Publications (3)10.06 Total impact
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Article: Variable O VI and N V Emission from the X-ray Binary LMC X-3: Heating of the Black Hole Companion
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ABSTRACT: Based on high-resolution ultraviolet spectroscopy obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Cosmic Origins Spectrograph, we present new detections of O VI and N V emission from the black hole X-ray binary (XRB) system LMC X-3. We also update the ephemeris of the XRB using recent radial velocity measurements obtained with the echelle spectrograph on the Magellan-Clay telescope. We observe significant velocity variability of the UV emission, and we find that the O VI and N V emission velocities follow the optical velocity curve of the XRB. Moreover, the O VI and N V intensities regularly decrease between binary phase = 0.5 and 1.0, which suggests that the source of the UV emission is increasingly occulted as the B star in the XRB moves from superior to inferior conjunction. These trends suggest that illumination of the B star atmosphere by the intense X-ray emission from the accreting black hole creates a hot spot on one side of the B star, and this hot spot is the origin of the O VI and N V emission. However, the velocity semiamplitude of the ultraviolet emission, K UV 180 km s–1, is lower than the optical semiamplitude; this difference could be due to rotation of the B star. Comparison of the FUSE observations taken in 2001 November and 2004 April shows a significant change in the O VI emission characteristics: in the 2001 data, the O VI region shows both broad and narrow emission features, while in 2004 only the narrow O VI emission is clearly present. Rossi X-ray Timing Explorer data show that the XRB was in a high/soft state in the 2001 November epoch but was in a transitional state in 2004 April, so the shape of the X-ray spectrum might change the properties of the region illuminated on the B star and thus change the broad versus narrow characteristics of the UV emission. If our hypothesis about the origin of the highly ionized emission is correct, then careful analysis of the emission occultation could, in principle, constrain the inclination of the XRB and the mass of the black hole.The Astronomical Journal 08/2010; 140(3):794. · 4.03 Impact Factor -
Article: A New Dynamical Model for the Black Hole Binary LMC X-1
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ABSTRACT: We present a dynamical model of the high mass X-ray binary LMC X-1 based on high-resolution optical spectroscopy and extensive optical and near-infrared photometry. From our new optical data we find an orbital period of P = 3.90917 ± 0.00005 days. We present a refined analysis of the All Sky Monitor data from RXTE and find an X-ray period of P = 3.9094 ± 0.0008 days, which is consistent with the optical period. A simple model of Thomson scattering in the stellar wind can account for the modulation seen in the X-ray light curves. The V – K color of the star (1.17 ± 0.05) implies AV = 2.28 ± 0.06, which is much larger than previously assumed. For the secondary star, we measure a radius of R 2 = 17.0 ± 0.8 R ☉ and a projected rotational velocity of V rotsin i = 129.9 ± 2.2 km s–1. Using these measured properties to constrain the dynamical model, we find an inclination of i = 3638 ± 192, a secondary star mass of M 2 = 31.79 ± 3.48 M ☉, and a black hole mass of 10.91 ± 1.41 M ☉. The present location of the secondary star in a temperature-luminosity diagram is consistent with that of a star with an initial mass of 35 M ☉ that is 5 Myr past the zero-age main sequence. The star nearly fills its Roche lobe (90% or more), and owing to the rapid change in radius with time in its present evolutionary state, it will encounter its Roche lobe and begin rapid and possibly unstable mass transfer on a timescale of a few hundred thousand years.The Astrophysical Journal 05/2009; 697(1):573. · 6.02 Impact Factor -
Article: On the Production and Survival of Carbon Fuel for Superbursts on Accreting Neutron Stars: Implications for Mass Donor Evolution
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ABSTRACT: (abridged) We have investigated the physical conditions under which accreting neutron stars can both produce and preserve sufficient quantities of carbon fuel to trigger superbursts. Our models span the plausible ranges of neutron star thermal conductivities, core neutrino emission mechanisms, and areal radii, as well as the CNO abundances in the accreted material. We find that neutron stars that accrete hydrogen-rich material with CNO mass fractions <~ that of the Sun will not exhibit superbursts under any circumstances. Neutron stars that accrete material with CNO mass fractions >~ 4 times that of the Sun will exhibit superbursts at accretion rates in the observed range. On this basis, we suggest that the mass donors of superburst systems must have enhanced CNO abundances. The accreted CNO acts only as a catalyst for hydrogen burning via the hot CNO cycle, and therefore it is only the sum of the three elements' mass fractions that is important. Systems that exhibit superbursts are observed to differ from those that do not exhibit superbursts in the nature of their helium-triggered Type I X-ray bursts: the bursts have shorter durations and much greater alpha-values. Increasing the CNO abundance of the accreted material in our models reproduces both of these observations. Many compact binary systems have been observed in which the abundances of the accreting material are distinctly non-solar. Though abundance analyses of the systems that exhibit superbursts currently do not exist, Bowen fluorescence blend profiles of 4U 1636-536 and Ser X-1 suggest that the mass donor stars may indeed have non-solar CNO metallicities. More detailed abundance analyses of the accreting matter in systems that exhibit superbursts are needed to verify our assertion that the matter is rich in CNO elements. Comment: accepted by ApJ08/2005;
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2009–2010
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The University of Warwick
- Department of Physics
Warwick, ENG, United Kingdom
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