[en] The Sloan Digital Sky Survey has identified a total of 212 cataclysmic variables, most of which are fainter than 18th magnitude. This is the deepest and most populous homogeneous sample of cataclysmic variables to date, and we are undertaking a project to characterise this population. We have found that the SDSS sample is dominated by a great 'silent majority' of old and faint CVs. We detect, for the first time, a population spike at the minimum period of 80 min which has been predicted by theoretical studies for over a decade.

[en] We present a spectroscopic study of the eclipsing binary system AS Camelopardalis, the first such study based on phase-resolved CCD echelle spectra. Via a spectral disentangling analysis we measure the minimum masses of the stars to be M_Asin ³ i = 3.213 ± 0.032 M_sun and M_Bsin ³ i = 2.323 ± 0.032 M_sun, their effective temperatures to be T_eff(A) = 12, 840 ± 120 K and T_eff(B) = 10, 580 ± 240 K, and their projected rotational velocities to be v_Asin i_A = 14.5 ± 0.1 km s^-1 and v_Bsin i_B ≤ 4.6 ± 0.1 km s^-1. These projected rotational velocities appear to be much lower than the synchronous values. We show that measurements of the apsidal motion of the system suffer from a degeneracy between orbital eccentricity and apsidal motion rate. We use our spectroscopically measured e = 0.164 ± 0.004 to break this degeneracy and measure ω-dot_obs = 0⁰.133±0⁰.010 yr^-1. Subtracting the relativistic contribution of ω-dot_GR = 0⁰.0963±0⁰0002 yr^-1 yields the contribution due to tidal torques: ω-dot_cl = 0⁰.037±0⁰.010 yr^-1. This value is much smaller than the rate predicted by stellar theory, 0.⁰40-0.⁰87 yr^-1. We interpret this as a misalignment between the orbital axis of the close binary and the rotational axes of its component stars, which also explains their apparently low rotational velocities. The observed and predicted apsidal motion rates could be brought into agreement if the stars were rotating three times faster than synchronous about axes perpendicular to the orbital axis. Measurement of the Rossiter-McLaughlin effect can be used to confirm this interpretation.

[en] WASP-19b has the shortest orbital period of any known exoplanet, orbiting at only 1.2 times the Roche tidal radius. By observing the Rossiter-McLaughlin effect we show that WASP-19b's orbit is aligned, with λ = 4.⁰6 ± 5.⁰2. Using, in addition, a spectroscopic vsin I and the observed rotation period we conclude that the obliquity, ψ, is less than 20⁰. Further, the eccentricity of the orbit is less than 0.02. We argue that hot Jupiters with orbital periods as short as that of WASP-19b are two orders of magnitude less common than hot Jupiters at the 3-4 day 'pileup'. We discuss the evolution of WASP-19b's orbit and argue that most likely it was first moved to near twice the Roche limit by third-body interactions, and has since spiralled inward to its current location under tidal decay. This is compatible with a stellar tidal-dissipation quality factor, Q'_*, of order 10⁷.

[en] SDSSJ125733.63+542850.5 (hereafter SDSSJ1257+5428) is a compact white dwarf binary from the Sloan Digital Sky Survey that exhibits high-amplitude radial velocity variations on a period of 4.56 hr. While an initial analysis suggested the presence of a neutron star or black hole binary companion, a follow-up study concluded that the spectrum was better understood as a combination of two white dwarfs. Here we present optical spectroscopy and ultraviolet fluxes which directly reveal the presence of the second white dwarf in the system. SDSSJ1257+5428's spectrum is a composite, dominated by the narrow-lined spectrum from a cool, low-gravity white dwarf (T_eff ≅ 6300 K, log g = 5-6.6) with broad wings from a hotter, high-mass white dwarf companion (11, 000-14, 000 K; ∼1 M_sun). The high-mass white dwarf has unusual line profiles which lack the narrow central core to Hα that is usually seen in white dwarfs. This is consistent with rapid rotation with vsin i = 500-1750 km s^-1, although other broadening mechanisms such as magnetic fields, pulsations, or a helium-rich atmosphere could also be contributory factors. The cool component is a puzzle since no evolutionary model matches its combination of low gravity and temperature. Within the constraints set by our data, SDSSJ1257+5428 could have a total mass greater than the Chandrasekhar limit and thus be a potential Type Ia supernova progenitor. However, SDSSJ1257+5428's unusually low-mass ratio q ∼ 0.2 suggests that it is more likely that it will evolve into an accreting double white dwarf (AM CVn star).

[en] We present a detailed study of KIC 2306740, an eccentric double-lined eclipsing binary system. Kepler satellite data were combined with spectroscopic data obtained with the 4.2 m William Herschel Telescope (WHT). This allowed us to determine precise orbital and physical parameters of this relatively long period (P = 10.ͩ3) and slightly eccentric (e = 0.3) binary system. The physical parameters have been determined to be M ₁ = 1.194 ± 0.008 M _⊙, M ₂ = 1.078 ± 0.007 M _⊙, R ₁ = 1.682 ± 0.004 R _⊙, R ₂ = 1.226 ± 0.005 R _⊙, L ₁ = 2.8 ± 0.4 L _⊙, L ₂ = 1.8 ± 0.2 L _⊙, and orbital separation a = 26.20 ± 0.04 R _⊙ through simultaneous solutions of the Kepler light curves and WHT radial velocity data. Binarity effects were extracted from the light curve in order to study intrinsic variations in the residuals. Five significant and more than 100 combination frequencies were detected. We modeled the binary system assuming nonconservative evolution models with the Cambridge stars (twin) code, and we show the evolutionary tracks of the components in the $\mathrm{l}\mathrm{o}\mathrm{g}L\text{--}\mathrm{l}\mathrm{o}\mathrm{g}T$ plane, the $\mathrm{l}\mathrm{o}\mathrm{g}R\text{--}\mathrm{l}\mathrm{o}\mathrm{g}M$ plane, and the $\mathrm{l}\mathrm{o}\mathrm{g}P\text{--}\mathrm{a}\mathrm{g}\mathrm{e}$ plane for both spin and orbital periods together with eccentricity e and $\mathrm{l}\mathrm{o}\mathrm{g}{R}_1$. The model of the nonconservative processes in the code led the system to evolve to the observed system parameters in roughly 5.1 Gyr.

[en] We identify SDSS 0110+1326, SDSS 0303+0054 and SDSS 1435+3733 as three eclipsing white dwarf plus main sequence binaries from the Sloan Digital Sky Survey, and report on their follow-up observations. Orbital periods for the three systems are established through multi-season photometry. Time-resolved spectroscopic observations lead to the determination of the radial velocities of the secondary stars. A decomposition technique of the SDSS spectra is used to estimate the surface gravities and effective temperatures of the white dwarfs, as well as the spectral types of the secondaries. By combining the constraints from the spectral decomposition, the radial velocity data and the modeling of the systems' light curves, we determine the physical parameters of the stellar components. Two of the white dwarfs are of low mass (M_wd ∼ 0.4 M_o-dot), while the third white dwarf is unusually massive (M_WD ∼ 0.8-0.9 M_o-dot) for a post-common envelope system.

[en] Post common envelope binaries (PCEBs) consisting of a white dwarf and a main sequence star are ideal systems to calibrate current theories of angular momentum loss in close compact binary stars. The potential held by PCEBs for further development of close binary evolution could so far not be exploited due to the small number of known systems and the inhomogeneity of the sample. The Sloan Digital Sky Survey is changing this scene dramatically, as it is very efficient in identifying white dwarf/main sequence (WDMS) binaries, including both wide systems whose stellar components evolve like single stars and - more interesting in the context of close binary evolution - PCEBs. We pursue a large-scale follow-up survey to identify and characterise the PCEBs among the WDMS binaries that have been found with SDSS. We here present preliminary results of our survey and derive first constraints on current models of white dwarf binary evolution.

[en] Given the potential of ensemble asteroseismology for understanding fundamental properties of large numbers of stars, it is critical to determine the accuracy of the scaling relations on which these measurements are based. From several powerful validation techniques, all indications so far show that stellar radius estimates from the asteroseismic scaling relations are accurate to within a few percent. Eclipsing binary systems hosting at least one star with detectable solar-like oscillations constitute the ideal test objects for validating asteroseismic radius and mass inferences. By combining radial velocity (RV) measurements and photometric time series of eclipses, it is possible to determine the masses and radii of each component of a double-lined spectroscopic binary. We report the results of a four-year RV survey performed with the échelle spectrometer of the Astrophysical Research Consortium’s 3.5 m telescope and the APOGEE spectrometer at Apache Point Observatory. We compare the masses and radii of 10 red giants (RGs) obtained by combining radial velocities and eclipse photometry with the estimates from the asteroseismic scaling relations. We find that the asteroseismic scaling relations overestimate RG radii by about 5% on average and masses by about 15% for stars at various stages of RG evolution. Systematic overestimation of mass leads to underestimation of stellar age, which can have important implications for ensemble asteroseismology used for Galactic studies. As part of a second objective, where asteroseismology is used for understanding binary systems, we confirm that oscillations of RGs in close binaries can be suppressed enough to be undetectable, a hypothesis that was proposed in a previous work.

[en] We report the discovery of a new totally eclipsing binary (R.A. = ${06}^{\mathrm{h}}{40}^{\mathrm{m}}{29}^{\mathrm{s}}11$; decl. = +38°56′52″2; J = 2000.0; R_max = 17.2 mag) with an sdO primary and a strongly irradiated red dwarf companion. It has an orbital period of P_orb = 0.187284394(11) day and an optical eclipse depth in excess of 5 mag. We obtained 2 low-resolution classification spectra with GTC/OSIRIS and 10 medium-resolution spectra with WHT/ISIS to constrain the properties of the binary members. The spectra are dominated by H Balmer and He ii absorption lines from the sdO star, and phase-dependent emission lines from the irradiated companion. A combined spectroscopic and light curve analysis implies a hot subdwarf temperature of T_eff(spec) = 55,000 ± 3000 K, surface gravity of log g (phot) = 6.2 ± 0.04 (cgs), and a He abundance of $\mathrm{l}\mathrm{o}\mathrm{g}(n\mathrm{H}\mathrm{e}/n\mathrm{H})=-<!--\; ???\; -->2.24\pm <!--\; ??\; -->0.40$. The hot sdO star irradiates the red dwarf companion, heating its substellar point to about 22,500 K. Surface parameters for the companion are difficult to constrain from the currently available data: the most remarkable features are the strong H Balmer and C ii-iii lines in emission. Radial velocity estimates are consistent with the sdO+dM classification. The photometric data do not show any indication of sdO pulsations with amplitudes greater than 7 mmag, and Hα-filter images do not provide evidence for the presence of a planetary nebula associated with the sdO star.

[en] We report the discovery of three new transiting hot Jupiters by WASP-South together with the TRAPPIST photometer and the Euler/CORALIE spectrograph. WASP-74b orbits a star of V = 9.7, making it one of the brighter systems accessible to southern telescopes. It is a 0.95M_Jup planet with a moderately bloated radius of 1.5 $R_{\mathrm{J}\mathrm{u}\mathrm{p}}$ in a 2 day orbit around a slightly evolved F9 star. WASP-83b is a Saturn-mass planet at 0.3 $M_{\mathrm{J}\mathrm{u}\mathrm{p}}$ with a radius of 1.0 $R_{\mathrm{J}\mathrm{u}\mathrm{p}}$. It is in a 5 day orbit around a fainter (V = 12.9) G8 star. WASP-89b is a 6 M_Jup planet in a 3 day orbit with an eccentricity of e = 0.2. It is thus similar to massive, eccentric planets such as XO-3b and HAT-P-2b, except that those planets orbit F stars whereas WASP-89 is a K star. The V = 13.1 host star is magnetically active, showing a rotation period of 20.2 days, while star spots are visible in the transits. There are indications that the planet’s orbit is aligned with the stellar spin. WASP-89 is a good target for an extensive study of transits of star spots.