ESOSAT and IUE observations of the symbiotic binary R Aquarii during maximum and minimum

Coordinated IUE and EXOSAT observations of the symbiotic Mira R Aqr, made in June and December 1985, at phases 0.0 and 0.5 of the Mira light curve, are discussed. A weak X-ray flux has been for the first time unambiquously detected without any significant change with the Mira light curve. Also the UV spectrum of the central object has not varied, while the presence of high ionization lines (NV and HeII) in the spectrum of the jet-like feature is confirmed. The data are discussed in the light of a model in which the jet is preexisting material illuminated by the recently increased X and UV radiation from the inner edge of the accretion disk around the degenerate companion of the Mira primary.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

UBV photometry of DX Aquarii

U, B, V photometry of the eclipsing binary DX Aqr has been presented for the first time. The period of the system comes out to be nearly half the period given by Strohmeier (1966) and a value of O^d.472502 has been determined. The colour of the system has been discussed. The primary eclipse is a total occulation. The orbit seems to be eccentric. The system belongs to Algol type. DX Aqr may be a very complicated system. The present results are considerably different from those of earlier investigations.     

Accretion stream mapping of HU Aquarii

We present a new mapping algorithm, the Accretion Stream Mapping (ASM), which uses the full phase-coverage of a light curve to derive spatially resolved intensity distributions along the accretion stream in magnetic cataclysmic variables of AM Herculis type (polars). The surface of the accretion stream is approximated as a 12-sided (duodecadon-shaped) tube. After successfully testing this method on artificial data we applied it to emission-line light curves of H β , H γ and He  ii λ 4686 of the bright eclipsing polar HU Aqr. We find hydrogen and helium line emission bright in the threading region of the stream where the stream couples on to magnetic field lines. It is particularly interesting that the stream is bright on the irradiated side facing the white dwarf, which highlights the interplay of collisional and radiative excitation/ionization.     

A tenuous X-ray corona enveloping AE Aquarii

In this paper we propose that the observed unpulsed X-ray emission in AE Aquarii is the result of a very tenuous hot corona associated with the secondary star, which is pumped magnetohydrodynamically by the propeller action of the fast rotating white dwarf. It is shown that the closed coronal field of the secondary star envelops a substantial portion of the binary system, including the fast rotating magnetized white dwarf. This implies that the propeller outflow of material in AE Aquarii is initiated inside an enveloping magnetic cavity. The outflow crossing the secondary dead-zone field constitutes a  β_gen= (8πρ v ²_esc/ B ²) ≫ 1  plasma, acting as a magnetohydrodynamic generator resulting in the induction of field-aligned currents in these closed magnetospheric circuits where  β_cir= (8π nkT / B ²) ≪ 1  . The Ohmic heating of the coronal circuit can readily account for a   T _x≥ 10⁷  K  plasma in the coronal flux tubes connecting the generator and the stellar surface. Further, the bremsstrahlung losses of the thermal electrons in the coronal circuit can readily drive the observed unpulsed X-ray luminosity of   L _x∼ 10³¹  erg s ⁻¹  , which correlates with the luminosity and relatively large source implied by recent XMM–Newton observations.     

Period variations of the eclipsing system EE Aquarii

The O–C diagrams of EE Aquarii have been presented for the first time, the period variations present in the system have been analysed, and tentative results have been presented. In all, four period decreases and three period increases are noted in the time interval 1940 to 1985. The strongest period change is noted in the time interval 1957 to 1959. Sufficiently strong period changes have also been noted in the time intervals, 1948 to 1950 and 1970 to 1976. Besides four period decreases and three period increases, eleven period fluctuations are also seen in the O–C diagram (II) of EE Aqr. The total period change in different portions of the O–C diagram (II) ranges from 1.7×10^–7 d to 8.2×10^–6 d. The period increases are stronger than the period decreases. An overall picture of the period variations suggests that weak period variations are present in the system EE Aqr.     

Photometric observations and light curve analysis of ST Aquarii

The system of ST Aquarii has been observed inB andV filters at KOTTAMIA Observatory in Egypt. Two light curves have been obtained and new times of minima have been calculated.The light curves have been analysed using the theory of Fourier transform of light changes in frequencydomain, and new geometrical and physical elements have been obtained.     

The Duplicity of Large Amplitude SX Phoenicis Star CY Aquarii

New photoelectric times of maximum light of the large amplitude SX Phoenicis star CY Aquarii are analyzed together with times of maximum light in the literature. The general shape of the fitted curve of the observed minus calculated (O-C) times of maximum light suggest the duplicity of the variable star, which causes long-term period variations in the light-time. The period changes of CY Aqr are probably consequences of a continuously increasing period combined with the light-time effect in a binary system. The secondary companion is less massive. Some spectroscopic orbital elements are derived from the O-C diagram. This revised version was published online in July 2006 with corrections to the Cover Date.     

New period and period variations of DX Aquarii

The new period (P=0 _. ^d 461700) of the eclipsing binary system DX Aqr has been presented, which is based on available times of minima. O–C diagram of DX Aqr has been presented for the first time, and the period variations present in the system have been analysed. In all five period increases and five period decreases are nothed, and four period increases and five period decreases have been discussed. The strongest period increase occurs between 1975 and 1976. The total period change in different portions of the O–C diagram ranges from 1.40×10^–4 d to 3.61×10^–6 d. Appreciable period fluctuations have been noted to have occurred in the time intervals, 1964–1965 and 1974–1975.     

Observations of the SW Sextantis star UU Aquarii

We present 14 nights of medium resolution (1–2 Å) spectroscopy of the eclipsing cataclysmic variable UU Aquarii obtained during a high accretion state in 1995 August–October. UU Aqr appears to be an SW Sextantis (SW Sex) star, as noted by Baptista, Steiner & Horne, and we discuss its spectroscopic behaviour in the context of the SW Sex phenomenon. Emission-line equivalent width curves, Doppler tomography, and line profile simulation provide evidence for the presence of a bright spot at the impact site of the accretion stream with the edge of the disc, and a non-axisymmetric, vertically and azimuthally extended absorbing structure in the disc. The absorption has maximum depth in the emission lines around orbital phase 0.8, but is present from φ≈0.4 to φ≈0.95. An origin is explored for this absorbing structure (as well as for the other spectroscopic behaviour of UU Aqr) in terms of the explosive impact of the accretion stream with the disc.     

On the ephemeris of the eclipsing polar HU Aquarii

The magnetic cataclysmic variable HU Aquarii displayed pronounced quasi‐periodic modulations of its eclipse timing. These were interpreted in terms of the light‐travel time (LTT) effect caused by a circumbinary planet or planetary system. We report new photometric observations that revealed another precise eclipse timing for the October 2013 epoch, the first obtained in a high accretion state after many years in low or intermediate states. The eclipse was observed to occur earlier by 95.3 ± 2.0 s or 62.8 ± 2.0 s than expected for an assumed linear or quadratic ephemeris, respectively. The implied apparent strong evolution of the orbital period calls for a revision of the current planetary model or the planetary parameters. The object deserves further monitoring to uncover the true nature of the observed variability and to constrain the properties of the proposed planet or planetary system. The new observations prove that advanced amateur equipment can successfully be used in the growing field of planet search in wide circumbinary orbits via the LTT effect. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Doppler signatures of Hα flares in AE Aquarii

We present high-speed spectrophotometric observations of the Hα emission in the exotic cataclysmic variable AE Aqr. Over 10 000 spectra with a sampling rate of ∼ 6 s were obtained. The well-known 16.5- and 33-s oscillations were not detected in either the continuum or the line, nor were any quasi-periodic oscillations detected. The Hα line shows remarkably complex behaviour, with changes in flux of up to a factor of 3 in a few hours. The line does not act as a single entity — the instantaneous line profile is highly asymmetric and consists of a superposition of emission components that are localized in velocity. We find that during flares the Hα emission is delayed and decays more slowly than the continuum. The Hα variations are not linearly correlated with the continuum variations. Examination of the trailed spectrograms and Doppler tomograms reveals no signatures of an accretion disc, but rather supports the idea that mass is being ejected by a propeller mechanism.