Stellar Expansion Research Articles

Type Ia Supernova Explosion: Gravitationally Confined Detonation

We present a new mechanism for Type Ia supernova explosions in massive white dwarfs. The scenario follows from relaxing assumptions of symmetry and involves a detonation born near the stellar surface. The explosion begins with an essentially central ignition of a deflagration that results in the formation of a buoyancy-driven bubble of hot material that reaches the stellar surface at supersonic speeds. The bubble breakout laterally accelerates fuel-rich outer stellar layers. This material, confined by gravity to the white dwarf, races along the stellar surface and is focused at the location opposite to the point of the bubble breakout. These streams of nuclear fuel carry enough mass and energy to trigger a detonation just above the stellar surface that will incinerate the white dwarf and result in an energetic explosion. The stellar expansion following the deflagration redistributes mass in a way that ensures production of intermediate-mass and iron group elements with ejecta having a strongly layered structure and a mild amount of asymmetry following from the early deflagration phase. This asymmetry, combined with the amount of stellar expansion determined by details of the evolution (principally the energetics of deflagration, timing of detonation, and structure of the progenitor), can be expected to create a family of mildly diverse Type Ia supernova explosions.

A Generalized Model for the Proton Expansion in Astrophysical Winds. II. The Associated Set of Transport Equations

In Paper I, we presented a new model of the velocity distribution function for protons composing a stellar atmosphere expanding in interstellar space, valid from collisional to collisionless regions. In this paper, the set of generalized transport equations associated with this model and the closure assumptions for higher order velocity moments are provided for 9 and 16 moment approximations. The study of the properties of such a set of transport equations in the collisionless limit is presented and discussed. A comparison with the similar bi-Maxwellian approximation is made using two kinds of analysis, in the context of an application to solar wind expansion. Our model is better adapted to high values of the heat flux and thus is able to provide a macroscopic parameter evolution for stellar atmosphere expansion in a state far from local equilibrium, as well as for the expansion of planetary polar winds.

Shock wave emergence at the stellar surface and the subsequent gas expansion into a vacuum - The sphericity involvement

view Abstract Citations (13) References (2) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Shock Wave Emergence at the Stellar Surface and the Subsequent Gas Expansion into a Vacuum: The Sphericity Involvement Kazhdan, Ia. M. ; Murzina, Marina Abstract Attention is given to a solution to describe the shock wave passage through the outer envelope of the star and the following stellar matter expansion into a vacuum. The solution takes into account the sphericity of the flow in the neighborhood of the stellar surface. Calculations are performed for the case gamma = 4/3, n = 3 (gamma is the adiabatic index, and n is the peripheric politropic index). At the stage of the shock wave emergence, the sphericity is shown to affect mostly the spatial distributions of density and pressure by increasing their slopes from the surface to the center of the star. For the stage of matter expansion, the solution describes the pressure-dominated acceleration of the outer envelope at arbitrary moments of time even up to t approaches infinity, and prolongs the analytical treatment of the envelope dynamics up to the stage of free expansion, contrary to the plane-approximation consideration. The sphericity results in decreasing pressure, density, and velocity of Lagrangian layers. Publication: The Astrophysical Journal Pub Date: November 1992 DOI: 10.1086/171986 Bibcode: 1992ApJ...400..192K Keywords: Gas Expansion; Shock Wave Interaction; Stellar Cores; Stellar Envelopes; Gravitational Collapse; Spatial Distribution; Supernovae; Astrophysics; HYDRODYNAMICS; SHOCK WAVES; ISM: SUPERNOVA REMNANTS full text sources ADS | data products SIMBAD (1)

Evolution of the Precursor of SN1987A

The evolution of a 17.5 M⊙ star, chosen to be similar to the precursor of SN1987A, has been studied using the input physics described in Wood and Faulkner (1987). The calculations: use opacities from the Astrophysical Opacity Library of Huebner et al (1977) with H, He, C, N, O and other metals in LMC ratios; treat semi-convection in the manner of Lamb, Iben and Howard (1976); and assume the mass loss rate to be the minimum of (a) α times the rate give in Waldron (1985) (this rate applied in the blue part of the HR diagram), and (b) L/(cv) (this rate applied in the red), where v is the stellar wind expansion velocity which was taken to be 12 km s−1.Typical evolutionary tracks resulting from these calculations are shown in Figure 1. The track shown as a continuous line is the one shown in Wood and Faulkner (1987) and corresponds to α = 2.5, while the track shown as a dotted line results from a slightly different treatment of semi-convection on the main-sequence and to α = 1.

X-ray bursts associated with envelope expansion

The precursor associated with a long X-ray burst is interpreted in terms of the stellar envelope expansion. The mass flow driven by the radiation pressure in excess of the local Eddington limit and the grey atmosphere model correctly describe the burst profiles in different energy ranges.

The evolution of a stripped giant-neutron star binary

view Abstract Citations (80) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The evolution of a stripped giant-neutron star binary. Taam, R. E. Abstract As a possible model for low-mass X-ray binaries in globular clusters and in the galactic bulge, the evolution of a stripped giant-neutron star binary system is investigated. The systems are characterized by masses less than 2.2 solar masses and periods greater than 0.766 days. It is found that mass transfer driven by nuclear evolution yields rates greater than or approximately equal to 10 to the -9th solar mass per yr for helium-core masses greater than or approximtely equal to 0.2 solar mass. The mass transfer rate varies slowly throughout until it abruptly ceases at the point when the stellar radius rapidly contracts from its critical Roche surface. The high mass transfer rates refect the more rapid stellar expansion associated with the giant in a more evolved state. Because the stellar radius is large in such models, the expected binary orbital periods are greater than or approximately equal to 1 day. Publication: The Astrophysical Journal Pub Date: July 1983 DOI: 10.1086/161160 Bibcode: 1983ApJ...270..694T Keywords: Binary Stars; Giant Stars; Neutron Stars; Stellar Evolution; X Ray Sources; Galactic Bulge; Globular Clusters; Hertzsprung-Russell Diagram; Stellar Mass Ejection; Stellar Models; X Ray Binaries; Astrophysics full text sources ADS | data products SIMBAD (2)

Stellar thermal expansion effects on the cooling of neutron stars

view Abstract Citations (15) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar thermal expansion effects on the cooling of neutron stars Baym, G. Abstract It is shown that the thermal contraction in the cooling of degenerate neutron stars produces a correction to the net luminosity of order (piT/Tf)2, where T is the temperature and Tf is the Fermi temperature of the supporting matter. Therefore, except in the atmosphere or at very early times, thermal effects on the netural star structure can be neglected in computing the cooling of neutron stars. Publication: The Astrophysical Journal Pub Date: September 1981 DOI: 10.1086/159200 Bibcode: 1981ApJ...248..767B Keywords: Neutron Stars; Stellar Temperature; Thermal Expansion; Cooling; Entropy; Equations Of State; Astrophysics full text sources ADS |

Emission envelopes of T Tauri stars

view Abstract Citations (56) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Emission envelopes of T Tauri stars. Kuan, P. Abstract It is shown that the existence of extended moving envelopes around T Tauri stars can most adequately account for the presence of emission lines. In particular, a single parameter model, characterized by the electron density or its equivalent, or the mass-loss rate if the stellar radius and expansion velocity are known, can reproduce the observed intensities of the lower Balmer lines. The excess continuous radiation found in these stars, from the ultraviolet to the near-infrared, can be explained by a model of free-free and free-bound emission from the ejected gas in the form of clumps close to the surface of the star. Publication: The Astrophysical Journal Pub Date: December 1975 DOI: 10.1086/153992 Bibcode: 1975ApJ...202..425K Keywords: Emission Spectra; Main Sequence Stars; Stellar Envelopes; Stellar Spectra; T Tauri Stars; Balmer Series; Clumps; Electron Density (Concentration); Line Spectra; Stellar Mass Ejection; Stellar Radiation; Astrophysics full text sources ADS | data products SIMBAD (6)