B. J. M. Hassall

Optical observations of the eclipsing binary radio pulsar PSR1957 + 20

The recently discovered1 1.6 ms binary radio pulsar PSR1957 + 20 shows radio eclipses whose duration indicates that the occulting body is substantially larger than the Roche lobe of the low-mass (∼10–2M⊙) companion star. This suggests1–4 that this companion is evaporating through the action of a strong pulsar energy flux5. An optical counterpart has been detected which shows brightness variations in phase with the 9.2 h orbital cycle6. We have obtained optical charge coupled device (CCD) images which show that the counterpart is one component of a close visual pair separated by ∼0.7 arcsec. At maximum both are equally bright with combined V magnitude of 19.9, while at minimum PSR1957 + 20 is invisible. From spectroscopic observations we find that the contaminating star is a normal G star. The spectrum of PSR1957 + 20 shows intermittent Hα emission. We confirm that the optical brightness of PSR1957 + 20 varies in phase with the radio Doppler velocity curve1, and find that the amplitude is probably more than 3 magnitudes, minimum light coinciding with the radio eclipse. The optical light curve is consistent with heating of a hydrogen-rich low-mass white dwarf by high-energy radiation from the nearby millisecond pulsar.

IUE observations of the dwarf nova BV Centauri

The IUE observations of the dwarf nova BV Cen in quiescence are summarized. The reprocessed spectra from January 1979 are analyzed to show that the maximum temperature of the white dwarf primary star, based on its brightness at 1375 A, ranges from 42,000 to about 125,000 K depending upon the adopted values of interstellar reddening, the mass of the white dwarf, and the distance to the system. Physical arguments based on the likely state of the quiescent accretion disk in the BV Cen system suggest that the effective temperature of the white dwarf is significantly lower than this maximum temperature. The disk is more likely to be optically thick than optically thin. The impact of these findings on models for dwarf nova outbursts is discussed, but no firm conclusions can be drawn. The ultraviolet emission-line spectrum from observations obtained in August 1985 is described in detail.

The dwarf nova dippers

Abstract Two previous papers /1,2/ have shown that the dwarf nova OY Car has extensive vertical disc structure during its (∼2 week) superoutbursts. This structure is analogous to that seen in the low mass X-ray binaries (LMXBs), in that the whole disc flares towards its edge, and there is a bulge or “dark spot” where the mass transfer stream meets the disc edge. In this paper we present evidence that two more dwarf novae may have such a stream impact bulge, which manifests itself as a dip in the UV light curve, analogous to those seen in the X-ray light curves of the LMXB dippers.

Accretion disc evolution in cataclysmic variables (the 1988 international time project in La Palma

A summary of data collected during a sixty night international campaign devoted to cataclysmic variables is presented.