On the Accretion Theory of Stellar Evolution

Hoyle, F.; Lyttleton, R. A.

doi:10.1093/mnras/101.4.227

Cited by 64 publications

(53 citation statements)

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“…1), leading to the decrease in wind terminal velocity with respect to nonirradiated winds. Within the classical Bondi-Hoyle-Lyttleton picture (Hoyle & Lyttleton 1941;Bondi & Hoyle 1944) this affects the accretion rate and the X-ray luminosity. This effect can, for example, explain, why the wind velocity required to explain the X-ray luminosity of 4U 2206+54 is significantly lower than the terminal velocity expected for this type of star (Ribó et al 2006).…”

Section: High-mass X-ray Binariesmentioning

confidence: 99%

X-ray irradiation of the winds in binaries with massive components

Krtička

Kubát

Krtičková

2015

A&A

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Context. Binaries with hot massive components are strong X-ray sources. Besides the intrinsic X-ray emission of individual binary members originating in their winds, X-ray emission stems from the accretion on the compact companion or from wind collision. Since hot star winds are driven by the light absorption in the lines of heavier elements, wind acceleration is sensitive to the ionization state. Therefore, the over-ionization induced by external X-ray source strongly influences the winds of individual components. Aims. We studied the effect of external X-ray irradiation on hot star winds. Methods. We used our kinetic equilibrium (NLTE) wind models to estimate the influence of external X-ray ionization for different X-ray luminosities and source distances. The models are calculated for parameters typical of O stars.Results. The influence of X-rays is given by the X-ray luminosity, by the optical depth between a given point and the X-ray source, and by a distance to the X-ray source. Therefore, the results can be interpreted in the diagrams of X-ray luminosity vs. the optical depth parameter. X-rays are negligible in binaries with low X-ray luminosities or at large distances from the X-ray source. The influence of X-rays is stronger for higher X-ray luminosities and in closer proximity of the X-ray source. There is a forbidden area with high X-ray luminosities and low optical depth parameters, where the X-ray ionization leads to wind inhibition. There is excellent agreement between the positions of observed stars in these diagrams and our predictions. All wind-powered high-mass X-ray binary primaries lie outside the forbidden area. Many of them lie close to the border of the forbidden area, indicating that their X-ray luminosities are self-regulated. We discuss the implications of our work for other binary types. Conclusions. X-rays have a strong effect on the winds in binaries with hot components. The magnitude of the influence of X-rays can be estimated from the position of a star in the diagram of X-ray luminosity vs. the optical depth parameter.

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Section: High-mass X-ray Binariesmentioning

confidence: 99%

X-ray irradiation of the winds in binaries with massive components

Krtička

Kubát

Krtičková

2015

A&A

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“…These authors obtain a time variation iṅ M that exhibits short flare-like events on time scales of ∼100 s, i.e. less than one pulse period of Vela X-1, for an accretion rate of 0.7Ṁ HL , whereṀ HL is the Hoyle-Lyttleton mass capture rate in terms of the Eddington rate (Hoyle & Lyttleton 1941, 1939, and a wind velocity of about 1000 km s −1 ; such behavior is typical for O-and B-type stars and precisely that required to explain the observed short-term variability. Watanabe et al (2006) studied the stellar wind of the Vela X-1 system and were able to explain the observed line intensities by using a wind model developed by Castor et al (1975) with a terminal wind velocity of 1100 km s −1 , which agrees with the calculations of Taam et al (1991).…”

Section: Short Term Variabilitymentioning

confidence: 99%

High variability in Vela X-1: giant flares and off states

Kreykenbohm

Wilms²,

Kretschmar

et al. 2008

A&A

128

246

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Aims. We investigate the spectral and temporal behavior of the high mass X-ray binary Vela X-1 during a phase of high activity, with special focus on the observed giant flares and off states. Methods. INTEGRAL observed Vela X-1 in a long almost uninterrupted observation for two weeks in 2003 Nov/Dec. The data were analyzed with OSA 7.0 and FTOOLS 6.2. We derive the pulse period, light curves, spectra, hardness ratios, and hardness intensity diagrams, and study the eclipse. Results. In addition to an already high activity level, Vela X-1 exhibited several intense flares, the brightest ones reaching a maximum intensity of more than 5 Crab in the 20-40 keV band and several off states where the source was no longer detected by INTEGRAL. We determine the pulse period to be 283.5320 ± 0.0002 s, which is stable throughout the entire observation. Analyzing the eclipses provided an improvement in the ephemeris. Spectral analysis of the flares indicates that there appear to be two types of flares: relatively brief flares, which can be extremely intense and show spectral softening, in contrast to high intensity states, which are longer and show no softening. Conclusions. Both flares and off states are interpreted as being due to a strongly structured wind of the optical companion. When Vela X-1 encounters a cavity with strongly reduced density, the flux will drop triggering the onset of the propeller effect, which inhibits further accretion, giving rise to off states. The sudden decrease in the density of the material required to trigger the propeller effect in Vela X-1 is of the same order as predicted by theoretical papers about the densities in OB star winds. A similarly structured wind can produce giant flares when Vela X-1 encounters a dense blob in the wind.

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“…Under the circumstances of uncertain X-ray luminosity based on observational constraints, Maccarone (2004) further assumes that the IMBH would accrete intracluster gas via a Bondi-Hoyle-Lyttleton (BHL) process (Hoyle & Lyttleton 1941;Bondi & Hoyle 1944;Bondi 1952). As shown by Ho et al (2003) and Fender et al (2003), the accretion efficiency ( ) could be as low as 0.1% of the BHL accretion rate, assuming a radiative efficiency (η) of 10%.…”

Section: Detecting Imbhs With Radio Continuum Observationsmentioning

confidence: 99%

Radio Continuum Observations of 47 Tucanae and Ω Centauri: Hints for Intermediate-Mass Black Holes?

Kong

2011

ApJ

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We present results of deep radio continuum observations of two galactic globular clusters 47 Tucanae (47 Tuc) and ω Centauri (ω Cen) with the Australia Telescope Compact Array. No statistically significant evidence for radio emission was found from the central region for the two clusters. However, both clusters show a 2.5σ detection near the center that may be confirmed by future deeper radio observations. The 3σ upper limits of the radio observations are 20 and 40 μJy beam −1 for ω Cen and 47 Tuc, respectively. By using the fundamental plane of accreting black holes, which describes the relationship between radio luminosity, X-ray luminosity, and black hole mass, we constrain the mass of a possible intermediate-mass black hole (IMBH) in the globualar clusters. We also compare our results with other globular clusters and discuss the existence of IMBHs in globular clusters.

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On the Accretion Theory of Stellar Evolution

Cited by 64 publications

References 0 publications

X-ray irradiation of the winds in binaries with massive components

X-ray irradiation of the winds in binaries with massive components

High variability in Vela X-1: giant flares and off states

Radio Continuum Observations of 47 Tucanae and Ω Centauri: Hints for Intermediate-Mass Black Holes?

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