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1.
We report on the detection of negative superhumps in KR Aur, a typical VY Scl star. The observations were obtained with a multi-channel photometer over 107 h. The analysis of the data clearly revealed brightness variations with a period of 3.771 (±0.005) h. This is 3.5 per cent shorter than P orb, suggesting that the observed oscillation is a negative superhump. Negative superhumps in VY Scl stars are widespread. The discovery of powerful soft X-rays from V751 Cyg suggests that VY Scl stars may contain white dwarfs, on to which nuclear burning of the accreted material occurs. If this suspicion is correct, it is possible that the powerful radiation emerging from the white dwarf may cause a tilt of the accretion disc to the orbital plane, and its retrograde precession may produce the negative superhumps seen in VY Scl stars.  相似文献   

2.
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3.
We present K -band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK Lyn, T Leo, SW UMa and WZ Sge, the nova-like variables DW UMa, V1315 Aql, RW Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral types ranging from K2 to M6.
The spectra of the dwarf novae are dominated by emission lines of H  i and He  i . The large velocity and equivalent widths of these lines, in conjunction with the fact that the lines are double-peaked in the highest inclination systems, indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which we obtained time-resolved data covering a complete orbital cycle, the emission lines show modulations in their equivalent widths that are most probably associated with the bright spot (the region where the gas stream collides with the accretion disc). There are no clear detections of the secondary star in any of the dwarf novae below the period gap, yielding upper limits of 10–30 per cent for the contribution of the secondary star to the observed K -band flux. In conjunction with the K -band magnitudes of the dwarf novae, we use the derived secondary star contributions to calculate lower limits to the distances to these systems.
The spectra of the nova-like variables are dominated by broad, single-peaked emission lines of H  i and He  i – even the eclipsing systems we observed do not show the double-peaked profiles predicted by standard accretion disc theory. With the exception of RW Tri, which exhibits Na  i , Ca  i and 12CO absorption features consistent with a M0V secondary contributing 65 per cent of the observed K -band flux, we find no evidence for the secondary star in any of the nova-like variables. The implications of this result are discussed.  相似文献   

4.
The light curves of VY Scl stars   总被引：1，自引：0，他引：1  
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5.
The observational properties of Z Cam stars, nova-like variables and nova remnants are discussed in terms of the disc instability model. The effects of irradiation on the secondary star, giving rise to high and low states of mass transfer, and on the inner disc, suppressing or greatly reducing the disc instability, are used to explain the light curves of VY Scl stars. Irradiation may also play a part in producing low amplitude modulations in brightness of nova-likes on time scales of tens of days.  相似文献   

6.
Variability on all time scales between seconds and decades is typical for cataclysmic variables (CVs). One of the brightest and best studied CVs is TT Ari, a nova‐like variable which belongs to the VY Scl subclass, characterized by occasional low states in their light curves. It is also known as a permanent superhumper at high state, revealing “positive” (PS > P0) as well as “negative” (PS < P0) superhumps, where PS is the period of the superhump and P0 the orbital period. TT Ari was observed by the Canadian space telescope MOST for about 230 hours nearly continuously in 2007, with a time resolution of 48 seconds. Here we analyze these data, obtaining a dominant “negative” superhump signal with a period PS = 0.1331 days and a mean amplitude of 0.09 mag. Strong flickering with amplitudes up to 0.2 mag and peak‐to‐peak time scales of 15–20 minutes is superimposed on the periodic variations. We found no indications for significant quasi‐periodic oscillations with periods around 15 minutes, reported by other authors. We discuss the known superhump behaviour of TTAri during the last five decades and conclude that our period value is at the upper limit of all hitherto determined “negative” superhump periods of TTAri, before and after the MOST run. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
We have identified three possible ways in which future XMM‐Newton observations can provide significant constraints on the equation of state of neutron stars. First, using a long observation of the neutron star X‐ray transient Cen X‐4 in quiescence one can use the RGS spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X‐ray spectral fitting of the pn and MOS spectra and allows us to investigate whether the variability observed in the quiescent X‐ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in NH. This will test whether the soft thermal spectral component can indeed be due to the hot thermal glow of the neutron star. Potentially such an observation could also reveal redshifted spectral lines from the neutron star surface. Second, XMM‐Newton observations of radius expansion type I Xray bursts might reveal redshifted absorption lines from the surface of the neutron star. Third, XMM‐Newton observations of eclipsing quiescent low‐mass X‐ray binaries provide the eclipse duration. With this the system inclination can be determined accurately. The inclination determined from the X‐ray eclipse duration in quiescence, the rotational velocity of the companion star and the semi‐amplitude of the radial velocity curve determined through optical spectroscopy, yield the neutron star mass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
We build a simple model of the optical/ultraviolet (UV) emission from irradiation of the outer disc by the inner disc and coronal emission in black hole binaries. We apply this to the broad-band Swift data from the outburst of the black hole binary XTE J1817−330 to confirm previous results that the optical/UV emission in the soft state is consistent with a reprocessing a constant fraction of the bolometric X-ray luminosity. However, this is very surprising as the disc temperature drops by more than a factor of 3 in the soft state, which should produce a marked change in the reprocessing efficiency. The easiest way to match the observed constant reprocessed fraction is for the disc skin to be highly ionized (as suggested 30 yr ago by van Paradijs), so that the bulk of the disc flux is reflected and only the hardest X-rays heat the disc. The constant reprocessed fraction also favours direct illumination of the disc over a scattering origin as the optical depth/solid angle of any scattering material (wind/corona) over the disc should decrease as the source luminosity declines. By contrast, the reprocessed fraction increases very significantly (by a factor of ∼6) as the source enters the hard state. This dramatic change is not evident from X-ray/UV flux correlations as it is masked by bandpass effects. However, it does not necessarily signal a change in emission, for example, the emergence of the jet dominating the optical/UV flux as the reflection albedo must change with the dramatic change in spectral shape.  相似文献   

9.
Since its discovery in 1990, UW CrB (also known as MS1603+2600) has remained a peculiar source without firm classification. Our current understanding is that it is an accretion disc corona (ADC) low-mass X-ray binary. In this paper, we present results from our photometric campaign dedicated to studying the changing morphology of the optical light curves. We find that the optical light curves show remarkable evidence for strongly evolving light curve shapes. In addition, we find that these changes show a modulation at a period of ∼5 d. We interpret these changes as either due to strong periodic accretion disc warping or due to other geometrical changes because of disc precession at a period of 5 d. Finally, we have detected 11 new optical bursts, the phase distribution of which supports the idea of a vertically extended asymmetric accretion disc.  相似文献   

10.
We investigate the role of the eccentric disc resonance in systems with mass ratios q ≳1/4, and demonstrate the effects that changes in the mass flux from the secondary star have upon the disc radius and structure. The addition of material with low specific angular momentum to the outer edge of a disc restricts that disc radially. Should the mass flux from the secondary be reduced, it is possible for the disc in a system with mass ratio as large as 1/3 to expand to the 3:1 eccentric inner Lindblad resonance and for superhumps to be excited.  相似文献   

11.
I discuss open questions regarding accreting black holes in binary systems, focusing on two questions: can we measure the spins of black holes and what is the nature of the ultraluminous X‐ray sources. XMM‐Newton could make significant strides in answering these questions and others over the next ten years. I suggest two observational programs designed to help increase our understanding of accreting black holes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
In this contribution, I briefly review recent progress in detecting and measuring the properties of relativistic iron lines observed in stellar‐mass black hole systems, and the aspects of these lines that are most relevant to studies of similar lines in Seyfert‐1 AGN. In particular, the lines observed in stellar‐mass black holes are not complicated by complex low‐energy absorption or partial‐covering of the central engine, and strong lines are largely independent of the model used to fit the underlying broad‐band continuum flux. Indeed, relativistic iron lines are the most robust diagnostic of black hole spin that is presently available to observers, with specific advantages over the systematics–plagued disk continuum. If accretion onto stellar‐mass black holes simply scales with mass, then the widespread nature of lines in stellar‐mass black holes may indicate that lines should be common in Seyfert‐1 AGN, though perhaps harder to detect. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
UW CrB (MS 1603+2600) is a peculiar short-period X-ray binary that exhibits extraordinary optical behaviour. The shape of the optical light curve of the system changes drastically from night to night, without any changes in overall brightness. Here we report X-ray observations of UW CrB obtained with XMM–Newton . We find evidence for several X-ray bursts, confirming a neutron star primary. This considerably strengthens the case that UW CrB is an accretion disc corona system located at a distance of at least 5–7 kpc (3–5 kpc above the Galactic plane). The X-ray and Optical Monitor (ultraviolet–optical) light curves show remarkable shape variation from one observing run to another, which we suggest are due to large-scale variations in the accretion disc shape resulting from a warp that periodically obscures the optical and soft X-ray emission. This is also supported by the changes in phase-resolved X-ray spectra.  相似文献   

14.
Inflow kinematics at the inner Lagrangian point L1, gas compressibility, and physical turbulent viscosity play a fundamental role on accretion disc dynamics and structure in a close binary (CB). Physical viscosity supports the accretion disc development inside the primary gravitational potential well, developing the gas radial transport, converting mechanical energy into heat. The Stellar‐Mass‐Ratio (SMR) between the compact primary and the secondary star (M1/M2) is also effective, not only in the location of the inner Lagrangian point, but also in the angular kinematics of the mass transfer and in the geometry ofthe gravitational potential wells. In this work we pay attention in particular to the role ofthe SMR, evaluating boundaries, separating theoretical domains in compressibility‐viscosity graphs where physical conditions allow a well‐bound disc development, as a function ofmass transfer kinematic conditions. In such domains, the lower is the gas compressibility (the higher the polytropic index γ), the higher is the physical viscosity (α) requested. In this work, we show how the boundaries of such domains vary as a function of M1/M2. Conclusions as far as dwarf novae outbursts are concerned, induced by mass transfer rate variations, are also reported. The smaller M1/M2, the shorter the duration of the active‐to‐quiet and vice‐versa transitional phases. Time‐scales are of the order of outburst duration of SU Uma, OY Car, Z Cha and SS Cyg‐like objects. Moreover, conclusions as far as active‐quiet‐active phenomena in a CB, according to viscous‐thermal instabilities, in accordance to such domains, are also reported (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
The high-mass X-ray binary RX J0146.9+6121, with optical counterpart LS I+61°235 (V831 Cas), is an intriguing system on the outskirts of the open cluster NGC 663. It contains the slowest Be type X-ray pulsar known with a pulse period of around 1400 s and, primarily from the study of variation in the emission line profile of Hα, it is known to have a Be decretion disc with a one-armed density wave period of approximately 1240 d. Here we present the results of an extensive photometric campaign, supplemented with optical spectroscopy, aimed at measuring short time-scale periodicities. We find three significant periodicities in the photometric data at, in order of statistical significance, 0.34, 0.67 and 0.10 d. We give arguments to support the interpretation that the 0.34 and 0.10 d periods could be due to stellar oscillations of the B-type primary star and that the 0.67 d period is the spin period of the Be star with a spin axis inclination of  23+10−8  degrees. We measured a systemic velocity of  −37.0 ± 4.3 km s−1  confirming that LS I+61°235 has a high probability of membership in the young cluster NGC 663 from which the system's age can be estimated as 20–25 Myr. From archival RXTE All Sky Monitor (ASM) data we further find 'super' X-ray outbursts roughly every 450 d. If these super outbursts are caused by the alignment of the compact star with the one-armed decretion disc enhancement, then the orbital period is approximately 330 d.  相似文献   

16.
Long-term monitoring of the recently discovered X-ray transient, IGR J17098−3628, by the All-Sky Monitor on-board the Rossi X-Ray Timing Explorer , has shown that it displays a long-term (≈163 d) quasi-periodic modulation in the data spanning its 'active' state (i.e. approximately MJD 53450–54200). Furthermore, this light curve is not typical of 'classical' soft X-ray transients, in that J17098−3628 has remained active since its initial discovery, and may be more akin to the pseudo-transient EXO 0748−676, which is now classified as a persistent low-mass X-ray binary (LMXB). However, EXO 0748−676 recently entered a more active phase (since approximately MJD 53050), and since then we find that it too displays a quasi-periodic modulation (≈181 d) in its light curve. This must be a 'superorbital' modulation, as the orbital period of EXO 0748−676 is well established (3.8 h), and hence we interpret both objects' long periods as representing some intrinsic properties of the accretion disc (such as coupled precessional and warping effects). By analogy, we therefore suggest that IGR J17098−3628 is another member of this class of pseudo-transient LMXBs and is likely to have a <1 d orbital period.  相似文献   

17.
A close high‐mass binary system consisting of a neutron star (NS) and a massive OB supergiant companion is expected to lead to a Thorne‐Żytkow object (TZO) structure, which consists of a NS core and a stellar envelope. We use the scenario machine program to calculate the formation tracks of TZOs in close high‐mass NS binaries and their subsequent evolution. We propose and demonstrate that the explosion and instant contraction of a TZO structure leave its stellar remnant as a soft gamma‐ray repeater and an anomalous X‐ray pulsar respectively. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
The 2006 outburst of GK Persei differed significantly at optical and ultraviolet (UV) wavelengths from typical outbursts of this object. We present multiwavelength (X-ray, UV and optical) Swift and AAVSO data, giving unprecedented broad-band coverage of the outburst, allowing us to follow the evolution of the longer-than-normal 2006 outburst across these wavelengths. In the optical and UV we see a triple-peaked morphology with maximum brightness ∼1.5 mag lower than in previous years. In contrast, the peak hard X-ray flux is the same as in previous outbursts. We resolve this dichotomy by demonstrating that the hard X-ray flux only accounts for a small fraction of the total energy liberated during accretion, and interpret the optical/UV outburst profile as arising from a series of heating and cooling waves traversing the disc, caused by its variable density profile.  相似文献   

19.
Since its conception, Doppler tomography has matured into a versatile and widely used tool. It exploits the information contained in the highly‐structured spectral line‐profiles typically observed in mass‐transferring binaries. Using inversion techniques akin to medical imaging, it permits the reconstruction of Doppler maps that image the accretion flow on micro‐arcsecond scales. I summarise the basic concepts behind the technique and highlight two recent results; the use of donor star emission as a means to system parameter determination, and the real‐time movies of the evolving accretion flow in the cataclysmic variable WZ Sge during its 2001 outburst. I conclude with future opportunities in Doppler tomography by exploiting the combination of superior data sets, second generation reconstruction codes and simulated theoretical tomograms to delve deeper into the physics of accretion flows. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
The optical light of the symbiotic binary BF Cyg during its last eruption after 2006 shows orbital variations because of an eclipse of the outbursting compact object. The first orbital minimum is deeper than the following ones. Moreover, the Balmer profiles of this system acquired additional satellite components indicating a bipolar collimated outflow at one time between the first and second orbital minima. This behaviour is interpreted in the framework of the model of a collimated stellar wind from the outbursting object. It is supposed that one extended disc‐like envelope covering the accretion disc of the compact object and collimating its stellar wind forms in the period between the first and second minima. The uneclipsed part of this envelope is responsible for the decrease of the depth of the orbital minimum. The calculated UBVRCIC fluxes of this uneclipsed part are in agreement with the observed residual of the depths of the first and second orbital minima. The parameters of the envelope require that it is the main emitting region of the line Hα but the Hα profile is less determined from its rotation and mostly from other mechanisms. It is concluded that the envelope is a transient nebular region and its destruction determines the increase of the depth of the orbital minimum with fading of the optical light. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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