The central black-hole masses of a sample of 30 luminous quasars are estimated using Hβ fwhm measurements from a combination of new and previously-published nuclear spectra. The quasar black-hole mass estimates are combined with reverberationmapping measurements for a sample of Seyfert galaxies (Wandel, Peterson & Malkan 1999) in order to study AGN black-hole masses over a wide range in nuclear...

We address the issue of the production of Lyman continuum photons by T Tauri stars, in an attempt to provide constraints on theoretical models of disc photoionisation. By treating the accretion shock as a hotspot on the stellar surface we show that Lyman continuum photons are produced at a rate approximately three orders of magnitude lower than that produced by a corresponding black body, and t...

We extend the model of King et al. (2004) for variability in black hole accretion discs, by taking proper account of the thermal properties of the disc. Because the degree of variability in the King et al. (2004) model depends sensitively on the ratio of disc thickness to radius, H/R, it is important to follow the time-dependence of the local disc structure as the variability proceeds. In commo...

Xylotrechus tristisfaciessp. n. (Coleoptera, Cerambycidae, Cerambycinae, Clytini) from China is described and illustrated. Characters distinguishing the new species from its close relatives, which possess an entirely black or dark brown pronotum with a black median stripe on the disc and dense yellowish to gray pubescent elytra with black or brown spots or bands, are presented.

We present new results based on RXTE observations of the millisecond pulsar SAX J1808.4–3658 carried out during the decay of the April 1998 outburst. The X-ray spectrum can be fitted by a two-component model. We interpret the soft component as blackbody emission from a heated spot on the neutron star, and the hard component as coming from Comptonization in plasma heated by the accretion shock a...

We present new results based on RXTE observations of the millisecond pulsar SAX J1808.4–3658 carried out during the decay of the April 1998 outburst. The X-ray spectrum can be fitted by a two-component model. We interpret the soft component as blackbody emission from a heated spot on the neutron star, and the hard component as coming from Comptonization in plasma heated by the accretion shock a...

We consider the properties of the warped accretion disc in NGC 4258 which is delineated by maser emission. We use our analytical models to consider whether the disc could be warped by Lense-Thirring precession. We show that such models fit the shape of the disc well and we determine the goodness of fit for various combinations of the warp radius and the disc and black hole configurations. Thoug...

The relation between accretion disc (thermal emission) and jet (non-thermal emission) in blazars is still a mystery as, typically, the beamed jet emission swamps the disc even in the ultraviolet band where disc emission peaks. In this paper we estimate the accretion disc component for 136 flat-spectrum radio quasars selected from the Deep X-ray Radio Blazar Survey. We do this by deriving the ac...