Niemeyer, J

[["dc.bibliographiccitation.firstpage","952"],["dc.bibliographiccitation.issue","2 I"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.lastpage","961"],["dc.bibliographiccitation.volume","588"],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Niemeyer, J. C."],["dc.contributor.author","Hillebrandt, W."],["dc.date.accessioned","2020-07-21T06:08:10Z"],["dc.date.available","2020-07-21T06:08:10Z"],["dc.date.issued","2003"],["dc.description.abstract","We present a numerical model which allows us to investigate thermonuclear flames in Type Ia supernova explosions. The model is based on a finite-volume explicit hydrodynamics solver employing PPM. Using the level-set technique combined with in-cell reconstruction and flux-splitting schemes we are able to describe the flame in the discontinuity approximation. We apply our implementation to flame propagation in Chandrasekhar-mass Type Ia supernova models. In particular we concentrate on intermediate scales between the flame width and the Gibson-scale, where the burning front is subject to the Landau-Darrieus instability. We are able to reproduce the theoretical prediction on the growth rates of perturbations in the linear regime and observe the stabilization of the flame in a cellular shape. The increase of the mean burning velocity due to the enlarged flame surface is measured. Results of our simulation are in agreement with semianalytical studies."],["dc.identifier.doi","10.1086/374216"],["dc.identifier.scopus","2-s2.0-0041760782"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/67316"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-0041760782&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1538-4357"],["dc.relation.issn","0004-637X"],["dc.title","On the small-scale stability of thermonuclear flames in type ia supernovae"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","14"],["dc.bibliographiccitation.volume","448"],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Hillebrandt, W."],["dc.contributor.author","Niemeyer, J. C."],["dc.contributor.author","Woosley, S. E."],["dc.date.accessioned","2020-07-09T08:36:38Z"],["dc.date.available","2020-07-09T08:36:38Z"],["dc.date.issued","2006"],["dc.description.abstract","We present a systematic survey of the capabilities of type Ia supernova explosion models starting from a number of flame seeds distributed around the center of the white dwarf star. To this end we greatly improved the resolution of the numerical simulations in the initial stages. This novel numerical approach facilitates a detailed study of multi-spot ignition scenarios with up to hundreds of ignition sparks. Two-dimensional simulations are shown to be inappropriate to study the effects of initial flame configurations. Based on a set of three-dimensional models, we conclude that multi-spot ignition scenarios may improve type Ia supernova models towards better agreement with observations. The achievable effect reaches a maximum at a limited number of flame ignition kernels as shown by the numerical models and corroborated by a simple dimensional analysis."],["dc.identifier.doi","10.1051/0004-6361:20053926"],["dc.identifier.scopus","2-s2.0-33644906974"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/66905"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-33644906974&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Multi-spot ignition in type la supernova models"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","411"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","422"],["dc.bibliographiccitation.volume","420"],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Hillebrandt, W."],["dc.contributor.author","Niemeyer, J. C."],["dc.date.accessioned","2020-07-07T13:31:54Z"],["dc.date.available","2020-07-07T13:31:54Z"],["dc.date.issued","2004"],["dc.description.abstract","We present a numerical investigation of the cellular burning regime in Type Ia supernova explosions. This regime holds at small scales (i.e. below the Gibson scale), which are unresolved in large-scale Type Ia supernova simulations. The fundamental effects that dominate the flame evolution here are the Landau-Darrieus instability and its nonlinear stabilization, leading to a stabilization of the flame in a cellular shape. The flame propagation into quiescent fuel is investigated addressing the dependence of the simulation results on the specific parameters of the numerical setup. Furthermore, we investigate the flame stability at a range of fuel densities. This is directly connected to the questions of active turbulent combustion (a mechanism of flame destabilization and subsequent self-turbulization) and a deflagration-to-detonation transition of the flame. In our simulations we find no substantial destabilization of the flame when propagating into quiescent fuels of densities down to ~10^7 g/cm^3, corroborating fundamental assumptions of large-scale SN Ia explosion models. For these models, however, we suggest an increased lower cutoff for the flame propagation velocity to take the cellular burning regime into account."],["dc.identifier.doi","10.1051/0004-6361:20035721"],["dc.identifier.scopus","2-s2.0-2942524063"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/66884"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-2942524063&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","The cellular burning regime in type ia supernova explosions I. Flame propagation into quiescent fuel"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.volume","11"],["dc.contributor.author","Hillebrandt, W."],["dc.contributor.author","Reinecke, M."],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Stehle, M."],["dc.contributor.author","Travaglio, C."],["dc.contributor.author","Niemeyer, J. C."],["dc.contributor.editor","Jorissen, A."],["dc.contributor.editor","Goriely, S."],["dc.contributor.editor","Rayet, M."],["dc.contributor.editor","Siess, L."],["dc.contributor.editor","Boffin, H."],["dc.date.accessioned","2020-07-16T13:04:44Z"],["dc.date.available","2020-07-16T13:04:44Z"],["dc.date.issued","2004"],["dc.description.abstract","Recent progress in modeling type Ia supernovae by means of 3-dimensional hydrodynamic simulations as well as several of the still open questions are addressed. Our models are based on the assumption that thermonuclear burning inside a Chandrasekhar-mass C+O white dwarf is similar to turbulent chemical combustion and that, thus, thermonuclear supernovae can be modeled by means of numerical methods which have been developed and tested for laboratory and technical flames. It is shown that the new models have considerable predictive power and allow to study observable properties of type Ia supernovae, such as their light curves and spectra, without adjustable non-physical parameters, and they make firm predictions for the nucleosynthesis yields from the explosions. This raises a quest for better data, covering the spectroscopical and photometric evolution in all wave bands from very early epochs all the way into the nebular phase. First such results obtained by the European Supernova Collaboration (ESC) for a sample of nearby SNe Ia and their implications for constraining the models and systematic differences between them are also discussed."],["dc.identifier.doi","10.1051/eas:2004010"],["dc.identifier.scopus","2-s2.0-28844472915"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/67196"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-28844472915&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.publisher","EDP Sciences"],["dc.relation.crisseries","EAS Publications Series"],["dc.relation.ispartofseries","EAS Publications Series;"],["dc.title","Thermonuclear supernovae"],["dc.type","book"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","363"],["dc.bibliographiccitation.lastpage","384"],["dc.contributor.author","Hillebrandt, W."],["dc.contributor.author","Reinecke, M."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Travaglio, C."],["dc.contributor.author","Niemeyer, J. C."],["dc.contributor.editor","Warnecke, G."],["dc.date.accessioned","2020-07-09T08:04:23Z"],["dc.date.available","2020-07-09T08:04:23Z"],["dc.date.issued","2005"],["dc.description.abstract","Type Ia supernovae, i.e. stellar explosions which do not have hydrogen in their spectra, but intermediate-mass elements such as silicon, calcium, cobalt, and iron, have recently received considerable attention because it appears that they can be used as ”standard candles” to measure cosmic distances out to billions of light years away from us. Observations of type Ia supernovae seem to indicate that we are living in a universe that started to accelerate its expansion when it was about half its present age. These conclusions rest primarily on phenomenological models which, however, lack proper theoretical understanding, mainly because the explosion process, initiated by thermonuclear fusion of carbon and oxygen into heavier elements, is difficult to simulate even on supercomputers. Here, we investigate a new way of modeling turbulent thermonuclear deflagration fronts in white dwarfs undergoing a type Ia supernova explosion. Our approach is based on a level set method which treats the front as a mathematical discontinuity and allows for full coupling between the front geometry and the flow field. New results of the method applied to the problem of type Ia supernovae are obtained. It is shown that in 2-D with high spatial resolution and a physically motivated subgrid scale model for the nuclear flames numerically “converged” results can be obtained, but for most initial conditions the stars do not explode. In contrast, simulations in 3-D do give the desired explosions and many of their properties, such as the explosion energies, lightcurves and nucleosynthesis products, are in very good agreement with observed type Ia supernovae."],["dc.identifier.doi","10.1007/3-540-27907-5_16"],["dc.identifier.scopus","2-s2.0-35348925773"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/66897"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-35348925773&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.publisher","Springer"],["dc.publisher.place","Berlin, Heidelberg"],["dc.relation.doi","10.1007/3-540-27907-5"],["dc.relation.eisbn","978-3-540-27907-5"],["dc.relation.isbn","978-3-540-24834-7"],["dc.relation.ispartof","Analysis and Numerics for Conservation Laws"],["dc.title","Simulations of turbulent thermonuclear burning in type Ia supernovae"],["dc.type","book_chapter"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","683"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","686"],["dc.bibliographiccitation.volume","464"],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Niemeyer, J. C."],["dc.date.accessioned","2020-07-01T07:37:59Z"],["dc.date.available","2020-07-01T07:37:59Z"],["dc.date.issued","2007"],["dc.description.abstract","Aims: We present the first full-star three-dimensional explosion simulations of thermonuclear supernovae including parameterized deflagration-to-detonation transitions that occur once the flame enters the distributed burning regime. Methods: Treating the propagation of both the deflagration and the detonation waves in a common front-tracking approach, the detonation is prevented from crossing ash regions. Results: Our criterion triggers the detonation wave at the outer edge of the deflagration flame and consequently it has to sweep around the complex structure and to compete with expansion. Despite the impeded detonation propagation, the obtained explosions show reasonable agreement with global quantities of observed type Ia supernovae. By igniting the flame in different numbers of kernels around the center of the exploding white dwarf, we set up three different models shifting the emphasis from the deflagration phase to the detonation phase. The resulting explosion energies and iron group element productions cover a large part of the diversity of type Ia supernovae. Conclusions: Flame-driven deflagration-to-detonation transitions, if hypothetical, remain a possibility deserving further investigation."],["dc.identifier.doi","10.1051/0004-6361:20066585"],["dc.identifier.scopus","2-s2.0-33947263128"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/66812"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-33947263128&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Delayed detonations in full-star models of type Ia supernova explosions"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","283"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","294"],["dc.bibliographiccitation.volume","450"],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Niemeyer, Jens C."],["dc.contributor.author","Hillebrandt, W."],["dc.contributor.author","Röpke, F. K."],["dc.date.accessioned","2020-07-22T09:38:43Z"],["dc.date.available","2020-07-22T09:38:43Z"],["dc.date.issued","2006"],["dc.description.abstract","The dynamics of the explosive burning process is highly sensitive to the flame speed model in numerical simulations of type Ia supernovae. Based upon the hypothesis that the effective flame speed is determined by the unresolved turbulent velocity fluctuations, we employ a new subgrid scale model which includes a localised treatment of the energy transfer through the turbulence cascade in combination with semi-statistical closures for the dissipation and non-local transport of turbulence energy. In addition, subgrid scale buoyancy effects are included. In the limit of negligible energy transfer and transport, the dynamical model reduces to the Sharp-Wheeler relation. According to our findings, the Sharp-Wheeler relation is insuffcient to account for the complicated turbulent dynamics of flames in thermonuclear supernovae. The application of a co-moving grid technique enables us to achieve very high spatial resolution in the burning region. Turbulence is produced mostly at the flame surface and in the interior ash regions. Consequently, there is a pronounced anisotropy in the vicinity of the flame fronts. The localised subgrid scale model predicts significantly enhanced energy generation and less unburnt carbon and oxygen at low velocities compared to earlier simulations."],["dc.identifier.doi","10.1051/0004-6361:20053618"],["dc.identifier.scopus","2-s2.0-33645835717"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/67389"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-33645835717&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","A localised subgrid scale model for fluid dynamical simulations in astrophysics II. Application to type la supernovae"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","783"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","795"],["dc.bibliographiccitation.volume","421"],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Hillebrandt, W."],["dc.contributor.author","Niemeyer, J. C."],["dc.date.accessioned","2020-07-16T12:55:45Z"],["dc.date.available","2020-07-16T12:55:45Z"],["dc.date.issued","2004"],["dc.description.abstract","We investigate the interaction of thermonuclear flames in Type Ia supernova explosions with vortical flows by means of numerical simulations. In our study, we focus on small scales, where the flame propagation is no longer dominated by the turbulent cascade originating from large-scale effects. Here, the flame propagation proceeds in the cellular burning regime, resulting from a balance between the Landau-Darrieus instability and its nonlinear stabilization. The interaction of a cellularly stabilized flame front with a vortical fuel flow is explored applying a variety of fuel densities and strengths of the velocity fluctuations. We find that the vortical flow can break up the cellular flame structure if it is sufficiently strong. In this case the flame structure adapts to the imprinted flow field. The transition from the cellularly stabilized front to the flame structure dominated by vortices of the flow proceeds in a smooth way. The implications of the results of our simulations for Type Ia Supernova explosion models are discussed."],["dc.identifier.doi","10.1051/0004-6361:20035778"],["dc.identifier.scopus","2-s2.0-3142744819"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/67193"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-3142744819&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","The cellular burning regime in type la supernova explosions ii. Flame propagation into vortical fuel"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1132"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.lastpage","1139"],["dc.bibliographiccitation.volume","668"],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Hillebrandt, W."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Niemeyer, J. C."],["dc.contributor.author","Blinnikov, S. I."],["dc.contributor.author","Mazzali, P. A."],["dc.date.accessioned","2020-07-20T10:10:11Z"],["dc.date.available","2020-07-20T10:10:11Z"],["dc.date.issued","2007"],["dc.description.abstract","A simulation of the thermonuclear explosion of a Chandrasekhar-mass C+O white dwarf, the most popular scenario of a type Ia supernova (SN Ia), is presented. The underlying modeling is pursued in a self-consistent way, treating the combustion wave as a turbulent deflagration using well tested methods developed for laboratory combustion and based on the concept of 'large eddy simulations' (LES). Such consistency requires to capture the onset of the turbulent cascade on resolved scales. This is achieved by computing the dynamical evolution on a 1024$^3$ moving grid, which resulted in the best-resolved three-dimensional SN Ia simulation carried out thus far, reaching the limits of what can be done on present supercomputers. Consequently, the model has no free parameters other than the initial conditions at the onset of the explosion, and therefore it has considerable predictive power. Our main objective is to determine to which extent such a simulation can account for the observations of normal SNe Ia. Guided by previous simulations with less resolution and a less sophisticated flame model, initial conditions were chosen that yield a reasonably strong explosion and a sufficient amount of radioactive nickel for a bright display. We show that observables are indeed matched to a reasonable degree. In particular, good agreement is found with the light curves of normal SNe Ia. Moreover, the model reproduces the general features of the abundance stratification as inferred from the analysis of spectra. This indicates that it captures the main features of the explosion mechanism of SNe Ia. However, we also show that even a seemingly best-choice pure deflagration model has shortcomings that indicate the need for a different mode of nuclear burning at late times, perhaps the transition to a detonation at low density."],["dc.identifier.doi","10.1086/521347"],["dc.identifier.scopus","2-s2.0-38049147764"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/67242"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-38049147764&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1538-4357"],["dc.relation.issn","0004-637X"],["dc.title","A three-dimensional deflagration model for Type Ia supernovae compared with observations"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1491"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.lastpage","1497"],["dc.bibliographiccitation.volume","696"],["dc.contributor.author","Ciaraldi-Schoolmann, F."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Niemeyer, J. C."],["dc.contributor.author","Röpke, F. K."],["dc.contributor.author","Hillebrandt, W."],["dc.date.accessioned","2020-07-03T07:16:49Z"],["dc.date.available","2020-07-03T07:16:49Z"],["dc.date.issued","2009"],["dc.description.abstract","We analyze the statistical properties of the turbulent velocity field in the deflagration model for Type Ia supernovae. In particular, we consider the question of whether turbulence is isotropic and consistent with the Kolmogorov theory at small length scales. Using numerical data from a high-resolution simulation of a thermonuclear supernova explosion, spectra of the turbulence energy and velocity structure functions are computed. We show that the turbulent velocity field is isotropic at small length scales and follows a scaling law that is consistent with the Kolmogorov theory until most of the nuclear fuel is burned. At length scales greater than a certain characteristic scale that agrees with the prediction of Niemeyer & Woosley, turbulence becomes anisotropic. Here, the radial velocity fluctuations follow the scaling law of the Rayleigh-Taylor instability, whereas the angular component still obeys the Kolmogorov scaling. In the late phase of the explosion, this characteristic scale drops below the numerical resolution of the simulation. The analysis confirms that a subgrid-scale model for the unresolved turbulence energy is required for the consistent calculation of the flame speed in deflagration models of Type Ia supernovae, and that the assumption of isotropy on these scales is appropriate."],["dc.identifier.doi","10.1088/0004-637X/696/2/1491"],["dc.identifier.scopus","2-s2.0-77149168049"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/66850"],["dc.identifier.url","http://www.scopus.com/inward/record.url?eid=2-s2.0-77149168049&partnerID=MN8TOARS"],["dc.language.iso","en"],["dc.relation.eissn","1538-4357"],["dc.relation.issn","0004-637X"],["dc.title","Turbulence in a three-dimensional deflagration model for type Ia supernovae. I. Scaling properties"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]