ar X iv : a st ro - p h / 96 05 07 0 v 2 1 7 Ju n 19 96 A time – dependent Cosmological ” Constant ”

ar X iv : a st ro - p h / 96 06 17 9 v 1 2 9 Ju n 19 96 LECTURE 1 Coalescence of Binary Neutron Stars

ar X iv : a st ro - p h / 96 05 17 6 v 1 2 9 M ay 1 99 6 A time – dependent “ Cosmological Constant ”

We construct a cosmological toy model in which a step-function “cosmological constant” is taken into consideration beside ordinary matter. We assume that Λ takes two values depending on the epoch, and matter goes from a radiation dominated era to a dust dominated era. The model is exactly solvable and it can be compared with recent observations. PACS: 98.80. Cq, 98.70. Vc e-mail address: capozz...

ar X iv : a st ro - p h / 96 05 07 0 v 1 1 4 M ay 1 99 6 A time – dependent Cosmological ” Constant ”

We extend the Wald cosmic no–hair theorem to a general class of scalar–tensor nonminimally coupled theories of gravity where ordinary matter is also present in the form of a perfect fluid. We give a set of conditions for obtaining a de Sitter expansion independently of any initial conditions, generalizing the treatment of such a problem as given by Wald. Finally we apply the results to some spe...

ar X iv : a st ro - p h / 96 01 12 9 v 1 2 3 Ja n 19 96 Is Her X - 1 a strange star

The possible identification of Her X-1 with a strange star (Li et al. 1995) is shown to be incorrect.

ar X iv : a st ro - p h / 96 07 14 6 v 1 2 9 Ju l 1 99 6 An Optical Ultrahigh Resolution Spectrograph for Use with Adaptive Optics