The diffuse nature of Strömgren spheres

Ritzerveld, Jelle

doi:10.1051/0004-6361:200500150

Cited by 31 publications

(53 citation statements)

References 6 publications

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“…Rather than a diffuse field arising from the repeated reprocessing of stellar radiation by dust grains, the ionizing radiation field in a star-forming region consists mostly of photons directly emitted from a stellar surface. Only in the outer parts of lowdensity ionized regions with sharp density gradients does reprocessed radiation make up a significant part of the photon field (Ritzerveld, 2005). The dominance of a relatively small number of point sources of radiation translates into a much simpler computational problem.…”

Section: Numerical Methods For Ionizing Radiationmentioning

confidence: 99%

Numerical Star-Formation Studies— A Status Report

Klessen¹,

Krumholz²,

Heitsch³

2011

adv sci lett

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The formation of stars is a key process in astrophysics. Detailed knowledge of the physical mechanisms that govern stellar birth is a prerequisite for understanding the formation and evolution of our galactic home, the Milky Way. A theory of star formation is an essential part of any model for the origin of our solar system and of planets around other stars. Despite this pivotal importance, and despite many decades of research, our understanding of the processes that initiate and regulate star formation is still limited. Stars are born in cold interstellar clouds of molecular hydrogen gas. Star formation in these clouds is governed by the complex interplay between the gravitational attraction in the gas and agents such as turbulence, magnetic fields, radiation and thermal pressure that resist compression. The competition between these processes determines both the locations at which young stars form and how much mass they ultimately accrete. It plays out over many orders of magnitude in space and time, ranging from galactic to stellar scales. In addition, star formation is a highly stochastic process in which rare and hard-to-predict events, such as the formation of very massive stars and the resulting feedback, can play a dominant role in determining the evolution of a star-forming cloud. As a consequence of the wide range of scales and processes that control star formation, analytic models are usually restricted to highly idealized cases. These can yield insight, but the complexity of the problem means that they must be used in concert with large-scale numerical simulations. Here we summarize the state of modern star formation theory and review the recent advances in numerical simulation techniques.

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Section: Numerical Methods For Ionizing Radiationmentioning

confidence: 99%

Numerical Star-Formation Studies— A Status Report

Klessen¹,

Krumholz²,

Heitsch³

2011

adv sci lett

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“…In the earlier days of heliospheric science, this lead to some confusion because r S for the heliosphere is on the order of 1000 AU, but interstellar neutrals were observed at 1 AU (for a review see Fahr 1990). There are also recent attempts (Mackey et al 2013(Mackey et al , 2014 to model the ionization fronts around hot stars with a relative motion to the ambient ISM and for Strömgren spheres (Ritzerveld 2005). All these arguments lead to the conclusion that neutrals are an important feature in modeling astrospheres, even around hot stars.…”

Section: Fluid Equationsmentioning

confidence: 99%

Shock structures of astrospheres

Scherer

Fichtner

Kleimann

et al. 2016

A&A

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Context. The interaction between a supersonic stellar wind and a (super-)sonic interstellar wind has recently been viewed with new interest. We here first give an overview of the modeling, which includes the heliosphere as an example of a special astrosphere. Then we concentrate on the shock structures of fluid models, especially of hydrodynamic (HD) models. More involved models taking into account radiation transfer and magnetic fields are briefly sketched. Even the relatively simple HD models show a rich shock structure, which might be observable in some objects. Aims. We employ a single-fluid model to study these complex shock structures, and compare the results obtained including heating and cooling with results obtained without these effects. Furthermore, we show that in the hypersonic case valuable information of the shock structure can be obtained from the Rankine-Hugoniot equations. Methods. We solved the Euler equations for the single-fluid case and also for a case including cooling and heating. We also discuss the analytical Rankine-Hugoniot relations and their relevance to observations. Results. We show that the only obtainable length scale is the termination shock distance. Moreover, the so-called thin shell approximation is usually not valid. We present the shock structure in the model that includes heating and cooling, which differs remarkably from that of a single-fluid scenario in the region of the shocked interstellar medium. We find that the heating and cooling is mainly important in this region and is negligible in the regions dominated by the stellar wind beyond an inner boundary.

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“…4.2). Even though the validity of this approach is not well established (Ritzerveld 2005) we will use the on-the-spot approximation for all the tests presented in this paper, in order to make a clean comparison between our results and the analytic solution or the results of other codes that all use the on-the-spot approximation.…”

Section: Scattering Processesmentioning

confidence: 99%

“…One can therefore ignore recombinations to the ground level, as they are cancelled out by the emitted radiation, and use the corresponding recombination coefficient α B (T ). However, Ritzerveld (2005) showed that, depending on the density distribution, if the source produces radiation just above the Lyman limit, this approximation is not valid. Most radiative transfer codes are incapable of including this diffuse recombination radiation since effectively every grid cell that is ionised becomes a source.…”

Section: Ionisation Processesmentioning

confidence: 99%

SimpleX2: radiative transfer on an unstructured, dynamic grid

Paardekooper¹,

Kruip²,

Icke³

2010

A&A

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Context. We present an improved version of the SimpleX method for radiative transfer on an unstructured Delaunay grid. The grid samples the medium through which photons are transported in an optimal way for fast radiative transfer calculations. Aims. We study the detailed working of SimpleX in test problems and show improvements over the previous version of the method. Methods. We have applied a direction conserving transport scheme that correctly transports photons in the optically thin regime, a regime where the original SimpleX algorithm lost its accuracy. In addition, a scheme of dynamic grid updates is employed to ensure correct photon transport when the optical depth changes during a simulation. For the application to large data sets, the method is parallellised for distributed memory machines using MPI. Results. To test the new method, we have performed standard tests for cosmological radiative transfer. We show excellent correspondence with both the analytical solution (when available) and to the results of other codes compared to the former version of SimpleX, without sacrificing the benefits of the high computational speed of the method.

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The diffuse nature of Strömgren spheres

Cited by 31 publications

References 6 publications

Numerical Star-Formation Studies— A Status Report

Numerical Star-Formation Studies— A Status Report

Shock structures of astrospheres

SimpleX2: radiative transfer on an unstructured, dynamic grid

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