Photometric observations and numerical modeling of AW Sge

In this work, we present R-band photometric light curves of Cataclysmic Variable AW Sge, an SU Uma type, near superoutburst maximum. The positive superhump shape changes over three days, from single peaked on October 11, 2013 to one maximum near phase ϕ ∼ 0.3 followed by minor peaks near phases ϕ ∼ 0.6 and ϕ ∼ 0.9, respectively, on October 13, 2013. Using the maxima from October 11–13, 2013 (JD 2456577–2356579), the observed positive superhump period is 0.074293 ± 0.000025 days.In addition to the observations, we also provide a three dimensional Smoothed Particle Hydrodynamic simulation near superoutburst maximum, for comparison, assuming a secondary-to-primary mass ratio $q=M_2/M_1$ = 0.6 M_⊙/0.132 M_⊙ = 0.22. The simulation produces positive superhump shapes that are similar to the observations. The simulated positive superhump has a period of 0.076923 days, which is approximately 6% longer than the orbital period, assuming an orbital period P_orb = 0.0724 days. The 3.5% difference from the observed positive superhump period is likely due to the assumptions used in generating the simulations, as the orbital period and masses are not well known. From an analysis of the simulated positive superhump shape near superoutburst maximum, the maximum occurs near ϕ ∼ 0.3, when the disk is highly elliptical and eccentric and at least one of the two density waves is compressing with the disk rim. Based on the simulation, we find that the disk may be tilted and precessing in the retrograde direction at a time that is just before the next outburst and/or superoutburst.     

The orbital and superhump periods of the dwarf nova HS 0417+7445 in Camelopardalis

We present the 2005–2010 outburst history of the SU UMa-type dwarf HS 0417+7445, along with a detailed analysis of extensive time-series photometry obtained in March 2008 during the second recorded superoutburst of the system. The mean outburst interval is 197 ± 59 d, with a median of 193 d. The March 2008 superoutburst was preceded by a precursor outburst, had an amplitude of 4.2 magnitudes, and the whole event lasted about 16 days. No superhumps were detected during the decline from the precursor outburst, and our data suggests instead that orbital humps were present during that phase. Early superhumps detected during the rise to the superoutburst maximum exhibited an unusually large fractional period excess of ? = 0.137 (P_sh = 0.0856(88) d). Following the maximum, a linear decline in brightness followed, lasting at least 6 days. During this decline, a stable superhump period of P_sh = 0.07824(2) d was measured. Superimposed on the superhumps were orbital humps, which allowed us to accurately measure the orbital period of HS 0417+7445, P_orb = 0.07531(8) d, which was previously only poorly estimated. The fractional superhump period excess during the main phase of the outburst was ? = 0.037, which is typical for SU UMa dwarf novae with similar orbital period. Our observations are consistent with the predictions of the thermal-tidal instability model for the onset of superoutbursts, but a larger number of superoutbursts with extensive time-series photometry during the early phases of the outburst would be needed to reach a definite conclusion on the cause of superoutbursts.     

Superhump evolution of WZ Sge-type dwarf nova ASASSN-14cv at rebrightening stage

We report the results of observations of a WZ Sge-type dwarf nova ASASSN-14cv, acquired in 2014 and covering the end of a superoutburst and a rebrightening stage. We detected 8 rebrightenings of this star. Based on the light curve profiles of the rebrightenings, we conclude on the existence of both the “inside-out” and “outside-in” outbursts. During the entire course of the rebrightening stage, a brightness variability with the mean period of P = 0.^d06042(8) was detected, which was identified as a superhump period during the stage B of the superoutburst. The character of the registered superhump evolution can be either described by a parabolic approximation with the negative P_dot = ?1.1 × 10^?5, or by an approximation with 2 linear areas with the corresponding periods of 0.^d06074(3) and 0.^d06046(9).     

A Time Evolution Study of the Superhumps of the Dwarf Nova 1RXS J232953.9+062814 by Wavelet Transform

The time evolution behaviour of the superhumps of the dwarf nova1RXS J232953.9+ 062814 is investigated with the wavelet analysis method. On the basis of two nights CCD photometry performed during its first superoutburst as well as other published brightness data, we reveal the superhump's time-dependence as a function of periods and time. Our light curves, which phased in the rapid decay ending portion of the superoutburst and in the dawn of a following normal outburst, are important to help trace the superhump evolution for the star. Both the superhump period and the orbital period of the binary system are detected in the present data. We obtain P _sh=0.0458±0.0002d and P _orb=0.0450±0.0002d. They agree with those existing values. The two periods exchanged their roles during the superhump evolution. The general profile of brightness fading over the outbursts roughly followed an exponential decay law or a form of a five-order polynomial. This revised version was published online in July 2006 with corrections to the Cover Date.     

A normal and superoutburst study of the eclipsing SU UMa star: DV Ursae Majoris

We report on time-resolved photometry carried out during the 1995 short outburst and the 1997 long outburst in the eclipsing dwarf nova DV UMa. The revised orbital period is 0.0858526172 (67) d. We detected gigantic superhumps with an amplitude of ∼0.6 mag in the mid-phase of the 1997 outburst, revealing the SU UMa nature of DV UMa. The superhump period is 0.0887 (4) d. The superhumps became less clear during the late phase of the superoutburst, and we found two possible periods of 0.0885 (15) and 0.0764 (15). During both outbursts, the eclipse was wide and shallow near the maximum, and then became narrower and deeper, which is qualitatively well explained by the current disc instability theory.     

Photometry of the Cataclysmic Variables V1159 Ori and BZ UMa

V1159 Ori is an ER UMa sub-type cataclysmic variable belonging to the SU UMa type, and the controversial BZ UMa lies between the U Gem type and the WZ Sge type, but it possesses also the periodicity characteristics of SU UMa. We have made photometric observations of these two cataclysmic variables with the 1m RCC optical telescope in Yunnan Astronomical Observatory from Feb. 24th to 25th, 2008. The obtained light curves of V1159 Ori exhibit superhumps in the descending stage of a normal outburst, this provides an observational evidence for the universal existence of superhumps in ER UMa-type stars. During our observations BZ UMa was at the maximum of an outburst, but no evident superhump period was detected. The previous observations made by AAVSO (American Association of Variable Star Observers) also have never found any definite superhump. This demonstrates that BZ UMa probably is not a SU UMa-type variable. According to the range of its magnitude variations, BZ UMa is closer to WZ Sge.     

Searching for superhump period of cataclysmic variable AY Psc

The results obtained from unfiltered photometric CCD observations of AY Psc made during 17, 20 and 12 nights, respectively, in 2003, 2004 and 2005 are presented. A period of 0.21732 ± 0.00001 d was detected in the data. This period is consistent with the previously proposed orbital period of P_orb = 0.2173209 d ((Diaz and Steiner, 1990)). Since this period was present in the light curves taken in all three years, with no apparent change in its value or amplitude, it is interpreted as the orbital period of this binary system. In addition, quasi-periodicities of 0.2057 ± 0.0001 d, 0.2063 ± 0.0001 d, 0.2072 ± 0.0001 d for the years 2003, 2004 and 2005, respectively, were also discovered. These periods were interpreted as negative superhump periods and it was seen that they changes from year to year. Therefore AY Psc is then classified as a negative superhump system.     

The SU Ursae Majoris Star TU Crateris

We have established that the cataclysmic variable TU Crateris is an SU UMa star. Superhumps were observed after 3 days of the 1998 March-April supermaximum, repeating with a mean period of P_s = 0d.08535(5). Timings of superhump maxima revealed a period decrease of P = 7.2 × 10^-5. Based on an empirical relationship, we estimated an orbital period of 0d.0810(25), just in the lower limit of the reported quiescence photometric period. H emission lines during quiescence vary with the orbital period with radial velocity half amplitude of 70 ± 19 km s^-1, evidencing a hotspot located in front of the standard position.     

Superhumps in a Peculiar SU Ursae Majoris-Type Dwarf Nova, ER Ursae Majoris

We report the photometry of a peculiar SU Ursae Majoris-type dwarf nova, ER Ursae Majoris, for 10 nights during 1998 December and 1999 March, covering a complete rise to the supermaximum and a normal outburst cycle. Superhumps have been found during the rise to the superoutburst. A negative superhump appeared in the December 22 light curve, while the superhump on the next night became positive and had a large-amplitude waveform distinct from that of the previous night. In the normal outbursts we captured, superhumps with larger or smaller amplitudes seem to always exist, although it is not necessarily true for every normal outburst. These results show great resemblance to V1159 Ori. It is more likely that superhumps occasionally exist at essentially all phases of the eruption cycles of ER UMa stars, which should be considered in modeling.     

Recurrent Population II X-ray transients — similarities to SU UMa cataclysmic variables

Quasi-periodic outburst activity is not uncommon among Population II X-ray binaries. This paper reports observations of such activity in several sources, made by the Vela 5B X-ray monitor. Typical periods are 1/2–2 years with an r.m.s. scatter in interval time of 10%. This activity is reminiscent of the superoutburst cycles of SU UMa CV's with respect to mean recurrence times, the variation of the recurrence times about their mean, and the total mass transferred during outburst. However, the outbursts in the X-ray sources have a substantially longer duration, 50–100 days instead of 10 days. I suggest that SU UMa and X-ray transient outbursts may be caused by similar mass-transfer instabilities.     

A ‘superoutburst’ in XTEJ1118+480

I propose that the properties of the two outbursts observed in the X‐ray transient XTEJ1118+480 in 2000 are akin to superoutbursts of SU UMa stars. In these systems a ‘normal’ outburst immediately precedes a 5–10 times longer (‘super’) outburst. The optical light curve of the outbursts of XTEJ1118+480 is remarkably similar to that seen in some SU UMa stars, such as UVPer and TLeo, where the precursor outburst is distinct from the superoutburst, but the time scales are a factor of ∼15 different. The first outburst of XTEJ1118+480 was relatively short (∼1 month) while the second outburst was ∼5 times longer. During the second outburst superhumps were seen, a feature characteristic for superoutbursts. The gap of about a month between the two outbursts is longer in X‐rays with respect to the optical, a feature not previously recognized for X‐ray transients. Also in SU UMa stars the precursor outburst becomes more distinct at shorter wavelengths. Finally, I show that the time of appearance of the superhumps in XTEJ1118+480 is consistent with the expected superhump growth time, if the superhump mechanism was triggered during the first outburst. I conclude that the similarity in outburst behaviour in the two types of systems provides further support that a common mechanism is at work to start the long (‘super’) outbursts.     

Superhumps in V348 Pup

The eclipsing nova-like cataclysmic variable star V348 Pup exhibits a persistent luminosity modulation with a period 6 per cent longer than its 2.44-h orbital period ( P _orb). This has been interpreted as a 'positive superhump' resulting from a slowly precessing non-axisymmetric accretion disc gravitationally interacting with the secondary. We find a clear modulation of mid-eclipse times on the superhump period, which agrees well with the predictions of a simple precessing eccentric disc model. Our modelling shows that the disc light centre is on the far side of the disc from the donor star when the superhump reaches maximum light. This phasing suggests a link between superhumps in V348 Pup and late superhumps in SU UMa systems. Modelling of the full light curve and maximum entropy eclipse mapping both show that the disc emission is concentrated closer to the white dwarf at superhump maximum than at superhump minimum. We detect additional signals consistent with the beat periods between the implied disc precession period and both and     

A ROSAT WFC observation of SW UMa: the EUV behaviour of dwarf novae in superoutburst explained

During re-processing and analysis of the entire ROSAT Wide Field Camera (WFC) pointed observations data base, we discovered a serendipitous, off-axis detection of the cataclysmic variable SW UMa at the onset of its 1997 October superoutburst. Although long outbursts in this SU UMa-type system are known to occur every ∼ 450 d, none had ever been previously observed in the extreme ultra-violet (EUV) by ROSAT . The WFC observations began just ≈13 hr after the optical rise was detected. With a peak count rate of ∼ 4.5 count s⁻¹ in the S1 filter, SW UMa was temporarily the third brightest object in the sky in this waveband. Over the next ≈19 hr the measured EUV flux dropped to < 2 count s⁻¹, while the optical brightness remained essentially static at m _v∼11 . Similar behaviour has also been recently reported in the EUV light curve of the related SU UMa-type binary OY Car during superoutburst, as reported by Mauche & Raymond. In contrast, U Gem-type dwarf novae show no such early EUV dip during normal outbursts. Therefore, this feature may be common in superoutbursts of SU UMa-like systems. We expand on ideas first put forward by Osaki and Mauche & Raymond and offer an explanation for this behaviour by examining the interplay between the thermal and tidal instabilities that affect the accretion discs in these systems.     

Systematics of superoutbursts in dwarf novae

Photometric properties of known and suspected members of the SU UMa subclass of dwarf novae are tabulated and discussed. The precessing disc model of superoutbursts gives a satisfactory quantitative explanation of the periods of superhumps and their changes during superoutburst. The systems such as WZ Sge and HV Vir that have very long intervals between superoutbursts are deduced to be beyond the orbital period minimum, and have degenerate secondaries. The systems such as V1159 Ori that have extremely short recurrence times have high rates of mass transfer and are the equivalent of the Z Cam subclass that occurs at longer orbital periods.A simplified analytical approach to the theory of accretion discs is able to explain the correlations between normal and superoutburst recurrence times. It also explains the slope of the plateau region of superoutbursts, and why the slope is shallower in the very short recurrence time systems.     

The K spectral type contact binary NSVS 1557555: Photometric solution and preliminary elements

We present the first CCD sets of complete light curves for the W Ursae Majoris system NSVS 1557555.The observations were performed in the B, V and I_c bands using the 0.25  m telescope of the Stazione Astronomica Betelgeuse Northern Italy, during 8 nights in October and November 2016.Based on our new eleven Time of Minima (ToM), and two recent ones found in bibliography, the short orbital period of the system is confirmed and revised to P = 0.2725163 days .A reasonable fit of the synthetic light curves of the data indicate that NSVS 1557555 is a late-type (K1+K3) shallow contact binary system of W-Subtype of the W Ursae Majoris systems, with a mass ratio of q = 1.8, a degree of contact factor f = 12.5%, a temperature difference between the components of 240K and inclination i = 85°.The light curves show asymmetries at the maxima with the maximum at phase 0.75 higher the other one (inverse O’Connell effect).To explain the light asymmetries we used a model that involves an hot spotted region on the surface of the cooler star.The definitive solution is only possible with a large amount of third light (L₃ = 0.58 in B Filter). It may come from a hot tertiary component.The absolute dimensions of the system are estimated. From the logM-logL diagram it is seen that both components of NSVS 1557555 follow the general pattern of the W subtype W Ursae Majoris systems.The orbital angular momentum is compared with those of other W UMa type binaries and is normal.     

New CCD photometry and light curve analysis of two WUMaBinaries: 1SWASP J133417.80+394314.4 and V2790 Orion

We present a new multicolor CCD photometry and light curve analysis of two eclipsing binary systems, 1SWASP J133417.80 + 394314.4 and V2790 Orion. The photometric solutions for both binaries were carried out using the updated version of the Wilson– Devinney code. The results showed that first systems is A- type W UMa with mass ratios q = 0.158 while the second system is W- type with q = 3.2. The systems show over contact configuration with fill-out factors of f = 43% and 14% respectively. We calculated the orbital and absolute physical parameters for both systems and investigated their evolutionary state.     

New CCD photometry of the eclipsing binary system V1067 Her

We present a new set of CCD photometric observations for the short period eclipsing binary 1SWASP J1743 (= V1067 Her). We have determined the available times of light minima and two new linear and quadratic ephemerides have been obtained. The photometric solutions for the system have been performed using Wilson and Devinney Code. The 3D and fill out configuration revealed that V1067 Her is an over contact W UMa binary with relatively low fill-out factor of about 16%.We investigated the period variation for the system. It showed a strong evidence of period changes by using the (O-C) residual diagram method and we have concluded long-term orbital period decrease rate dP/dt= −3.0 × 10⁻⁷ d/yr, corresponding to a time scale 8.6 × 10⁵ yr. Such period decrease in the A-type W UMa systems is usually interpreted to be due to mass transfer from the more to the less massive component.     

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.     

The first photometric study of W UMa eclipsing binary OQ Dra

The present study is an analysis of V-band CCD observations of new W UMa contact binary OQ Dra. To carry out the analysis, Primary and secondary minimum were obtained and new epoch was calculated. The computed period of system was 0.33967 day. Light curve analysis was performed using Binary Maker 3 and PHOEBE that uses the latest Wilson–Devinney code. We obtained photometric mass ratio of q_ptm = 0.55.O’Connell effect also was seen in the fitted model. Finally, the best model was achieved by introducing 2 spots on each component.     

Are superhumps good measures of the mass ratio for AM CVn systems?

We extend recent work that included the effect of pressure forces to derive the precession rate of eccentric accretion discs in cataclysmic variables to the case of double degenerate systems. We find that the logical scaling of the pressure force in such systems results in predictions of unrealistically high primary masses. Using the prototype AM CVn as a calibrator for the magnitude of the effect, we find that there is no scaling that applies consistently to all the systems in the class. We discuss the reasons for the lack of a superhump period to mass ratio relationship analogous to that known for SU UMa systems and suggest that this is because these secondaries do not have a single valued mass–radius relationship. We highlight the unreliability of mass ratios derived by applying the SU UMa expression to the AM CVn binaries.