ar X iv : a st ro - p h / 98 05 07 7 v 1 6 M ay 1 99 8 Long - Term X - ray Variability in GX 354 – 0

ar X iv : a st ro - p h / 99 05 11 9 v 1 1 1 M ay 1 99 9 A state transition of GX 339 - 4 observed with RXTE

We report the results of observations with the Rossi X-ray Timing Explorer of the black-hole candidate GX 339-4 during the state transition of 1998. We find that both the X-ray spectrum and the characteristic of the time variability after the transition are typical of a high/soft state. We cannot exclude that the source went through an Intermediate State before entering the high state. We discu...

ar X iv : a st ro - p h / 98 11 24 4 v 1 1 6 N ov 1 99 8 Fast X - ray Variability of PKS 2155 – 304 : A Cross

ar X iv : a st ro - p h / 99 05 37 6 v 1 2 8 M ay 1 99 9 A 6 . 4 - hr positive superhump period in TV

ar X iv : a st ro - p h / 98 05 04 7 v 1 6 M ay 1 99 8 The energy distribution of β CrB for the specific stellar abundances

The comparison of the observed and computed energy distributions of β CrB has shown that a model with the specific chemical composition of the star can account for the visual enery distribution, while it is still unable to reproduce ultraviolet observations shortward of 1700Å. Furthermore, the predicted absorption of strong Fe ii and Mg ii UV lines is much larger than the observed one.

ar X iv : a st ro - p h / 98 05 05 8 v 1 6 M ay 1 99 8 The effects of convection on the colours of A and F stars

We present a discussion on the effects of convection on the uvby colours of A and F stars. The mixing-length theory used in ATLAS9 is compared to the turbulent convection theory of Canuto & Mazzitelli (1991, 1992). Comparison with fundamental stars reveals that colours calculated using the Canuto & Mazzitelli convection theory are generally in better agreement than those obtained using mixing-l...