We present an analysis of photometric observations of the eclipsing novalike variable DW UMa made by the CBA consortium between 1999 and 2015. Analysis of 372 new and 260 previously published eclipse timings reveals a 13.6 year period or quasi-period in the times of minimum light. The seasonal light curves show a complex spectrum of periodic signals: both positive and negative superhumps, likely arising from a prograde apsidal precession and a retrograde nodal precession of the accretion disc. These signals appear most prominently and famously as sidebands of the orbital frequency but the precession frequencies themselves, at 0.40 and 0.22 cycles per day, are also seen directly in the power spectrum. The superhumps are sometimes seen together and sometimes separately. The depth, width and skew of eclipses are all modulated in phase with both nodal and apsidal precession of the tilted and eccentric accretion disc. The superhumps, or more correctly the precessional motions which produce them, may be essential to understanding the mysterious SW Sextantis syndrome. Disc wobble and eccentricity can both produce Doppler signatures inconsistent with the true dynamical motions in the binary, and disc wobble might boost the mass-transfer rate by enabling the hot white dwarf to directly irradiate the secondary star.

V1432 Aquilae is the only known eclipsing asynchronous polar. In this respect it is unique and therefore merits our attention. We report the results of a 15-year campaign by the globally distributed Center for Backyard Astrophysics to observe V1432 Aql and investigate its return to synchronism. Originally knocked out of synchrony by a nova explosion before observing records began, the magnetic white dwarf in V1432 Aql is currently rotating slower than the orbital period but is gradually catching up. The fortuitously high inclination of the binary orbit affords us the bonus of eclipses providing a regular clock against which these temporal changes can be assessed. At the present rate, synchronism should be achieved around 2100. The continually changing trajectory of the accretion stream as it follows the magnetic field lines of the rotating white dwarf produces a complex pattern of light emission which we have measured and documented, providing comprehensive observational evidence against which physical models of the system can be tested.

A recent analysis by Hoard et al. of FUSE and optical spectra of the nova-like cataclysmic variable MV Lyrae derived a system model and associated synthetic spectrum which accurately fit the observed spectra. Yet that model, with an orbital inclination from the literature of i = 12◦, produced a synthetic light curve with an amplitude appreciably larger than observed. We show that optimized light curve fitting, based on our spectrum analysis model, determines an orbital inclination of 7◦.

PG 1553+11 was the target of a coordinated 3 week multiwavelength campaign during 2003 April and May. A significant X-ray flare was observed during the second half of this campaign. Although no optical flare was recorded during the X-ray campaign, optical observations obtained immediately prior to the campaign displayed a flux higher than that recorded during the campaign. An optical flare was observed a few days after the end of the X-ray campaign and may be related to the X-ray flare. Radio observations were made at three frequencies, with no significant changes in flux detected near the times of the optical and X-ray flares. The spectral energy distributions and flux ratios in different wave bands observed for this object are compared to other X-ray-selected blazars to demonstrate that PG 1553+11 is an extreme member of this group.

We report on successes and failures in searching for positive superhumps in cataclysmic variables, and show the superhumping fraction as a function of orbital period. Basically, all short‐period system do, all long‐period systems do not, and a 50% success rate is found at Porb = 3.1 ± 0.2 hr. We can use this to measure the critical mass ratio for the creation of superhumps. With a mass‐radius relation appropriate for cataclysmic variables, and an assumed mean white‐dwarf mass of 0.75 M⊙, we find a mass ratio qcrit = 0.35 ± 0.02. We also report superhump studies of several stars of independently known mass ratio: OU Vir, XZ Eri, UU Aqr, and KV UMa (=XTE J1118+480). The latter two are of special interest, because they represent the most extreme mass ratios for which accurate superhump measurements have been made. We use these to improve the ε(q) calibration, by which we can infer the elusive q from the easy‐to‐measure ε (the fractional period excess of Psuperhump over Porb). This relation allows mass and radius estimates for the secondary star in any cataclysmic variable (CV) showing superhumps. The consequent mass‐radius law shows an apparent discontinuity in radius near 0.2 M⊙, as predicted by the disrupted magnetic braking model for the 2.1–2.7 hr period gap. This is effectively the “empirical main sequence” for CV secondaries.

We report detailed follow-up observations of the cataclysmic variable HS 2331+3905, identified as an emission-line object in the Hamburg Quasar Survey. An orbital period of 81.08 min is unambiguously determined from the detection of eclipses in the light curves of HS 2331+3905. A second photometric period is consistently detected at P ≃ 83.38 min, ∼ 2.8% longer than Porb, which we tentatively relate to the presence of permanent superhumps. High time resolution photometry exhibits short-timescale variability on time scales of ≃ 5 − 6 min which we interpret as non-radial white dwarf pulsations, as well as a coherent signal at 1.12 min, which is likely to be the white dwarf spin period. A large-amplitude quasi-sinusoidal radial velocity modulation of the Balmer and Helium lines with a period ∼ 3.5 h is persistently detected throughout three seasons of time-resolved spectroscopy. However, this spectroscopic period, which is in no way related to the orbital period, is not strictly coherent but drifts in period and/or phase on time scales of a few days. Modeling the far-ultraviolet to infrared spectral energy distribution of HS 2331+3905, we determine a white dwarf temperature of Teff ≃ 10 500 K (assuming Mwd = 0.6 M⊙), close to the ZZ Ceti instability strip of single white dwarfs. The spectral model implies a distance of d = 90 ± 15 pc, and a low value for the distance is supported by the large proper motion of the system, μ = 0.14 yr. The non-detection of molecular bands and the low J , H , and K fluxes of HS 2331+3905 make this object a very likely candidate for a brown-dwarf donor.

AbstractFrom a 45ks Chandra observation of V42G Oph we have obtained high-resolution X-ray spectra at moderate signal-to-noise, and a, good quality, uninterrupted lightcurve. The spectra are reasonably fit with a cooling flow model, similar to EX Hya and U Gem. Our analysis of the Chandra and additional X-ray/optical lightcurves reveals a persistent modulation at 4.2 hr from 1988 to 2003, likely the white dwarf spin period indicating an intermediate polar nature for V426 Oph.

We present far-UV observations of three peculiar magnetic cataclysmic variables (MCVs), BY Cam, V 1309 Ori and AE Aqr, obtained with the FUSE satellite. Previous IUE spectra of these three objects revealed quite unusual resonance lines compared to other MCVs: an intense NV line and a weak CIV line. The FUSE spectra of these sources exhibit broad OVI lines as well as a strong NIII line at 991 Angstrom, while the CIII 1175Angstrom line is nearly absent. Photoionisation models fail to produce the observed line intensities. This confirms non-solar CNO abundances. We discuss possible origins for these peculiar abundances, including the signature of nova thermonuclear runaways (TNR) at the surface of the magnetized white dwarf.

We obtained EUV photometry, optical spectroscopy, and multicolor optical photometry for WX Cet during its 1998 November superoutburst. WX Cet is only the second short‐period, low mass transfer cataclysmic variable (TOAD) to ever be observed in the EUV. Our determined superhump period is consistent with that found by Kato et al. (0.059 day), and we confirm that superhumps are gray in the optical. The optical spectra provide direct evidence that the line emission region is optically thick, and our multiwavelength photometric measurements are used to determine the inner accretion disk and boundary layer temperatures during superoutburst. Using a determined distance to WX Cet of ∼130 pc, we find TID = 21,000 K and TBL ∼ 72,500 K. Both values are in good agreement with that expected by models of the superoutburst continuum being produced by the inner disk and boundary layer.

We report the results of long observing campaigns on two novalike variables: V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra, complex line profiles signifying mass loss at particular orbital phases, and similar orbital periods (respectively, 0.12433 and 0.12056 days). They are well-credentialed members of the SW Sex class of cataclysmic variables. Their light curves are also quite complex. V442 Oph shows periodic signals with periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar signals at 0.11696(8) and 4.05(12) days. We interpret these short and long periods, respectively, as a "negative superhump" and the wobble period of the accretion disk. The superhump could then possibly arise from the heating of the secondary (and structures fixed in the orbital frame) by inner-disk radiation, which reaches the secondary relatively unimpeded since the disk is not coplanar. At higher frequencies, both stars show another type of variability: quasi-periodic oscillations with a period near 1000 s. Underlying these strong signals of low stability may be weak signals of higher stability. Similar quasi-periodic oscillations, and negative superhumps, are quite common features in SW Sex stars. Both can in principle be explained by ascribing strong magnetism to the white dwarf member of the binary; and we suggest that SW Sex stars are borderline AM Herculis binaries, usually drowned by a high accretion rate. This would provide an ancestor channel for AM Hers, whose origin is still mysterious.

We present optical and ifra-red photometry of the new X-ray transient source XTE J1859+226. The source exhibits a typical X-ray nova behaviour with a fast rise (~5 days) and an exponential decline (~23 days). Week photometric modulations are seen at several periods ranging from 9.15 hours to 20 minutes. The evolution of the spectral energy distribution of the source can be fitted very well with a model of an X-ray irradiated accretion disc.

We obtained ASCA observations of the cataclysmic variables LS Peg and T Leo in order to refine the X-ray characteristics of these two systems with unusual stream behaviors and to search for orbital features that might signify the presence of material above the orbital plane. Simultaneous (LS Peg) and contemporaneous (T Leo) optical observations showed the systems undergoing their typical stream behaviors (absorption, high-velocity component, and quasi-periodic oscillations in LS Peg; stream flow to the far side of the disk in T Leo). The X-ray light curve of LS Peg shows a low but constant count rate throughout its orbit. To fit the spectrum with a reasonable temperature requires a 7 keV partial-absorber model with high column (6x10(22) cm(-2)). This may be evidence for material thrown high above the disk by the disk-stream interaction or a magnetic accretion funnel sometimes suggested to explain other SW Sex stars. The spectrum of T Leo is consistent with a simple 4-6 keV thermal model with lower column (3-5 x 10(20) cm(-2)) and a small contribution from a cooler 1 keV component. Its light curve shows enhanced flux between phases 0.8 and 1.0, which is not due to a change in temperature or column. The difference in behavior of this light curve from that of U Gem may be due to the lower accretion in this shorter period system.

The Polar BY Cam is characterized by a UV emission resonance line ratio of NV/CIV much greater than observed in other Polars. The far-UV FUSE observations reveal a broad resonance OVI line weaker than in the prototype of Polars, AM Her, which, together with the presence of a strong NIII line and weak CIII lines would indicate a mix of CNO redistribution following thermonuclear runaways at the surface of the magnetized white dwarf, and of the chemical composition of the companion atmosphere.

We report photometric and spectroscopic observations of the nova‐like variable V751 Cygni. The radial velocities indicate an underlying binary period of 0.1445(2) day; the long‐term cycle count is not firmly decided, but the best choice implies a period of 0.144464(1) day. The star shows a moderately low excitation spectrum with transient P Cygni absorption suggestive of a wind origin, occasionally seen in cataclysmic variables accreting at a high rate. Curiously, the P Cygni absorption appears correlated with binary phase in our two most extensive data sets. A photometric wave with P = 0.1394(1) day, slightly shorter than Porb, rumbles through the light curve, as well as a low‐frequency wiggle at 3.94(6) days. We identify the former as a "negative superhump" and the latter as the wobble period of a tilted accretion disk. These characteristics all suggest classification as an ordinary, accretion‐powered cataclysmic variable of the VY Sculptoris class. We discuss possible origins for the observed soft X‐rays at quiescence.

To explore the amount of secondary irradiation and the long-term effects of a superoutburst (SOB) on tremendous outburst amplitude dwarf novae (TOADs), we obtained spectra of EG Cnc for 3-17 months past its SOB, of SW UMa, WX Cet, and USNO 1425.09823278 at 2 months past their SOBs and HV Vir and LL And during their quiescent states at 3 and 5 yr past SOB. The quiescent spectra of EG Cnc, HV Vir, LL And, and USNO 1425 show emission cores surrounded by broad absorption lines from the white dwarf, consistent with very low mass accretion onto low-temperature white dwarfs. SW UMa and WX Cet likely have higher accretion rates and more extensive disks. SW UMa exhibits unusual disk structure, with three zones of emission that persist for 3 days, while EG Cnc and USNO 1425 have a strong orbital modulation of the Balmer lines that may be related to long-lasting irradiation after superoutburst.