Superhumps linked to X-ray emission Neustroev, V. V.; Page, K. L.; Kuulkers, E. ...
Astronomy and astrophysics (Berlin),
03/2018, Letnik:
611
Journal Article
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Context. We present more than 4 years of Swift X-ray observations of the 2013 superoutburst, subsequent decline and quiescence of the WZ Sge-type dwarf nova SSS J122221.7−311525 (SSS J122222) from 6 ...days after discovery. Aims. Only a handful of WZ Sge-type dwarf novae have been observed in X-rays, and until recently GW Lib was the only binary of this type with complete coverage of an X-ray light curve throughout a superoutburst. We collected extensive X-ray data of a second such system to understand the extent to which the unexpected properties of GW Lib are common to the WZ Sge class. Methods. We collected 60 Swift-XRT observations of SSS J122222 between 2013 January 6 and 2013 July 1. Four follow-up observations were performed in 2014, 2015, 2016 and 2017. The total exposure time of our observations is 86.6 ks. We analysed the X-ray light curve and compared it with the behaviour of superhumps which were detected in the optical light curve. We also performed spectral analysis of the data. The results were compared with the properties of GW Lib, for which new X-ray observations were also obtained. Results. SSS J122222 was variable and around five times brighter in 0.3–10 keV X-rays during the superoutburst than in quiescence, mainly because of a significant strengthening of a high-energy component of the X-ray spectrum. The post-outburst decline of the X-ray flux lasted at least 500 d. The data show no evidence of the expected optically thick boundary layer in the system during the outburst. SSS J122222 also exhibited a sudden X-ray flux change in the middle of the superoutburst, which occurred exactly at the time of the superhump stage transition. A similar X-ray behaviour was also detected in GW Lib. Conclusions. We show that the X-ray flux exhibits changes at the times of changes in the superhump behaviour of both SSS J122222 and GW Lib. This result demonstrates a relationship between the outer disc and the white dwarf boundary layer for the first time, and suggests that models for accretion discs in high mass ratio accreting binaries are currently incomplete. The very long decline to X-ray quiescence is also in strong contrast to the expectation of low viscosity in the disc after outburst.
We present an analysis of time-resolved, medium-resolution optical spectroscopic observations of UX Ursae Majoris (UX UMa) in the blue (3920-5250 Å) and red (6100-7200 Å) wavelength ranges that were ...obtained in 1999 April and 2008 March, respectively. The observed characteristics of our spectra indicate that UX UMa has been in different states during those observations. The blue spectra are very complex. They are dominated by strong and broad single-peaked emission lines of hydrogen. The high-excitation lines of He ii λ4686 and the Bowen blend are quite strong as well. All the lines consist of a mixture of absorption and emission components. Using Doppler tomography, we have identified four distinct components of the system: the accretion disc, the secondary star, the bright spot from the gas stream/disc impact region and the unique compact area of absorption in the accretion disc seen as a dark spot in the lower left-hand quadrant of the tomograms. In the red wavelength range, both the hydrogen (Hα) and neutral helium (He i λ6678 and He i λ7065) lines were observed in emission and both exhibited double-peaked profiles. Doppler tomography of these lines reveals spiral structure in the accretion disc, but in contrast to the blue wavelength range, there is no evidence for either the dark spot or the gas stream/disc impact region emission, while the emission from the secondary star is weak. During the observations in 1999, UX UMa showed many of the defining properties of the SW Sextantis stars. However, all these features almost completely disappeared in 2008. We have also estimated the radial velocity semi-amplitudes K
1 and K
2 and evaluated the system parameters of UX UMa. These estimates are inconsistent with previous values derived by means of analysis of white dwarf eclipse features in the light curve in different wavelength ranges.
Tensile properties of austenitic stainless steels used for pressure vessel internals of WWER type reactors (18Cr–10Ni–Ti steel and its weld metal) in the initial and irradiated conditions were ...investigated. Based on the presented original investigations and generalization of the available experimental data the dependences of yield strength and ultimate strength on a neutron damage dose up to 108dpa, irradiation temperature range 320–450°С and test temperature range 20–450°С were obtained. The method of determination of the stress–strain curve parameters was proposed which does not require uniform elongation of a specimen as an input parameter. The dependences was proposed allowing one to calculate the stress–strain curve parameters for 18Cr–10Ni–Ti steel and its weld metal for different test temperatures, different irradiation temperatures and doses. The dependences were obtained to describe the fracture strain decrease under irradiation at a temperature range 320–340°С when irradiation swelling is absent.
The paper describes the results of post-irradiation examinations for pressurized specimens that varied in design and were made of austenitic steels 08Х18Н10Т and 07Х16Н12М3Т. They were under ...irradiation testing in the BOR-60 reactor to attain different damage dose values. The contribution of irradiation creep to the overall change in diameter was studied. Irradiation creep moduli data were obtained for austenitic steels 08Х18Н10Т and 07Х16Н12М3Т at the stage of steady-state creep in the damage dose range of 5–90 dpa.
We present high- and medium-resolution spectroscopic observations of the cataclysmic variable BF Eridani (BF Eri) during its low and bright states. The orbital period of this system was found to be ...0.270881(3) d. The secondary star is clearly visible in the spectra through the absorption lines of the neutral metals Mg i, Fe i and Ca i. Its spectral type was found to be K3±0.5. A radial velocity study of the secondary yielded a semi-amplitude of K2= 182.5 ± 0.9 km s−1. The radial velocity semi-amplitude of the white dwarf was found to be K1= 74 ± 3 km s−1 from the motion of the wings of the Hα and Hβ emission lines. From these parameters, we have obtained that the secondary in BF Eri is an evolved star with a mass of 0.50–0.59 M⊙, whose size is about 30 per cent larger than a zero-age main-sequence single star of the same mass. We also show that BF Eri contains a massive white dwarf (M1≥ 1.2 M⊙), which allows us to consider the system as a Type Ia supernova progenitor. BF Eri also shows a high γ-velocity (γ=−94 km s−1) and substantial proper motion. With our estimation of the distance to the system (d≈ 700 ± 200 pc), this corresponds to a space velocity of ∼350 km s−1 with respect to the dynamical local standard of rest. The cumulative effect of repeated nova eruptions with asymmetric envelope ejection might explain the high space velocity of the system. We analyse the outburst behaviour of BF Eri and question the current classification of the system as a dwarf nova. We propose that BF Eri might be an old nova exhibiting ‘stunted’ outbursts.
ABSTRACT
OGLE-LMC-DPV-065 is an interacting binary whose double-hump long photometric cycle remains hitherto unexplained. We analyze photometric time series available in archive data sets spanning ...124 yr and present the analysis of new high-resolution spectra. A refined orbital period is found of 10${^{\rm d}_{.}}$031 6267 ± 0${^{\rm d}_{.}}$000 0056 without any evidence of variability. In spite of this constancy, small but significant changes in timings of the secondary eclipse are detected. We show that the long period continuously decreases from 350 to 218 d during 13 yr, then remains almost constant for about 10 yr. Our study of radial velocities indicates a circular orbit for the binary and yields a mass ratio of 0.203 ± 0.001. From the analysis of the orbital light curve, we find that the system contains 13.8 and 2.81 M⊙ stars of radii 8.8 and 12.6 R⊙ and absolute bolometric magnitudes −6.4 and −3.0, respectively. The orbit semimajor axis is 49.9 R⊙ and the stellar temperatures are 25 460 K and 9825 K. We find evidence for an optically and geometrically thick disc around the hotter star. According to our model, the disc has a radius of 25 R⊙, central and outer vertical thickness of 1.6 R⊙ and 3.5 R⊙, and temperature of 9380 K at its outer edge. Two shock regions located at roughly opposite parts of the outer disc rim can explain the light-curve asymmetries. The system is a member of the double periodic variables and its relatively high-mass and long photometric cycle make it similar in some aspects to β Lyrae.
Data are presented from BOR-60 irradiations showing that significant radiation-induced swelling causes severe embrittlement in austenitic stainless steels, reducing the service life of structural ...components and introducing limitations on low temperature handling especially. It is shown that the degradation is actually a form of quasi-embrittlement arising from intense flow localization with high levels of localized ductility involving micropore coalescence and void-to-void cracking. Voids initially serve as hardening components whose effect is overwhelmed by the void-induced reduction in shear and Young’s moduli at high swelling levels. Thus the alloy appears to soften even as the ductility plunges toward zero on a macroscopic level although a large amount of deformation occurs microscopically at the failure site. Thus the failure is better characterized as “quasi-embrittlement” which is a suppression of uniform deformation. This case should be differentiated from that of real embrittlement which involves the complete suppression of the material’s capability for plastic deformation.
New results of measurements of the dependences of the flux of reactor antineutrinos and their spectrum on the distance from the center of the core of the SM-3 reactor (Dimitrovgrad, Russia) in the ...range from 6 to 12 m are presented. Additional measurements were conducted. The volume of accumulated experimental data was increased nearly by a factor of two. A model-independent analysis was performed on the basis of all data in order to determine the oscillation parameters
and
. The method of a coherent summation of measurement results makes it possible to demonstrate directly the oscillation effect. We observed the oscillation effect at a level of three standard deviations (
) in the vicinities of parameters values of
eV
and
. Combining the results of the Neutrino-4 experiment with results for the gallium anomaly and for the reactor anomaly, we obtained the following value:
.
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