First photometric investigation of two short-period eclipsing binaries NSVS 7377756 and for UCAC3 276-106147

We present the first CCD sets of complete light curves for two W Ursae Majoris Systems, UCAC3 276-106147 and NSVS 7377756. These light curves are here analyzed and modelled using the latest version of the Wilson-Devinney Code. We found that UCAC3 276-106147 is a W-subtype shallow-contact eclipsing binary (fill-out factor 7.5%), with a mass ratio of q = 2.88 (1/q = 0.347), a small temperature difference between the components of about ΔT =200K. NSVS 7377756 is an H-subtype binary system with a high mass ratio of q = 1.09 (1/q = 0.947), a weak degree of contact factor f = 3.8% and a temperature difference between the components of ΔT = 398 K. The light curves of both the systems appear to be unspotted. By using our 4 and 7 times of minimum light and the 30 and 104 ToMs extract from the SWASP observations, respectively for UCAC3 276-106147 and NSVS 7377756, the orbital periods are here revised. The elements obtained from this analysis are used to compute the physical parameters of the systems combining our photometric solution with the 3-D correlation obtained for contact binaries by Gazeas (2009). Based on these estimated parameters the evolutionary state of the components of the systems is investigated and discussed.     

NSVS 7051868: A system in a key evolutionary stage. First multi-color photometric study

The first CCD photometric complete light curves of the eclipsing binary NSVS 7051868 were obtained during six nights in January 2016 in the B, V and I_c bands using the 0.25 m telescope of the Stazione Astronomica Betelgeuse in Magnago, Italy.These observations confirm the short period (P = 0.517 days) variation found by Shaw and collaborators in their online list (http://www.physast.uga.edu/~jss/nsvs/) of periodic variable stars found in the Northern Sky Variability Survey.The light curves were modelled using the Wilson–Devinney code and the elements obtained from this analysis are used to compute the physical parameters of the system in order to study its evolutionary status.A grid of solutions for several fixed values of mass ratio was calculated.A reasonable fit of the synthetic light curves of the data indicate that NSVS 7051868 is an A-subtype W Ursae Majoris contact binary system, with a low mass ratio of q = 0.22, a degree of contact factor f = 35.5% and inclination i = 85°. Our light curves shows a time of constant light in the secondary eclipse of approximately 0.1 in phase. The light curve solution reveals a component temperature difference of about 700 K. Both the value of the fill-out factor and the temperature difference suggests that NSVS 7051868 is a system in a key evolutionary stage of the Thermal Relaxation Oscillation theory.The distance to NSVS 7051868 was calculated as 180 pc from this analysis, taking into account interstellar extinction.     

The eclipsing binary star V380 Gem: First V and Rc light curve analysis and estimation of its absolute elements

We obtained complete V and R_c light curves of the eclipsing binary V380 Gem in 2012. With our data we were able to determine six new times of minimum light and refine the orbital period of the system to 0.3366088 days. The 2003 version of the Wilson–Devinney code was used to analyze the light curves in the V and R_c bands simultaneously. It is shown that V380 Gem may be classified as an W-type W Ursae Majoris system with a high mass ratio q = 1.45, a degree of contact f = 10.6% the same temperature for both the components (ΔT = 10 K) and an orbital inclination of i  = 81.5°. Our observations show symmetric light curves in all passbands with brightness in both maxima at the same level. The absolute dimensions of V380 Gem are estimated and its dynamical evolution is inferred.     

Radial Velocity and Light Curves Analysis of the Contact Binary V1073 Cygni

In this study complete BV light curves of the W Ursae Majoris binary V1073 Cygni obtained in 2005 are presented. We have used the spectroscopic data of V1073 Cyg obtained by Ahn et al. (1992) for analysis. The analysis of radial velocity and light curves was made with Wilson} program (1998) and the geometric and physical elements} of the system were derived. By searching the simultaneous} solutions of the system, we have determined the masses and radii of the components: 1.64M_⊙, 2.275R_⊙ for the primary component and 0.55M_⊙, 1.397R_⊙ for the secondary component respectively. The effective temperature of 6494 ± 53 K for the secondary component was also estimated.     

Radial Velocity and Light Curves Analysis of the Contact Binary V839 Ophiuchi

Complete UBV light curves of the W Ursae Majoris binary V839 Ophobtained in the year 2000 are presented. The available spectroscopic data of V839 Oph is new and we used the first radial velocity data of this system obtained by Rucinski and Lu (1999)for analysis. The radial velocity and light curves analysis was made with the latest version of Wilson programme (1998) and the geometric and physical elements of the system are derived. By searching the simultaneous solutions of the system we have determined the masses and radii of the components: 1.61M _⊙and 1.49402R _⊙ for the primary component; 0.50M _⊙and 0.90147R _⊙ for the secondary component. We estimate deffective temperatures of 6650±18 (K) for the primary and6554±15 (K) for the secondary component. This revised version was published online in July 2006 with corrections to the Cover Date.     

First multi-color photometric investigation of the shortest-period semi-detached binary SWASPJ222302.02+195031.8

SuperWASPJ222302.02+195031.8 is an eclipsing binary with an orbital period about 0.22517657 days that is close to the short-period limit of contact binaries. Multi-color photometric light curves of the short-period binary in B, V, R_c and I_c bands are presented and analyzed by using the Wilson–Devinney (W–D) method. It is discovered that the system is a semi-detached binary where the secondary component is already filling the critical Roche lobe, while the primary is filling just 77.1% of its Roche lobe. The temperature of the primary is about 4300 K, and the temperature difference between the two components is about 500 K. The asymmetries in the light curves are explained by the coverage of stellar dark spots on the less massive component via magnetic activity. An analysis of all available eclipse times suggests that there are no any changes in the O-C diagram. This may indicate that there are no mass transfers between the two components. The semi-detached configuration with the dark spot on the surface of the lobe-filling secondary and no variations in the orbital period make the binary an interesting target for further investigations.     

W Ursae Majoris stars: Period-spectral type relation and period changes

The relation between period and spectral type is examined for 33 W Ursae Majoris stars for which accurate observations have enabled us to clearly classify their eclipse types at the primary minimum (transit (A) or occultation (W)). About a half of the examined stars are of A-type, and the rest correspond to W-type. Periods of W-type systems are found to fall within 0.25–0.5 days, while periods of A-type systems range between 0.25–0.9 days. For A-type systems certain period-spectral type relations seem to hold, but for W-type systems no definite relation could be found. Statistically, a W Ursae Majoris star will undergo a period change every ～17000 cycles, on the average, and a time scale for the period change (d lnP/dt)^?1 is estimated to be about 10⁶ years.     

Photometric study of three contact binary systems

The first complete light curves of two eclipsing binaries in Camelopardalis, NX Cam and V584 Cam, are here presented together with the new observations of the system NSVS 2643686 obtained in 2014. The light curves were modelled using the latest version of the Wilson-Devinney code. Our results show that all the three systems have an extreme mass ratio q < 0.2, two of them, NX Cam and NSVS 2643686, having the fill-out f > 50%, belong to the class of the so called Deep Low Mass Ratio systems (DLMR) but show different physical characteristics. The two above systems are totally eclipsed binaries with the duration of the secondary eclipse of 87 min for NX Cam and 51 min for NSVS 2643686. The other system, V584 Cam, shows a middle fill-out value of f = 33% and low inclination. Using our Times of Minima (ToM) derived from the observations as well as those found in the literature, the ephemerides of the three systems are here revised. The absolute dimensions are estimated and, from statistical diagram, it is found that all the components of the systems follow the general pattern of the well known W UMa contact binaries.     

The dynamical stability of W Ursae Majoris-type systems

Theoretical study indicates that a contact binary system would merge into a rapidly rotating single star due to tidal instability when the spin angular momentum of the system is more than a third of its orbital angular momentum. Assuming that W Ursae Majoris (W UMa) contact binary systems rigorously comply with the Roche geometry and the dynamical stability limit is at a contact degree of about 70 per cent, we obtain that W UMa systems might suffer Darwin's instability when their mass ratios are in a region of about 0.076–0.078 and merge into the fast-rotating stars. This suggests that the W UMa systems with mass ratio   q ≤ 0.076  cannot be observed. Meanwhile, we find that the observed W UMa systems with a mass ratio of about 0.077, corresponding to a contact degree of about 86 per cent would suffer tidal instability and merge into the single fast-rotating stars. This suggests that the dynamical stability limit for the observed W UMa systems is higher than the theoretical value, implying that the observed systems have probably suffered the loss of angular momentum due to gravitational wave radiation (GR) or magnetic stellar wind (MSW).     

A photometric study of the short-period eclipsing binary 1SWASP J204932.94-654025.8, showing strong third light

1SWASP J204932.94-654025.8 (hereafter J2049) is a newly discovered eclipsing binary system with an orbital period of 0.2299103 days. BVR_c light curves (LCs) are presented and analyzed by using the 2013 version of the Wilson–Devinney (W–D) program. Because the observed LCs are asymmetric, a hot star-spot was employed on the secondary component during our analysis. We found that J2049 is a W-subtype shallow contact eclipsing binary system with an orbit inclination of 62^∘.69 ± 0^∘.95 and a mass ratio of q =1.326 ± 0.056. More importantly, we found the presence of a strong third light, with an average luminosity contribution of 31.3% of the total light. Based on times of the light minima, the orbital period changes of J2049 are studied for the first time, and there is no evidence for any significant dp/dt now. Considering the presence of the third light and the short time span of the eclipse times, more observations are needed in the future.     

Global parameters of the totally-eclipsing W UMa stars NSVS 6673994, NSVS 4316778, PP Lac and NSVS 1926064

Photometric observations of four totally-eclipsing W UMa binaries, NSVS 6673994, NSVS 4316778, PP Lac and NSVS 1926064, are presented. Their global parameters were determined from the light curve solutions and GAIA distances. The main results are as follows: (i) NSVS 6673994, NSVS 4316778 and PP Lac are of W subtype while NSVS 1926064 is of A subtype; (ii) The mass ratios of NSVS 4316778 and NSVS 1926064 are close to the lower mass-ratio limit; (iii) NSVS 4316778 has double contact configuration while NSVS 1926064 is in deep contact; (iv) The changes of the PP Lac period seem cyclic and are accompanied with episodes of essentially constant value; (v) The relations between the global parameters of the four W UMa stars differ considerably from those of Main Sequence (MS) stars. The deviations of the radii, temperatures and luminosities of the stellar components from those of MS stars with the same masses are bigger for the two targets with extremely small mass ratio.     

Photometric analysis of the contact binary star V829 Hercules using light curves on three consecutive years

New BVR light curves and photometric analysis of the contact binary star V829 Her are presented. The light curves were obtained at the ÇOMU Observatory in the consecutive years 2003, 2004 and 2005. Firstly, the variation of the orbital period of the system was studied. The sinusoidal and secular changes were found and examined in terms of two plausible mechanisms, namely (i) the conservative mass transfer between the components of the system and (ii) the light-time effect due to an unseen component in the system. The instrumental magnitudes of all observed stars in this study were converted into standard magnitudes. We also study nature of asymmetries and the intrinsic variability in the light curves of the system. Light variations are summarized: (a) changes of light levels of both maxima and (b) changes of the depths of both primary and secondary eclipses. These peculiar asymmetries were interpreted in terms of dark spot(s) on the surface of the large and more massive component star. The present BVR light curves and radial velocity curves obtained by Lu, W., Rucinski, S. M., 1999. AJ 118, 515 were analysed by means of the latest version of the Wilson–Devinney program, simultaneously. Thus, the absolute parameters of the system were also derived.     

The cycle length of the U Geminorum star HT Cassiopeiae

The mean cycle length of the catalysmic binary HT Cas, which is remarkable because of the shortness of its orbital period, has been determined as 400^d±50^d. The hitherto assuixed value of 30^d proved unfounded. Some aspects arising when classifying long-cycle objects and SU Ursae Majoris variables are pointed out, a s well as the relation between large cycle length and small accretion rate.     

A photometric study of BO Canum Venaticorum

Photometric BV light curves of BO CVn obtained in 1992 and new times of minima are presented. The primary minimum shows a transit, whereas the secondary minimum, shows an occultation. The system may be classified as an A‐type W UMa system. A complete study of minima allows one to detect a possibly increasing period by about 0.037 s/yr. This indicates that the conservative mass transfer rate from the less massive component to the more massive one is 1.57 10^—10M_⊙ /yr. Because of the variable period, the new ephemeris is determined for future observations. Using the Wilson‐Devinney code a simultaneous solution of the B and V light curves is also performed. The analysis shows that the system is in a contact configuration with q = 0.205 ± 0.001 and fillout factor (f) = 0.18, T₁ = 7240 K (fixed), T₂ = 7150± 10 K. The high orbital inclination i = 87°.54 ± 0.26 was con firmed by photometric observations of the secondary minimum.     

Photometric analysis of recently discovered eclipsing binary GSC 00008-00901

Photometric analysis of BVR _C light curves of newly discovered eclipsing binary GSC 0008-00901 is presented. The orbital period is improved to 0.28948(11) days. Photometric parameters are determined as well. The analysis yielded to conclusion that system is an over-contact binary of W UMa type with components not in thermal contact. The light curves from 2005 show the presence of a spot on the surface of one of the components, while light curves from 2006 are not affected by maculation.     

Photoelectric UBV observations and period study of AK Herculis system

New photoelectric UBV observations of the W Ursae Majoris-type eclipsing binary AK Her are presented. The system exhibits many phenomena such as O'Connell effect, unequal depth, phase shift and different duration in secondary eclipse due to its totality, which have been studied. O'Connell effect-duration relation may be exist. The (O-C) curve has been obtained and the new light elements have been calculated. The analysis of the minima-times data of the system reveals possible sinusoidal orbital period variation (LITE). The study of the (O-C)curve, the light curves, O'Connell effect and the duration effect have led to that the system is likely a case which undergoes cyclic around the marginal contact state conservatively with mass transfers between its components, i.e.in TRO mode. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solving wolf’s uvbyRI light curves for the star BM Ori

We solve the uvbyRI light curves obtained by Wolf (1994) with a CCD photometer. Wolf did not solve the light curves, while particular interest in them stems from the fact that a secondary minimum, which other observers failed to detect, is clearly seen in the byRI light curves. This enables us to consider a new eclipse model in which we hypothesize that the secondary component at primary minimum completely obscures the primary, smaller B star, but, at the same time, the light from a third star is observed. Based on this hypothesis, we computed the brightness of each of the three stars for the six bands by analyzing the depths of the primary and secondary minima. Satisfactory agreement between theoretical and observed light curves was achieved by assuming the following parameters for the stars: effective temperature T ₁=17000 K, radius R ₁ = 2.5 R _⊙, spectral type Sp₁ = B3—B4 for the primary; T ₂=5700 K, R ₂ = 8.4 R _⊙, Sp₂ = G0—G2 for the secondary; and T ₃=29000 K, R ₃ = 1.0 R _⊙, Sp₃=B0 for the third star. In the Hertzsprung-Russell diagram, the first star lies on the zero-age main sequence, the second is on the way from the birthline to the main sequence in the region of giants, and the third falls within the region of hot subdwarfs.     

A CCD photometric study of the late type contact binary EK Comae Berenices

We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 m telescope of IUCAA Girawali Observatory, India. The star was classified as a W UMa type binary of subtype-W by Samec et al. (1996). The new V band photometric observations of the star reveal that shape of the light curve has changed significantly from the one observed by Samec et al. (1996). A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 ± 0.005. A temperature difference of ΔT = 141 ± 10 K between the components and an orbital inclination of i[°] = 89.800 ± 0.075 were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O’Connell effect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O’Connell effect is explained by the presence of a hot spot on the primary component.     

The effect of metallicity on the minimum mass ratio of W Ursae Majoris-type systems

According to the prevenient theoretical study, the minimum mass ratio for tidal stability of W Ursae Majoris (W UMa) systems is q _min?=(M ₂/M ₁)～0.071–0.078. However, the mass ratios of some observed W UMa binaries are smaller than the theoretical minimum mass ratio. Using Eggleton’s stellar evolution code, we study the effects of metallicity and evolution on the minimum mass ratio of W UMa systems (M ₁=1.2M _⊙). We assume that $k_{1}^{2}=k_{2}^{2}$ for the component’s dimensionless gyration radii and that the contact degree is about 70 per cent. We find that the dynamical stability of W UMa binaries depends on the metallicity of W UMa systems. For the W UMa systems at age = 0 Gyr, the distribution of the minimum mass ratio has a fairly wide range, from 0.083 to 0.064, with the metallicity range from Z=0.0001 to 0.03. W UMa systems with Z=0.01 have the smallest value of the minimum mass ratio, which is about 0.064. The existence of low-q systems can be explained partly by the dependence of the dimensionless gyration radius on the metallicity. In addition, the dependence of the minimum mass ratio on the evolution, as suggested by previously work, is confirmed.