首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
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   

2.
We obtained CCD photometric observations of the Algol-type semidetached binary XX Cephei (XX Cep) during 15 nights from 2002 September 17 to 2003 February 2, and also on 2005 January 21. Except for those data taken on the last night of the concentrated observing season, the 3881 measurements were obtained over an interval of only 106 nights. From these data, four new times of minimum light were calculated. The  (O− C)  diagram formed from all available timings, and thus the orbital period of the system, can be partly represented as a beat effect between two cyclical variations with different periods (      yr,      yr) and amplitudes  ( K 1=0.015 d, K 2=0.103 d)  , respectively. Both physical and non-physical interpretations of these cycles were investigated. The long-term sinusoidal variation is too long for magnetic cycling in solar-type single and close binary stars. In addition, we have studied the effect of a possible secular period variation. By analysing the residuals from our Wilson–Devinney (WD) binary model, we found small light variations with a period of 5.99 d with amplitudes growing toward longer wavelengths. We think that these oscillations may be produced by instabilities at the systemic L 1 point (also occupied by the point of the cool star) and that these instabilities are, in turn, caused by non-uniform and sporadic convection. There is also a short-period oscillation of about 45 min in the WD light residuals that is attributed to accretion on to the mass-gaining primary component from a feeble gas stream originating on the cool donor star.  相似文献   

3.
We report on the discovery of a 25.5-min superhump period for the suspected helium dwarf nova system KL Draconis in a high state. The presence of superhumps combined with the previously observed helium spectrum and large-amplitude photometric variations confirm that KL Dra is an AM CVn system similar to CR Bootis, V803 Cen and CP Eridani. We also find a low-state photometric period at 25.0 min that we suggest may be the orbital period. With this assumption, we estimate   q =0.075  ,   M 1=0.76 M⊙  and   M 2=0.057 M⊙  .  相似文献   

4.
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   

5.
Photometric observations of V4633 Sgr (Nova Sagittarii 1998) during 1998–2005 reveal the presence of a stable photometric periodicity at   P 1= 180.8 min  which is probably the orbital period of the underlying binary system. A second period was present in the light curve of the object for 6 yr. Shortly after the nova eruption it was measured as   P 2= 185.6 min  . It has decreased monotonically in the following few years reaching the value   P 2= 183.9 min  in 2003. In 2004 it was no longer detectable. We suggest that the second periodicity is the spin of the magnetic white dwarf of this system that rotates nearly synchronously with the orbital revolution. According to our interpretation, the post-eruption evolution of Nova V4633 Sgr follows a track similar to the one taken by V1500 Cyg (Nova Cygni 1975) after that nova eruption, on a somewhat longer time-scale. The asynchronism is probably the result of the nova outburst that led to a considerable expansion of the white dwarf's photosphere. The increase in the moment of inertia of the star was associated with a corresponding decrease in its spin rate. Our observations have followed the spinning-up of the white dwarf resulting from the contraction of its outer envelope as the star is slowly returning to its pre-outburst state. It is thus the second known asynchronous polar classical nova.  相似文献   

6.
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   K 2= 182.5 ± 0.9 km s−1  . The radial velocity semi-amplitude of the white dwarf was found to be   K 1= 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  ( M 1≥ 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.  相似文献   

7.
We present phase resolved optical spectroscopy and X-ray timing of the neutron star X-ray binary EXO 0748−676 after the source returned to quiescence in the autumn of 2008. The X-ray light curve displays eclipses consistent in orbital period, orbital phase and duration with the predictions and measurements before the return to quiescence. Hα and He  i emission lines are present in the optical spectra and show the signature of the orbit of the binary companion, placing a lower limit on the radial velocity semi-amplitude of   K 2 > 405 km s−1  . Both the flux in the continuum and the emission lines show orbital modulations, indicating that we observe the hemisphere of the binary companion that is being irradiated by the neutron star. Effects due to this irradiation preclude a direct measurement of the radial velocity semi-amplitude of the binary companion; in fact, no stellar absorption lines are seen in the spectrum. Nevertheless, our observations place a stringent lower limit on the neutron star mass of   M 1 > 1.27 M⊙  . For the canonical neutron star mass of   M 1= 1.4 M⊙  , the mass ratio is constrained to  0.075 < q < 0.105  .  相似文献   

8.
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   

9.
Two nights of phase-resolved medium-resolution Very Large Telescope spectroscopy of the extra-galactic low-mass X-ray binary LMC X−2 have revealed a 0.32 ± 0.02 d spectroscopic period in the radial velocity curve of the He  ii λ4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disc in LMC X−2. This is strengthened by He  ii λ4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMC X−2, with a velocity of   K em= 351 ± 28 km s−1  , that we tentatively interpret as coming from the irradiated side of the donor star. Since K em must be smaller than K 2, this leads to the first upper limit on the mass function of LMC X−2 of   f ( M 1) ≥ 0.86  M⊙  (95 per cent confidence), and the first constraints on its system parameters.  相似文献   

10.
Continuous CCD photometry of the classical nova DN Gem during 52 nights in the years 1992–1998 reveals a modulation with a period of 0.127844 d. The semi-amplitude is about 0.03 mag. The stability of the variation suggests that it is the orbital period of the binary system. This interpretation makes DN Gem the fourth nova inside the cataclysmic variable (CV) period gap, as defined by Diaz & Bruch, and it bolsters the idea that there is no period gap for classical novae. However, the number of known nova periods is still too small to establish this idea statistically. We eliminate several possible mechanisms for the variation, and propose that the modulation is driven by an irradiation effect. We find that model light curves of an irradiated secondary star fit the data well. The inclination angle of the system is restricted by this model to 10°≲ i ≲65°. We also refine a previous estimate of the distance to the binary system, and find d =1.6±0.6 kpc.  相似文献   

11.
We present phase resolved optical spectroscopy and Doppler tomography of V1341 Cygni, the optical counterpart to the neutron star low-mass X-ray binary (LMXB) Cygnus X-2 (Cyg X-2). We derive a radial velocity (RV) curve for the secondary star, finding a projected RV semi-amplitude of   K 2= 79 ± 3 km s−1  , leading to a mass function of  0.51 ± 0.06 M⊙, ∼30  per cent lower than the previous estimate. We tentatively attribute the lower value of K 2 (compared to that obtained by other authors) to variations in the X-ray irradiation of the secondary star at different epochs of observations. The limited phase coverage and/or longer timebase of previous observations may also contribute to the difference in K 2. Our value for the mass function implies a primary mass of  1.5 ± 0.3 M⊙  , somewhat lower than previous dynamical estimates, but consistent with the value found by analysis of type-I X-ray bursts from this system. Our Doppler tomography of the broad He  ii λ4686 line reveals that most of the emission from this line is produced on the irradiated face of the donor star, with little emission from the accretion disc. In contrast, the Doppler tomogram of the N  iii λ4640.64 Bowen blend line shows bright emission from near the gas stream/accretion disc impact region, with fainter emission from the gas stream and secondary star. This is the first LMXB for which the Bowen blend is dominated by emission from the gas stream/accretion disc impact region, without comparable emission from the secondary star. This has implications for the interpretation of Bowen blend Doppler tomograms of other LMXBs for which the ephemeris may not be accurately known.  相似文献   

12.
Intermediate-resolution (0.5–1 Å) optical spectroscopy of the cataclysmic variable (CV) SY Cnc reveals the spectrum of the donor star. Our data enable us to resolve the orbital motion of the donor and provide a new orbital solution, binary mass ratio and spectral classification. We find that the donor star has spectral-type G8 ± 2 V and orbits the white dwarf with   P = 0.382 3753 ± 0.000 0003  d,   K 2= 88.0 ± 2.9  km s−1 and   V sin  i = 75.5 ± 6.5  km s−1. Our values are significantly different from previous works and lead to   q = M 2/ M 1= 1.18 ± 0.14  . This is one of the highest mass ratios known in a CV and is very robust, because it is based on resolving the rotational broadening over a large number of metallic absorption lines. The donor could be a slightly evolved main sequence or descendant from a massive star which underwent an episode of thermal time-scale mass transfer.  相似文献   

13.
In this paper, we discuss the early phases of the ongoing outburst that CI Cyg, a prototype symbiotic star, is currently undergoing after 30-year quiescence. We have tightly monitored CI Cyg in   B V R C I C  bands, starting a whole year before the onset of the outburst, and in addition we obtained numerous Echelle high- and low-resolution absolutely flux-calibrated spectra. The outburst started while the accreting white dwarf (WD) was being eclipsed by the Roche lobe filling M giant companion, and it was discovered during the egress phase on the second half of 2008 August. The system reached peak V -band brightness in early 2008 October and has been characterized by amplitudes  Δ B = 1.9, Δ V = 1.5, Δ R C= 0.9, Δ I C= 0.4  mag. At maximum V -band brightness, the outbursting WD had expanded to closely resemble an F3 II/Ib star, with   MV =−3.5, T eff∼ 6900 K  and   R = 28 R⊙  . The high-ionization emission lines ([Ne  v ], [Fe  vii ], He  ii ) disappeared and only lower ionization lines were visible. Balmer and He  i emission lines declined in equivalent width but increased in absolute flux. The output radiated by the hot component during the outburst corresponds to nuclear burning proceeding at a  2 × 10−8 M⊙ yr−1  rate.  相似文献   

14.
We present extensive, high-density Swift observations of V2491 Cyg (Nova Cyg 2008 No. 2). Observing the X-ray emission from only one day after the nova discovery, the source is followed through the initial brightening, the super-soft source phase and back to the pre-outburst flux level. The evolution of the spectrum throughout the outburst is demonstrated. The UV and X-ray light curves follow very different paths, although changes occur in them around the same times, indicating a link between the bands. Flickering in the late-time X-ray data indicates the resumption of accretion. We show that if the white dwarf (WD) is magnetic, it would be among the most magnetic known; the lack of a periodic signal in our later data argues against a magnetic WD, however. We also discuss the possibility that V2491 Cyg is a recurrent nova, providing recurrence time-scale estimates.  相似文献   

15.
We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g -mode with frequency 0.3428 d−1 reported before is detected in our spectroscopy. We identify the four main modes as  (ℓ1, m 1) = (1, 1), (ℓ2, m 2) = (0, 0), (ℓ3, m 3) = (1, 0)  and  (ℓ4, m 4) = (2, 1)  for   f 1= 5.178 964 d−1, f 2= 5.334 224 d−1, f 3= 5.066 316 d−1  and   f 4= 5.490 133 d−1  , respectively. Our seismic modelling shows that f 2 is likely the radial first overtone and that the core overshooting parameter  αov  is lower than 0.4 local pressure scale heights.  相似文献   

16.
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   

17.
Simultaneous spectroscopic and photometric observations of the Z Cam type dwarf nova SY Cancri were used to obtain absolute flux calibrations. A comparison of the photometric calibration with a wide-slit spectrophotometric calibration showed that either method is equally satisfactory. A radial velocity study of the secondary star, made using the far-red Na  i doublet, yielded a semi-amplitude of   K 2= 127 ± 23 km s−1  . Taking the published value of  86 ± 9 km s−1  for K 1 gives a mass ratio of   q = M 2/ M 1= 0.68 ± 0.14  ; this is very different from the value of  1.13 ± 0.35  quoted in the literature. Using the new lower mass ratio, and constraining the mass of the white dwarf to be within reasonable limits, then leads to a mass for the secondary star that is substantially less than would be expected for its orbital period if it satisfied a main-sequence mass–radius relationship. We find a spectral type of M0 that is consistent with that expected for a main-sequence star of the low mass we have found. However, in order to fill its Roche lobe, the secondary must be significantly larger than a main-sequence star of that mass and spectral type. The secondary is definitely not a normal main-sequence star.  相似文献   

18.
High-resolution spectroscopic observations around the Hα line and BVRI photometry of the eclipsing short-period RS CVn star UV Leo are presented. The simultaneous light-curve solution and radial velocity-curve solution led to the following values of the global parameters of the binary: temperatures   T 1= 6000 ± 100 K  and   T 2= 5970 ± 20 K  ; masses   M 1= 0.976 ± 0.067 M⊙  and   M 2= 0.931 ± 0.052 M⊙  ; separation   a = 3.716 ± 0.048 R⊙  ; orbital inclination     ; radii   R 1= 1.115 ± 0.052 R⊙  and   R 2= 1.078 ± 0.051 R⊙  ; equatorial velocities   V 1= 98.8 ± 2.3 km s−1  and   V 2= 89.6 ± 2.7 km s−1  . These results lead to the conclusion that the two components of UV Leo are slightly oversized for their masses and lie within the main-sequence band on the mass–radius diagram, close to the isochrone 9 × 1010 yr.  相似文献   

19.
We present the spectroscopy of nova V2467 Cyg acquired at the Loiano Observatory, Italy, during the first six months after the outburst. We have used the optical spectroscopy to study the physical properties of the ejected material and the photometry to estimate the nova distance. V2467 Cyg is a fast nova, with decline rates by two or three magnitudes of 7.6 and 14.6 days respectively. The light curve exhibited oscillations during the transition stage. The nova achieved an absolute magnitude at maximum in the range –8.5… –9.1. The distance is in the range 2.6… 3.6 kpc. V2467 Cyg showed an early appearance of forbidden lines during the transition stage. Its evolution is similar to the behavior of V1494 Aql (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
In this study we present and re-analyse the historical, 1889–1998, light curve (LC) of the eclipsing symbiotic binary AR Pav. For the first time, we show that the timing of mid-points of eclipses observed during a quiescent phase obeys a quadratic ephemeris, with an initial orbital period P 0=605.18 d and a rate of period change     .
We determined a distance to the system of 5.8±1.5 kpc, the mass ratio of the giant to the hot star, M g M h=0.4±0.1, the mass of the giant, M g=1.8+1/−0.5 M⊙ and its radius, R g=167±15 R⊙.
During quiescence, the LC has characteristic features similar to those observed in cataclysmic variables (CVs). It can be well reproduced by a model of a large accretion disc surrounding the hot star. However, it is probable that the geometry of the transferred material in the Roche lobe of the accretor in AR Pav is different from that of CVs.
During active phases the shape of the LC changes considerably. A complex wave-like variation developed as a function of the orbital phase with an amplitude of ∼1 mag. It is interpreted in terms of a collisionally heated emission region located on the giant surface and arising from the hot star eruption.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号