Population I Cepheids and understanding star formation history of the Small Magellanic Cloud

In this paper, we study the age and spatial distributions of Cepheids in the Small Magellanic Cloud(SMC) as a function of their ages using data from the OGLE III photometric catalogue. A period- age relation derived for Classical Cepheids in the Large Magellanic Cloud(LMC) has been used to find the ages of Cepheids. The age distribution of the SMC Classical Cepheids is found to have a peak at log(Age) = 8.40 ± 0.10 which suggests that a major star formation event might have occurred in the SMC about 250 ± 50 Myr ago. It is believed that this star forming burst had been triggered by close interactions of the SMC with the LMC and/or the Milky Way. A comparison of the observed spatial distributions of the Cepheids and open star clusters has also been carried out to study the star formation scenario in the SMC.     

Physical parameters and orbital period variation of a newly discovered cataclysmic variable GSC 4560-02157

GSC 4560-02157 is a new eclipsing cataclysmic variable with an orbital period of 0.265359 days.By using the published V- and R-band data together with our observations,we discovered that the O-C curve of GSC 4560-02157 may show a cyclic variation with a period of 3.51 years and an amplitude of 1.40 min.If this variation is caused by a light travel-time effect via the existence of a third body,then its mass can be derived as M_3 sin i′≈91.08 M_(Jup),and it should be a low-mass star.In addition,several physical parameters were measured.The color of the secondary star was determined to be V-R =0.77(±0.03) which corresponds to a spectral type of K2-3.The secondary star's mass was estimated as M_2 = 0.73(±0.02) M_☉ by combing the derived V-R value around phase 0 with the assumption that it obeys the mass-luminosity relation for main sequence stars.This mass is consistent with the mass-period relation for CV donor stars.For the white dwarf,the eclipse durations and contacts of the white dwarf yield an upper limit on the white dwarf's radius corresponding to a lower limit on mass of M_1≈0.501 M_☉.The overestimated radius and previously published spectral data indicate that the boundary layer may have a very high temperature.     

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

Time-series photometry was made for the large-amplitude δ Scuff 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 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.     

牧夫座TZ星的周期变化

TZ Bootes is a W UMa-type eclipsing binary system. It was well known as its short and long term changes on its light curves. Its depths of minimum of light curve usually appears interchanging variation. This star was observed by us since 1980 and a total of 41 photoelectric minimum times was obtained. We had collected a total of 101 minimum times, mostly derived from photoelectric observations, our observational data were included in them. From analysis of     

NUV Star Catalog from the Lunar-based Ultraviolet Telescope Survey: First Release

We present a star catalog extracted from the Lunar-based Ultraviolet Telescope(LUT) survey program. LUT's observable sky area is a circular belt around the Moon's north pole, and the survey program covers a preferred area of about 2400 deg~2 which includes a region of the Galactic plane. The data are processed with an automatic pipeline which copes with stray light contamination, artificial sources, cosmic rays, flat field calibration, photometry and so on. In the first release version, the catalog provides high confidence sources which have been cross-identified with the Tycho-2 catalog. All the sources have signalto-noise ratio larger than 5, and the corresponding magnitude limit is typically 14.4 mag, but can be as deep as ～16 mag if stray light contamination is at the lowest level. A total of 86 467 stars are recorded in the catalog. The full catalog in electronic form is available online.     

ALMA observations of the circumstellar envelope around EP Aqr

Atacama Large Millimetre/sub-millimetre Array(ALMA) observations of CO(1–0) and CO(2–1) emissions from the circumstellar envelope of the asymptotic giant branch(AGB) star EP Aqr have been made with four times better spatial resolution than previously available. They are analysed with emphasis on the de-projection in space of the effective emissivity and flux of matter using as input a prescribed configuration of the velocity field, assumed to be radial. The data are found to display an intrinsic axisymmetry with respect to an axis making a small angle with respect to the line of sight. A broad range of wind configurations, from prolate(bipolar) to oblate(equatorial) has been studied and found to be accompanied by significant equatorial emission. Qualitatively, the effective emissivity is enhanced near the equator to produce the central narrow component observed in the Doppler velocity spectra and its dependence on star latitude generally follows that of the wind velocity with the exception of an omni-present depression near the poles. In particular, large equatorial expansion velocities produce a flared disc or a ring of effective emissivity and mass loss. The effect on the determination of the orientation of the star axis of radial velocity gradients, and possibly competing rotation and expansion in the equatorial disc, is discussed. In general,the flux of matter is found to reach a broad maximum at distances of the order of 500 AU from the star.Arguments are given that may be used to favour one wind velocity distribution over another. As a result of the improved quality of the data, a deeper understanding of the constraints imposed on morphology and kinematics has been obtained.     

ASAS J174406+2446.8 is identified as a marginal-contact binary with a possible cool third body

ASAS J174406+2446.8 was originally found as a δ Scuti-type pulsating star with the period P=0.189068 d by ASAS survey.However,the LAMOST stellar parameters reveal that it is far beyond the red edge of pulsational instability strip on the log g-T diagram of δ Scuti pulsating stars.To understand the physical properties of the variable star,we observed it by the 1.0-m Cassegrain reflecting telescope at Yunnan Observatories.Multi-color light curves in B,V,R_c and I_c bands were obtained and are analyzed by using the W-D program.It is found that this variable star is a shallow-contact binary with an EB-type light curve and an orbital period of 0.3781 d rather than a δ Scuti star.It is a W-subtype contact binary with a mass ratio of 1.135(±0.019) and a fill-out factor of 10.4%(±5.6)%.The situation of ASAS J174406+2446.8 resembles those of other EB-type marginal-contact binaries such as UU Lyn,Ⅱ Per and GW Tau.All of them are at a key evolutionary phase from a semi-detached configuration to a contact system predicted by the thermal relaxation oscillation theory.The linear ephemeris was corrected by using 303 new determined times of light minimum.It is detected that the O-C curve shows a sinusoidal variation that could be explained by the light-travel-time effect via the presence of a cool red dwarf.The present investigation reveals that some of the δ Scuti-type stars beyond the red edge of pulsating instability strip on the log g-T diagram are misclassified eclipsing binaries.To understand their structures and evolutionary states,more studies are required in the future.     

New photometric investigation of the low-mass-ratio contact binary star V1853 Orionis

Four-color charge-coupled device(CCD) light curves in the B, V, Rc and I c bands of the totaleclipsing binary system V1853 Orionis(V1853 Ori) are presented. By comparing our light curves with those published by previous investigators, it is determined that the O'Connell effect on the light curves has disappeared. By analyzing those multi-color light curves with the Wilson-Devinney code(W-D code),it is discovered that V1853 Ori is an A-type intermediate-contact binary with a degree of contact factor of f = 33.3%(3.7%) and a mass ratio of q = 0.1896(0.0013). Combining our 10 newly determined times of light minima together with others published in the literature, the period changes of the system are investigated. We found that the general trend of the observed minus calculated(O-C) curve shows a downward parabolic variation that corresponds to a long-term decrease in the orbital period with a rate of d P/dt =-1.96(0.46)×10~(-7) d yr~(-1). The long-term period decrease could be explained by mass transfer from the more-massive component to the less-massive one. By combining our photometric solutions with data from Gaia DR_2, absolute parameters were derived as M_1 = 1.20 M⊙, M_2 = 0.23 M⊙, R_1 = 1.36 R⊙and R_2 = 0.66 R⊙. The long-term period decrease and intermediate-contact configuration suggest that V1853 Ori will evolve into a high fill-out overcontact binary.     

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.     

CN Andromedae:a shallow contact binary with a possible tertiary component

In this study, new photometric observations of shallow contact binary CN Andromedae(CN And)were performed and multi-color(BV R) CCD light curves(LCs) were obtained. Simultaneous analysis of new LCs and published radial velocity(RV) data reveals that the system is an early contact binary in which both components have recently filled their inner Roche lobes. Asymmetric LCs were modeled by a dark spot on the primary component and a hot spot on the secondary component that probably resulted from magnetic activity and mass transfer, respectively. Modeling of LCs and RV data allows us to estimate the following absolute parameters: M1= 1.40 ± 0.02 M⊙, M2= 0.55 ± 0.01 M⊙, R1= 1.45 ± 0.02 R⊙and R2= 0.94 ± 0.02 R⊙. A decreasing orbital period with a rate of d P/dt =-1.5 × 10-7d yr-1can be seen as evidence that the system is evolving into a contact binary with higher contact degree. Cyclic oscillation of the O-C data was interpreted by the Applegate mechanism and light-time effect due to an unseen component around the close binary system. The hypothetical third component is probably a fully convective red dwarf star with a minimal mass of 0.1 M⊙. CN And is at the early phase of the contact stage of its evolution and is an interesting example for studying the formation and evolution of close binaries.     

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.     

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.     

ISO-SWS Observations of the Time Variability of Oxygen-righ Mira Variables

We present the first observation of variation of the infrared spectrum of circumstellar dust emission around an oxygen-rich Mira variable star, Z Cyg, over an entire light variation cycle, based on the periodic SWS01 observations. The 10 μm and 20 μm ‘silicate features’ become stronger relative to the photospheric emission at maximum that at minimum. In addition, the relative intensity of the 10 μm to the 20 μm features increases at maximum, indicating an increase of the temperature of circumstellar dust grain. A simple model analysis suggests enhanced dust formation near the photosphere around maximum, leading to a scenario that dust nucleation may have occurred near minimum and the dust grains may have subsequently grown till maximum. The strong observed variation suggests that the variability must be taken into account in the interpretation of the infrared spectra of oxygen-rich Mira variables. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Photometric Study of the W UMa-type Eclipsing Binary System GSC 0445-1993

Several new light minimum times for the eclipsing binary GSC 0445-1993 have been determined from the observations by Koppelman et al. and the orbital period of this system was revised. A photometric analysis was carried out using the 2003 version of the Wilson-Devinney code. The results reveal that GSC 0445-1993 is a W-type eclipsing binary with a mass ratio of q = 0.323(±0.002) and an over-contact degree of f = 22.8%(±4.2%). A small temperature difference between the components of △T = 135 K and an orbital inclination of i = 65.7°(±0.3°) were obtained. The asymmetry of its light curve (i.e., the O'Connell effect) for this binary star is explained by the presence of a dark spot on the more massive component.     

The first photometric analysis and period investigation of the K-type W UMa type binary system V0842 Cep

V0842 Cep is a W UMa-type binary star that has been neglected since its discovery.We analysed the VR_cI_c light curves,obtained by the 1 m telescope at Weihai Observatory of Shandong University,using the Wilson-Devinney code.V0842 Cep was found to be a shallow contact binary system(f=8.7%) with a mass ratio of 2.281.Because its orbital inclination is greater than 80°,the photometric results are reliable.A period study is included which reveals a continually decreasing orbital period(dp/dt=1.50(±0.42)×10~(-7)d yr~(-1)).This trend could be attributed to the angular momentum loss via stellar wind.     

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 peculiar case of the “double-humped” super-luminous supernova SN 2006oz

SN 2006oz is a super-luminous supernova with a mysterious bright precursor that has resisted explanation in standard models.However,such a precursor has been predicted in the dual-shock quark nova model of super-luminous supernovae–the precursor is the supernova event while the main light curve of the super-luminous supernova is powered by the Quark-Nova（explosive transition of the neutron star to a quark star）.As the supernova is fading,the Quark-Nova re-energizes the supernova ejecta,producing a＂double-humped＂light curve.We show that the quark nova model successfully reproduces the observed light curve of SN 2006oz.     

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.