The period-gap cataclysmic variable CzeV404 Her: A link between SW Sex and SU UMa systems

Context: We present a new study of the eclipsing cataclysmic variable CzeV404 Her (Porb = 0.098 d) that is located in the period gap. Aims: This report determines the origin of the object and the system parameters and probes the accretion flow structure of the system. Methods: We conducted simultaneous time-resolved photometric and spectroscopic observations of CzeV404 Her. We applied our light-curve modelling techniques and the Doppler tomography method to determine the system parameters and analyse the structure of the accretion disk. Results: We found that the system has a massive white dwarf M_WD = 1.00(2) M_sun a mass ratio of q = 0.16, and a relatively hot secondary with an effective temperature T_2 = 4100(50) K. The system inclination is i = 78.8{\deg}. The accretion disk spreads out to the tidal limitation radius and has an extended hot spot or line region. The hot spot or line is hotter than the remaining outer part of the disk in quiescence or in intermediate state, but does not stand out completely from the disk flux in (super)outbursts. Conclusions: We claim that this object represents a link between two distinct classes of SU UMa-type and SW Sex-type cataclysmic variables. The accretion flow structure in the disk corresponds to the SW Sex systems, but the physical conditions inside the disk fit the behaviour of SU UMa-type objects

Period and period change measurements for 143 SuperWASP eclipsing binary candidates near the short-period limit and discovery of a doubly eclipsing quadruple system

Building on previous work, a new search of the SuperWASP archive was carried out to identify eclipsing binary systems near the short-period limit. 143 candidate objects were detected with orbital periods between 16 000 and 20 000 s, of which 97 are new discoveries. Period changes significant at 1σ or more were detected in 74 of these objects, and in 38 the changes were significant at 3σ or more. The significant period changes observed followed an approximately normal distribution with a half-width at half-maximum of ~0.1 s yr-1. There was no apparent relationship between period length and magnitude or direction of period change. Amongst several interesting individual objects studied, 1SWASP J093010.78+533859.5 is presented as a new doubly eclipsing quadruple system, consisting of a contact binary with a 19 674.575 s period and an Algol-type binary with a 112 799.109 s period, separated by 66.1 AU, being the sixth known system of this type

Discovery of a double eclipsing binary with periods near a 3:2 ratio

The evolution of multiple stellar systems can be driven by Kozai cycles and tidal friction (KCTF), which shrink the orbit of the inner binary. There is an interesting possibility that two close binaries on a common long-period orbit experience mutually-induced KCTF. We present the discovery of a possible new quadruple system composed of two unresolved eclipsing binaries (EBs), CzeV343 (V ~ 13.5 mag). We obtained photometric observations of CzeV343 that completely cover the two orbital periods and we successfully model the light curves as the sum of two detached EBs. We provide confidence intervals for the model parameters and minima timings by bootstrap resampling of our data. One of the EBs shows a distinctly eccentric orbit with a total eccentricity of about 0.18. The two orbital periods, 1.20937 and 0.80693 days, are within 0.1% of a 3:2 ratio. We speculate that this might be the result of KCTF-driven evolution of a quadruple system and we discuss this hypothesis in the context of other quadruple systems composed of two EBs. We make our double EB fitting code publicly available to provide a tool for long-term monitoring of the mutual orbit in such systems

Light-time effect detected in fourteen eclipsing binaries

The available minima timings of 14 selected eclipsing binaries (V1297 Cas, HD 24105, KU Aur, GU CMa, GH Mon, AZ Vel, DI Lyn, DK Her, GQ Dra, V624 Her, V1134 Her, KIC 6187893, V1928 Aql, V2486 Cyg) were collected and analyzed. Using the automatic telescopes, surveys, and satellite data, we derived more than 2500 times of eclipses, accompanied with our own ground-based observations. These data were used to detect the period variations in these multiple systems. The eclipse timing variations were described using the third-body hypothesis and the light-time effect. Their respective periods were derived as 2.5, 16.2, 27, 20, 64, 5.6, 22, 115, 27, 42, 6.9, 11.2, 4.1, and 8.4 years for these systems, respectively. The predicted minimal mass of the third body was calculated for each of the systems, and we discuss here their prospective detectability. The light curves of HD 24105, GH Mon, DK Her, V1134 Her, KIC 6187893, V1928 Aql, and V2486 Cyg were analyzed using the PHOEBE program, resulting in physical parameters of the components. Significant fractions of the third light were detected during the light-curve analysis, supporting our hypothesis of the triple-star nature of all these systems. The majority of these systems (nine out of 14) were already known as visual doubles. Our study shifts them to possible quadruples, what makes them even more interesting

Doubly eclipsing systems

Context. Only several doubly eclipsing quadruple stellar systems are known to date, and no dedicated effort to characterize population properties of these interesting objects has yet been made. Aims. Our first goal was to increase number of known doubly eclipsing systems such that the resulting dataset would allow us to study this category of objects via statistical means. In order to minimize biases, we used long-lasting, homogeneous, and well-documented photometric surveys. Second, a common problem of basically all known doubly eclipsing systems is the lack of proof that they constitute gravitationally bound quadruple system in the 2+2 architecture (as opposed to two unrelated binaries that are projected onto the same location in the sky by chance). When possible, we thus sought evidence for the relative motion of the two binaries. In that case, we tried to determine the relevant orbital periods and other parameters. Methods. We analysed photometric data for eclipsing binaries provided by the OGLE survey and we focused on the LMC fields. We found a large number of new doubly eclipsing systems (our discoveries are three times more numerous than the previously known cases in this dataset). In order to prove relative motion of the binaries about a common centre of mass, we made use of the fact that OGLE photometry covers several years. With a typical orbital period of days for the observed binaries, we sought eclipse time variations (ETVs) on the timescale comparable to a decade (this is the same method used for an archetype of the doubly eclipsing system, namely V994 Her). In the cases where we were able to detect the ETV period, the difference between the inner and outer periods in the quadruple system is large enough. This allows us to interpret ETVs primarily as the light-time effect, thus providing an interesting constraint on masses of the binaries. Results. In addition to significantly enlarging the database of known doubly eclipsing systems, we performed a thorough analysis of 72 cases. ETVs for 28 of them (39% of the studied cases) showed evidence of relative motion. Among these individual systems, we note OGLE BLG-ECL-145467, by far the most interesting case; it is bright (12.6 mag in I filter), consists of two detached binaries with periods of ≃3.3 d and ≃4.9 d (making it a candidate for a 3:2 resonant system) revolving about each other in only ≃1538 d. Distribution of the orbital period ratio PA/PB of binaries in 2+2 quadruples shows statistically significant excess at ≃1 and ≃1.5. The former is likely a natural statistical preference in weakly interacting systems with periods within the same range. The latter is thought to be evidence of a capture in the 3:2 mean motion resonance of the two binaries. This sets important constraints on evolutionary channels in these systems. Conclusions. The total number of doubly eclipsing systems increased to 146, more than 90% of which are at low declinations on the southern sky. This motivates us to use southern hemisphere facilities to further characterize these systems, and to seek possibilities to complement this dataset with northern sky systems