Pulsation and Long-Term Variability of the High-Amplitude δ Scuti Star AD Canis Minoris

Time-series photometry was made for the large-amplitude δ Scuti star AD CMi in 2005 and 2006. High-quality photometric data provided in the literature were used to analyze the pulsation of the star, with the derived multiple frequencies fitted to our new data. Besides the dominant frequency and its harmonics, one low frequency (2.27402 c d -1) is discovered, which provides a reasonable interpretation for the long-noticed luminosity variation at the maximum and minimum light. Combining the nine new times of light maxima determined from the new data with the 64 times collected from the literature, we analyzed the long-term variability of AD CMi with the O - C technique. The results provide the updated value of period of 0.122974478 days, and seem to be in favor of the model of combination of the evolutionary effect and light-time effect of a binary system, of which some parameters are hereby deduced.     

Pulsation analysis of the high amplitude δ Scuti star CW Serpentis

Time-series photometric observations were made for the high amplitudeδScuti star CW Ser between 2011 and 2012 at the Xinglong Station of National Astronomical Observatories,Chinese Academy of Sciences.After performing the frequency analysis of the light curves,we confirmed the fundamental frequency of f=5.28677 c d 1,together with seven harmonics of the fundamental frequency,which are newly detected.No additional frequencies were detected.The O C diagram,produced with the 21 newly determined times of maximum light combined with those provided in the literature,helps to obtain a new ephemeris formula of the times of maximum light with the pulsation period of 0.189150355±0.000000003 d.     

Eclipsing binary XZ CMi in a hierarchical quadruple system

The new complete BV Rc Ic light curves and spectra of the short-period eclipsing binary XZ CMi are presented. The results from the combined analysis based on the photometric and spectroscopic data show that XZ CMi is a near contact binary with the secondary component filling its critical Roche lobe while the primary filling 91% of its Roche lobe. The investigation of the O-C diagram reveals that its orbital period is continuously increasing, which is consistent with the derived configuration and caused by the mass transfer from the less massive star to the more massive one. In addition, an obvious periodic modulation with the amplitude of0.0187(±0.0016) d and a high eccentric of 0.86(±0.04) is detected, which could be the results of the light time effect as a third star with the mass no less than 0.42(±0.09) M⊙orbiting around the central eclipsing binary once every 95.7(±2.1) yr. Furthermore, we found a visual companion star at 2.4′′ east by south of this system at a much greater distance by direct image. The large third light contribution found from the light curve analysis could be well explained by the existence of the third star and the fourth visual one.The similar parallax and proper motion imply that the components of this hierarchical quadruple system might be bounded by gravitation. Spectroscopic observations for two visual components were carried out by the LAMOST and 2.16 m telescopes, respectively. Their different values of [Fe/H] suggest that they were not born from the same origin. Thus, XZ CMi system is an interesting and important target to study the formation of the multiple stars.     

The high-amplitude δ Scuti variable CY Aqr is probably a triple system

Data representing 864 times of light maxima of the high-amplitude δ Scuti star CY Aqr were collected from the literature,based on which,long-term period changes of the variable star were investigated.A revised period and new ephemerides were given for the pulsating star.Remarkable cyclic variations were found in the O-C residuals which can be attributed to the light-time effects due to probable unseen components of the object.By using Kopal's method,the orbital parameters of the supposed component stars were derived.The solution suggests that CY Aqr is very probably in a triple system orbited eccentrically by two low-mass companions with periods of 54.2 and 47.3 yr.The lower limits on masses were estimated as0.04 M_⊙and 0.02 M_⊙,respectively,for the two hidden companions.     

High amplitude δ Scuti star BO Lyn with evidence of a late A-type companion in an elliptical orbit

We present 145 times of light maximum for high amplitude δ Scuti star BO Lyn based on several sky surveys(CRTS,DASCH,NSVS,OMC and Super WASP)and our photometric observations.Combining with the data in literature,a total of 179 times of light maximum are used to analyze the O-C diagram of BO Lyn.We find that it can be described by an upward parabolic component and a periodic variation with a period of 34.5±0.1 yr.The latter could be caused by the light travel time effect as a result of an additional companion orbiting in a highly elliptical orbit(e=0.64±0.03).Our study indicates that the companion’s luminosity cannot be ignored,and it should be a late A-type main-sequence star.The long-term period change of BO Lyn is also detected,and its value,1.52±0.26×10~(-3)d Myr~(-1),is consistent with evolutionary models.We suggest that more spectroscopic and photometric observations are needed in the future to confirm the nature of the BO Lyn system.     

LO And: an A-subtype contact binary with a very cool third component

Despite the intensive investigations since the discovery of LO And approximately 60 yr ago, its evolutionary status and subtype are still a matter of controversy. By simultaneously modeling the radialvelocity curves and new light curves with the Wilson-Devinney code, we present new geometric,photometric and absolute parameters for this system. The simultaneous solution suggests that LO And is an A-subtype contact binary with a contact degree of 32.4%. The absolute parameters are modified to become M_1= 1.409 M⊙, M_2= 0.449 M⊙, R_1= 1.36 R⊙and R_2= 0.83 R⊙. From our observations and data from surveys, we determined 334 eclipse timings. The O-C diagram, constructed from the new eclipse timings and those reported in the literature, reveals a secular increase and a cyclic variation in its orbital period. The former is caused by conservative mass transfer from the secondary component with less mass to the primary one with more mass. The latter may be explained by either the cyclic magnetic activity on the two components or the light-time effect due to a third body. With the absolute physical parameters,we investigated its evolutionary status, and find that LO And is an unevolved contact binary undergoing thermal relaxation oscillation, which will eventually coalesce into a single star with rapid rotation.     

Photometric study and preliminary elements of the low-mass ratio W UMa system ASAS 021209+2708.3

We present CCD B and V light curves,obtained in the year 2006,and a photometric solution of the low-mass ratio contact binary ASAS 021209+2708.3. With our data we were able to determine six new times of minimum light and refine the orbital period of the system to 0.3181963 days.The light curves are analyzed using the 2003 version of the Wilson-Devinney program and the analysis was performed with and without adding a spot on the surface of one star because the light curves appear to exhibit a typical O’Conne...     

Investigation of near-contact semi-detached binary W UMi through observations and evolutionary models

W UMi is a near contact, semi-detached, double-lined eclipsing binary star with an orbital period of 1.7 d. Simultaneous analysis of new BV R multi-color light curves and radial velocity data yields the main astrophysical parameters of the binary and its component stars. We determined mass and radius to be M_1 = 3.22 ± 0.08 M_⊙, R_1 = 3.63 ± 0.04 R_⊙ for the primary star and M_2 = 1.44 ± 0.05 M_⊙,R_2 = 3.09 ± 0.03 R_⊙ for the secondary star. Based on analysis of mid-eclipse times, variation in the orbital period is represented by a cyclic term and a downward parabola. Mass loss from the system is suggested for a secular decrease(-0.02 s yr~(-1)) in the period. Both the mechanisms of a hypothetical tertiary star orbiting around W UMi and the surface magnetic activity of the less massive cooler companion were used to interpret periodic changes. Observational parameters were found to be consistent with binary stellar evolution models produced in the non-conservative approach of MESA at a higher metallicity than the Sun and an age of about 400 Myr for the system. Evidence that the system is rich in metal was obtained from spectral and kinematic analysis as well as evolution models. W UMi, a high mass ratio system compared to classical semi-detached binaries, is an important example since it is estimated from binary evolutionary models that the system may reach its contact phase in a short time interval.     

RT Leonis Minoris： an Unstable W Ursae Majoris System with a Spotted Component

Complete BV light curves of the W UMa type binary RT LMi are presented. From the observations, four times of minimum light were determined. Based on the new times of minimum light and those collected from the literature, changes in the orbital period of the system were found and analyzed with Kalimeris et al.'s method. The result shows that the orbital period possibly oscillates with a cycle of about 64 years and an amplitude of 1.2 × 10-6 days. The present CCD photometric observations reveal that the light curves are obviously asymmetrical, and show a positive O'Connell effect, while the light curves obtained in 1982 exhibit a negative O'Connell effect. The present light curves were analyzed by means of the latest version of the Wilson-Devinney code, which was also used to correct the photometric effects, including the distortion on the radial-velocity curves obtained by Rucinski et al. The following absolute dimensions have been derived: MI -1.28 ±0.08 M⊙, M2 = 0.48 ±0.06 M⊙, R1 = 1.28 ±0.06 R⊙,     

Non-sinusoidal transit timing variations for the exoplanet HAT-P-12b

Considering the importance of investigating the transit timing variations(TTVs) of transiting exoplanets,we present a follow-up study of HAT-P-12 b.We include six new light curves observed between2011 and 2015 from three different observatories,in association with 25 light curves taken from the published literature.The sample of the data used thus covers a time span of ～10.2 years with a large coverage of epochs(1160) for the transiting events of the exoplanet HAT-P-12 b.The light curves are utilized to determine the orbital parameters and conduct an investigation of possible TTVs.The new linear ephemeris shows a large value of reduced χ~2,i.e.X~2_(red)(23)=7.93,and the sinusoidal fitting using the prominent frequency coming from a periodogram shows a reduced χ~2 around 4.Based on these values and the corresponding O-C diagrams,we suspect the presence of a possible non-sinusoidal TTV in this planetary system.Finally,we find that a scenario with an additional non-transiting exoplanet could explain this TTV with an even smaller reduced χ~2 value of around 2.     

A study of the global magnetic activity of the star Kepler-17 using light curve inversion with bipartite regularization

A new method of light curve inversion with bipartite regularization(LIBR),which is complementary to the previous treatments by Bonomo and Lanza and Estrela and Valio,is used to reconstruct the physical properties of star spots on the solar-type star Kepler-17 by using the full Q1-Q17 data set.The Markov Chain Monte Carlo(MCMC) method was applied to find the best profile of the reconstructed surface.The known value of the rotation inclination of Kepler-17 allows the generation of a star spot model in a sequence of stellar rotation with a period of 12.26 d.Because of the nature of the light curve inversion,the spot model is limited to the equatorial region.We also investigated the starspot lifetimes of Kepler-17 utilizing the MCMC method.Combined with the LIBR inversion results,it was found that the star spots typically last from one to several stellar rotations.From the time evolution of the spot size,a magnetic cycle period of 437 d can be derived.This value is comparatively shorter than the solar cycle which might be a consequence of the younger age(～1.78 Gyr) of Kepler-17.The light curve of Kepler-17 is characterized by the presence of large-amplitude variation caused by star spots but no superflare activity.An interesting possibility is that the magnetic energy stored in the star spot regions could have been constantly dissipated by electrodynamic interaction between the central star and the hot Jupiter,Kepler-17 b,via a lower-level energy release process.     

Pulsations of the High-Amplitude δ Scuti star YZ Bootis

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.     

Photometric analysis of the eclipsing polar MN Hya

As an eclipsing polar with a 3.39 h orbital period, MN Hya was going through a state change when we observed it during 2009–2016. Ten new mid-eclipse times, along with others obtained from literature, allow us to give a new ephemeris. The residuals of a linear fit show that period decreased during the phase of state change, which means angular momentum was lost during this phase. The associated X-ray observation indicates the mass accretion rate was about 3.6 × 10~(-9) M⊙yr~(-1). The period decrease indicates that at least 60% of mass being transferred from the secondary was lost,maybe in the form of spherically symmetric stellar wind. In the high state, the data show the intensity of flickering reduced when the system had a higher accretion rate, and that flickering sticks out with a primary timescale of about 2 min, which implies the position of the threading point was about 30 white dwarf radii above its surface. The trend of light curves for the system in its high state follows that of the low state for a large fraction of the phase interval from phase 0 to phase 0.4 since, starting at phase0.4, the cyclotron feature is visible, and the primary intensity hump of the light curves near phase 0.7 when the system is in the high state did not appear on the curve when it was in the low state. Those facts contradict predictions of the two-pole model.     

Identifying Carbon stars from the LAMOST pilot survey with the efficient manifold ranking algorithm

Carbon stars are excellent kinematic tracers of galaxies and can serve as a viable standard candle,so it is worthwhile to automatically search for them in a large amount of spectra.In this paper,we apply the efficient manifold ranking algorithm to search for carbon stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) pilot survey,whose performance and robustness are verified comprehensively with four test experiments.Using this algorithm,we find a total of183 carbon stars,and 158 of them are new findings.According to different spectral features,our carbon stars are classified as 58 C-H stars,11 C-H star candidates,56C-R stars,ten C-R star candidates,30 C-N stars,three C-N star candidates,and four C-J stars.There are also ten objects which have no spectral type because of low spectral quality,and a composite spectrum consisting of a white dwarf and a carbon star.Applying the support vector machine algorithm,we obtain the linear optimum classification plane in the J — H versus H — K_s color diagram which can be used to distinguish C-H from C-N stars with their J — H and H — K_s colors.In addition,we identify 18 dwarf carbon stars with their relatively high proper motions,and find three carbon stars with FUV detections likely have optical invisible companions by cross matching with data from the Galaxy Evolution Explorer.In the end,we detect four variable carbon stars with the Northern Sky Variability Survey,the Catalina Sky Survey and the LINEAR variability databases.According to their periods and amplitudes derived by fitting light curves with a sinusoidal function,three of them are likely semiregular variable stars and one is likely a Mira variable star.     

Long-term transit timing monitoring and homogenous study of WASP-32

We report new photometric observations of the transiting exoplanetary system WASP-32 made by using CCD cameras at Yunnan Observatories and Ho Koon Nature Education cum Astronomical Centre, China from 2010 to 2012. Following our usual procedure, the observed data are corrected for systematic errors according to the coarse decorrelation and SYSREM algorithms so as to enhance the signal of the transit events. Combined with radial velocity data presented in the literature, our newly observed data and earlier photometric data in the literature are simultaneously analyzed to derive the physical parameters describing the system by employing the Markov chain Monte Carlo technique. The derived parameters are consistent with the result published in the original paper about WASP-32b, but the uncertainties of the new parameters are smaller than those in the original paper. Moreover, our modeling result supports a circular orbit for WASP-32b. Through the analysis of all available mid-transit times, we have refined the orbital period of WASP-32b; no evident transit timing variation is found in these transit events.     

Sensitivity function analysis of gravitational wave detection with single-laser and large-momentum-transfer atomic sensors

Recently, a configuration using atomic interferometers(AIs) had been suggested for the detection of gravitational waves. A new AI with some additional laser pulses for implementing large momentum transfer was also put forward, in order to reduce the effect of shot noise and laser frequency noise. We use a sensitivity function to analyze all possible configurations of the new AI and to distinguish how many momenta are transferred in a specific configuration. By analyzing the new configuration,we further explore a detection scheme for gravitational waves, in particular, that ameliorates laser frequency noise. We find that the amelioration occurs in such a scheme,but novelly, in some cases, the frequency noise can be canceled completely by using a proper data processing method.     

Time-dependent Behaviour of the Low Amplitude δ Scuti Star HD 52788

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.     

Updating the orbital ephemeris of the dipping source XB 1254–690 and the distance to the source

XB 1254–690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining a more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply, for the first time, an orbital timing technique to XB 1254–690, using the arrival times of the dips present in the light curves that have been collected during 26 yr of X-ray pointed observations acquired from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254–690, improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M_2 = 0.42 ± 0.04 M_⊙for the donor star, in agreement with estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 M_⊙. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6±0.8 kpc. Finally, we discuss the evolution of the system, suggesting that it is compatible with a conservative mass transfer driven by magnetic braking.     

盾牌座δ型星的混沌现象的测定与研究

Chaos is universal phenomenon in the nature. Some scientists think that chaos theory is the third revolution in physics of this century, following relativity theory and quantum mechanics. The δSct type stars are pulsating variable stars with light amplitudes in Ⅴ from 0~m.003to 0~m.9 and periods from 0~d.01 to 0~d.2. The spectral types are A0-F5Ⅲ-Ⅴ. Some stars such as ρ Puppis and AD CMi show light curves which repeat beautifully from cycle to cycle.The light curves of many stars, especially the small-amplitude variables, often appear vari-     

Adaptive scale model reconstruction for radio synthesis imaging

A sky model from CLEAN deconvolution is a particularly effective high dynamic range reconstruction in radio astronomy,which can effectively model the sky and remove the sidelobes of the point spread function(PSF)caused by incomplete sampling in the spatial frequency domain.Compared to scale-free and multi-scale sky models,adaptive-scale sky modeling,which can model both compact and diffuse features,has been proven to have better sky modeling capabilities in narrowband simulated data,especially for large-scale features in high-sensitivity observations which are exactly one of the challenges of data processing for the Square Kilometre Array(SKA).However,adaptive scale CLEAN algorithms have not been verified by real observation data and allow negative components in the model.In this paper,we propose an adaptive scale model algorithm with non-negative constraint and wideband imaging capacities,and it is applied to simulated SKA data and real observation data from the Karl G.Jansky Very Large Array(JVLA),an SKA precursor.Experiments show that the new algorithm can reconstruct more physical models with rich details.This work is a step forward for future SKA image reconstruction and developing SKA imaging pipelines.