Photometric light curve solutions of three ultra-short period eclipsing binaries

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,Rcand Iccomplete light curves.The ultra-short period nature of these stars,as reported by Drake et al.,is confirmed and the system’s periods are revised.The light curves were modeled using the 2003 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 500 K.LINEAR 1286561 and LINEAR2602707 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 with similar temperatures.The marginal contact,fill-out factor and temperature difference between components of CSS J112237.1+395219 suggest that this system may be at a key evolutionary state predicted by thermal relaxation oscillation(TRO)theory.From the estimated absolute parameters,we conclude that our systems share common properties with other ultrashort period binaries.

Absolute parameters of the three totally-eclipsing W UMa stars NSVS 2443858,NSVS 780649 and V1098 Her

We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ)Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ)The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB)systems;(ⅲ)All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR)systems;(ⅳ)The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ)The sum 0.871 M⊙of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M⊙assumed for the known contact binary stars.

DZ Lyn:a contact binary with components in poor thermal contact

CCD photometric observations of the short-period eclipsing binary DZ Lyn were obtained during seven nights in March-April 2008 in the B, V, Rc and Ic bands; these observations confirm the short-period （P = 0.378 d） of the system. The presented light curves are analyzed by means of the 2003 version of the Wilson-Devinney （WD） program. A grid of solutions for several fixed values of mass ratio was calculated. The best fitting possible is for a mass ratio of q -- 0.885, a degree of contact f = 0.18 and a low orbital inclination of i = 57.6°. The results show that DZ Lyn is an A-subtype W Ursae Majoris contact binary in poor thermal contact; in fact the difference between the mean temperatures of the components is about 1800 K. The star DZ Lyn seems to be another member of the class of poorly understood close binaries in or near geometrical contact but far from thermal contact. The absolute dimensions are estimated and its dynamical evolution is inferred.

Photometric study and preliminary elements of the low-mass ratio W UMa system ASAS 021209+2708.3

We present CCD B and V light curves,obtained in the year 2006,and a photometric solution of the low-mass ratio contact binary ASAS 021209＋2708.3. With our data we were able to determine six new times of minimum light and refine the orbital period of the system to 0.3181963 days.The light curves are analyzed using the 2003 version of the Wilson-Devinney program and the analysis was performed with and without adding a spot on the surface of one star because the light curves appear to exhibit a typical O’Connell effect,with Maximum I brighter than Maximum II.The results show that ASAS 021209＋2708.3 may be classified as an A-subtype W Ursae Majoris system with a small mass ratio q=0.1889,a large over-contact degree of f= 0.587,a very small difference between the component temperatures of Δ T=53 K and an orbital inclination of i=81°.It is known that deep（f50%） ,low-mass ratio（q0.25） overcontact binary stars are a very important resource for understanding the phenomena of Blue Straggler/FK Com-type stars.The formations of Blue Straggler stars and FK Com-type stars are unsolved problems in stellar astrophysics.One of the possible explanations for their formation is from the coalescence of W UMa-type overcontact binary systems.The absolute dimensions of ASAS 021209＋2708.3 are estimated and its dynamical evolution is inferred.