A Spectroscopic Study of the SU Uma-type Dwarf Nova YZ Cnc during its 2002 Superoutburst

We report on time-resolved spectroscopic observations of the SU Ursae Majoris dwarf nova, YZ Cnc for over 11 h on two nights during its 2002 January superoutburst. The spectra on the first day only showed absorption-line profiles, while on the second day the lines showed "W" profiles with blue and red troughs. The radial velocity curve of the absorption troughs and emission peaks of Hβ has an amplitude of 49±10 km s-1 and a phase offset of -0.07±0.04, which are very similar to those measured in quiescence. However, the γ velocity deviates strongly from the systemic velocity measured in quiescence, by some ±60 km s-1. Large shifts of -70 km s-1 in the orbital-averaged velocity and -0.09 in the phase are also found in our observations. All these features can be well explained by a precessing, eccentric disk.     

Detection of the optical counterpart of the proposed double degenerate polar RX J1914+24

We have detected the optical counterpart of the proposed double degenerate polar RX J1914+24. The I -band light curve is modulated on the 9.5-min period seen in X-rays. There is no evidence for any other periods. No significant modulation is seen in J . The infrared colours of RX J1914+24 are not consistent with a main-sequence dwarf secondary star. Our ASCA spectrum of RX J1914+24 is typical of a heavily absorbed polar and our ASCA light curve also shows only the 9.5-min period. We find that the folded I band and X-ray light curves are out of phase. We attribute the I -band flux to the irradiated face of the donor star. The long-term X-ray light curve shows a variation in the observed flux of up to an order of magnitude. These observations strengthen the view that RX J1914+24 is indeed the first double degenerate polar to be detected. In this light, we discuss the synchronizing mechanisms in such a close binary and other system parameters.     

Eccentric discs in binaries with intermediate mass ratios: superhumps in the VY Sculptoris stars

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.     

Stokes imaging of the AM Her system ST LMi

The Stokes imaging technique of Potter, Hakala & Cropper is applied to the polarized emission from the AM Her system ST LMi. For the first time, the cyclotron emission region on the surface of the white dwarf is mapped in terms of optical depth/density in an analytical and objective manner. The region is found to consist of a less dense region leading a higher density region in orbital phase. It is demonstrated that the emission region needs to have a multi-temperature structure in order to explain the spectral slope and the general morphology of the cyclotron humps observed in the IR during the bright phase in ST LMi.
Furthermore, it is shown that a secondary emission region, fed by the same magnetic field lines that feed the main emission region, could be responsible for the positive circular polarization in the IR, the position angle variation and the excess flux during the faint phase of the white light observations which cannot be accounted for with a single emission region.     

激变变星及相关天体的与近红外电离钙三重线的光谱分析

给出了1997年4月15日至17日在北京天文台用2.16 m望远镜卡焦光谱仪观测获得的6颗激变变星 (AB Boo, UX UMa, T CrB, AH Her, Z Cam 和 V426 Oph) 及3颗相关天体(UMa3, EG UMa 和 Leo3)的CCD光谱, 并同时拍摄了5颗晚型星(3 Dra, Vir, Leo, 34 Boo 和36Com) 的CCD 光谱, 作为晚型星参考谱. 测量了观测样本星的和近红外Ca II的三重线(8498, 8542和 8662)的等值宽度(EW),谱线半极大全宽(FWHM)和视向速度(Vr), 并分析了这些星的活动性.     

A TiO study of the dwarf nova IP Pegasi

We present red spectra in the region ∼ λ 7000–8300 Å of the eclipsing dwarf nova IP Peg, with simultaneous narrow-band photometry centred at 7322 Å. We show that by placing a second star on the slit we can correct for the telluric absorption bands which have hitherto made the TiO features from the secondary star unusable. We use these TiO features to carry out a radial velocity study of the secondary star, and find this gives an improvement in the signal-to-noise ratio of a factor of 2 compared with using the Na  i doublet. In contrast with previous results, we find no apparent ellipticity in the radial velocity curve. As a result we revise the semi-amplitude to K ₂=331.3±5.8 km s⁻¹, and thus the primary and secondary star masses to 1.05^-0.07_+0.14 M⊙ and 0.33^-0.05_+0.14 M⊙ respectively. Although this is the lowest mass yet derived for the secondary star, it is still overmassive for its observed spectral type. However, the revised mass and radius bring IP Peg into line with other cataclysmic variables in the mass–radius–period relationships.
By fitting the phase-resolved spectra around the TiO bands to a mean spectrum, we attempt to isolate the light curve of the secondary star. The resulting light curve has marked deviations from the expected ellipsoidal shape. The largest difference is at phase 0.5, and can be explained as an eclipse of the secondary star by the disc, indicating that the disc is optically thick when viewed at high inclination angles.     

The remnant of Nova Cassiopeiae 1993 (V705 Cassiopeiae)

We have detected radio emission from the remnant of V705 Cas, beginning 221 d after visual maximum. We follow the remnant from first detection while still optically thick through the turn-over to optically thin emission, and finally confirming the absence of emission due to expansion and fading by the end of 1998. While the emission is consistent with thermal bremsstrahlung, as seen in most previous novae, the small-scale structure shows two ridge-like features, which develop significantly from day 585 until our last detection on day 1544. While the development is fairly rapid, it is also much smoother than that seen in V1974 Cyg, in that we can follow individual features as they change over almost 1000 d. Our optical spectra unequivocally indicate some form of axial symmetry, as derived from the velocity structure. This is difficult to reconcile with the observed development in the radio images. We suggest a number of possible explanations.     

Polarimetry and spectroscopy of RX J1141.3−6410: a single‐pole AM Her system

We present polarimetric and spectroscopic observations of the ROSAT source RX J1141.3−6410, recently identified as a polar. The detection of circular polarization variations, with an amplitude of 10 per cent, over a 3.16-h period confirms that the system is a polar (AM Herculis star). Supporting evidence comes from the nature of the emission lines and their radial velocity variability. In addition, we observe continuum slope changes in the far-red spectral region (∼6000–8200 Å), indicative of phase dependent cyclotron emission. Polarimetric modelling at two wavelengths establishes RX J1141.3−6410 as a single-pole system, with i ∼ β ∼70°. The accretion region is extended in magnetic longitude, and is totally self-occulted for ∼25 per cent of the orbit. The radial velocity curves derived from the emission lines show a phasing with maximum blueshift occurring with Δ φ ∼0.05 of maximum intensity and circular polarisation. In addition, the broader component of the lines exhibit a substantial radial velocity phase shift with respect to the narrower component, in the sense that the broad component preceeds the narrow. This can be readily understood if the narrower component is principally a result of orbital motion of the stream material and the broad component mainly a result of streaming motion near the coupling region. The phasing of the Ca  ii near-infrared line radial velocities also supports this general picture.     

Thermal stability and nova cycles in permanent superhump systems

Archival data on permanent superhump systems are compiled to test the thermal stability of their accretion discs. We find that their discs are almost certainly thermally stable as expected. This result confirms Osaki's suggestion that permanent superhump systems form a new subclass of cataclysmic variables (CVs), with relatively short orbital periods and high mass-transfer rates. We note that if the high accretion rates estimated in permanent superhump systems represent their mean secular values, then their mass-transfer rates cannot be explained by gravitational radiation, therefore, either magnetic braking should be extrapolated to systems below the period gap or they must have mass-transfer cycles. Alternatively, a new mechanism that removes angular momentum from CVs below the gap should be invoked.
We suggest applying the nova cycle scenarios offered for systems above the period gap to the short orbital period CVs. Permanent superhumps have been observed in the two non-magnetic ex-novae with binary periods below the gap. Their post-nova magnitudes are brighter than their pre-outburst values. In one case (V1974 Cyg) it has been demonstrated that the pre-nova should have been a regular SU UMa system. Thus, it is the first nova whose accretion disc was observed to change its thermal stability. If the superhumps in this system indicate persistent high mass-transfer rates rather than a temporary change induced by irradiation from the hot post-nova white dwarf, it is the first direct evidence for mass-transfer cycles in CVs. The proposed cycles are driven by the nova eruption.