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Register a new userPhotometric observations and light curve solutions of the W UMa stars NSVS 2244206, NSVS 908513, CSS J004004.7+385531 and VSX J062624.4+570907
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Added by
Doroteya Vasileva Lyubenova
Publication date
2016
fields
Physics
and research's language is
English
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Photometric observations in Sloan g and i bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7+385531, VSX J062624.4+570907, are presented. The light curve solutions reveal that all targets have overcontact configurations with fillout factor within 0.15-0.26. Their components are of G-K spectral type and almost in thermal contacts. They are relatively close also in size and luminosity: the radius rations r_2/r_1 are within 0.75-0.90; the luminosity ratios l_2/l_1 are within 0.53-0.63. The results of the light curve solution of CSS J004007.7+385531 imply weak limb-darkening effect of its primary component and possible presence of additional absorbing feature in the system.
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The paper presents observations and light curve solutions of the eclipsing stars CSS J075205.6+381909 and NSVS 691550. As a result their initial epochs were determined. The target periods turned out almost equal to the previous values. We found that NSVS 691550 is overcontact system whose components are close in temperature while CSS J075205.6+381909 has almost contact configuration and temperature difference of its components is around 2000 K. Both targets undergo partial eclipses. Their stellar components seem to obey the relations mass-temperature of MS stars.
Photometric observations in V and I bands of six eclipsing binaries at the lower limit of the orbital periods of W UMa stars are presented. Three of them are newly discovered eclipsing systems. The light curve solutions revealed that all short-period targets were contact or overcontact binaries and added new six binaries to the family of short-period systems with estimated parameters. Four binaries have equal in size components and mass ratio near 1. The phase variability of the V-I colors of all targets may be explained by lower temperatures of their back surfaces than those of their side surfaces. Five systems revealed OConnell effect that was reproduced by cool spots on the side surfaces of their primary components. The light curves of V1067 Her in 2011 and 2012 were fitted by diametrically opposite spots. The applying of the criteria for subdivision of the W UMa stars to our targets led to ambiguous results.
Using multicolour photometry we have confirmed the binary nature of the new W-type W UMa eclipsing binary VSX J053024.8+842243 and established its primary eclipse ephemeris to be HJD = 2455924.38150(26) + 0.4322929(1) * E. Using the light curve modelling code PHOEBE and published data on the evolution of W-type contact binaries we found the primary and secondary components to have masses 0.50 Msun and 1.44 Msun, radii 0.87 Rsun and 1.42 Rsun, luminosities 0.98 Lsun and 1.91 Lsun, temperatures 6145 K and 5702 K and binary orbit inclination 59.4{deg}. We found the distance to the binary to be 511 parsec, its E(B-V) colour excess 0.04 and its intrinsic (B-V) colour index 0.62. A low resolution spectrum corrected for interstellar reddening confirmed its spectral type as G2V.
We present the new results of our long-term observational project to detect the small variations in the orbital periods of low-mass and short-period eclipsing binaries. About 120 new precise mid-eclipse times were obtained for three relatively well-known dwarf eclipsing binaries: SDSS J143547.87+373338.5 (P = 0.126 d), NSVS 07826147 (0.162 d), and NSVS 14256825 (0.110 d). Observed-minus-calculated (O-C) diagrams of these systems were analyzed using all accurate timings, and, where possible, new parameters of the light-time effect were calculated. For the first time, we derive (or improve upon previous findings with regard to) the short orbital periods of 13 and 10 years of possible third bodies for SDSS J143547.87+373338.5 and NSVS 07826147, respectively. In these binaries, our data show that period variations can be modeled simply on the basis of a single circumbinary object. For the first two objects, we calculated the minimum mass of the third components to be 17 MJ, and 1.4 MJ respectively, which corresponds to the mass of a brown dwarf or a giant planet. For NSVS 14256825, the cyclical period changes caused by a single additional body cannot be confirmed by our recent eclipse time measurements. More complex behavior connected with two orbiting bodies, or yet unknown effects, should be taken into account.
We present an analysis of UBVR$_{rm C}$I$_{rm C}$JH photometry and phase-resolved optical spectroscopy of NSVS 14256825, an HW Vir type binary. The members of this class consist of a hot subdwarf and a main-sequence low-mass star in a close orbit ($P_{rm orb} ~ 0.1$ d). Using the primary-eclipse timings, we refine the ephemeris for the system, which has an orbital period of 0.11037 d. From the spectroscopic data analysis, we derive the effective temperature, $T_1 = 40000 pm 500$ K, the surface gravity, $log g_1 = 5.50pm0.05$, and the helium abundance, $n(rm He)/n(rm H)=0.003pm0.001$, for the hot component. Simultaneously modelling the photometric and spectroscopic data using the Wilson-Devinney code, we obtain the geometrical and physical parameters of NSVS 14256825. Using the fitted orbital inclination and mass ratio ($i = 82fdg5pm0fdg3$ and $q = M_2/M_1 = 0.260pm0.012$, respectively), the components of the system have $M_1 = 0.419 pm 0.070 M_{odot}$, $R_1 = 0.188 pm 0.010 R_{odot}$, $M_2 = 0.109 pm 0.023 M_{odot}$, and $R_2 = 0.162 pm 0.008 R_{odot}$. From its spectral characteristics, the hot star is classified as an sdOB star.
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