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Accretion on to magnetic white dwarfs

Wickramasinghe, Dayal

Description

The Magnetic Cataclysmic Variables (MCVs) are close interacting binaries where mass is transferred from a late type secondary star to a magnetic white dwarf. Two modes of accretion can be identified depending on the strength of the magnetic field, the mass transfer rate and orbital parameters. (a) Disced Accretion: In the Intermediate polars (IPs), the mass transfer stream circularises and forms an accretion disc. Material couples on to field lines in a narrow inner transition region where the...[Show more]

dc.contributor.authorWickramasinghe, Dayal
dc.date.accessioned2015-12-13T22:17:37Z
dc.date.available2015-12-13T22:17:37Z
dc.identifier.issn2100-014X
dc.identifier.urihttp://hdl.handle.net/1885/71243
dc.description.abstractThe Magnetic Cataclysmic Variables (MCVs) are close interacting binaries where mass is transferred from a late type secondary star to a magnetic white dwarf. Two modes of accretion can be identified depending on the strength of the magnetic field, the mass transfer rate and orbital parameters. (a) Disced Accretion: In the Intermediate polars (IPs), the mass transfer stream circularises and forms an accretion disc. Material couples on to field lines in a narrow inner transition region where the velocity in the orbital plane changes from Keplerian to co-rotation (b) Discless Accretion: In the polars, the accretion stream is disrupted by the magnetic field before it can circularise. Material couples on to field lines via an inner transition region where the velocity changes from essentially free fall to co-rotation. The polars have no counterparts in neutron star systems and their study provides unique insights into the complex nature of the magnetospheric boundary. The observed properties of accretion shocks at the white dwarf surface such as the anomalous soft-X-ray excess and its time variability provide strong support for the hypothesis that under certain circumstances the field channelled funnel flow is "blobby". This has been attributed to interchange instabilities such as the Magnetic Rayleigh-Taylor instability in the shocked gas at the stream-magnetosphere boundary where the stream fragments into discrete clumps of gas. As the clumps penetrate into the magnetosphere, they are shredded into smaller mass blobs via the Kelvin-Helmholtz instability that then couple on to field lines over an extended inner transition region in the orbital plane. The more massive blobs penetrate deep into the photosphere of the white dwarf releasing their energy as a reprocessed soft-X-ray black body component. Although similar instabilities are expected in the inner transition region in disced accretion albeit on a different scale there has been no direct observational evidence for blobby accretion in the generally lower field and disced IPs.
dc.publisherE D P Sciences
dc.sourceEPJ Web of Conferences
dc.titleAccretion on to magnetic white dwarfs
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume64
dc.date.issued2014
local.identifier.absfor020110 - Stellar Astronomy and Planetary Systems
local.identifier.ariespublicationU3488905xPUB2625
local.type.statusPublished Version
local.contributor.affiliationWickramasinghe, Dayal, College of Physical and Mathematical Sciences, ANU
local.bibliographicCitation.issue03001
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage12
local.identifier.doi10.1051/epjconf/20136403001
local.identifier.absseo970102 - Expanding Knowledge in the Physical Sciences
dc.date.updated2015-12-11T07:35:35Z
local.identifier.scopusID2-s2.0-84893593810
CollectionsANU Research Publications

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