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Register a new userThe W-subtype active contact binary PZ UMa with a possible more massive tertiary component
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Two sets of multiple-color ($B, V, R_c, I_c$) light curves of PZ UMa were observed in dependently with the 2.4 meter telescope at the Thai National Observatory and the 1 meter telescope at Yunnan Observatories. The light curves were analyzed with the Wilson-Devinney program and the two sets of light curves produced consistent results, which show that PZ UMa is a W-subtype contact binary with an extreme mass ratio ($M_{1}/M_{2} = 0.18)$. The basic physical parameters of PZ UMa were determined to be $M_{2} = 0.77(2)M_odot$, $M_{1} = 0.14(1)M_odot$, $R_{2} = 0.92(1)R_odot$, $R_{1} = 0.43(1)R_odot$, $L_{2} = 0.46(2)L_odot$ and $L_{1} = 0.15(3)L_odot$. The orbital period analysis of PZ UMa revealed a 13.22 year periodicity, which implies that there may be a tertiary component orbiting around the binary system. The mass and orbital radius of the tertiary component were calculated to be $M_{3} = 0.88 M_odot$ and $a_{3} = 3.67 AU$, if the orbit was coplanar with the central binary system. It is interesting that the minimum mass of the tertiary was calculated to be $M_{3min} = 0.84 M_odot$, which means the tertiary component is even larger than the primary star and the secondary one of PZ UMa. PZ UMa is a late-type contact binary with stellar activity. The OConnell effect appeared on its light curves when it was observed on April 2016. However, the OConnell effect reversed when the target was observed again on December 2016. The changes of the OConnell effect in such a short time-scale strongly support the occurrence of rapidly changing magnetic activity on this W UMa binary.
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Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at Thai National Observatory and the Wilson-Devinney (W-D) program is used to model the observational light curves. The photometric solutions reveal that V1197 Her is a W-subtype shallow contact binary system with a mass ratio of $q = 2.61 $ and fill-out factor to be $f = 15.7,%$. The temperature difference between the primary star and secondary star is only $140K$ in spite of the low degree of contact, which means that V1197 Her is not only in geometrical contact configuration but also already under thermal contact status. The orbital inclination of V1197 Her is as high as $i = 82.7^{circ}$, and the primary star is completely eclipsed at the primary minimum. The totally eclipsing characteristic implies that the determined physical parameters are highly reliable. The masses, radii and luminosities of the primary star (star 1) and secondary star (star 2) are estimated to be $M_{1} = 0.30(1)M_odot$, $M_{2} = 0.77(2)M_odot$, $R_{1} = 0.54(1)R_odot$, $R_{2} = 0.83(1)R_odot$, $L_{1} = 0.18(1)L_odot$ and $L_{2} = 0.38(1)L_odot$. The evolutionary status of the two component stars are drawn in the H - R diagram, which shows that the less massive but hotter primary star is more evolved than the secondary star. The period of V1197 Her is decreasing continuously at a rate of $dP/dt=-2.58times{10^{-7}}daycdot year^{-1}$, which can be explained by mass transfer from the more massive star to the less massive one with a rate of $frac{dM_{2}}{dt}=- 1.61times{10^{-7}}M_odot/year$. The light curves of V1197 Her is reported to have the OConnell effect. Thus, a cool spot is added to the massive star to model the asymmetry on light curves.
Two sets of light curves in $V$ $R_c$ $I_c$ bands for a newly discovered binary system UCAC4 436-062932 are obtained and analyzed using the Wilson-Devinney (W-D) code. The two sets of light curves get almost consistent results. The determined mass ratio is about $q = 2.7$ and the less massive component is nearly $250K$ hotter than the more massive one. The solutions conclude that UCAC4 436-062932 is a W-subtype shallow contact (with a contact degree of $f = 20,%$) binary system. Since the OConnell effect appears on one set of the light curves, theories proposed to explain the effect are discussed. We assume that spot model may be the more plausible one to the OConnell effect appeared on the asymmetric light curves of the binary system UCAC4 436-062932. Therefore, we add a cool spot on the surface of the more massive star (component with lower effective temperature) and get a quite approving results for the light curve fitting. It will provide evidence to support the spot model in the explanatory mechanism of OConnell effect.
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.
The first four-color light curves of V868 Mon in the $B$ $V$ $R_c$ and $I_c$ bands are presented and analyzed by using the Wilson-Devinney method of the 2013 version. It is discovered that V868 Mon is an A-subtype contact binary (f=$58.9,%$) with a large temperature difference of 916$K$ between the two components. Using the eight new times of light minimum determined by the authors together with those collected from literatures, the authors found that the general trend of the observed-calculate ($O$-$C$) curve shows a upward parabolic variation that corresponds to a long-term increase in the orbital period at a rate of $dP/dt=9.38times{10^{-7}}daycdot year^{-1}$. The continuous increase may be caused by a mass transfer from the less massive component to the more massive one.
ROTSE1 J164341.65+251748.1 was photometrically observed in the V band during three epochs with the 0.84-m telescope of the San Pedro Martir Observatory in Mexico. Based on additional BVR photometry, we find that the primary star has a spectral type around G0V. The light curve of the system is typical of a W~UMa type binary stars and has an orbital period of $sim$ 0.323 days. In an effort to gain a better understanding of the binary system and determine its physical properties, we analyzed the light curve with the Wilson and Devinney method. We found that ROTSE1 J164341.65+251748.1 has a mass ratio of $sim$ 0.34 and that the less massive component is over 230 K hotter than the primary star. The inclination of the system is $sim$ 84.6 degrees, and the {bf degree} of over-contact is 11%. The analysis shows the presence of variable bright spots on the primary star.
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