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1.
We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while it was in a low brightness state, at B  ≃ 16.2 mag. In comparison with the average IUE spectra, the ultraviolet continuum and emission lines appear reduced by factors of, respectively, ≃ 4 and ≃ 5. Flickering activity is mostly suppressed and the light curve shows the eclipse of a compact white dwarf at the disc centre which contributes ≃ 60 per cent of the total light at 3900–4300 Å. We use measurements of contact phases in the eclipse light curve to derive the binary geometry and to estimate masses and relevant dimensions. We find a mass ratio of q  = 0.19 ± 0.03 and an inclination of i  = 83 ± 2°. The masses of the component stars are M 1 = 0.78 ± 0.06 M⊙ and M 2 = 0.15 ± 0.03 M⊙. Our photometric model predicts K 1 = 83 ± 12 km s−1 and K 2 = 436 ± 11 km s−1. The predicted value of K1 is in accordance with the velocity amplitude obtained from the emission lines after a correction for asymmetric line emission in the disc is made. The secondary of V2051 Oph is significantly more massive than the secondaries of the other ultrashort period dwarf novae. V2051 Oph is probably a relatively young system, with a secondary star that has not had enough time to evolve out of thermal equilibrium.  相似文献   

2.
We have detected coherent oscillations, at multiple frequencies, in the line and continuum emission of the eclipsing dwarf nova V2051 Ophiuchi using the 10-m Keck II telescope. Our own novel data acquisition system allowed us to obtain very fast spectroscopy using a continuous readout of the CCD on the LRIS spectrograph. This is the first time that dwarf nova oscillations have been detected and resolved in the emission lines. The accretion disc is highly asymmetric with a stronger contribution from the blueshifted side of the disc during our observations. The disc extends from close to the white dwarf out to the outer regions of the primary Roche lobe.
Continuum oscillations at 56.12 s and its first harmonic at 28.06 s are most likely to originate on the surface of a spinning white dwarf with the fundamental period corresponding to the spin period. Balmer and helium emission lines oscillate with a period of 29.77 s at a mean amplitude of 1.9 per cent. The line kinematics and the eclipse constraints indicate an origin in the accretion disc at a radius of 12±2 R wd. The amplitude of the emission-line oscillation modulates (0–4 per cent) at a period of 488 s, corresponding to the Kepler period at R =12 R wd. This modulation is caused by the beating between the white dwarf spin and the orbital motion in the disc.
The observed emission-line oscillations cannot be explained by a truncated disc as in the intermediate polars. The observations suggest a non-axisymmetric bulge in the disc, orbiting at 12 R wd, is required. The close correspondence between the location of the oscillations and the circularization radius of the system suggests that stream overflow effects may be of relevance.  相似文献   

3.
A period analysis of CCD unfiltered photometry of V4745 Sgr (Nova Sgr 2003 #1) performed during 23 nights in the years 2003–2005 is presented. The photometric data are modulated with a period of  0.20 782 ± 0.00 003 d (4.98 768 ± 0.00 072 h)  . Following the shape of the phased light curve and the presence of the periodicity in all data sets with no apparent change in its value, we interpret this periodicity as orbital in nature and this is consistent with a cataclysmic variable above the period gap. We found a probable short-term periodicity of  0.017 238 ± 0.000 037 d (24.82 272 ± 0.05 328 min)  which we interpret as the probable spin period of the white dwarf or the beat period between the orbital and spin period. Therefore, we propose that nova V4745 Sgr should be classified as an intermediate polar candidate, supporting the proposed link between transition-oscillation novae and intermediate polars. The mass–period relation for cataclysmic variables yields a secondary mass of about  0.52 ± 0.05 M⊙  .  相似文献   

4.
We report the results of observations of V4633 Sgr (Nova Sagittarii 1998) during     . Two photometric periodicities were present in the light curve during the three years of observations: a stable one at     , which is probably the orbital period of the underlying binary system; and a second one of lower coherence, approximately 2.5 per cent longer than the former. The latter periodicity may be a permanent superhump, or, alternatively, the spin period of the white dwarf in a nearly synchronous magnetic system. A third period, at     , corresponding to the beat between the two periods was probably present in 1999. Our results suggest that a process of mass transfer has taken place in the binary system since no later than two-and-a-half months after the nova eruption. We derive an interstellar reddening of     from our spectroscopic measurements and published photometric data, and estimate a distance of     to this nova.  相似文献   

5.
We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of   K R= 198 ± 5 km s−1  . The rotational velocity of the secondary star in V347 Pup is found to be   v sin  i = 131 ± 5 km s−1  and the system inclination is   i = 840 ± 23  . From these parameters we obtain masses of   M 1= 0.63 ± 0.04 M⊙  for the white dwarf primary and   M 2= 0.52 ± 0.06 M⊙  for the M0.5V secondary star, giving a mass ratio of   q = 0.83 ± 0.05  . On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc.  相似文献   

6.
The eclipsing nova-like cataclysmic variable star V348 Pup exhibits a persistent luminosity modulation with a period 6 per cent longer than its 2.44-h orbital period ( P orb). This has been interpreted as a 'positive superhump' resulting from a slowly precessing non-axisymmetric accretion disc gravitationally interacting with the secondary. We find a clear modulation of mid-eclipse times on the superhump period, which agrees well with the predictions of a simple precessing eccentric disc model. Our modelling shows that the disc light centre is on the far side of the disc from the donor star when the superhump reaches maximum light. This phasing suggests a link between superhumps in V348 Pup and late superhumps in SU UMa systems. Modelling of the full light curve and maximum entropy eclipse mapping both show that the disc emission is concentrated closer to the white dwarf at superhump maximum than at superhump minimum. We detect additional signals consistent with the beat periods between the implied disc precession period and both and  相似文献   

7.
We present XMM–Newton observations of the eclipsing polar V2301 Oph which cover nearly 2.5 binary orbital cycles and two eclipses. This polar is believed to have the lowest magnetic field strength (7 MG) of any known polar. We find evidence for structure in the X-ray eclipse profile which shows a 'standstill' feature lasting  26 ± 4  s. This allows us to place an upper limit on the mass of the white dwarf of  ∼1.2 M⊙  . We find no evidence for quasi-periodic oscillations (QPOs) in the frequency range 0.02–10 Hz. This coupled with the absence of QPOs in RXTE data suggests that, if present, any oscillations in the shock front have a minimal effect on the resultant X-ray flux. We find no evidence for a distinct soft X-ray component in its spectrum – it therefore joins another seven systems which do not show this component. We suggest that those systems which are asynchronous, have low mass-transfer rates or have accretion occurring over a relatively large fraction of the white dwarf are more likely to show this effect. We find that the specific mass-transfer rate has to be close to 0.1 g cm−2 s−1 to predict masses which are consistent with that derived from our eclipse analysis. This may be due to the fact that the low magnetic field strength allows accretion to take place along a wide range of azimuth.  相似文献   

8.
We analyse high time resolution spectroscopy of the AM CVn stars HP Librae and V803 Centauri, taken with the New Technology Telescope (NTT) and the Very Large Telescope (VLT) of the European Southern Observatory, Chile.
We present evidence that the literature value for V803 Cen's orbital period is incorrect, based on an observed ' S -wave' in the binary's spectrogram. We measure a spectroscopic period   P V803 Cen= 1596.4 ± 1.2 s  of the S -wave feature, which is significantly shorter than the 1611-s periods found in previous photometric studies. We conclude that the latter period likely represents a 'superhump'. If one assumes that our S -wave period is the orbital period, V803 Cen's mass ratio can be expected to be much less extreme than previously thought, at   q ∼ 0.07  rather than   q ∼ 0.016  . This relaxes the constraints on the masses of the components considerably: the donor star then does not need to be fully degenerate, and the mass of the accreting white dwarf no longer has to be very close to the Chandrasekhar limit.
For HP Lib, we similarly measure a spectroscopic period   P HP Lib= 1102.8 ± 0.2 s  . This supports the identification of HP Lib's photometric periods found in the literature, and the constraints upon the masses derived from them.  相似文献   

9.
RXTE observations confirm that the X-ray light curve of V2400 Oph is pulsed at the beat cycle, as expected in a discless intermediate polar. There are no X-ray modulations at the orbital or spin cycles, but optical line profiles vary with all three cycles. We construct a model for line-profile variations in a discless accretor, based on the idea that the accretion stream flips from one magnetic pole to the other, and show that this accounts for the observed behaviour over the spin and beat cycles. The minimal variability over the orbital cycle implies that (1) V2400 Oph is at an inclination of only ≈10°, and (2) much of the accretion flow is not in a coherent stream, but is circling the white dwarf, possibly as a ring of denser, diamagnetic blobs. We discuss the light that this sheds on disc formation in intermediate polars.  相似文献   

10.
Intermediate polars (IPs) are a group of cataclysmic variables (CVs) which are thought to contain white dwarfs which have a magnetic field strength in the range ∼0.1–10 MG. A significant fraction of the X-ray sources detected in recent deep surveys has been postulated to consist of IPs. Until now two of the defining characteristics of IPs have been the presence of high (and complex) absorption in their X-ray spectra and the presence of a stable modulation in the X-ray light curve which is a signature of the spin period, or the beat period, of the accreting white dwarf. Three CVs, V426 Oph, EI UMa and LS Peg, have characteristics which are similar to IPs. However, there has been only tentative evidence for a coherent period in their X-ray light curve. We present the results of a search for coherent periods in XMM–Newton data of these sources using an autoregressive analysis which models the effects of red noise. We confirm the detection of a ∼760 s period in the soft X-ray light curve of EI UMa reported by Reimer et al. and agree that this represents the spin period. We also find evidence for peaks in the power spectrum of each source in the range 100–200 s which are just above the 3σ confidence level. We do not believe that they represent genuine coherent modulations. However, their X-ray spectra are very similar to those of known IPs. We believe that all three CVs are bona fide IPs. We speculate that V426 Oph and LS Peg do not show evidence for a spin period since they have closely aligned magnetic and spin axes. We discuss the implications that this has for the defining characteristics of IPs.  相似文献   

11.
A time-resolved spectroscopic study of V603 Aql (Nova Aquilae 1918) is presented. An orbital period of P orb=01385±00002, consistent with previous results, and a radial velocity semi-amplitude of K =20±3 km s1 are obtained from the radial velocity variations of the H emission line. Similar K values are also found in H , H , and He  i emission lines. Using the measured FWHM of the H line and assuming that the derived semi-amplitude is that of the white dwarf, we deduce a most likely mass ratio of q =0.24±0.05 and stellar masses of M 2=0.29±0.04 M and M 1=1.2±0.2 M for the secondary and primary (the white dwarf) star, respectively. The dynamical solution also indicates a very low orbital inclination, i =13°±2°. We find that the continuum and line variations are modulated with both the positive and the negative superhump periods, indicating that they arise from similar regions of the accretion disc. Moreover, we find, for the first time from spectroscopy, evidence of negative superhumps in addition to the positive superhumps. Positive superhumps are explained within the disc instability model as caused by an eccentric disc surrounding the white dwarf, which is precessing (apsidal advance) because of tidal instabilities, causing the observed positive superhumps. A nodal precession in the accretion disc is currently believed to be the cause of the observed negative superhumps. The low value of q is consistent with the expected value for systems that show superhumps, in accordance with the eccentric disc model. We find no evidence of periodicity associated with the spin period.  相似文献   

12.
We present medium-resolution VLT/FORS2 spectroscopy of six cataclysmic variables (CVs) discovered by the Sloan Digital Sky Survey (SDSS). We determine orbital periods for  SDSS J023322.61+005059.5 (96.08 ± 0.09 min), SDSS J091127.36+084140.7 (295.74 ± 0.22 min), SDSS J103533.02+055158.3 (82.10 ± 0.09 min)  and SDSS J121607.03+052013.9 (most likely 98.82 ± 0.16 min, but the one-day aliases at 92 and 107 min are also possible) using radial velocities measured from their Hα and Hβ emission lines. Three of the four orbital periods measured here are close to the observed 75–80 min minimum period for CVs, indicating that the properties of the population of these objects discovered by the SDSS are substantially different to those of the CVs found by other means. Additional photometry of SDSS J023322.61+005059.5 reveals a periodicity of approximately 60 min which we interpret as the spin period of the white dwarf, suggesting that this system is an intermediate polar with a low accretion rate. SDSS J103533.02+055158.3 has a period right at the observed minimum value, a spectrum dominated by the cool white dwarf primary star and exhibits deep eclipses, so is an excellent candidate for an accurate determination of the parameters of the system. The spectroscopic orbit of SDSS J121607.03+052013.9 has a velocity amplitude of only  13.8 ± 1.6 km s−1  , implying that this system has an extreme mass ratio. From several physical constraints we find that this object must contain either a high-mass white dwarf or a brown-dwarf-mass secondary component or both.  相似文献   

13.
The dwarf nova oscillations observed in cataclysmic variable (CV) stars are interpreted in the context of a low-inertia accretor model, in which accretion on to an equatorial belt of the white dwarf primary causes the belt to vary its angular velocity. The rapid deceleration phase is attributed to propellering. Evidence that temporary expulsion rather than accretion of gas occurs during this phase is obtained from the large drop in extreme ultraviolet flux.
We show that the quasi-periodic oscillations are most probably caused by a vertical thickening of the disc, moving as a travelling wave near the inner edge of the disc. This alternately obscures and 'reflects' radiation from the central source, and is visible even in quite low inclination systems. A possible excitation mechanism, caused by winding up and reconnection of magnetic field lines, is proposed.
We apply the model, deduced largely from VW Hyi observations, to re-interpret observations of SS Cyg, OY Car, UX UMa, V2051 Oph, V436 Cen and WZ Sge. In the last of these we demonstrate the existence of a 742-s period in the light curve, arising from obscuration by the travelling wave, and hence show that the two principal oscillations are a dwarf nova oscillation and its reprocessed companion.  相似文献   

14.
We present spectroscopic and high-speed photometric data of the eclipsing polar V895 Cen. We find that the eclipsed component is consistent with it being the accretion regions on the white dwarf. This is in contrast to Stobie et al. who concluded that the eclipsed component was not the white dwarf. Further, we find no evidence for an accretion disc in our data. From our Doppler tomography results, we find that the white dwarf has   M ≳0.7 M⊙  . Our indirect imaging of the accretion stream suggests that the stream is brightest close to the white dwarf. When we observed V895 Cen in its highest accretion state, emission was concentrated along field lines leading to the upper pole. There is no evidence for enhanced emission at the magnetic coupling region.  相似文献   

15.
We present time-resolved, J ‐band (1.025–1.340 μm) infrared spectra of the short-period dwarf novae (DNe) WZ Sge and VY Aqr, and single spectra of the short-period DN EF Peg and the nova-like variable PX And. There is some evidence in the spectra of VY Aqr and EF Peg that we have detected the secondary star, both in the continuum slope and also through the possible presence of spectral features. The spectra of WZ Sge and PX And, on the other hand, show no evidence for the secondary star, with upper limits for its contribution to the J ‐band light of 10 and 20 per cent respectively. The spectral type of the secondary in WZ Sge is constrained to be later than M7.5V. Using skew mapping, we have been able to derive a value for the radial velocity semi-amplitude of the secondary star in VY Aqr of K R =320±70 km s−1, which in conjunction with K W from Thorstensen & Taylor gives a mass ratio of q =0.15±0.04.  相似文献   

16.
We present surface spot maps of the K2V primary star in the pre-cataclysmic variable binary system, V471 Tau. The spot maps show the presence of large high-latitude spots located at the sub-white dwarf longitude region. By tracking the relative movement of spot groups over the course of four nights (eight rotation cycles), we measure the surface differential rotation rate of the system. Our results reveal that the star is rotating rigidly with a surface shear rate,  dΩ= 1.6 ± 6 mrad d−1  . The single active star AB Dor has a similar spectral type, rotation period and activity level as the K star in V471 Tau, but displays much stronger surface shear  (46 < dΩ < 58 mrad d−1)  . Our results suggest that tidal locking may inhibit differential rotation; this reduced shear, however, does not affect the overall magnetic activity levels in active K dwarfs.  相似文献   

17.
We determine the mass of the white dwarf in the eclipsing intermediate polar XY Ari following the method given in Cropper, Ramsay &38; Wu using a multitemperature bremsstrahlung model. By fitting X-ray spectra from Ginga RXTE and ASCA we find that the mean of the best fits to the data taken using different detectors is M wd = 1.28 ± 0.04 M⊙. This figure is too high to be consistent with the mass of the white dwarf found by Hellier from X-ray eclipse timings. There are also small systematic differences between the masses derived using different X-ray satellites.  相似文献   

18.
We have discovered that the spectrum of the well-known dwarf nova EM Cyg is contaminated by light from a K25V star (in addition to the K-type mass donor star). The K25V star contributes approximately 16 per cent of the light from the system and if not taken into account has a considerable effect upon radial velocity measurements of the mass donor star. We obtain a new radial velocity amplitude for the mass donor star of K 2=202±3 km s1, compared with the value of K 2=135±3 km s1 obtained in Stover, Robinson & Nather's classic study of EM Cyg. The revised value of the amplitude, combined with a measurement of rotational broadening of the mass donor, v  sin  i =140±6 km s1, leads to a new mass ratio of q M 2 M 1=0.88±0.05. This solves a long-standing problem with EM Cyg, because Stover et al.'s measurements indicated a mass ratio q >1, a value that should have led to dynamically unstable mass transfer for the secondary mass deduced by Stover et al. The revised value of the mass ratio, combined with the orbital inclination i =67±2°, leads to masses of 0.99±0.12 M and 1.12±0.08 M for the mass donor and white dwarf respectively. The mass donor is evolved, because it has a later spectral type (K3) than its mass would imply.
We discuss whether the K star could be physically associated with EM Cyg or not, and present the results of the spectroscopic study.  相似文献   

19.
An investigation of the orbital period changes of the neglected eclipsing binaries, RY Aqr, SZ Her, RV Lyr and V913 Oph, is presented based on all published minima times. Although the explanation of magnetic activity on the surface of the secondaries of the studied Algols is still open, the preferred light‐time effect due to the unseen components around the systems seems more plausible in explaining the tilted sinusoidal variations with relatively high‐amplitudes. The minimal mass values of possible tertiary components have been estimated to be about 1.06, 0.25, 0.78 and 2.85 M⊙ for RY Aqr, SZ Her, RV Lyr and V913 Oph, respectively and the results indicate that their contributions to the total light of the eclipsing pairs are measurable with high accuracy photometric and spectroscopic data, if they exist. Applegate's (1992) model has been discussed as an alternative mechanism assuming that the cooler components have magnetic cycles. It is found that the model parameters of RY Aqr and V913 Oph are consistent with the required values in Applegate's model. In addition to the first detailed orbital study on these systems, a statistical survey on the character of the O – C variations of classical Algols has revealed that about 50 percent of the systems show cyclic behavior. This means that the presence of possible third bodies around classical Algols should be tested with careful analysis using new data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
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   

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