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Register a new userThe first light curve modeling and orbital period change investigation of nine contact binaries around the short period cut-off
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In this paper, we present the first light curve synthesis and orbital period change analysis of nine contact binaries around the short period limit. It is found that all these systems are W-subtype contact binaries. One of them is a medium contact system while the others are shallow contact ones. Four of them manifest obvious OConnell effect explained by a dark spot or hot spot on one of the component stars. Third light was detected in three systems. By investigating orbital period variations, we found that four of the targets display a secular period decrease while the others exhibit a long-term period increase. The secular period decrease is more likely caused by angular momentum loss while the long-term period increase is due to mass transfer from the less massive component to the more massive one. Based on the statistic of 19 ultrashort period contact binaries with known orbital period changes, we found that seven of them display long-term decrease (three of them also exhibit cyclic variations), ten of them manifest long-term increase while two of them only show cyclic variation and that most of them are shallow contact binaries supporting the long timescale angular momentum loss theory suggested by Stepien. For the three deep contact systems, we found that they are probably triple systems. The tertiary companion plays an essential role during their formation and evolution.
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Orbital period and multi-color light curves investigation of OW Leo are presented for the first time. The orbital period of OW Leo is corrected from $P = 0.325545$ days to $P = 0.32554052$ days in our work, and the observational data from the All-Sky Automated Survey for SuperNovae (ASAS-SN) are used to test the newly determined orbital period. Then, the phased light curves are calculated with the new period and the Wilson-Devinney program is applied to model the light curves, which reveal that OW Leo is a W-subtype shallow contact binary system ($q = 3.05$, $f = 12.8,%$). The absolute physical parameters of the two component stars are estimated to be $M_{1} = 0.31(1)M_odot$, $M_{2} = 0.95(3)M_odot$, $R_{1} = 0.63(1)R_odot$, $R_{2} = 1.04(1)R_odot$, $L_{1} = 0.43(1)L_odot$ and $L_{2} = 1.01(2)L_odot$. The evolutionary status show that the more massive star is less evolved than the less massive star. OW Leo has very low metal abundance, which means its formation and evolution are hardly influenced by any additional component. It is formed from an initially detached binary systems through nuclear evolution and angular momentum loss via magnetic braking, and have passed a very long time of main sequence evolution.
We present the results of our study of the eclipsing binary systems CSS J112237.1+395219, LINEAR 1286561 and LINEAR 2602707 based on new CCD $B$, $V$, $R_c$ and $I_c$ complete light curves. The ultra-short period nature of the stars citep{Drake2014} is confirmed and the systems periods are revised. The light curves were modelled using the 2005 version of the Wilson-Devinney code. When necessary, cool spots on the surface of the primary component were introduced to account for asymmetries in the light curves. As a result, we found that CSS J112237.1+395219 is a W UMa type contact binary system belonging to W subclass with a mass ratio of $q=1.61$ and a shallow degree of contact of 14.8% where the primary component is hotter than the secondary one by $500K$. LINEAR 1286561 and LINEAR 2602707 are detached binary systems with mass ratios $q=3.467$ and $q=0.987$ respectively. These detached systems are low-mass M-type eclipsing binaries of similar temperatures. The marginal contact, the fill-out factor and the temperature difference between components of CSS J112237.1+395219 suggest that this system may be at a key evolutionary state predicted by the Thermal Relaxation Oscillation theory (TRO). From the estimated absolute parameters we conclude that our systems share common properties with others ultra-short period binaries.
We performed the first light curve analysis of GW Leo and a new ephemeris is obtained for QT Boo. In the present photometric study of two contact binary systems, we found that the period of these binary systems is decreasing at a rate of dp/dt=-6.21*10^(-3) days yr^(-1) for GW Leo, and dp/dt=-4.72*10^(-3) days yr^(-1) for QT Boo, respectively. The light curve investigation also yields that the system GW Leo is a contact W UMa eclipsing binary with a photometric mass ratio of q=0.881+-0.030, a fillout factor of f=3%, and an inclination of 54.060+-0.066 deg. Due to the OConnell effect which is known as asymmetries in the light curves maxima, a cold spot is employed along with the solution. We also calculate the distance of GW Leo from the distance modulus formula as 465.58+-23 pc, which is relatively close to the quantity measured by the Gaia DR2 using the binary systems parallax. Moreover, the positions of their components on the H-R diagram are represented.
Photometric observations in V and I bands and low-dispersion spectra of ten ultrashort-period binaries (NSVS 2175434, NSVS 2607629, NSVS 5038135, NSVS 8040227, NSVS 9747584, NSVS 4876238, ASAS 071829-0336.7, SWASP 074658.62+224448.5, NSVS 2729229, NSVS 10632802) are presented. One of them, NSVS 2729229, is newly discovered target. The results from modeling and analysis of our observations revealed that: (i) Eight targets have overcontact configurations with considerable fillout factor (up to 0.5) while NSVS 4876238 and ASAS 0718-03 have almost contact configurations; (ii) NSVS 4876238 is rare ultrashort-period binary of detached type; (iii) all stellar components are late dwarfs; (iv) the temperature difference of the components of each target does not exceed 400 K; (v) NSVS 2175434 and SWASP 074658.62+224448.5 exhibit total eclipses and their parameters could be assumed as well-determined; (v) NSVS 2729229 shows emission in the H_{alpha} line. Masses, radii and luminosities of the stellar components were estimated by the empirical relation period, orbital axis for short- and ultrashort-period binaries. We found linear relations mass-luminosity and mass-radius for the stellar components of our targets.
The first analysis of the photometric observation in BVR filters of a W UMa type binary system BQ Ari was performed. Light curve analysis was performed using Wilson-Devinney (W-D) code combined with a Monte Carlo (MC) simulation to determine its photometric and geometric elements and their uncertainties. These results show that BQ Ari is a contact binary system with a photometric mass ratio q=0.548pm0.019, a fillout factor f=24pm0.8 percent, and an orbital inclination of i=85.09pm0.45. We used the parallax from Gaia EDR3 for calculating the absolute parameters of the binary system. This study suggested a new linear ephemeris for BQ Ari, combining our new mid-eclipse times and the previous observations, which we analyzed using the Monte Carlo Markov Chain (MCMC) method. We present the first analysis of the systems orbital period behavior by analyzing the O-C diagram using the Genetic Algorithm (GA) and the MCMC approaches in OCFit code. We attempted to explain the analysis of the residuals of linear fit in the O-C diagram with two approaches; LiTE + Quadratic and Magnetic activity + Quadratic. Although we consider the magnetic activity to be probable, the system should be studied further in order to reveal the nature of orbital period variations.
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