26 research outputs found
The structure of thin accretion discs around magnetised stars
Aims: We determine the steady-state of an axisymmetric thin accretion disc
with an internal dynamo around a magnetised star.
Methods: Starting from the vertically integrated equations of
magnetohydrodynamics we derive a single ordinary differential equation for a
thin accretion disc around a massive magnetic dipole and integrate this
equation numerically from the outside inwards.
Results: Our numerical solution shows that the torque between the star and
the accretion disc is dominated by the contribution from the dynamo in the
disc. The location of the inner edge of the accretion disc varies between
and depending mainly on the strength and direction of
the magnetic field generated by the dynamo in the discComment: 9 pages, 10 figures. The paper is accepted for publication in
Astronomy & Astrophysic
VAST: An ASKAP Survey for Variables and Slow Transients
The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an
unprecedented opportunity to investigate the transient sky at radio
wavelengths. In this paper we present VAST, an ASKAP survey for Variables and
Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP
to enable the discovery and investigation of variable and transient phenomena
from the local to the cosmological, including flare stars, intermittent
pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar
scintillation, radio supernovae and orphan afterglows of gamma ray bursts. In
addition, it will allow us to probe unexplored regions of parameter space where
new classes of transient sources may be detected. In this paper we review the
known radio transient and variable populations and the current results from
blind radio surveys. We outline a comprehensive program based on a multi-tiered
survey strategy to characterise the radio transient sky through detection and
monitoring of transient and variable sources on the ASKAP imaging timescales of
five seconds and greater. We also present an analysis of the expected source
populations that we will be able to detect with VAST.Comment: 29 pages, 8 figures. Submitted for publication in Pub. Astron. Soc.
Australi