D. H. P. Jones

On the nature of SW Sex

We present spectrophotometry of the eclipsing nova-like variable SW Sex. The continuum is deeply eclipsed and shows asymmetries as a result of the presence of a bright-spot. We derive a new ephemeris and, by measuring the eclipse width, we are able to constrain the inclination to i > 75° and the disc radius to RD > 0.6L1• In common with other members of its class (of which it is the prototype), SW Sex shows single-peaked emission lines which show transient absorption features and large phase shifts in their radial velocity curves. In addition, the light curves of the emission lines show a reduction in flux around phase 0.5 and asymmetric eclipse profiles which are not as deep as the continuum eclipse. Using Doppler tomography, we find that most of the line emission in SW Sex appears to originate from three sources: the secondary star, the accretion disc and an extended bright-spot. The detection of the red star allows us to constrain the radial velocity semi-amplitude of the secondary to KR> 180 km S-1 and hence the component masses to M1 ,..., 0.30.7 M0 and M2 < 0.3 M0. The Doppler maps suggest a simple new model for SW Sex, in which the dominance of single-peaked line emission from the bright-spot over the weak double-peaked disc emission gives SW Sex its single-peaked profiles and forces the radial velocity curves to follow the motion of the bright-spot and thus exhibit large phase shifts. The transient absorption features in the Balmer line profiles are mostly artefacts of the complex intertwining of the emission components from the secondary star, bright-spot and accretion disc and involve little true absorption. While the accretion disc and secondary star components of this model appear to be secure, the dominant bright-spot component fails in one important area - its inconsistency with the Balmer line light curves. The eclipse profile requires the material emitting the Balmer lines to ( a) be eclipsed as early as phase 0.8, (b) not be as deeply eclipsed as the continuum, and (c) exhibit a flat-bottomed eclipse and then come out of eclipse very sharply around phase 0.05. Although it is possible to explain the early ingress with a raised disc rim downstream from the bright-spot, the rapid egress is difficult to account for without speculating either that there are regions of strong Balmer absorption in the disc, the changing visibility of which during eclipse alters the shape of the light curve, or that there is Balmer emission from above the orbital plane which shares the velocity of the bright-spot.

Spectral evolution of the peculiar Ic Supernova 1998bw

Supernova 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supernovae and probably the first supernova associated with a γ-ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the Anglo-Australian Telescope, the UK Schmidt Telescope and the Siding Springs Observatories 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 d after V-band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from observations of classical Ic supernovae (SNe), we find that the evolution from the photospheric to nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10–50 per cent higher than other SNe and on day 94 emission lines are 45 per cent broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that an additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope.

The Isaac Newton Group

Abstract The Isaac Newton Group on the Roque de los Muchachos consists at the time of writing of the 1.0m Jacobus Kapteyn Telescope and 2.5m Isaac Newton Telescope. In this article we summarise the design parameters and performance of the two telescopes and their principal instruments, and give examples of the first results from them.

The Long Period Dwarf Nova Uy Pup in Outburst

UY Pup is a little studied, frequently outbursting dwarf nova whose brightness varies from V ⋃ 13.5 mag in outburst to V ⋃ 15.8 mag in quiescence, which typically lasts ⋃15...25d. We observed it spectroscopically at the INT in La Palma on 1989 Febuary 15 and 16 during outburst maximum. In this outburst, the rise lasted at least 3d and there was a long decline of about 6...9d. The whole outburst lasted about 18d (Mattei, private communication).

A Low-Dispersion Spectroscopic Survey

We obtained 146 spectra of 22 cataclysmic variables on the nights of 1991 April 27 to May 1, using the ISIS triple-beam spectrograph at the Cassegrain focus of the 4.2-m William Herschel Telescope at the Roque de los Muchachos Observatory on the island of La Palma. A dichroic was used to split the beam, reflecting the blue light onto the EEV3 CCD chip in the blue arm, and the red light onto the EEV2 CCD chip in the red arm. In both arms a 158 line/mm grating was used giving a resolution of ∼ 5A, yielding a wavelength range of λλ3450-5550A in the blue and λλ5810-8910A in the red. The reduction procedure followed was standard, using an optimal extraction procedure.

Interacting and Active IRAS Galaxies

We decided to study a complete sample of, predominantly high IR luminosity, IRAS galaxies to determine the fractions that were interacting or active.

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.

Red spectroscopy of IP Pegasi

Time resolved spectroscopy of the dwarf nova IP Pegasi in the range λλ 7670-8320A shows absorption lines originating from the cool secondary. A radial velocity curve for this component has been derived by cross-correlation with a normal M star. The curve has semi-amplitude K2 = 288.3 ± 4 km s-1, and is slightly distorted. This distortion is equivalent to an orbit with an apparent eccentricity of 0.075 ± 0.024. The mass function of the primary is 0.394 ± 0.016Mʘ. From this we derive constraints on the component masses of 0.62 < M1.14M◉ and 0. 17 < M2 < 0.71M◉. The red star has a radius in the range 0.32 < R2 <0. 51R◉ and is probably on the main sequence.