reveal mass transfer from the secondary component to the primary one at a rate of 6.8 × 10-7 M yr-1. One large cyclical change of 116.04 yr may be caused by disturbance of visual component ADS 9706B orbiting TW Dra （ADS 9706A）, while the other two cyclical changes with shorter periods of 22.47 and 37.27 yr can be explained as the result of two circumbinary companions that are orbiting around TW Dra, where the two companions are in simple 3 ： 5 orbit-rotation resonances. TW Dra itself is a basic binary in a possible sextuple system with the configuration （1 ＋ 1） ＋ （1 ＋ 1） ＋ （1 ＋ 1）, which further suggests that multiplicity may be a fairly common phenomenon in close binary systems.展开更多
V0405 Dra is a W UMa-type binary star.Based on the TESS data,we have conducted an orbital period study and performed a light curve analysis for the system.The orbital period study reveals that the O-C curve for V0405 ...V0405 Dra is a W UMa-type binary star.Based on the TESS data,we have conducted an orbital period study and performed a light curve analysis for the system.The orbital period study reveals that the O-C curve for V0405 Dra exhibits secular decrease at an extremely high rate of d P/dt=-2.71×10^(-6)day year^(-1),along with periodic variations characterized by an amplitude of A_(3)=0.0032 day and a period of P_(3)=1.413 years.The orbital periodic change is possibly due to the light-travel time effect resulting from an additional third body in the system,for which we estimate a minimum mass of M_(3)=0.77M_(⊙).By employing the 2013 version of the Wilson-Devinney(W-D)method to synthesize a light curve,we derived photometric solutions indicating that V0405 Dra is a new deep(f=68.7%)and low-mass ratio(q=0.175)contact binary.The fast decrease in its orbital period is likely caused by mass transfer from the more massive primary star to the less massive secondary star,or due to angular momentum loss.With further mass transfer and loss of angular momentum,the binary will gradually evolve into a tighter contact configuration,eventually leading to a merger into a single star,following the evolutionary paths suggested for such deep and low mass ratio contact binaries.展开更多
We present the results of a time-resolved photometric and time-series analysis of an RR Lyrae type star RR Gem. The main results are as follows: we found RR Gem’s pulsation period, 0.39689 d, and its V and I mean mag...We present the results of a time-resolved photometric and time-series analysis of an RR Lyrae type star RR Gem. The main results are as follows: we found RR Gem’s pulsation period, 0.39689 d, and its V and I mean magnitudes, 11.277(V) and 11.063(I) mag respectively. We confirm its variability type as RRab/BL because it manifests the Blazhko effect, and it also exhibits asymmetric light curves(steep ascending branches), periods from 0.3 to 1.0 d and amplitudes from 0.3 to 2 mag in V. They are fundamental mode pulsators.展开更多
We present a period analysis of the near-contact binary CN And using all available times of light minima. It is revealed that the orbital period exhibits a long-term decrease as well as a small-amplitude cyclic oscill...We present a period analysis of the near-contact binary CN And using all available times of light minima. It is revealed that the orbital period exhibits a long-term decrease as well as a small-amplitude cyclic oscillation. This result suggests that the secular period decrease at the rate of d P/dt =-1.4017 ×10-7 d yr-1 is caused by a combination of mass transfer and angular momentum loss due to magnetic braking. The periodic variation with an amplitude of A = 0.0036 d and a period of Pmod = 28.3542 yr should be rooted in the light-time effect of a third body, rather than cyclic magnetic activity.展开更多
We utilize the PAdova and TRieste Stellar Evolution Code(PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters.Multicolor-photometric ob...We utilize the PAdova and TRieste Stellar Evolution Code(PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters.Multicolor-photometric observations of AL Cas have been performed in 2016 and 2017. We use the WilsonDevinney(W-D) code to analyze the light curves and find that AL Cas is probably an A-subtype contact binary(f = 35.7±0.9%) with a mass ratio q = 0.6399±0.0230 and an effective temperature difference?T = 78 K. The mass-radius relation of a higher luminosity component for AL Cas is obtained by two methods: depending on calculation of the Roche lobe(DCRL method) and depending on calculation of the W-D code(DCWD method). Using this relationship with the PARSEC model, we investigate the component masses of AL Cas as M1 = 1.19±0.23 M⊙ with M2 = 0.76±0.18 M⊙ by the DCRL method and M1 = 1.22±0.26 M⊙ with M2 = 0.78±0.20 M ⊙ by the DCWD method. By means of the photometric studies, we examine the related physical properties of AL Cas with the latest findings. We update the orbital period(Porb = 0.50055593 d) of AL Cas according to six new times of light minimum together with those collected from the literature. Meanwhile, the(O-C)2 curve analysis suggests that the orbital period of AL Cas has a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 d. This cyclic change would be caused by the light-travel time effect from a third body. A similar mass of the third body(M3 sin i′= 0.279 M⊙) is derived from our two methods.展开更多
We present a study on pulsations of the high-amplitudeδScuti star YZ Boo based on photometric observations in Johnson V and R bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory（XAO）and t...We present a study on pulsations of the high-amplitudeδScuti star YZ Boo based on photometric observations in Johnson V and R bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory（XAO）and the Xinglong 85-cm telescope of National Astronomical Observatories,Chinese Academy of Sciences（NAOC）.Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics,with the fourth and fifth being newly detected.Thirtynine new times of maximum light are determined from the light curves,and combined with those in the literature,we construct the O-C diagram,derive a new ephemeris and determine a new value for the updated period of 0.104091579（2）.In addition,the O-C diagram reveals an increasing rate of period change for YZ Boo.Theoretical models are calculated and constrained with the observationally determined parameters of YZ Boo.The mass and age of YZ Boo are hence derived as M=1.61±0.05 M_⊙ and age=（1.44±0.14）×10~9 yr,respectively.With both the frequency of the fundamental radial mode and the rate of period change,YZ Boo is located at the post main sequence stage.展开更多
The best physical and geometrical parameters of the main sequence close visual binary system(CVBS), HIP 105947, are presented. These parameters have been constructed conclusively using Al-Wardat’s complex method for ...The best physical and geometrical parameters of the main sequence close visual binary system(CVBS), HIP 105947, are presented. These parameters have been constructed conclusively using Al-Wardat’s complex method for analyzing CVBSs, which is a method for constructing a synthetic spectral energy distribution(SED) for the entire binary system using individual SEDs for each component star. The model atmospheres are in its turn built using the Kurucz(ATLAS9) line-blanketed plane-parallel models. At the same time, the orbital parameters for the system are calculated using Tokovinin’s dynamical method for constructing the best orbits of an interferometric binary system. Moreover, the mass-sum of the components, as well as the ?θ and ?ρ residuals for the system, is introduced. The combination of Al-Wardat’s and Tokovinin’s methods yields the best estimations of the physical and geometrical parameters. The positions of the components in the system on the evolutionary tracks and isochrones are plotted and the formation and evolution of the system are discussed.展开更多
基金financial support from the Universidad Nacional Aut ónoma de México (UNAM) and DGAPA (PAPIIT IN 100918)supported by the National Natural Science Foundation of China (NSFC) (No. 11703016)+3 种基金by the Joint Research Fund in Astronomy (No. U1431105)by the Natural Science Foundation of Shandong Province (No. ZR2014AQ019)by the Young Scholars Program of Shandong University, Weihai (No. 20820171006)by the Open Research Program of Key Laboratory for the Structure and Evolution of Celestial Objects (No. OP201704)
文摘New light curves and photometric solutions of FP Lyn,FV CVn and V354 UMa are presented.We found that these three systems are W-subtype shallow contact binaries.In addition,it is obvious that the light curves of FP Lyn and V354 UMa are asymmetric.Therefore,a hot spot was added on the primary star of FP Lyn and a dark spot was added on the secondary star of V354 UMa.At the same time,we added a third light to the photometric solution of FP Lyn for the final result.The obtained mass ratios and fill-out factors are q = 1.153 and f = 13.4% for FP Lyn,q = 1.075 and f = 4.6% for FV CVn,and q = 3.623 and f = 10.7% for V354 UMa respectively.The investigations of orbital period for these three systems indicate that the periods are variable.FP Lyn and V354 UMa were discovered to have secularly increasing components with rates of dp/dt = 4.19 ×10^-7 dyr^-1 and dp/dt = 7.70 ×10^-7 dyr^-1 respectively,which are feasibly caused by conservative mass transfer from the less massive component to the more massive component.In addition,some variable components were discovered for FV CVn,including a rate of dp/dt =-1.13 ×10^-6 dyr^-1 accompanied by a cyclic oscillation with amplitude and period of 0.0069 d and 10.65 yr respectively.The most likely explanation for the long-term decrease is angular momentum loss.The existence of an additional star is the most plausible explanation for the periodic variation.
基金partly supported by the National Natural Science Foundation of China (Nos. 11573063 and 11611530685)the Key Science Foundation of Yunnan Province (No. 2017FA001)the CAS “Light of West China” Program and the CAS Interdisciplinary Innovation Team
文摘TZ Eri and TU Her are both classic Algol-type systems(Algols). By observing and collecting times of minimum light, we constructed the O-C curves for the two systems. The long-time upward and downward parabolas shown in these diagrams are considered to be the result of the combination of mass transfer and angular momentum loss. The secular orbital period change rates are d P/dt = 4.74(±0.12) ×10-7 d yr-1 and d P/dt =-2.33(±0.01) × 10-6 d yr-1, respectively. There are also cyclic variations in their O-C curves which might be caused by the light-travel time effect(LTTE). A circumbinary star may exist in the TZ Eri system with a mass of at least 1.34 M⊙, while there are possibly two celestial bodies that almost follow a 2 : 1 resonance orbit around the TU Her binary pair. Their masses are at least 2.43 M⊙and 1.27 M⊙.
基金supported by the Joint Research Fund in Astronomy (U1631236 and U1431114) under cooperative agreement between the NSFC and CASpartially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories, Chinese Academy of Sciences
文摘We present eight sets of new light curves for binaries FG Sct,VZ Lib and VZ Psc,which are all contact eclipsing binaries with short orbital periods.We carried out our observations from 2016 to 2017 using the 60-cm telescope administered by National Astronomical Observatories,Chinese Academy of Sciences,the Holcomb Observatory at Butler University and the SARA-CT telescope in Chile.We firstly determined the orbital parameters of FG Sct using the O-C method and obtained photometric solutions utilizing the updated W-D program.We also studied its period variation and discovered that its orbital period is decreasing at a rate of 6.39(±0.24)×10^-8 d yr-1,which was likely caused by mass transfer from the primary component to the secondary component or angular momentum interchange between the two components via magnetic interactions.For VZ Lib and VZ Psc,we simultaneously analyzed their BV RI light curves in conjunction with the published radial velocities.In order to obtain the orbital parameters of VZ Lib,we also analyzed its period variation and revised cyclic change,which could be attributed to either the light-time effect due to a tertiary companion or magnetic activity cycle mechanism.We derived the periods of the tertiary component of VZ Lib to be 48.7(±0.1) yr or magnetic cycle to be 46.9(±1.9) yr.Strong emission lines at Ca II H+K,Hα,Hβ,Hγ and Ca II IRT were detected in the LAMOST spectra of VZ Psc,which imply chromospheric activities in this binary system.
基金funded by the National Aeronautics and Space Administrationthe National Science Foundation+1 种基金partly supported by the National Science Fund of the Ministry of Education and Science of Bulgaria under grants DM 08-2/2016, DN 08-1/2016, DN 08-20/2016 and DN 18-13/2017funds of the project RD-08112/2018 of the University of Shumen
文摘This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010-October 2017. The stars from our study are located in the star-forming HII region IC 5070. These objects were previously detected as either emission line stars, flare stars, T Tauri variables or Herbig Ae/Be stars. Photometric observations, especially concerning the long-term behavior of the objects, are missing in the literature. We present the first photometric monitoring for all stars from our study. The analysis of the obtained BV RI photometric data allows us to draw the conclusion that all investigated objects are variable stars. In the case of LkHα 146,we identified previously unknown periodicity in its photometric variability.
基金Support by the National Natural Science Foundation of China.
文摘Wavelet transform is applied to reanalyze the low amplitude δ Scuti star HD 52788, which exhibits complex light variations with uncertain frequency solutions. We gain an insight into the strong instability of pulsation present in the star. Based on an estimate of the star's physical parameters, its evolutionary status is determined. An attempt of asteroseismic modelling failed to predict the observed dense frequencies. Because of its varying pulsation spectrum, HD 52788 is a distinctive and very interesting object among δ Sct stars for testing current models of stellar evolution and pulsation.
基金supported by the National Natural Science Foundation of China (Nos. 11873085, 11673059 and 11521303)Chinese Academy of Sciences (Nos. QYZDB-SSW-SYS001 and KJZD-EW-M06-01)Yunnan Province (Nos. 2017HC018 and 2018FB005)
文摘It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a double carbon-oxygen white dwarf(CO WD) merges. It has been recently found that the nucleus of the bipolar planetary nebula Henize 2–428 consists of a double CO WD system that has a total mass of^1.76 M⊙, a mass ratio of^1 and an orbital period of^4.2 h, which is the first and only discovered progenitor candidate for an SN Ia predicted by the violent merger scenario. In this work, we aim to reproduce the evolutionary history of the central double CO WD of Henize 2–428. We find that the planetary nebula Henize 2–428 may originate from a primordial binary that has a^5.4 M⊙primary and a^2.7 M⊙secondary with an initial orbital period of^15.9 d. The double CO WD was formed after the primordial binary experienced two Roche-lobe overflows and two common-envelope ejection processes.According to our calculations, it takes about^840 Myr for the double CO WD to merge and form an SN Ia driven by gravitational wave radiation after their birth. To produce the current status of Henize 2–428,a large common-envelope parameter is needed. We also estimate that the rate of SNe Ia from the violent merger scenario is at most 2.9 × 10^(-4) yr^(-1), and that the delay time is in the range of^90 Myr to the Hubble time.
基金supported by the National Basic Research Program of China(973 Program,Grant 2014CB845800)the National Natural Science Foundation of China(Grant Nos.11203057,11103061,11133005 and 11121062)the Strategic Priority Research Program“The Emergence of Cosmological Structures”of the Chinese Academy of Sciences(Grant XDB09000000)
文摘The radiative mechanism of black hole X-ray transients （BHXTs） in their quiescent states （defined as the 2-10 keV X-ray luminosity ≤ 10^34 erg s-1） remains unclear. In this work, we investigate the quasi-simultaneous quiescent state spectrum （including radio, infrared, optical, ultraviolet and X-ray） of two BHXTs, A0620-00 and XTE J1118＋480. We find that these two sources can be well described by a coupled accretion - jet model. More specifically, most of the emission （radio up to infrared, and the X-ray waveband） comes from the collimated relativistic jet. Emission from hot accretion flow is totally insignificant, and it can only be observed in mid-infrared （the synchrotron peak）. Emission from the outer cold disk is only evident in the UV band. These results are consistent with our previous investigation on the quiescent state of V404 Cyg and confirm that the quiescent state is jet-dominated.
基金partly supported by the National Science Fund of the Ministry of Education and Science of Bulgaria under grant DN 18-10/2017funds of the project RD-08-125/2021 of the University of Shumen。
文摘Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented.These stars are located in the association Cepheus OB3,in the field of the young star V733 Cephei.Photometric observations,especially concerning the long-term variability of the stars,are missing in the literature.We present the first longterm V(RI)c monitoring for them,that cover 13 years.Results from our study indicate that all of the investigated stars manifest strong photometric variability.The presented paper is a part of our program for the photometric study of pre-main-sequence stars located in active star-forming regions.
基金supported partly by project DN08/20 of Scientific Foundation of the Bulgarian Ministry of Education and Scienceproject RD 0-92/2019 of Shumen Universitythe support of the private IRIDA OBSERVATORY。
文摘We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ)Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ)The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB)systems;(ⅲ)All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR)systems;(ⅳ)The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ)The sum 0.871 M⊙of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M⊙assumed for the known contact binary stars.
基金funded in part by the National Science Foundation(NSF 1517474,1909109)the National Aeronautics and Space Administration(NASA 17-ADAP17-68)。
文摘The first multi-color light curve analysis of the AH Mic binary system is presented.This system has very few past observations from the southern hemisphere.We extracted the minima times from the light curves based on the Markov Chain Monte Carlo(MCMC)approach and obtained a new ephemeris.To provide modern photometric light curve solutions,we used the Physics of Eclipsing Binaries(PHOEBE)software package and the MCMC approach.Light curve solutions yielded a system temperature ratio of 0.950,and we assumed a cold starspot for the hotter star based on the O’Connell effect.This analysis reveals that AH Mic is a W-subtype W UMa contact system with a fill-out factor of 21.3%and a mass ratio of 2.32.The absolute physical parameters of the components are estimated by using the Gaia Early Data Release 3(EDR3)parallax method to be M_(h)(M_(⊙))=0.702(26),M_(c)(M_(⊙))=1.629(104),R_(h)(R_(⊙))=0.852(21),R_(c)(R_(⊙))=1.240(28),L_(h)(L_(⊙))=0.618(3)and L_(c)(L_(⊙))=1.067(7).The orbital angular momentum of the AH Mic binary system was found to be 51.866(35).The components’positions of this system are plotted in the Hertzsprung-Russell diagram.
文摘The Van Hoof effect is a phase shift existing between the radial velocity curves of hydrogen and metallic lines within the atmosphere of pulsating stars.In this article,we present a study of this phenomenon through the spectra of the brightest pulsating star RR Lyr of RR Lyrae stars recorded for 22 yr.We based ourselves,on the one hand,on 1268 spectra(41 nights of observation)recorded between the years 1994 and 1997 at the Observatory of Haute Provence(OHP,France)previously observed by Chadid and Gillet,and on the other hand on 1569 spectra(46nights of observation)recorded at our Oukaimeden Observatory(Morocco)between 2015 and 2016.Through this study,we have detected information on atmospheric dynamics that had not previously been detected.Indeed,the Van Hoof effect which results in a clear correlation between the radial velocities of hydrogen and those of the metallic lines has been observed and analyzed at different Blazhko phases.A correlation between the radial velocities of different metallic lines located in the lower atmosphere has been observed as well.For the first time,we were able to show that the amplitude of the radial velocity curves deduced from the lines of hydrogen and that of FeⅡ(λ4923.921?)increases toward the minimum of the Blazhko cycle and decreases toward the maximum of the same Blazhko cycle.Furthermore,we found that the Van Hoof effect is also modulated by the Blazhko effect.Thus,toward the minimum of the Blazhko cycle the Van Hoof effect is more visible and at the maximum of the Blazhko cycle,this effect is minimal.We also observed the temporal evolution of the amplitudes of the radial velocities of the lower and upper atmosphere.When observed over a long time,we can interpret it as a function of the Blazhko phases.
基金supported by the Major Science and Technology Program of Xinjiang Uygur Autonomous Region(grant no.2022A03013-4)the Zhejiang Provincial Natural Science Foundation of China(grant no.LY23A030001)+4 种基金the National SKA Program of China(grant no.2020SKA0120100,2022YFC2205201,2020SKA0120200)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(grant no.2022D01D85)the National Natural Science Foundation of China(NSFC,grant Nos.12041304,12273100,and 12041303)the West Light Foundation of Chinese Academy of Sciences(grant no.WLFC 2021-XBQNXZ-027)the open program of the Key Laboratory of Xinjiang Uygur Autonomous Region(grant no.2020D04049)。
文摘Rotating Radio Transients(RRATs)are a relatively new subclass of pulsars that emit detectable radio bursts sporadically.We analyzed 10 RRATs observed using the Parkes telescope,with eight of these observed via the ultra-wide-bandwidth low-frequency(UWL)receiver.We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs.We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs.All of their integrated pulses follow a simple power law,consistent with the known range of pulsar spectral indices.Their average spectral indices of single pulses are-0.9,-1.2,and-1.0 respectively,which are within the known range of pulsar spectral indices.Additionally,we find that the spreads of single-pulse spectral indices for these RRATs(ranging from-3.5 to+0.5)are narrower compared to what has been observed in other RRATs.Notably,the average spectral index and scatter of single pulses are both relatively small.For the remaining five RRATs observed at the UWL receiver,we also provide the upper limits on fluence and flux density.In addition,we obtain the timing solution of PSR J1709-43.Our analysis shows that PSRs J1919+1745,J1709-43,and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.
文摘We present the complete set of physical and geometrical parameters of the visual close binary system GJ 9830 for the first time by applying Al-Wardat’s complex method.This method combines magnitude difference from speckle interferometry,synthetic spectral energy distributions of the binary components which are constructed based on grids of Kurucz blanketed models(ATLAS9),and the orbital solution using Tokovinin’s dynamical method to estimate the parameters of individual components.The analysis of the system by employing synthetic photometry resulted in the following set of parameters:Teff= 6220 ± 100 K,log g = 4.30 ± 0.12,R = 1.10 ± 0.08 R⊙for the primary component and Teff= 4870 ± 100 K,log g = 4.60 ± 0.11,R = 0.709 ± 0.07 R⊙for the secondary component.The recently published dynamical parallax from the Gaia space mission was used to calculate the total mass of the binary system as 1.75 ± 0.06 M⊙,which coincides with those estimated using Al-Wardat’s method as MA= 1.18 ± 0.10 M⊙,MB= 0.75 ± 0.08 M⊙.The analysis of the system reveals that both components are characteristic of main sequence stars and have an age of around 1.4 ± 0.50 Gyr.The evolutionary tracks and isochrones of the system’s components are discussed,and the fragmentation process is suggested as the most likely process for the formation of the system.
基金supported by the Key Research Program of Chinese Academy of Sience (KGEDEW-603)the National Natural Science Foundation of China (Nos.11403095,11133007 and 11325315)+2 种基金the Yunnan Natural Science Foundation (2014FB187)the Science Foundation of Yunnan Province (Grant No.2012HC011)the Strategic Priority Research Program “The Emergence of Cosmological Structures” of the Chinese Academy of Sciences (Grant No.XDB09010202)
文摘By using the Lunar-based Ultraviolet Telescope （LUT） from 2014 December 2 to December 4, the first near-UV light curve of the well-known Algol-type binary TW Dra is reported, which is analyzed with the 2013 version of the W-D code. Our solutions confirmed that TW Dra is a semi-detached binary system where the secondary component fills its Roche lobe. The mass ratio and a high inclination are obtained （q = 0.47, i = 86.68°）. Based on 589 available data spanning more than one century, the complex period changes are studied. Secular increase and three cyclical changes are found in the corresponding orbital period analysis. The secular increase changes reveal mass transfer from the secondary component to the primary one at a rate of 6.8 × 10-7 M yr-1. One large cyclical change of 116.04 yr may be caused by disturbance of visual component ADS 9706B orbiting TW Dra （ADS 9706A）, while the other two cyclical changes with shorter periods of 22.47 and 37.27 yr can be explained as the result of two circumbinary companions that are orbiting around TW Dra, where the two companions are in simple 3 ： 5 orbit-rotation resonances. TW Dra itself is a basic binary in a possible sextuple system with the configuration （1 ＋ 1） ＋ （1 ＋ 1） ＋ （1 ＋ 1）, which further suggests that multiplicity may be a fairly common phenomenon in close binary systems.
基金supported by the Joint Research Fund in Astronomy(grant No.U1631108)under a cooperative agreement between the National Natural Science Foundation of China(NSFC)the Chinese Academy of Sciences(CAS)the Chinese National Natural Science Foundation of China(NSFC,grant No.12103030)。
文摘V0405 Dra is a W UMa-type binary star.Based on the TESS data,we have conducted an orbital period study and performed a light curve analysis for the system.The orbital period study reveals that the O-C curve for V0405 Dra exhibits secular decrease at an extremely high rate of d P/dt=-2.71×10^(-6)day year^(-1),along with periodic variations characterized by an amplitude of A_(3)=0.0032 day and a period of P_(3)=1.413 years.The orbital periodic change is possibly due to the light-travel time effect resulting from an additional third body in the system,for which we estimate a minimum mass of M_(3)=0.77M_(⊙).By employing the 2013 version of the Wilson-Devinney(W-D)method to synthesize a light curve,we derived photometric solutions indicating that V0405 Dra is a new deep(f=68.7%)and low-mass ratio(q=0.175)contact binary.The fast decrease in its orbital period is likely caused by mass transfer from the more massive primary star to the less massive secondary star,or due to angular momentum loss.With further mass transfer and loss of angular momentum,the binary will gradually evolve into a tighter contact configuration,eventually leading to a merger into a single star,following the evolutionary paths suggested for such deep and low mass ratio contact binaries.
文摘We present the results of a time-resolved photometric and time-series analysis of an RR Lyrae type star RR Gem. The main results are as follows: we found RR Gem’s pulsation period, 0.39689 d, and its V and I mean magnitudes, 11.277(V) and 11.063(I) mag respectively. We confirm its variability type as RRab/BL because it manifests the Blazhko effect, and it also exhibits asymmetric light curves(steep ascending branches), periods from 0.3 to 1.0 d and amplitudes from 0.3 to 2 mag in V. They are fundamental mode pulsators.
基金supported by the Joint Research Funds in Astronomy (U1731110, U1731106 and U1531108) under cooperative agreement between the National Natural Science Foundation of China and the Chinese Academy of Sciencespartially supported by the National Natural Science Foundation of China (11703020)
文摘We present a period analysis of the near-contact binary CN And using all available times of light minima. It is revealed that the orbital period exhibits a long-term decrease as well as a small-amplitude cyclic oscillation. This result suggests that the secular period decrease at the rate of d P/dt =-1.4017 ×10-7 d yr-1 is caused by a combination of mass transfer and angular momentum loss due to magnetic braking. The periodic variation with an amplitude of A = 0.0036 d and a period of Pmod = 28.3542 yr should be rooted in the light-time effect of a third body, rather than cyclic magnetic activity.
基金supported by the program of the Light in China’s Western Region (LCWR,Grant No. 2015-XBQN-A-02)the National Natural Science Foundation of China (Grant Nos. 11273051, 11661161016, 11473024 and 11863005)+1 种基金the 13th Fiveyear Information Plan of Chinese Academy of Sciences (Grant No. XXH13503-03-107)the Youth Innovation Promotion Association CAS (Grant No. 2018080)
文摘We utilize the PAdova and TRieste Stellar Evolution Code(PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters.Multicolor-photometric observations of AL Cas have been performed in 2016 and 2017. We use the WilsonDevinney(W-D) code to analyze the light curves and find that AL Cas is probably an A-subtype contact binary(f = 35.7±0.9%) with a mass ratio q = 0.6399±0.0230 and an effective temperature difference?T = 78 K. The mass-radius relation of a higher luminosity component for AL Cas is obtained by two methods: depending on calculation of the Roche lobe(DCRL method) and depending on calculation of the W-D code(DCWD method). Using this relationship with the PARSEC model, we investigate the component masses of AL Cas as M1 = 1.19±0.23 M⊙ with M2 = 0.76±0.18 M⊙ by the DCRL method and M1 = 1.22±0.26 M⊙ with M2 = 0.78±0.20 M ⊙ by the DCWD method. By means of the photometric studies, we examine the related physical properties of AL Cas with the latest findings. We update the orbital period(Porb = 0.50055593 d) of AL Cas according to six new times of light minimum together with those collected from the literature. Meanwhile, the(O-C)2 curve analysis suggests that the orbital period of AL Cas has a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 d. This cyclic change would be caused by the light-travel time effect from a third body. A similar mass of the third body(M3 sin i′= 0.279 M⊙) is derived from our two methods.
基金support from the National Natural Science Foundation of China(NSFC,Grant No.11273051)partially supported by the Chinese Academy of Sciences(CAS) “Light of West China” program(2015-XBQN-A-02)+4 种基金supported by the Strategic Priority Research Program of CAS(Grant No.XDB23040100)support from the Joint Fund of Astronomy of NSFC and CAS(Grant U1231202 and 11673003)the National Basic Research Program of China(973 Program 2014CB845700 and 2013CB834900)the LAMOST FELLOWSHIP supported by Special Funding for Advanced Users,budgeted and administrated by the Center for Astronomical MegaScience,Chinese Academy of Sciences(CAMS)support from the NSFC(No.11403088)
文摘We present a study on pulsations of the high-amplitudeδScuti star YZ Boo based on photometric observations in Johnson V and R bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory（XAO）and the Xinglong 85-cm telescope of National Astronomical Observatories,Chinese Academy of Sciences（NAOC）.Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics,with the fourth and fifth being newly detected.Thirtynine new times of maximum light are determined from the light curves,and combined with those in the literature,we construct the O-C diagram,derive a new ephemeris and determine a new value for the updated period of 0.104091579（2）.In addition,the O-C diagram reveals an increasing rate of period change for YZ Boo.Theoretical models are calculated and constrained with the observationally determined parameters of YZ Boo.The mass and age of YZ Boo are hence derived as M=1.61±0.05 M_⊙ and age=（1.44±0.14）×10~9 yr,respectively.With both the frequency of the fundamental radial mode and the rate of period change,YZ Boo is located at the post main sequence stage.
基金the Human Development Fund for the scholarshipHadhramout University in Yemen for ongoing support
文摘The best physical and geometrical parameters of the main sequence close visual binary system(CVBS), HIP 105947, are presented. These parameters have been constructed conclusively using Al-Wardat’s complex method for analyzing CVBSs, which is a method for constructing a synthetic spectral energy distribution(SED) for the entire binary system using individual SEDs for each component star. The model atmospheres are in its turn built using the Kurucz(ATLAS9) line-blanketed plane-parallel models. At the same time, the orbital parameters for the system are calculated using Tokovinin’s dynamical method for constructing the best orbits of an interferometric binary system. Moreover, the mass-sum of the components, as well as the ?θ and ?ρ residuals for the system, is introduced. The combination of Al-Wardat’s and Tokovinin’s methods yields the best estimations of the physical and geometrical parameters. The positions of the components in the system on the evolutionary tracks and isochrones are plotted and the formation and evolution of the system are discussed.
