On the stability of thermonuclear shell sources in stars

Yoon, Sung‐Chul; Langer, N.; Sluys, M. van der

doi:10.1051/0004-6361:20040231

Cited by 43 publications

(55 citation statements)

References 25 publications

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“…A more recent study of accretion onto WDs can be found in Yoon, Langer, and van der Sluys. 39 Examining their work, the calculations done with NOVA are initially in their stable regime but evolve into instability.…”

Section: Discussionmentioning

confidence: 99%

The accretion of solar material onto white dwarfs: No mixing with core material implies that the mass of the white dwarf is increasing

Starrfield

2014

AIP Advances

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Cataclysmic Variables (CVs) are close binary star systems with one component a white dwarf (WD) and the other a larger cooler star that fills its Roche Lobe. The cooler star is losing mass through the inner Lagrangian point of the binary and some unknown fraction of this material is accreted by the WD. One consequence of the WDs accreting material, is the possibility that they are growing in mass and will eventually reach the Chandrasekhar Limit. This evolution could result in a Supernova Ia (SN Ia) explosion and is designated the Single Degenerate Progenitor (SD) scenario. One problem with the single degenerate scenario is that it is generally assumed that the accreting material mixes with WD core material at some time during the accretion phase of evolution and, since the typical WD has a carbon-oxygen (CO) core, the mixing results in large amounts of carbon and oxygen being brought up into the accreted layers. The presence of enriched carbon causes enhanced nuclear fusion and a Classical Nova (CN)explosion. Both observations and theoretical studies of these explosions imply that more mass is ejected than is accreted, and that the process repeats. Thus, the WD in a Classical Nova system is decreasing in mass and cannot be a SN Ia progenitor. However, the composition in the nuclear burning region is important and, in new calculations reported here, the consequences to the WD of no mixing of accreted material with core material have been investigated and it is assumed that the material involved in the explosion has only a Solar composition. WDs with a large range in initial masses and mass accretion rates have been evolved. I find that once sufficient material has been accreted, nuclear burning occurs in all evolutionary sequences and continues until a thermonuclear runaway (TNR) occurs and the WD either ejects a small amount of material or its radius grows to about 10 12 cm and the calculations are stopped. In all cases where mass ejection occurs, the mass of the ejecta is far less than the mass of the accreted material. Therefore, all the WDs are growing in mass. It is also found that the accretion time to explosion can be sufficiently short for a 1.0M ⊙ WD that a recurrent nova explosion can occur on a WD that is lower than typically assumed for the WDs in these systems. Finally, the predicted surface temperatures when the WD is near the peak of the explosion imply that only the most massive WDs will be significant X-ray emitters at this time.

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Section: Discussionmentioning

confidence: 99%

The accretion of solar material onto white dwarfs: No mixing with core material implies that the mass of the white dwarf is increasing

Starrfield

2014

AIP Advances

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“…In sequence NR4, the mean temperature in the shell source remains nearly constant, around T 2.02 × 10 8 K during the stable shell burning phase. Figure 9 shows the border between stability and instability for T = 2 × 10 8 K, as obtained by Yoon et al (2004), as a dotted line. The shell source becomes more degenerate and thinner as the white dwarf mass grows, and finally enters the unstable regime when M WD 1.03 M , resulting in the onset of thermal pulses as shown in Fig.…”

Section: Stability Of Helium Shell Burningmentioning

confidence: 98%

Effects of rotation on the helium burning shell source in accreting white dwarfs

Yoon

Langer

Scheithauer

2004

A&A

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Abstract.We investigate the effects of rotation on the behavior of the helium-burning shell source in accreting carbon-oxygen white dwarfs, in the context of the single degenerate Chandrasekhar mass progenitor scenario for type Ia supernovae (SNe Ia). We model the evolution of helium-accreting white dwarfs of initially 1 M , assuming four different constant accretion rates (2, 3, 5 and 10 × 10 −7 M /yr). In a one-dimensional approximation, we compute the mass accretion and subsequent nuclear fusion of helium into carbon and oxygen, as well as angular momentum accretion, angular momentum transport inside the white dwarf, and rotationally induced chemical mixing. Our models show two major effects of rotation: a) The helium-burning nuclear shell source in the rotating models is much more stable than in corresponding non-rotating models -which increases the likelihood that accreting white dwarfs reach the stage of central carbon ignition. This effect is mainly due to rotationally induced mixing at the CO/He interface which widens the shell source, and due to the centrifugal force lowering the density and degeneracy at the shell source location. b) The C/O-ratio in the layers which experience helium shell burning -which may affect the energy of an SN Ia explosion -is strongly decreased by the rotationally induced mixing of α-particles into the carbon-rich layers. We discuss implications of our results for the evolution of SNe Ia progenitors.

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“…To understand the behavior of increasing L crit for higher values ofṀ, we follow the stability analysis of thermonuclear burning in a thin shell by Giannone & Weigert (1967) (see also Yoon et al 2004b). These authors derive an expression for the inverse of the growth timescale of temperature perturbations, τ −1 pert , by considering both thermonuclear burning and radiative cooling (Eq.…”

Section: Mass Accretion Rate Dependencementioning

confidence: 99%

The effect of rotation on the stability of nuclear burning in accreting neutron stars

Keek

Langer²,

Zand

2009

A&A

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107

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Hydrogen and/or helium accreted by a neutron star from a binary companion may undergo thermonuclear fusion. Different burning regimes are discerned at different mass accretion rates. Theoretical models predict helium fusion to proceed as a thermonuclear runaway for accretion rates below the Eddington limit and as stable burning above this limit. Observations, however, place the boundary close to 10% of the Eddington limit. We study the effect of rotationally induced transport processes on the stability of helium burning. For the first time, detailed calculations of thin-shell helium burning on neutron stars are performed using a hydrodynamic stellar evolution code including rotation and rotationally induced magnetic fields. We find that in most cases the instabilities from the magnetic field provide the dominant contribution to the chemical mixing, while Eddington-Sweet circulations become important at high rotation rates. As helium is diffused to greater depths, the stability of the burning is increased, such that the critical accretion rate for stable helium burning is found to be lower. Combined with a higher heat flux from the crust, as suggested by recent studies, turbulent mixing could explain the observed critical accretion rate. Furthermore, close to this boundary we find oscillatory burning, which previous studies have linked to mHz QPOs. In models where we continuously lower the heat flux from the crust, the period of the oscillations increases by up to several tens of percents, similar to the observed frequency drift, suggesting that this drift could be caused by the cooling of deeper layers.

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On the stability of thermonuclear shell sources in stars

Cited by 43 publications

References 25 publications

The accretion of solar material onto white dwarfs: No mixing with core material implies that the mass of the white dwarf is increasing

The accretion of solar material onto white dwarfs: No mixing with core material implies that the mass of the white dwarf is increasing

Effects of rotation on the helium burning shell source in accreting white dwarfs

The effect of rotation on the stability of nuclear burning in accreting neutron stars

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