arXiv subjects

Duncan Forgan

Publications and source records attributed to Duncan Forgan.

39 records · Page 3Linked to original sources

arXiv2008

Introducing a Hybrid Method of Radiative Transfer for Smoothed Particle Hydrodynamics

A new means of incorporating radiative transfer into smoothed particle hydrodynamics (SPH) is introduced, which builds on the success of two previous methods - the polytropic cooling approximation as devised by Stamatellos et al (2007), and flux limited diffusion (e.g. Mayer et al 2007). This hybrid method preserves the strengths of its individual components, while removing the need for atmosphere matching or other boundary conditions to marry optically thick and optically thin regions. The code uses a non-trivial equation of state to calculate temperatures and opacities of SPH particles, which captures the effects of molecular hydrogen dissociation, atomic hydrogen ionisation, He0 and He+ ionisation, ice evaporation, dust sublimation, molecular absorption, bound-free and free-free transitions and electron scattering. The method is tested in several scenarios, including: (1) the evolution of a 0.07 solar mass protoplanetary disc surrounding a 0.5 solar mass star; (2) the collapse of a 1 solar mass protostellar cloud, and (3) the thermal relaxation of temperature fluctuations in a static homogeneous sphere.

astro-ph↗

arXiv2008

A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence

The search for extraterrestrial intelligence (SETI) has been heavily influenced by solutions to the Drake Equation, which returns an integer value for the number of communicating civilisations resident in the Milky Way, and by the Fermi Paradox, glibly stated as: "If they are there, where are they?". Both rely on using average values of key parameters, such as the mean signal lifetime of a communicating civilisation. A more accurate answer must take into account the distribution of stellar, planetary and biological attributes in the galaxy, as well as the stochastic nature of evolution itself. This paper outlines a method of Monte Carlo realisation which does this, and hence allows an estimation of the distribution of key parameters in SETI, as well as allowing a quantification of their errors (and the level of ignorance therein). Furthermore, it provides a means for competing theories of life and intelligence to be compared quantitatively.

astro-ph↗

arXiv2008

Introducing a Hybrid Method of Radiative Transfer in Smoothed Particle Hydrodynamics

We present a new method of incorporating radiative transfer into Smoothed Particle Hydrodynamics (SPH). There have been many recent attempts at radiative transfer in SPH (Stamatellos et al 2005, 2005, Mayer et al 2007, Whitehouse and Bate 2006), however these are becoming increasingly complex, with some methods requiring the photosphere to be mapped (which is often of non-trivial geometric shape), and extra conditions to be applied there (matching atmospheres as in Cai et al (2008), or specifying cooling at the photosphere as in Mayer et al (2007)). The method of identifying the photosphere is usually a significant addition to the total simulation runtime, and often requires extra free parameters, the changing of which will affect the final results. Our method is not affected by such concerns, as the photosphere is constructed implicitly by the algorithm without the need for extra free parameters. The algorithm used is a synergy of two current formalisms for radiative effects: a) the polytropic cooling formalism proposed by Stamatellos et al (2007), and b) flux-limited diffusion, used by many authors to simulate radiation transport in the optically thick regime (e.g. Mayer et al 2007). We present several tests of this method: (1) The evolution of a 0.07 solar mass protoplanetary disc around a 0.5 solarmass star (Pickett et al 2003, Mejia et al 2005, Boley et al 2006, Cai et al 2008); (2) The collapse of a non-rotating 1 solar mass molecular cloud (Masunaga & Inutsuka 2000, Stamatellos et al 2007); (3) The thermal relaxation of temperature fluctuations in an static homogeneous sphere (Masunaga et al 1998, Spiegel 1957, Stamatellos et al 2007)

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