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Soft X-Ray Transients are Like ER UMA Cataclysmic Variables

Published online by Cambridge University Press:  14 August 2015

Enikő Regső  and
Nicola Masetti
Enikő Regső
Affiliation:
Department of Mathematics, Monash University, Clayton, Victoria 3168, Australia.
Nicola Masetti
Affiliation:
Dipartimento di Astronomia, Universit di Padova, vicolo dell’Osservatorio, 5 1-35122 Padua, Italy

Abstract

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We discuss how soft X-ray transients exhibit light curves associated with two accretion-disc instabilities that are well known to operate in cataclysmic variables. A thermal instability that is due to hydrogen ionization leads to the transient nature but is modified by X-ray irradiation of the disc. Growth of the disc between the ensuing outbursts leads to a 3:1 commensurability instability at the outer edge of the disc that drives superoutbursts and produces superhumps in the lightcurve if the mass ratio is sufficiently small. Superhumps are observed only in the short period SU UMa CVs but black hole primaries allow SXTs to exhibit superoutbursts and superhumps at much larger periods. We point out similarities between SXT superhump shapes and those of the small class of ER UMa CVs, The similarity between these systems stems from the fact that the mass-transfer rates are almost large enough to stabilize the disc against the thermal instability in both cases.

Type
II. Joint Discussions
Information
Highlights of Astronomy , Volume 11 , Issue 2: Highlights of Astronomy. As presented at the XXIIIrd General Assembly of the IAU (Part B), 1997 , 1998 , pp. 794 - 797
Copyright
Copyright © Kluwer 1998

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