We present time-resolved spectroscopy and photometry of the dwarf nova SBSS 1108+574, obtained during the 2012 outburst. Its quiescent spectrum is unusually rich in helium, showing broad, ...double-peaked emission lines from the accretion disc. We measure a line flux ratio He i 5875/Hα = 0.81 ± 0.04, a much higher ratio than typically observed in cataclysmic variable stars (CVs). The outburst spectrum shows hydrogen and helium in absorption, with weak emission of Hα and He i 6678, as well as strong He ii emission.
From our photometry, we find the superhump period to be 56.34 ± 0.18 min, in agreement with the previously published result. The spectroscopic period, derived from the radial velocities of the emission lines, is found to be 55.3 ± 0.8 min, consistent with a previously identified photometric orbital period, and significantly below the normal CV period minimum. This indicates that the donor in SBSS 1108+574 is highly evolved. The superhump excess derived from our photometry implies a mass ratio of q = 0.086 ± 0.014. Our spectroscopy reveals a grazing eclipse of the large outbursting disc. As the disc is significantly larger during outburst, it is unlikely that an eclipse will be detectable in quiescence. The relatively high accretion rate implied by the detection of outbursts, together with the large mass ratio, suggests that SBSS 1108+574 is still evolving towards its period minimum.
Abstract
We report the results of long-term time series photometry on RX J2133.7+5107, an intermediate polar distinguished by its long orbital period (7.14 h) and rapid rotation (571 s) of its white ...dwarf. The light curves show the presence of a conspicuous modulation with a 6.72-h period, 6.1 ± 0.1 per cent shorter than the orbital period, which we interpret as a (negative) superhump associated with the nodal precession of the accretion disc. This detection may prove a challenge to the idea that superhumps are limited to binaries of short orbital period. Our rotational timings over the 7 yr spanned by our observations show spin-up at a rate of 3.41(2) ms yr−1 or, equivalently, on a time-scale $| P/\dot{P}|=0.17 \times 10^{6}$ yr. The latter is sensibly shorter than the time-scale of spin period variations reported for other intermediate polars, possibly due to a greater accretion rate.
The paper describes a target setting of searching for apsidal motion in 21 eclipsing binaries. We estimate the capability of its determination for the systems of interest in the coming years, as well ...as present results of observations in 2009–2018, in which the minima of the light curves of these stars have been obtained. The accuracy of orbital period determination of the studied binaries is 10–100 times greater in comparison with the previously available data. For two systems, photometric elements are determined. As a by-product of the study, a close eclipsing binary of the W UMa type was discovered.
Abstract
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 yr 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 that 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.
We present time-resolved CCD photometry of 15 cataclysmic variables (CVs) identified by the Sloan Digital Sky Survey (SDSS). The data were obtained as part of the 2004/2005 International Time ...Programme on La Palma. We discuss the morphology of the light curves and the CV subtypes, and give accurate orbital periods for 11 systems. Nine systems are found below the 2–3 h orbital period gap, of which five have periods within a few minutes of the ∼80 min minimum orbital period. One system each is found within and above the gap. This confirms the previously noted trend for a large fraction of short-period systems among the SDSS CVs. Objects of particular interest are SDSS J0901+4809 and SDSS J1250+6655 which are deeply eclipsing. SDSS J0854+3905 is a polar with an extremely modulated light curve, which is likely due to a mixture of cyclotron beaming and eclipses of the accretion region by the white dwarf. One out of five systems with white dwarf dominated optical spectra exhibits non-radial pulsations.
We present time-resolved photometry of a cataclysmic variable discovered in the Isaac Newton Telescope Photometric Halpha Survey of the northern galactic plane, IPHAS J062746.41+014811.3, and ...classify the system as the fourth deeply eclipsing intermediate polar known with an orbital period of P sub(orb) = 8.16 hr and a spin period of P sub(spin) = 2210 s. The system shows mild variations of its brightness that appear to be accompanied by a change in the amplitude of the spin modulation at optical wavelengths and a change in the morphology of the eclipse profile. The inferred magnetic moment of the white dwarf is mu sub(wd) ~ (6-7) x 10 super(33) G cm super(3), and in this case IPHAS J062746.41+014811.3 will evolve either into a short-period EX Hya-like intermediate polar with a large R sub(spin)/P sub(orb) ratio or, perhaps more likely, into a synchronized polar. Swift observations show that the system is an ultraviolet and X-ray source, with a hard X-ray spectrum that is consistent with those seen in other intermediate polars. The ultraviolet light curve shows orbital modulation and an eclipse, while the low signal-to-noise ratio X-ray light curve does not show a significant modulation on the spin period. The measured X-ray flux is about an order of magnitude lower than would be expected from scaling by the optical fluxes of well-known X-ray-selected intermediate polars.
Aims. We investigate the physical nature of the X-ray emitting source 1RXS J165443.5−191620 through optical photometry and time-resolved spectroscopy. Methods. Optical photometry is obtained from a ...variety of telescopes all over the world spanning ≈27 days. Additionally, time-resolved spectroscopy is obtained from the MDM observatory. Results. The optical photometry clearly displays modulations consistent with those observed in magnetic cataclysmic variables: a low-frequency signal interpreted as the orbital period, a high-frequency signal interpreted as the white dwarf spin period, and an orbital sideband modulation. Our findings and interpretations are further confirmed through optical, time-resolved spectroscopy that displays Hα radial velocity shifts modulated on the binary orbital period. Conclusions. We confirm that 1RXS J165443.5−191620 is an intermediate polar with a spin period of 546 s and an orbital period of 3.7 h. In particular, 1RXS J165443.5−191620 is part of a growing subset of intermediate polars that display hard X-ray emission above 15 keV, white dwarf spin periods below 30 min, and spin-to-orbital ratios below 0.1.
We report the observation of the first gravitational microlensing event in a sparse stellar field, involving the brightest (V = 11.4 mag) and closest ( similar to 1 kpc) source star to date. This ...event was discovered by an amateur astronomer, A. Tago, on 2006 October 31 as a transient brightening, by similar to 4.5 mag during a similar to 15 day period, of a normal A-type star (GSC 3656-1328) in the Cassiopeia constellation. Analysis of both spectroscopic observations and the light curve indicates that this event was caused by gravitational microlensing rather than an intrinsically variable star. Discovery of this single event over a 30 year period is roughly consistent with the expected microlensing rate for the whole sky down to V = 12 mag stars. However, the probability for finding events with such a high magnification ( similar to 50) is much smaller, by a factor of similar to 1/50, which implies that the true event rate may be higher than expected. This discovery indicates the potential of all sky variability surveys, employing frequent sampling by telescopes with small apertures and wide fields of view, for finding such rare transient events, and using the observations to explore Galactic disk structure and search for exoplanets.
BZ UMa is a cataclysmic variable star whose specific classification has eluded researchers since its discovery in 1968. It has outburst and spectral properties consistent with both U Gem class dwarf ...novae and intermediate polars. We present new photometric and polarimetric measurements of recent outbursts, including the first detected superoutburst of the system. Statistical analysis of these and archival data from outbursts over the past 40 years presents a case for BZ UMa as a nonmagnetic, U Gem class, SU UMa subclass dwarf nova.
The eclipsing variable GSC 4513 2537= V1176 Cas is a recently discovered binary system. We have made high precision CCD observations of it during 2009-2010 and obtained light curves. The photometric ...parameters and orbital elements, periods of the primary and secondary minima, and U, B, and V magnitudes have also been obtained. The rate of rotation of the apsidal line is estimated to be
= 0.08 ± 0.04 / year. This is 5 times the theoretically predicted
= 0.016 ± 0.005 /year. The bulk (80%) of the theoretical rate of rotation of the orbit is in the relativistic component. Unfortunately, the accuracy of the observed rate of orbital rotation of the orbit is low, so getting a more reliable result will require repeating this study in a few years.
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