Observation And Investigation On Am Chemically Peculiar Eclipsing Binaries

Chemically Peculiar Stars?CP stars?are the stars with abnormal strong or weak spectral lines of some elements,the formation and evolution of which are still open questions in astrophysics.CP stars mainly consist of main sequence B,A and F type stars.CP stars show quite hight binaries percentage.For Am stars,the percentage is more than 90%,and some Am stars are in eclipsing bi-naries.Eclipsing binary is a significant way to obtain the fundamental physical parameters of stars,such as mass,radius and others,which can supply the fun-damental information for the investigation of Am and CP stars.We have taken observation and investigation on four eclipsing Am binaries and two normal near contact binaries with A or F spectra type.Their light curves,period change and other characteristic of each target are studied,which may promote the pre-liminary investigation on the formation of the chemical anomalies composition of Am stars.Here are our results for each target:1.New multi-color B-V-R_c-I_cphotometric observations are presented for the Am type W UMa type eclipsing binary V1073 Cyg.The multi-color light curve analysis with the Wilson-Devinney procedure yielded the absolute parameters of this system,showing that V1073 Cyg is a shallow contact binary system with a fill-out factor f=0.124?±0.011?.We collected all available times of light minima spanning 119yr,including CCD data to construct the O-C curve,and performed detailed O-C analysis.The O-C diagram shows that the period change is complex.A long-term continuous decrease and a cyclic variation exist.The period is decreasing at a rate of?P=-1.04?±0.18?×10^-10d·y^-1,with the period decrease,V1073 Cyg will evolve to the deep contact stage.The cyclic variation with a period of P₃=82.7?±3.6?yr and an amplitude of A=0.028?±0.002?d may be explained by magnetic activity of one or both components or the light travel time effect caused by a distant third companion with M₃?i^?=90^??=0.511M_?.2.The first complete multi-color CCD light curves and low resolution spec-tra of the short-period Am-type eclipsing binary V2787 Ori are presented.The atmospheric parameters of the system including the effective temperature?T?,the gravitational acceleration?log g?and the metallicity[Fe/H]are determined as T_{ef f}=6993±82K,log g=4.10±0.22cm/s²,and[F e/H]=-0.40±0.18dex,respectively.Wilson-Devinney?W-D?code was used to analyze those BV R_cI_c light curves and the photometric solutions of this eclipsing binary were derived for the first time.It is discovered that V2787 Ori is a shallow-contact total-eclipsing binary with a factor of f?fill-out?=0.133?±0.084?and an extremely low mass ratio of q=0.120?±0.002?.The primary contributes about 95%lumi-nosity to the total system,and the difference between the two component stars exceed 1600K.This target maybe is smallest mass ratio B-subtype system,but definitely is among the smallest mass ratio B-subtype systems.The tempera-ture of the secondary is determined as 5386 K,while its mass is estimated as M₂=0.17?±0.01?M_?.These properties indicate that the binary may undergo a special evolution where the secondary may be the original more massive compo-nent and have transferred most of its mass to its companion.We combined our newly determined eclipse times with those collected from previous literature and found that the O-C curves of the binary system shows a cyclic variation with an amplitude of of 0.0054 days and a period of 17.3 years which is explained as the result of the light-time effect due to a third body orbiting around the cen-tral binary or the magnetic activity of one or both components.The minimal mass of the third body is 0.208M_?and the corresponding orbital radius is about7.24AU.The shallow-contact configuration,the extremely low mass ratio,the evolved components,and the presence of a tertiary component,all make the Am-type B-subtype contact binary a significative target for further investigations.3.First BV light curves and low resolution spectra of Am eclipsing binary TYC6408-989-1 are presented.Through spectra fitting,we determined the at-mospheric parameters of the system as:the effective temperatureT_{ef f}=6990±117K,the gravitational acceleration log g=4.25±0.26cm/s²and the metallicity[F e/H]=-0.45±0.03dex.photometric solutions reveals TYC 6408-989-1 should be a low mass ratio?0.230?5??marginal contact binary?f?fill-out?=0.02?10??with a large temperature difference of about 1860 K between the two compo-nents.This target may just lie in the oscillation around the state of marginal contact predicted by the theory of thermal relaxation oscillations?TRO?.4.The lander of China's Chang'e 3 spacecraft was equipped with a 15-cm telescope that is very useful to monitor celestial objects in the UV band?245nm-340nm?.The lunar-based ultraviolet telescope?LUT?is the first long-term lunar-based astronomical observatory,making continuous and uninterrupt-ed observations of a target from the Moon.Here we present the continuous complete UV light curve of the eclipsing binary TX Her.The analysis of the light curve suggests that TX Her is a detached binary.The dip in the light curve was explained by the emerging of a stellar dark spot on the less massive F0 type component.The cyclic change of arrival eclipse times for the system reveals that its contains an additional stellar companions with minimal mass of 0.35 M_?and a period of 48.92 years,which is supported by the detected light contribution of the third body from light curve analysis.This third body may play an important role on the formation of the present short-period system TX Her.5.Complete multi-color photometric observations on BV R_cI_cbands and low-resolution spectra of the short-period binary V723 Per are presented for the first time.The stellar atmospheric parameters including the effect tem-perature,the gravitational acceleration,and the metallicity are determined as T_{ef f}=7407±53K,log g=3.98±0.10cm/s²,and[F e/H]=-0.25±0.10dex,respectively.Photometric solutions are obtained by analyzing the phased light curves with Wilson-Devinney method.We found that V723 Per is an Algol-like semi-detached type near-contact binary with a mass ratio of q=0.3168±0.0011.The secondary component is filling the critical Roche Lobe,while the primary is nearly filling its Roche lobe?the filling degree is about 80.93%?.The primary component contributes about 96%of the luminosity to the total system,and the temperature difference between the two component stars is about 3000K.All available times of light minimum including three new observed eclipse times were used to construct the O-C curve.The period shows a continuously increase at a rate of dP/dt=+7.63?±0.75?×10^-6d·y^-1superposed with a periodic oscillation with an amplitude of 0.0392 days and a period of 17.4 years.The period increase could be explained by the mass transfer from the secondary component to the pri-mary one on the thermal timescale,which is in agreement with the semi-detached configuration.The cyclic change maybe caused by the light-time effect due to a massive?M₃=3.03M_??but quite faint tertiary companion orbiting around the central binary.Such third body itself might be a black hole or a binary with two nearly identical stars.More observations are required in the future to confirm our conclusion about the cycle variation and tertiary companion.6.Two photometric observations for short period W UMa eclipsing binary TT Cet on R_cand BV R_cI_cbands were presented firstly.Spectral observation obtained the low-resolution spectra.The stellar atmospheric parameters were es-timated through spectra fitting as:T_{ef f}=7091±124K,log g=4.15±0.33cm/s²,[F e/H]=-0.23±0.04dex.Wilson-Devinney method was used to analysis the light curves.The photometric solutions suggests that TT Cet is marginal contact binary with a factor of 3.16?±0.78?%.The luminosity enhancing around the first quadrature may caused by the existence of a hot spot on the surface of secondary component.The O-C analysis found that the period is undergoing long-term decrease at a rate of dP/dt=-5.01?±0.06?×10^-8d·y^-1,which can be explained by the mass transfer form the primary to the secondary component.TT Cet should be in the oscillations state predicted by the theory of thermal relaxation oscillations?TRO?.With the period decrease,the contact degree will be deep and TT Cet will evolved to a true thermal contact binary.V1073 Cyg?V2787 Ori and TYC 6408-989-1 are the only three?marginal?contact eclipsing binaries.Most Am eclipsing binaries are long period systems like TX Her.Cycle changes of the system period occur in these systems very common,which means hight existence frequency of third body.With our in-vestigation results,we infer that the Am peculiarity may be the result of mass transfer between the components of binaries.The components of Am type near contact binaries may have been striped more of the hydrogen shell,the uncovered stellar core made the components more hotter,which will lead to the components still staying in the main sequence.The mass transfer between two components will carry off the production of core reaction and resulted in chemical anomalies composition of the companion stars,such as the marginal contact binary V1073Cyg and V2787 Ori laying in the oscillations state.Long period Am type e-clipsing binaries like TX Her may occur mass transfer after long time evolution in the main sequence.The tertiary components of these systems may extrac-t angular momentum of systems and make the components closer,which will promote mass transfer.We made investigation on the three of four Am type eclipsing binaries with periods less than one day.With the large-scale photo-metric and spectroscopic sky survey observation,more observation information of more Am eclipsing binaries will obtained,which will promote the investigation on structure,formation and evolution of Am type eclipsing binaries.