High-Speed BVRI Photometry of SS Cyg at Quiescence and at Outburst

BVRI photometry of SS Cyg from the end of 1996 and the beginning of 1997 is presented. The star underwent an eruption around December 11. The amplitude of which was slightly bigger than those of observed earlier eruptions. We saw some indication of the future outburst in the decreasing of brightness in all colours by about 0.4 mag during the last two weeks before the event. The emission of the system moved strongly to the shorter wavelengths at outburst. Our multicolour data confirm the existence of a light variability with the orbital (spectroscopic) period at quiescence. Moreover we found for the first time that this variability exists also at outburst but its amplitude is 3–5 times smaller. Whereas the amplitudes of the orbital variability at quiescence decrease to the longer wavelengths, they increase at outburst to the longer wavelengths. The orbital folded curve at quiescence has two-wave shape and was fitted well by the different visibility of two diametrical opposite hot spots (210000 K) with angular size 10⁰ on the magnetic poles of the white dwarf. An analogy between the two basic states of the U Gem-star SS Cyg, the polar AM Her and Z Cam-star RX And was found.     

The newly discovered eclipsing cataclysmic star 2MASS J16211735 + 4412541 and its peculiarity

We present our observations of the newly discovered, eclipsing cataclysmic star 2MASS J16211735 + 4412541 carried out two weeks after its outburst at the beginning of June 2016. Its main peculiarity is the big increasing of eclipse depth during outburst. We qualitatively modelled the folded light curves at quiescence and outburst in order to explain the reason for increase of the primary luminosity about two hundred times. The light curve fits revealed that such an effect can be reproduced by a flat disc whose radius and temperature are several times bigger than those of the primary at quiescence.     

2MASS J01074282+4845188: A new nova-like cataclysmic star with a deep eclipse

We present V RI photometry and low-resolution spectroscopy of the object 2MASS J01074282+4845188. The V-shape of the eclipse, the phase variability of the colour indices as well as the presence of a pre-eclipse hump, standstill and flickering allow us to conclude that it is a nova-like cataclysmic star. This is supported by the observed broad emission Hα line. Its single profile with a relatively narrow FWHM but large FWZI is typical for a nova-like variable of SW Sex subtype. The observed deep eclipses make the newly discovered cataclysmic star 2MASS J01074282+4845188 an interesting object for future investigation.     

Short-term brightness variations of V747 Cyg

We have conducted high-speed photometric observations of the suspected cataclysmic variable V747 Cyg. The literature data about the spectra of this star are conflicting. Zwitter and Munari [A&AS 107 (1994) 503] obtained spectroscopic observations which confirmed the cataclysmic variable nature of V747 Cyg, whereas Downes et al. [AJ 110 (1995) 1824] have concluded that this object may be a Be + M binary rather than a cataclysmic variable. Our observations revealed the complete absence of the rapid flickering in this star at a millimagnitude level. This phenomenon is to be inherent in all cataclysmic variables. Instead, the lightcurves of V747 Cyg showed probably periodic smooth low-amplitude variations that were visible during each observational night. When V747 Cyg was observed in two colours simultaneously, these variations had the equal phases and amplitudes. A periodogram analysis revealed probable periods of 5.77, 7.41 and 7.59 h. These periods and the amplitude as well as the oscillation behaviour in the different colours are typical of variable Be stars. Hence, V747 Cyg may be a variable Be star but not a cataclysmic variable.     

Detection of eclipses in the suspected V Sge star IPHAS J025827.88+635234.9

We report results of photometry of the suspected V Sge star IPHAS J025827.88+635234.9. The observations were obtained over 25 nights in 2011 and 2012. The total duration of the observations was 153 h. We discovered eclipses typical of cataclysmic variables and flickering, which is also a hallmark of cataclysmic variables. These discoveries characterise this star as a normal cataclysmic variable but not as a star of the V Sge type, as was previously supposed. The eclipse period is equal to 5.882274±0.000008 h. Its depth is equal to 0.3 mag. The full eclipse width is quite large and equal to $(0.160\pm0.011)P_{\rm orb}$ . We obtained an eclipse ephemerid with a formal shelf life of about 500 yr (a 1σ confidence level). This ephemerid is good for investigations of long-term period changes. The eclipse has a complicated two-component V-shaped profile. This profile suggests that the accretion disc is very structured and can consist of an extended disc halo and a quite distinct central part. The off-eclipse light curve is also complicated. It shows two orbital humps at the orbital phases 0.4 and 0.9 and a deep depression at the orbital phase 0.14. By using the period-luminosity-colours relation found by Ak et al., we estimate the distance of this star in the range 660–730 pc. The corresponding absolute visual magnitude is roughly by 1 mag brighter than that for an average cataclysmic variable with the same orbital period. The noted unusual properties of the eclipse profile and off-eclipse light curve can be related with this enlarged luminosity.     

The orbital period and variability of the dwarf nova ES Draconis

A radial velocity study of the cataclysmic variable ES Dra (PG 1524+622) is presented. ES Dra is found to have an orbital period of 0.17660 ± 0.00006 day (4.2384 ± 0.0014 h). The mass-losing secondary star of ES Dra is detectable in the spectrum, and it has a spectral type of M2 ± 1. From this, we estimate the absolute magnitude of ES Dra during our spectroscopic observations to have been M_R = 6.5 ± 0.5, and its distance to be 720 ± 150 pc. The long-term light curve of ES Dra compiled by the American Association of Variable Star Observers (AAVSO) shows that ES Dra is a Z Cam star, which between 1995 and 2009 spent most of its time in standstill.     

The photometric period of the cataclysmic variable HV Andromedae

We present four nights of time-resolved photometry of the cataclysmic variable star HV And. Our time series analysis has revealed a prominent period at 3.368 ± 0.060 h, as well as some low frequency power. We interpret this signal, from saw-tooth waves in the light curve, as evidence of superhumps in HV And.     

Detection of the optical counterpart of the proposed double degenerate polar RX J1914+24

We have detected the optical counterpart of the proposed double degenerate polar RX J1914+24. The I -band light curve is modulated on the 9.5-min period seen in X-rays. There is no evidence for any other periods. No significant modulation is seen in J . The infrared colours of RX J1914+24 are not consistent with a main-sequence dwarf secondary star. Our ASCA spectrum of RX J1914+24 is typical of a heavily absorbed polar and our ASCA light curve also shows only the 9.5-min period. We find that the folded I band and X-ray light curves are out of phase. We attribute the I -band flux to the irradiated face of the donor star. The long-term X-ray light curve shows a variation in the observed flux of up to an order of magnitude. These observations strengthen the view that RX J1914+24 is indeed the first double degenerate polar to be detected. In this light, we discuss the synchronizing mechanisms in such a close binary and other system parameters.     

The Orbital Period of the Be/Neutron Star Binary RX J0812.4-3114

We present the results of Rossi X-Ray Timing Explorer (RXTE) observations of the Be star X-ray binary system RX J0812.4-3114. A light curve obtained with the RXTE All-Sky Monitor (ASM) shows that the source is currently in an active state with outbursts occurring at approximately 80 day intervals. The source underwent a transition from an inactive state to this regular outburst state early in 1998. An observation of RX J0812.4-3114 was obtained with the RXTE Proportional Counter Array (PCA) close to the time of a predicted maximum in 1999 March, and strong pulsations were detected at a period of 31.88 s. This confirms the result of an earlier PCA observation by Reig & Roche that was also obtained serendipitously near the predicted maximum flux of the 80 day period and also near the start of the current active state. We interpret the periodicity in the ASM light curve as indicating the orbital period of RX J0812.4-3114 with outbursts occurring around periastron passage.     

Miscellaneous photometric variations in cataclysmic variables: V455 And,SS Cyg,AQ Men,LQ Peg,RW Tri and UX UMa

Cataclysmic variables are among the photometrically most unstable star in the zoo of stellar objects, exhibiting light variations on all time-scales between millennia and seconds. The literature is full of reports on variable phenomena which often require independent confirmation before they can be accepted as established facts. In this contribution I investigate accounts on miscellaneous variable features observed in six cataclysmic variables, drawing for this purpose largely on archival data, most of which have not been investigated in detail in the past, and complementing these data with some new observations. This enabled to confirm and expand upon some hitherto unconfirmed features in the light curves of these star, as well as the rejection of some others, while in still other cases an unambiguous answer to questions arising from previous papers was not possible.     

The complete set of ASCA X-ray observations of non-magnetic cataclysmic variables

We present the complete set of 34 ASCA observations of non-magnetic cataclysmic variables. Timing analysis reveals large X-ray flux variations in dwarf novae in outburst (Z Cam, SS Cyg and SU UMa) and orbital modulation in high inclination systems (including OY Car, HT Cas, U Gem, T Leo). We also found episodes of unusually low accretion rate during quiescence (VW Hyi and SS Cyg). Spectral analysis reveals broad temperature distributions in individual systems, with emission weighted to lower temperatures in dwarf novae in outburst. Absorption in excess of interstellar values is required in dwarf novae in outburst, but not in quiescence. We also find evidence for subsolar abundances and X-ray reflection in the brightest systems.
LS Peg, V426 Oph and EI UMa have X-ray spectra that are distinct from the rest of the sample and all three exhibit candidate X-ray periodicities. We argue that they should be reclassified as intermediate polars.
In the case of V345 Pav we found that the X-ray source had been previously misidentified.     

GD 552: a cataclysmic variable with a brown dwarf companion?

GD 552 is a high proper motion star with the strong, double-peaked emission lines characteristic of the dwarf nova class of cataclysmic variable (CV) star, and yet no outburst has been detected during the past 12 yr of monitoring. We present spectroscopy taken with the aim of detecting emission from the mass donor in this system. We fail to do so at a level which allows us to rule out the presence of a near-main-sequence star donor. Given GD 552's orbital period of 103 min, this suggests that it is either a system that has evolved through the ∼80-minute orbital period minimum of CV stars and now has a brown dwarf mass donor, or that has formed with a brown dwarf donor in the first place. This model explains the low observed orbital velocity of the white dwarf and GD 552's low luminosity. It is also consistent with the absence of outbursts from the system.     

Gamma-ray emission from pulsars: strength of the acceleration field in the outer gap

In this study we present and re-analyse the historical, 1889–1998, light curve (LC) of the eclipsing symbiotic binary AR Pav. For the first time, we show that the timing of mid-points of eclipses observed during a quiescent phase obeys a quadratic ephemeris, with an initial orbital period P ₀=605.18 d and a rate of period change     .
We determined a distance to the system of 5.8±1.5 kpc, the mass ratio of the giant to the hot star, M _g M _h=0.4±0.1, the mass of the giant, M _g=1.8+1/−0.5 M_⊙ and its radius, R _g=167±15 R_⊙.
During quiescence, the LC has characteristic features similar to those observed in cataclysmic variables (CVs). It can be well reproduced by a model of a large accretion disc surrounding the hot star. However, it is probable that the geometry of the transferred material in the Roche lobe of the accretor in AR Pav is different from that of CVs.
During active phases the shape of the LC changes considerably. A complex wave-like variation developed as a function of the orbital phase with an amplitude of ∼1 mag. It is interpreted in terms of a collisionally heated emission region located on the giant surface and arising from the hot star eruption.     

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables – IV. Observations of frequency doubling and tripling in VW Hyi

We present new observations of the rapid oscillations in the dwarf nova VW Hyi, made late in outburst. These dwarf nova oscillations (DNOs) increase in period until they reach 33 s, when a transition to a strong 1st harmonic and weak fundamental takes place. After further period increase, the 2nd harmonic appears; often all three components are present simultaneously. This 1:2:3 frequency suite is similar to what has been seen in some neutron star and black hole X-ray binaries, but has not previously been seen in a cataclysmic variable. When studied in detail, the fundamental and 2nd harmonic vary similarly in phase, but the 1st harmonic behaves independently, though keeping close to twice the frequency of the fundamental. The fundamental period of the DNOs, as directly observed or inferred from the harmonics, increases to ∼100 s before the oscillation disappears as the star reaches quiescence. Its maximum period is close to that of the 'longer-period' DNOs observed in VW Hyi. The quasi-periodic oscillations (QPOs), which have fundamental periods 400–1000 s, behave in the same way, showing 1st and 2nd harmonics at approximately the same times as the DNOs. We explore some possible models. One in which the existence of the 1st harmonic is due to the transition from viewing a single accretion region to viewing two regions, and the rate of accretion on to the primary is modulated at the frequency of the 1st harmonic, as in the 'beat frequency model', can generate the suite of DNO frequencies observed. But the behaviour of the QPOs is not yet understood.     

The period gap and the AM Herculis type systems

We argue that the period distribution of AM Herculis binaries in the enlarged sample incorporating results from the recent ROSAT X-ray survey differs significantly from that of other cataclysmic variables. In particular, there is no evidence for a pronounced period gap at 2—3 hr and the significance of the period spike at about 114 min is brought into question. We present an alternative evolutionary scenario for the AM Herculis binaries based on the hypothesis that magnetic braking by the stellar wind of the M star secondary either ceases or is severely curtailed when the rotation of the magnetic white dwarf becomes synchronised with the orbital motion, The orbital evolution of the AM Herculis binaries is thereafter driven mainly by angular momentum loss due to gravitational radiation. This scenario not only explains the higher proportion of AM Herculis binaries in the period gap when compared with other cataclysmic variables but also provides a natural explanation for the low mass transfer rates in these binaries and for the existence of an apparent upper limit for the surface magnetic fields of their white dwarfs.     

Brown dwarfs and the cataclysmic variable period minimum

Using improved, up-to-date stellar input physics tested against observations of low-mass stars and brown dwarfs, we calculate the secular evolution of low-mass donor cataclysmic variables (CVs), including those that form with a brown-dwarf donor. Our models confirm the mismatch between the calculated minimum period ( P _min70 min) and the observed short-period cut-off (80 min) in the CV period histogram. We find that tidal and rotational corrections applied to the one-dimensional stellar structure equations have no significant effect on the period minimum. Theoretical period distributions synthesized from our model sequences always show an accumulation of systems at the minimum period, a feature absent from the observed distribution. We suggest that non-magnetic CVs become unobservable as they are effectively trapped in permanent quiescence before they reach P _min, and that small-number statistics may hide the period spike for magnetic CVs.     

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.     

Superhump and outburst activity of the cataclysmic variable RZ LMi in the $$- and optical passbands

An analysis of the new \(U,B,V,R_{C},I_{C}\)-photometry of the cataclysmic variable RZ LMi obtained in 2016–17 showed the largest \((U-B)\) colour excess in quiescence as well as during the decline of brightness, associated with the outbursts activity. The smallest \((U-B)\) colour excess was found during the brightness increase from the quiescence. In contrast to the \((U-B)\) colour index, the \((B-V),(V-R_{C}),(R_{C}-I_{C})\) colour indices exhibits the largest colour excesses near the maximum of the outburst and the smallest during the quiescence. The \((B-V)\) colour index showed also a large excess 1–2 days before a minimum. The detailed study of superhumps during the maximum of activity reveals the largest \((U-B)\) colour excess at the time of the minimum brightness of superhumps. The \((B-R_{C})\) colour index exhibits a similar behaviour, but with a phase shift of \(+0.1\mbox{--}{+}0.2\) period of superhumps. The tracks in two-colour and colour-magnitude diagrams during superoutbursts are compared with the data for other cataclysmic variables during their outbursts as well as with published theoretical calculations.     

The new intermediate polar RX J1238 − 38: a system below the period gap?

We present optical observations of the recently discovered ROSAT source RX J1238 − 38, which is a new member of the intermediate polar class of asynchronous magnetic cataclysmic variables (CVs). Optical photometry reveals two coherent periodicities at 1860 and 2147 s respectively, with similar amplitudes of ∼ 8 per cent. Infrared ( J -band) intensity variations are detected only at the 1860-s period, at an amplitude of ∼ 15 per cent. The initial hypothesis, that these two periods were the spin and synodic (i.e., beat) period respectively, appears not to be supported by the spectroscopic data. The emission lines vary on the longer photometric period, and radial velocity variations are detected at this period and at a longer period of ∼ 5300 s, which we identify as the spin and orbital periods respectively. The most likely explanation for the 1860-s period is that it is the first harmonic of the ω − Ω sideband, leading to an improved determination of the orbital period as 5077 s (= 84 min). If this interpretation is correct, RX J1238 − 38 joins EX Hya as the only other intermediate polar below the 2–3 h period gap, and with an orbital period close to the minimum for CVs with non-degenerate secondaries. The spin-modulated emission-line radial velocities and widths appear to be anticorrelated, with maximum width occurring at maximum blueshift. Such an anticorrelation is expected for aspect changes of accretion curtains. Polarimetric observations of RX J1238 − 38 were inconclusive, although we can put a limit of 0.4 per cent on any variability on the circular polarization, and certainly there is no indication of variations at the photometric or spectroscopic periods.     

Gemini J ‐band observations of RX J0806.4–4123

The detection of near‐infrared (NIR) excess at the position of a star can indicate either a substellar companion or a disk around the respective star. In this work we probed whether a 2.5σ H ‐band flux enhancement at the position of the isolated neutron star RX J0806.4–4123 can be confirmed at another NIR wavelength. We observed RXJ0806.4–4123 in the J ‐band with Gemini South equipped with FLAMINGOS‐2. There was no significant detection of a J ‐band source at the neutron star position. However, similarly to the H ‐band we found a very faint (1.4σ) flux enhancement with a nominal magnitude of J = 24.8 ± 0.5. The overall NIR‐detection significance is 3.1σ. If real, this emission is too bright to come from the neutron star alone. Deeper near‐infrared observations are necessary to confirm or refute the potential NIR excess. The confirmation of such NIR excess could imply that there is a substellar companion or a disk around RXJ0806.4–4123. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)