Roche tomography of the secondary stars in CVs

Watson, C. A.; Dhillon, V. S.

doi:10.1002/asna.200310222

Cited by 5 publications

(5 citation statements)

References 10 publications

(13 reference statements)

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“…For example, Roche tomography (for a description, see e.g. Rutten et al 1996, Watson et al 2004) uses the Roche approximation in order to reconstruct the surface features of secondaries for a number of CV systems from the velocity profiles (Watson et al 2001, Watson et al 2003, Dunford et al 2012. Given the extreme tidal forces acting on some short period hot-Jupiters, it was decided to model their shapes using the Roche approximation.…”

Section: Methodsmentioning

confidence: 99%

Tidally Distorted Exoplanets: Density Corrections for Short-Period Hot-Jupiters Based Solely on Observable Parameters

Burton¹,

Watson

Fitzsimmons

et al. 2014

ApJ

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The close proximity of short period hot-Jupiters to their parent star means they are subject to extreme tidal forces. This has a profound effect on their structure and, as a result, density measurements that assume that the planet is spherical can be incorrect. We have simulated the tidally distorted surface for 34 known short period hot-Jupiters, assuming surfaces of constant gravitational equipotential for the planet, and the resulting densities have been calculated based only on observed parameters of the exoplanet systems. Comparing these results to the density values assuming the planets are spherical shows that there is an appreciable change in the measured density for planets with very short periods (typically less than two days). For one of the shortest-period systems, WASP-19b, we determine a decrease in bulk density of 12% from the spherical case and, for the majority of systems in this study, this value is in the range of 1-5%. On the other-hand, we also find cases where the distortion is negligible (relative to the measurement errors on the planetary parameters) even in the cases of some very short period systems, depending on the mass ratio and planetary radius. For high-density gas-planets requiring apparently anomalously large core masses, density corrections due to tidal deformation could become important for the shortest-period systems.

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Section: Methodsmentioning

confidence: 99%

Tidally Distorted Exoplanets: Density Corrections for Short-Period Hot-Jupiters Based Solely on Observable Parameters

Burton¹,

Watson

Fitzsimmons

et al. 2014

ApJ

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“…The procedure is fully tested and artefacts caused by systematic errors are well characterized and understood. For a detailed review of the technique see ; ; Watson & Dhillon (2004). In summary, Roche tomography uses phase-resolved spectral-line profiles to produce a map of the lineintensity distribution across the secondary star's surface in threedimensional real space.…”

Section: Evidence For Starspotsmentioning

confidence: 99%

The spotty donor star in the X-ray transient Cen X−4

Shahbaz¹,

Watson²,

Dhillon³

2014

Monthly Notices of the Royal Astronomical Society

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We accurately determine the fundamental system parameters of the neutron-star X-ray transient Cen X-4 solely using phase-resolved high-resolution UVES spectroscopy. We first determine the radial-velocity curve of the secondary star and then model the shape of the phase-resolved absorption line profiles using an X-ray binary model. The model computes the exact rotationally broadened phase-resolved spectrum and does not depend on assumptions about the rotation profile, limb-darkening coefficients and the effects of contamination from an accretion disk. We determine the secondary star-to-neutron star binary mass ratio to be 0.1755 ± 0.0025, which is an order of magnitude more accurate than previous estimates. We also constrain the inclination angle to be 32 •+8 • −2 • . Combining these values with the results of the radial velocity study gives a neutron star mass of 1.94 +0.37 −0.85 M ⊙ consistent with previous estimates. Finally, we perform the first Roche tomography reconstruction of the secondary star in an X-ray binary. The tomogram reveals surface inhomogeneities that are due to the presence of cool starspots. A large cool polar spot, similar to that seen in Doppler images of rapidly-rotating isolated stars is present on the Northern hemisphere of the K7 secondary star and we estimate that ∼4 per cent of the total surface area of the donor star is covered with spots. This evidence for starspots supports the idea that magnetic braking plays an important role in the evolution of low-mass X-ray binaries.

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“…Vogt & Penrod 1983) and has now been successfully applied to the donor stars of CVs on several occasions (Rutten & Dhillon 1994, 1996; Watson et al 2003; Schwope et al 2004; Watson et al 2006). Rather than repeating a detailed description of the methodology and axioms of Roche Tomography here, we refer the reader to the references above and the technical reviews of Roche Tomography by Watson & Dhillon (2001), Dhillon & Watson (2001) and Watson & Dhillon (2004). The pertinent points with respect to this work are that we employ a moving uniform default map, where each element is set to the average value of the reconstructed map.…”

Section: Roche Tomographymentioning

confidence: 99%

Roche tomography of cataclysmic variables - IV. Star-spots and slingshot prominences on BV Cen

Watson¹,

Steeghs²,

Shahbaz³

et al. 2007

Monthly Notices of the Royal Astronomical Society

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We present Roche tomograms of the G5–G8 IV/V secondary star in the long‐period cataclysmic variable BV Cen reconstructed from Magellan Inamori Kyocera Echelle spectrograph echelle data taken on the Magellan Clay 6.5‐m telescope. The tomograms show the presence of a number of large, cool star‐spots on BV Cen for the first time. In particular, we find a large high‐latitude spot which is deflected from the rotational axis in the same direction as seen on the K3–K5 IV/V secondary star in the cataclysmic variable AE Aqr. BV Cen also shows a similar relative paucity of spots at latitudes between 40° and 50° when compared with AE Aqr. Furthermore, we find evidence for an increased spot coverage around longitudes facing the white dwarf which supports models invoking star‐spots at the L1 point to explain the low states observed in some cataclysmic variables. In total, we estimate that some 25 per cent of the Northern hemisphere of BV Cen is spotted. We also find evidence for a faint, narrow, transient emission line with characteristics reminiscent of the peculiar low‐velocity emission features observed in some outbursting dwarf novae. We interpret this feature as a slingshot prominence from the secondary star and derive a maximum source size of 75 000 km and a minimum altitude of 160 000 km above the orbital plane for the prominence. The entropy landscape technique was applied to determine the system parameters of BV Cen. We find M1= 1.18 ±0.280.16 M⊙ and M2= 1.05 ±0.230.14 M⊙ and an orbital inclination of i= 53°± 4° at an optimal systemic velocity of γ=−22.3 km s‐1. Finally, we also report on the previously unknown binarity of the G5IV star HD 220492.

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Roche tomography of the secondary stars in CVs

Cited by 5 publications

References 10 publications

Tidally Distorted Exoplanets: Density Corrections for Short-Period Hot-Jupiters Based Solely on Observable Parameters

Tidally Distorted Exoplanets: Density Corrections for Short-Period Hot-Jupiters Based Solely on Observable Parameters

The spotty donor star in the X-ray transient Cen X−4

Roche tomography of cataclysmic variables - IV. Star-spots and slingshot prominences on BV Cen

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