Constraints on the Wind Structure of OB Stars from Theoretical He<scp>ii</scp>Lines

Venero, R. O. J.; Cidale, L. S.; Ringuelet, A. E.

doi:10.1086/342465

Cited by 7 publications

(13 citation statements)

References 28 publications

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“…100 days within periastron passage, the X-ray emission from the shocked wind can slow down the secondary wind by up to a few 10%. Venero et al (2002) find that the He II λ4686 emission line intensity is sensitive to the wind temperature and increases as the wind temperature increases and/or as the region of maximum temperature in the wind moves outward. We therefore examine the heating of the wind by the X-ray.…”

Section: Wind Velocitymentioning

confidence: 87%

“…The He II λ4686 line intensity very sensitively increases with increasing wind's temperature T 0 . In the different relevant models of Venero et al (2002), the wind temperature T wind = T 0 spans the range 15, 000−32, 000 K. Consequently, we assume a fixed temperature of T 0 = 20, 000K. The velocity, density, and the temperature profiles of the wind model are plotted in the upper panel of Figure 2.…”

Section: The Binary Systemmentioning

confidence: 99%

“…Grady et al (1983) argue that the He II λ4686 line intensity variability is connected to changes in the entire wind acceleration zone. The changes in the acceleration zone can be in the ionization balance, and the mass loss rate (e.g., Venero et al 2002). Kunasz (1980) found that when the He II λ4686 line is only slightly in emission it is very sensitive to the wind parameters.…”

Section: The Proposed Modelmentioning

confidence: 99%

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Accretion onto the Companion of η Carinae during the Spectroscopic Event. III. The Heiiλ4686 Line

Soker

Behar

2006

ApJ

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We continue to explore the accretion model of the massive binary system η Car by studying the anomalously high He II λ4686 line. The line appears just before periastron and disappears immediately thereafter. Based on the He II λ4686 line emission from O-stars and their modeling in the literature, we postulate that the He II λ4686 line comes from the acceleration zone of the secondary stellar wind. We attribute the large increase in the line intensity to a slight increase in the density of the secondary stellar wind in its acceleration zone. The increase in density could be due to the ionization and subsequent deceleration of the wind by the enhanced X-ray emission arising from the shocked secondary wind further downstream or to accretion of the primary stellar wind. Accretion around the secondary equatorial plane gives rise to collimation of the secondary wind, which increases its density, hence enhancing the He II λ4686 emission line. In contrast with previous explanations, the presently proposed model does not require a prohibitively high X-ray flux to directly photoionize the He.

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Section: Wind Velocitymentioning

confidence: 87%

Section: The Binary Systemmentioning

confidence: 99%

Section: The Proposed Modelmentioning

confidence: 99%

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Accretion onto the Companion of η Carinae during the Spectroscopic Event. III. The Heiiλ4686 Line

Soker

Behar

2006

ApJ

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“…11) is compatible with the W-R scenario. It is expected that if the He II emission originates in the fast winds of a W-R star, the profile of the line is the typical P-Cygni profile (Venero et al 2002). It is also worth noting that a correlation between the starformation rate of the galaxy and the number of W-R stars (and thus the He II luminosity) is expected for the W-R scenario, with the only caution that the W-R phase might be very short, and would not match the global star-formation rate of the galaxy.…”

Section: Wolf-rayet Starsmentioning

confidence: 99%

He II emitters in the VIMOS VLT Deep Survey: Population III star formation or peculiar stellar populations in galaxies at 2 <z< 4.6?

Cassata

Fèvre

Charlot

et al. 2013

A&A

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Aims. The aim of this work is to identify He II emitters at 2 < z < 4.6 and to constrain the source of the hard ionizing continuum that powers the He II emission. Methods. We assembled a sample of 277 galaxies with a highly reliable spectroscopic redshift at 2 < z < 4.6 from the VIMOS-VLT Deep Survey (VVDS) Deep and Ultra-Deep data, and we identified 39 He II λ1640 emitters. We studied their spectral properties, measuring the fluxes, equivalent widths (EW), and full width at half maximum (FWHM) for most relevant lines, including He II λ1640, Lyα line, Si II λ1527, and C IV λ1549. Results. About 10% of galaxies at z ∼ 3 and i AB ≤ 24.75 show He II in emission, with rest frame equivalent widths EW 0 ∼ 1-7 Å, equally distributed between galaxies with Lyα in emission or in absorption. We find 11 (3.9% of the global population) reliable He II emitters with unresolved He II lines (FWHM 0 < 1200 km s −1 ), 13 (4.6% of the global population) reliable emitters with broad He II emission (FWHM 0 > 1200 km s −1 ), 3 active galactic nuclei (AGN), and an additional 12 possible He II emitters. The properties of the individual broad emitters are in agreement with expectations from a Wolf-Rayet (W-R) model. Instead, the properties of the narrow emitters are not compatible with this model, nor with predictions of gravitational cooling radiation produced by gas accretion, unless this is severely underestimated by current models by more than two orders of magnitude. Rather, we find that the EW of the narrow He II line emitters are in agreement with expectations for a Population III (PopIII) star formation, if the episode of star formation is continuous, and we calculate that a PopIII star formation rate (SFR) of 0.1-10 M yr −1 alone is enough to sustain the observed He II flux. Conclusions. We conclude that narrow He II emitters are powered either by the ionizing flux from a stellar population rare at z ∼ 0 but much more common at z ∼ 3, or by PopIII star formation. As proposed by Tornatore and collaborators, incomplete interstellar medium mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z ∼ 2 or lower. If this interpretation is correct, we measure at z ∼ 3 a star formation rate density in PopIII stars of 10 −6 M yr −1 Mpc −3 , higher than, but qualitatively comparable to the value predicted by Tornatore and collaborators.

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“…As the velocity field grows nearly exponentially near the photosphere, we transform w and w to logarithmic variables. Compared to standard methods this gives a better resolution close to the photosphere which is important for the line formation (Venero et al 2003). We define logarithmic variables as…”

Section: Logarithmic Coordinatesmentioning

confidence: 99%

A new numerical method for solving radiation driven winds from hot stars

Curé¹,

Rial

2007

Astron Nachr

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We present a general method for solving the non-linear differential equation of monotonically increasing steady-state radiation driven winds. We graphically identify all the singular points before transforming the momentum equation to a system of differential equations with all the gradients explicitly give. This permits a topological classification of all singular points and to calculate the maximum and minimum mass-loss of the wind. We use our method to analyse for the first time the topology of the non-rotating frozen in ionisation m-CAK wind, with the inclusion of the finite disk correction factor and find up to 4 singular points, three of the x-type and one attractor-type. The only singular point (and solution passing through) that satisfies the boundary condition at the stellar surface is the standard m-CAK singular point.

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Constraints on the Wind Structure of OB Stars from Theoretical HeiiLines

Cited by 7 publications

References 28 publications

Accretion onto the Companion of η Carinae during the Spectroscopic Event. III. The Heiiλ4686 Line

Accretion onto the Companion of η Carinae during the Spectroscopic Event. III. The Heiiλ4686 Line

He II emitters in the VIMOS VLT Deep Survey: Population III star formation or peculiar stellar populations in galaxies at 2 <z< 4.6?

A new numerical method for solving radiation driven winds from hot stars

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