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The defining characteristics of intermediate polars - the case of three-candidate systems

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Ramsay, G. (Gavin), Wheatley, P. J., Norton, Andrew J., Hakala, P. and Baskill, Darren. (2008) The defining characteristics of intermediate polars - the case of three-candidate systems. Monthly Notices of the Royal Astronomical Society, Volume 387 (Number 3). pp. 1157-1162. ISSN 0035-8711

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Official URL: http://dx.doi.org/10.1111/j.1365-2966.2008.13299.x

Abstract

Intermediate polars (IPs) are a group of cataclysmic variables (CVs) which are thought to contain white dwarfs which have a magnetic field strength in the range similar to 0.1-10 MG. A significant fraction of the X-ray sources detected in recent deep surveys has been postulated to consist of IPs. Until now two of the defining characteristics of IPs have been the presence of high (and complex) absorption in their X-ray spectra and the presence of a stable modulation in the X-ray light curve which is a signature of the spin period, or the beat period, of the accreting white dwarf. Three CVs, V426 Oph, EI UMa and LS Peg, have characteristics which are similar to IPs. However, there has been only tentative evidence for a coherent period in their X-ray light curve. We present the results of a search for coherent periods in XMM-Newton data of these sources using an autoregressive analysis which models the effects of red noise. We confirm the detection of a similar to 760 s period in the soft X-ray light curve of EI UMa reported by Reimer et al. and agree that this represents the spin period. We also find evidence for peaks in the power spectrum of each source in the range 100-200 s which are just above the 3 sigma confidence level. We do not believe that they represent genuine coherent modulations. However, their X-ray spectra are very similar to those of known IPs. We believe that all three CVs are bona fide IPs. We speculate that V426 Oph and LS Peg do not show evidence for a spin period since they have closely aligned magnetic and spin axes. We discuss the implications that this has for the defining characteristics of IPs.

Item Type:

Journal Article

Subjects:

Q Science > QB Astronomy

Divisions:

Faculty of Science > Physics

Library of Congress Subject Headings (LCSH):

Double stars, Stars, New, Cataclysmic variable stars

Journal or Publication Title:

Monthly Notices of the Royal Astronomical Society

Publisher:

Wiley

ISSN:

0035-8711

Official Date:

1 July 2008

Dates:

Date	Event
1 July 2008	Published

Volume:

Volume 387

Number:

Number 3

Number of Pages:

Page Range:

pp. 1157-1162

Identification Number:

10.1111/j.1365-2966.2008.13299.x

Status:

Peer Reviewed

Publication Status:

Published

Access rights to Published version:

Restricted or Subscription Access

Funder:

Northern Ireland. Department of Culture, Arts & Leisure

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