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    The nature of the companion star in Circinus X-1

    239002_239002.pdf (806.5Kb)
    Access Status
    Open access
    Authors
    Johnston, H.
    Soria, Roberto
    Gibson, J.
    Date
    2016
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    Johnston, H. and Soria, R. and Gibson, J. 2016. The nature of the companion star in Circinus X-1. Monthly Notices of the Royal Astronomical Society. 456 (1): pp. 347-355.
    Source Title
    Monthly Notices of the Royal Astronomical Society
    DOI
    10.1093/mnras/stv2669
    ISSN
    0035-8711
    School
    Department of Physics and Astronomy
    Remarks

    This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

    URI
    http://hdl.handle.net/20.500.11937/45808
    Collection
    • Curtin Research Publications
    Abstract

    © 2015 The Authors. We present optical spectra and images of the X-ray binary Circinus X-1. The optical light curve of Cir X-1 is strongly variable, changing in brightness by 1.2 mag in the space of four days. The shape of the light curve is consistent with that seen in the 1980s, when the X-ray and radio counterparts of the source were at least ten times as bright as they are currently. We detect strong, variable H a emission lines, consisting of multiple components which vary with orbital phase. We estimate the extinction to the source from the strength of the diffuse interstellar bands and the Balmer decrement; the two methods give AV = 7.6 ± 0.6mag and AV > 9.1 mag, respectively. The optical light curve can be modelled as arising from irradiation of the companion star by the central X-ray source, where a low-temperature star fills its Roche lobe in an orbit of moderate eccentricity (e ~ 0.4). We suggest that the companion star is overluminous and underdense, due to the impact of the supernova which occurred less than 5000 yr ago.

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