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NUMERICAL ASTROPHYSICS AND ITS ROLE IN STAR FORMATION

Cardiff, 19-23 January 2009

Talk & poster abstracts



Serena Emily Arena

University of Tuebingen

SPH simulations of solid bodies for studying planetesimal formation [P]



Rhianne Attwood

Cardiff University

The role of turbulence and thermodynamics on star formation in molecular cloud cores [T]

In Smoothed Particle Hydrodynamical (SPH) simulations of star formation a simple barotropic equation of state is normally used in every situation. However, in practice this is not realistic because it does not take account of the thermal history of a protostar and is unable to capture thermal inertia effects. We perform a large ensemble of SPH simulations of the collapse and fragmentation of low-mass, low-turbulence cores, using a new, more realistic treatment of thermodynamics, developed by Stamatellos et al. (2007). This algorithm captures the transport of cooling radiation against opacity due to both dust and gas (including the effects of dust sublimation, molecules, and H^-ions). We quantify the difference between simulations performed using a standard barotropic equation of state and simulations which treat the energy equation and associated radiation transport. We show the influence the treatment of thermodynamics has on the mass distribution, binary statistics and kinematics of the resulting stars.



Edouard Audit

Service d'Astrophysique, CEA/Saclay

Radiative transfer using the Moment  Method, and its application to radiative shocks [T]



Robi Banerjee

 Institute for Theoretical Astophysics (ITA) University of Heidelberg

 Contemporary Star Formation with the FLASH code [T]



Thomas Bisbas

Cardiff University

 SPH simulations of expanding HII regions [T]


We describe a new algorithm for including the dynamical effects of ionizing radiation in SPH simulations. We use the HEALPix software to tessellate the sky, and we solve the equation of ionization equilibrium along a ray towards each of the resulting tesserae. We exploit the hierarchical nature of HEALPix to make the algorithm adaptive, so that fine angular resolution is invoked only where it is needed, and the computational cost is kept low. We present simulations of (i) the spherically symmetric expansion of an HII region inside a uniform-density, non-self-gravitating cloud; (ii) the spherically symmetric expansion of an HII region inside a uniform-density, self-gravitating cloud; (iii) the expansion of an off-centre HII region inside a uniform-density, non-self-gravitating cloud, resulting in rocket acceleration and dispersal of the cloud; and (iv) radiatively driven compression and ablation of a core overrun by an HII region. This new algorithm provides the means to explore and evaluate the role of ionizing radiation in regulating the efficiency and statistics of star formation.



Ian Bonnell

University of St Andrews

Cluster and distributed modes and the efficiency of star formation [T]


I will present recent results on simulations of star formation on the scale of individual molecular clouds. The simulations probe both the clustered and distributed modes of star formation and how these relate to the efficiency of star formation. Clustered star formation occurs in bound regions of the cloud which produce a higher efficiency of star formation. Conversely, unbound regions form fewer stars in a distributed mode with very low efficiencies. The overall efficiency is low with a time integrated SFE of only a few percent per dynamical time of the cloud.



Annabel Cartwright

Cardiff University

 The effect of Poisson noise on the accuracy of SPH calculations: does increasing particle numbers help? [T]


A standard technique in SPH simulations is to create the initial particle distribution using a random number generator, relying on SPH to even out the small scale density fluctuations in a 'settling' phase of the simulation. Here we compare an almost perfectly smooth density distribution with a standard random distribution, and show how pressure, density, viscosity and gravity calculations are affected differently by the random noise. In particular, increasing particle numbers does not make the problem disappear and does not affect all calculated quantities in the same way.



Paola Caselli 

School of Physics & Astronomy, University of Leeds

Pedagogical Talk on Diagnostic Chemistry [T]


A symbiotic relationship exists between the chemistry occurring in interstellar gas and its evolution to form stars and planets. The chemistry produces coolants, which enable gravitationally induced collapse, and also establishes the ionisation balance, which governs how the magnetic field regulates the collapse. The physical evolution changes the chemical composition. The detected molecules include water and numerous organic species, which become incorporated into comets, meteors, and planets. Molecules are tools to track star and planet formation. In this talk I shall review basic chemical processes in the interstellar medium and the diagnostic power of those species which are particularly important for our understanding of star and planet forming regions.



 Seung-Hoon Cha

Theoretical Astrophysics Group, Department of Physics and Astronomy,University of Leicester

The Kelvin-Helmholtz instability by the Godunov-type SPH [P]


The Kelvin-Helmholtz instability (KHI) has been performed by the new formulation of SPH (Inutsuka,2002). The standard SPH shows the absence of the KHI across the density contrast, but the new formulation describes the KHI even in a high density contrast. The blob test has been performed to check the performance of the new formulation, and the result is similar to that of grid-based codes. we will explain the new formulation, and show some 1-dimensional test results in this presentation.



Gilles Chabrier

ENS-Lyon, France

The basics of the early evolution of young objects: from the proto-star/BD to the PMS phase [T]


Paul C. Clark

ITA Universitaet Heidelberg

The formation of discs in clusters [T]



Benoît Commerçon

  CEA Saclay (France)

Protostellar collapse: numerical methods comparison and development [T]


I will present our work done one the numerical study of the collapse and fragmentation of prestellar dense core.  First I will present a comparison between standard SPH and AMR calculations we made in the context of low-mass star formation.  We adopt simple initial conditions (Boss-Bodenheimer type test) and a barotropic EOS to mimic the thermal behaviour of the gas during the collapse.  We investigate the influence of numerical resolution on angular momentum conservation and fragmentation. It comes out  that convergence between SPH and AMR calculations is obtained, providing strong resolution criteria on the Jeans length/mass are used. In a second part, I will present our implementation of Flux Limited Diffusion model within the RAMSES code and first results of radiation-magnetohydrodynamics calculations.  We discuss the impact of radiative transfer using FLD on fragmentation and on the outflow due to magnetic field. We compare these results to thus obtained using usual barotropic equation of state.

 


Timea Csengeri

CEA-Saclay

 Origin of high-mass stars and clusters in DR21(OH) [P]


We study the DR21 filament located in the Cygnus-X star forming region - one of the closest site hosting high-mass star formation, where significant amount of the gas is concentrated at very high density. With single-dish (IRAM 30m) data we study the properties of the collapsing filament on large scale (1 pc), while with interferometric data (PdBI) we obtain the distribution of matter and the kinematics on smaller scale (0.01 pc). Therefore we aim to understand: (1) the initial conditions of the collapsing filament, which forms massive protostars; (2) to study the fragmentation and the kinematic properties of individual massive condensations on small scales; (3) to follow the link between the protostars and their close environment to test different theoretical views for their evolution.



James Dale

 Astronomical Institute, Czech Academy of Sciences

 Stellar feedback - modelling HII regions, stellar winds and fragmenting shells in SPH [T]


I will discuss the importance of feedback from high-mass stars in the general context of star formation, focussing in particular on the problems of triggered star formation and the unbinding of embedded clusters. I will explain the techniques I have developed for modelling the photoionizing radiation and winds from massive stars in SPH simulations and present results from simulations of the influence of feedback on protoclusters.



 Clare Dobbs, Kevin Douglas, Dave Acreman

University of Exeter

How Do You Solve a Problem Like Molecular Cloud Formation? [P]


The earliest stage of the star formation process may be considered to be the formation of large molecular clouds, as initially atomic hydrogen (HI) gas cools and condenses as it enters the Galaxy's spiral arms. Observationally, cold and dense HI seen in self-absorption may reveal the onset of H2 formation, and the CO J=1-0 line is used to trace the wide-spread distribution of molecular gas.

The high resolution available for our own Galaxy is however offset by large uncertainties in estimating the distances to HI and CO features.  There are no such problems for simulations, but we need to produce HI and CO maps equivalent to those from observations. We show gas at different stages of molecular cloud evolution from both simulations and observations, and outline our overall aim to produce synthetic maps of HI and CO from the simulations.



Barbara Ercolano

Institute of Astronomy, University of Cambridge

Geometry Independent Radiative Transfer through Gas and Dust using the Monte Carlo method [T]

 

In this talk I will review the basics of the Monte Carlo (MC) method as applied to radiative transfer through astrophysical gas and dust. I will also briefly compare and constrast the architecture of photoionisation (gas) and pure dust radiative transfer MC codes and  demonstrate how the two problems can (and should in many cases) be treated simultaneously and self-consistently. The main features and capabilities of the MOCASSIN code will be briefly described and demonstrated via a number of recent astrophysical applications.



Christoph Federrath

ITA/ZAH Heidelberg

 Interstellar Turbulence: Solenoidal versus Compressive Forcing [P]


The influence of turbulence forcing on density and velocity statistics is compared in high-resolution numerical simulations of supersonic isothermal turbulence with up to 1024^3 grid points. We demonstrate that the relative strength of solenoidal and compressive modes of the turbulence forcing has significant influence on the resulting density and velocity statistics. Two extreme cases are considered: 1) the usually adopted solenoidal forcing (divergence-free), i.e., turbulence is driven by a vortex field without any compressive component, and 2) compressive forcing (curl-free), where the forcing is a pure divergence field. Extensive studies of turbulence statistics have been presented in various works and our results are consistent with these studies using solenoidal forcing. We extend these studies and show that compressive forcing yields a Probability Density Function of the gas density, that is ~3 times broader than the corresponding solenoidal one. This has important consequences for analytical models of the Initial Mass Function, for which the width of the density-PDF is a key parameter. Additionally, we find that the Fourier spectrum functions of density fluctuations differ significantly between solenoidal and compressive forcing on scales above the sonic scale, while below the sonic scale, both forcing schemes asymptotically approach the subsonic incompressible limit. We furthermore demonstrate convergence of our results in terms of numerical resolution.



 Duncan Forgan

Institute for Astronomy, University of Edinburgh, SUPA

Introducing a Hybrid Method of Radiative Transfer for SPH [T]


I will introduce a new means of incorporating radiative transfer into smoothed particle hydrodynamics (SPH), 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.  I will describe this equation of state, as well as the construction of the hybrid method.  The method has been tested in several scenarios, the results of which I will show: (1) the evolution of a protoplanetary disc; (2) the collapse of a protostellar cloud, and (3) the thermal relaxation of temperature fluctuations in a static homogeneous sphere.



Sebastien Fromang

 CEA Saclay, France

 Numerical dissipation in MHD turbulence simulations performed with ZEUS [T]


 Using a set of simulations of MRI turbulence performed using the codes ZEUS (finite difference) and RAMSES (finite volume), I will describe various methods to quantify numerical dissipation in these codes. I will show that the results is not as simple as one might naively guess and discuss the consequences when applied to the problem of angular momentum transport in accretion disks.



Evghenii Gaburov

Leiden Observatory

 A star cluster on a desktop (1) [T]


Star clusters in the Milky Way contain up to hundreds of thousands of stars held together by gravitational interactions. As the vast majority of stars is formed in clusters, clusters provide crucial information on the star formation process. N-body simulations are frequently used to constrain the past and future evolution of star clusters. In these presentations we provide an overview of the different N-body techniques and their advantages and disadvantages. We discuss the birth, life, and death of a star cluster, and present several related applications.



Simon Glover

Institut fuer Theoretische Astrophysik, University of Heidelberg

Simulating chemically reactive flows in astrophysics [T]


Chemistry plays a key role in star formation in environments ranging from local GMCs to the earliest protogalaxies. In this talk, I will discuss some of the problems that one faces when trying to simulate the behaviour of chemically reactive gas, and how to go about solving them.


 C. McNally, J. Maron, S. Glover, M.-M. Mac Low

 GPM Lagrangian Hydrodynamics [P]


The Gradient Particle Method (GPM) is a quasi-Lagrangian particle-based method (originally presented in Maron & Howes, 2003) that allows fluid derivatives to be computed far more accurately than in SPH. We present several extensions of the original algorithm that allow GPM to cope with non-uniform particle distributions, enabling it to be used to model supersonic flows. We also compare its behaviour with SPH for several standard test problems.



 Manuel Neri Gómez

Centro de Radioastronomía y Astrofísica, UNAM

 Physical properties of interstellar atomic dense structures from  turbulent simulations [P]


We present a detailed study of the physical properties of atomic dense structures resulting from turbulent numerical simulations. Our simulations are 2d models of the atomic interstellar gas at 100pc, including thermal instability and random turbulent driving at different Mach numbers. For each simulation we study the  evolution of individual condensations and we compare the resulting trends for size, density, pressure, dynamical properties, and life time.



Simon Goodwin

Sheffield University

The collapse of cold fractal star clusters [T]


I will present simulations of the collapse of initially cold and clumpy star clusters. From these initial conditions I will show that dynamical mass segregation almost always results in only a crossing time. I will talk about how the setting-up of initial conditions is vital, and the interpretion of results often very problematic.



Oliver Gressel

Queen Mary University London

 Magnetic field amplification in turbulent flows [T]


 The magnetisation of the ISM displays an important initial condition for star formation. Magnetic fields are recognised to play a significant role in the fragmentation and rotational braking of protostellar cores. They are also a possible candidate for the regulation of star formation, and might thus explain the low observed SF efficiency. Moreover, magnetic fields influence the intermittent structure of the turbulent cascade, whose inertial range slope is a key parameter in understanding the initial core mass function.


Since the early works of Parker in the 1950s, it is well known that turbulent flows which lack certain symmetries can produce mean magnetic fields out of unordered motion. In the 1960s this phenomenon has been mathematically formalised in the framework of so-called mean-field MHD by Krause and Rädler. Based on this approach, the field amplification in the Sun, in convective stars, and even in galaxies can be studied by means of dynamo models. Within those large eddy simulations, one only considers the mean-flow, while the effect of the turbulence is modelled via the so-called alpha parameter. Recently, it has become possible to derive this closure parameter from direct simulations, e.g. of the turbulent ISM, by means of a passive tracer-field method. Here I give a short introduction on how this method is implemented numerically.



Matthias Gritschneder

University Observatory, Munich

Ionization in SPH Simulations: iVINE and VINERY [T]

We present two implementations of ionizing radiations in the tree-SPH code VINE: iVINE and VINERY. iVINE is a highly efficient parallelized approach which allows for high resolution simulations under the assumption of plane-parallel irradiation of the simulated area. VINERY, the combination of VINE and SPHRAY (Altay et al. 2008), is a Monte Carlo approach with a very efficient ray-shooting algorithm which allows for the simulation of point sources as well. In addition, we present some first  results. We show that radiation from hot stars penetrates the ISM, efficiently heats cold low density gas and amplifies over-densities seeded by the initial turbulence. The formation of observed pillar-like structures in star forming regions (e.g. in M16) can be explained by this scenario. At the tip of the pillars gravitational collapse can be induced, eventually leading to the formation of low mass stars.  Detailed analysis of the evolution of the turbulent spectra shows that UV-radiation indeed provides an excellent mechanism to sustain and even drive turbulence in the ISM. A wide range parameter study enables us to derive an analytic approach to determine the density and shape of the resulting pillars.



 Tim Harries
University of Exeter
 The simulation of line emission from protostars and discs [T]

Emission lines encode information on the geometry and dynamics of the gas and dust as it flows around and onto the protostar. In order to extract this information it is necessary to compute synthetic profiles and compare them with observations. This is a challenging problem, since it involves frequency-dependent radiative-transfer in a moving medium where departures from spherical symmetry are significant. In this talk I will review the techniques used to solve the rate equations in atoms and molecules and hence calculate line profiles in cores, discs, and magnetospheric accretion streams.


Calen Barnett Henderson

Vanderbilt University
A Search for Pre-Main Sequence Eclipsing Binary Stars in the Lagoon Nebula [P]


We report time-series CCD I-band photometry for the pre-main-sequence cluster NGC 6530, located within the Lagoon Nebula. The data were obtained with the 4Kx4K imager on the SMARTS 1.0m telescope at CTIO on 36 nights over the summers of 2005 and 2006. In total we have light curves for ~50,000 stars in an area ~1 deg2, with a sampling cadence of ~1 hour. The stars in our sample have masses in the range 0.25-4.0 M(sun), assuming a distance of 1.25 kpc to the cluster. Our goals are to look for stars with rotation periods and to identify eclipsing binary candidates. Here we present light curves of photometrically variable stars and potential eclipsing binary star systems. These light curves were derived in conjunction with ACCRE (Advanced Computing Center for Research and Education), the Vanderbilt University supercomputing center. We will test these data against current stellar evolution theories that predict specific relationships between a star’s mass, radius, temperature, and luminosity as a function of age. These relationships are important, as they are the basis for determining the fundamental properties of stars. Our measurements of these properties will test the basic theories that are central to the determination of stellar ages and masses. We will also examine the distribution of stellar rotation periods. This is essential to understanding how the angular momenta of stars evolve with time, a problem that remains one of the longest outstanding questions in star formation research.



Patrick Hennebelle

Ecole normale superieure, Observatoire de Paris

Pedagogical talk on Finite Difference Hydrodynamics [T]


Seyit Hocuk


Kapteyn Astronomical Institute, University of Groningen

The Metallicity and Rotational Moment Dependence of Molecular Cloud Fragmentation [P]



David Hubber

Oslo University

SPH in 60 mins [T]

Smoothed Particle Hydrodynamics (SPH) is one of the principle numerical algorithms used to study astrophysical fluid dynamics problems. We will review the fundamentals of SPH in detail including the derivation of the SPH equations, methods of including artificial dissipation and extending SPH to include self-gravity.  We will discuss various caveats that should be considered including the resolution requirements and sources of error in SPH simulations.  Finally, we briefly discuss algorithms and optimizations that can significantly speed up SPH simulations, such as trees, block time-stepping and sink particles.



Richard Jackson

 Astrophysics Group, Keele University UK

 Are the spin axes of stars randomly aligned in young  clusters? [P]

 

If the spin axes of stars in young clusters are randomly orientated in space, then it becomes possible, with measurements of period and projected equatorial velocity, to obtain accurate estimates of distance, mean age and age dispersion of the cluster (Jeffries 2007a,b). A new technique is presented which can be used to test this assumption. The inclination of a set of stars, found from their projected equatorial velocity, period and angular diameter is analyzed to determine whether their spin axes are randomly distributed in space or if there is a preferred direction of rotation. The method is used to assess the degree of alignment of stars in the Pleiades and Alpha-Persei clusters. Both clusters show results consistent with a uniform distribution. Using period and Vsini data to estimate distance to the Pleiades gives a result consistent with main sequence fitting and higher than the value found from Hipparcos measurements.



Anne-Katharina Jappsen

 Cardiff University, School of Physics and Astronomy

The influence of  thermodynamics on the star formation process [T]


 The thermodynamic behavior of the star-forming gas plays a crucial role in fragmentation and determines the stellar mass function as well as the dynamic properties of the formed stars. This holds for star formation in molecular clouds in the solar neighborhood as well as for the formation of the very first stars in the early universe. In this talk, I will discuss results from various numerical simulations of star cluster formation and show how the thermodynamic state of the turbulent interstellar medium influences the collapse of the star-forming gas.



Rob Jeffries

Keele University

Tests of Early Stellar Evolution Models [T]


I will review the current status of a number of observational tests of evolutionary models, covering the period of time between the emergence of a star as a class II object and its approach to the main sequence. Topics will include the mass-radius relationship; age spreads in young clusters and lithium depletion.



Amit Kashi

 Technion - Israel Institute of Technology

Physical processes during the periastron passage of Eta Carinae [P]

Eta Carinae is a unique massive binary star system in our Galaxy, presenting some basic undetermined parameters and open questions. Its 5.54 year periodicity in a very eccentric orbit is observed in all wavelengths. We identify the important physical processes that we expect to take place at periastron passage, and use these to explain observations. In particular, we show that mass accretion onto the companion is expected to occur, and might explain some basic observations. For example, the accreted mass possesses enough angular momentum to form a thick disk, or a belt, around the secondary, and shut down the secondary wind for about ten weeks. After periastron the belt dissipates as its mass is blown away by the reestablished secondary wind. We also study the wind collision in detail, and come up with straightforward explanations to some key observations, like Doppler shifts, X-ray absorption, and the absorption of the He I 10830 lines.



Jongsoo Kim

Canvendish Astrophysics Group, and Korea Astronomy and Space Science Institute

An Explicit Scheme for Incorporating Ambipolar Diffusion in a Magnetohydrodynamics Code [P]


We describe a method for incorporating single-fluid ambipolar diffusion in thestrong coupling approximation into a multidimensional magnetohydrodynamic code based on the total variation diminishing |scheme. Contributions from am-bipolar diffusion terms are included by explicit finite difference operators in a fully unsplit way, maintaining second order accuracy. The divergence-free condition of magnetic fields is exactly ensured at all times by a flux-interpolated constrained transport scheme. The super time stepping method is used to accelerate the timestep in high resolution calculations and/or in strong ambipolar diffusion. We perform two test problems, the steady-state oblique C-type shocks and the decay of Alfven waves, confirming the accuracy and robustness of our numerical approach. Results from the simulations of the compressible MHD turbulence with ambipolar diffusion show the flexibility of our method as well as its  ability to follow complex MHD flows in the presence of ambipolar diffusion.These simulations show that the dissipation rate of MHD turbulence is strongly affected by the strength of ambipolar diffusion.



 Pamela Klaassen

ESO

 Rotation in Regions of Massive Star Formation [P]


The processes involved in the formation of massive stars is not nearly as well understood as those for lower mass stars.  For instance, stable circumstellar disks have been observed towards a large number of low mass protostars, while the short formation timescales and large average distances to massive star forming regions make it much more challenging to observe such phenomena.  We do not yet have the resolution and sensitivity required to observe disks around all but the closest massive star forming regions (this will require the capabilities of ALMA), but here we present evidence for rotating ionized and molecular gas in a few massive star forming regions.  With the Submillimeter Array and Very Large Array, we consistently see what appears to be Keplerian rotation of the hot and warm gas in and around these ultracompact HII regions.  This suggests that we may be able to see smaller disk like structures at higher resolution.



Thijs Kouwenhoven

Sheffield University

 A star cluster on a desktop (2) [T]


Star clusters in the Milky Way contain up to hundreds of thousands of stars held together by gravitational interactions. As the vast majority of stars is formed in clusters, clusters provide crucial information on the star formation process. N-body simulations are frequently used to constrain the past and future evolution of star clusters. In these presentations we provide an overview of the different N-body techniques and their advantages and disadvantages. We discuss the birth, life, and death of a star cluster, and present several related applications.




Giuseppe Lodato 

University of Leicester (UK)/University of Milan (Italy)

Angular momentum transport in protostellar discs: clues from SPH simulations of self-gravitating discs [T]



Andres Suarez Madrigal

Centro de Radioastronomia y Astrofisica, UNAM

Wavelet analysis of a molecular cloud in simulations [P]


Recent studies have given emphasis to the idea that molecular cloud cores'  environment can influence the evolution of the cores themselves. The  present study applies a wavelet analysis to a numerical simulation of  an evolving molecular cloud. Such an analysis allows to filter out the  large-scale emission from images, leaving small-scale emission only.  We found that, by discriminating emission from large-scale structures, cores that indeed proceed to collapse appear to be gravitationally unbound in the analysis. This result stresses the importance of the environment inside molecular clouds and suggests that obtaining cores? masses via a wavelet analysis may result in an underestimation of their actual mass.



 George Mamatsashvili

Institute for Astronomy, University of Edinburgh

Vortices in self-gravitating gaseous discs [P]


Vortices are believed to greatly help the formation of km sized planetesimals by collecting dust particles in their centers. However, vortex dynamics is commonly studied in non-self-gravitating disks. The main goal here is to examine the effects of disk self-gravity on the vortex dynamics via numerical simulations. In the self-gravitating case, when quasi-steady gravitoturbulent state is reached, vortices appear as transient structures undergoing recurring phases of formation, growth to sizes comparable to a local Jeans scale, and eventual shearing and destruction due to gravitational instability. Each phase lasts over 2 orbital or less periods. Vortices and density waves appear to be coupled implying that, in general, one should consider both vortex and density wave modes for a proper understanding of self-gravitating disk dynamics. Although this study is in the context of protoplanetary discs, the results can be applied to any self-gravitating disc. For example, AGN disc out of which stars form.



Milica Milosavljevic

 Institute for Theoretical Astrophysics, Heidelberg, Germany

Stability of organic molecules against shocks in the early Solar nebula [P]


One of the fundamental astrobiology questions is how life has formed in our Solar System. In this context the formation and stability of abiotic organic molecules such as CH4, formic acid and amino acids, is important for understanding how organic material has formed and survived shocks and energetic particle impact from winds in the early Solar System. Shock waves have been suggested as a plausible scenario to create chondrules, small meteoritic components that have been completely molten by energetic events such as shocks and high velocity particle impacts. We study here the formation and destruction of certain gas-phase molecules such as methane and water during such shock events and compare the chemical timescales with the timescales for shocks arising from gravitational instabilities in a protosolar nebula.



Nickolas Moeckel

University of St Andrews

 Testing binary formation scenarios with SPH [T]


I will present results of experiments testing two routes toward massive binary formation.  The first method, capture of a passing star by a massive protostellar disk, is tested with SPH simulations of star-disk encounters.  I will discuss how these results are incorporated into an N-body code.  Secondly, I will present experiments wherein we extract accretion information from a large-scale SPH simulation, and re-simulate accretion onto a proto-binary at much higher resolution.



 Takanori Nagakura

National Astronomical Observatory of Japan

 Evolution of a supernova shell and triggered star formation in low-metallicity [P]


 We study the evolution of a single supernova remnant and a dense shell triggered by the explosion under low-metallicity  environments (10^{-4}< Z/Zsun<10^{-2}),  using one-dimensional hydrodynamics simulations with non-equilibrium radiative cooling. We find that regardless of the metallicity, the mean shell temperature can decrease enough if the shell acquires a large amount of the surrounding medium. Such a cooled and dense shell is expected to become gravitationally unstable and fragment into stars.  We constrain the ambient density, explosion energy, and metallicity where the shell fragments through gravitational instability by utilizing a linear stability analysis of an expanding  and decelerating shell suggested by Elmegreen.  We find that the conditions for the shell fragmentation depend heavily on the ambient density and explosion energy, while hardly on the metallicity.



Dave Nutter
Cardiff University

JCMT Gould Belt Legacy Survey [P]


With the James Clerk Maxwell Telescope (JCMT) Gould Belt Legacy Survey, we will map almost all of the well-known star-formation regions within 0.5 kpc with the Submillimetre Common User Bolometer Array 2 (SCUBA2). Most of these regions are associated with a ring of star formation, known as the Gould Belt. We will produce a flux-limited snapshot of nearby star formation over almost 700 deg2 of sky.  The resulting images will yield the first catalogue of prestellar and protostellar sources selected by submillimetre continuum emission. We will also obtain maps of a large sample of prestellar and protostellar sources in three CO isotopologues using the Heterodyne Array Receiver Program (HARP). Finally, we will map the brightest hundred sources with the SCUBA2 polarimeter (POL-2), producing the first statistically significant set of polarization maps in the submillimetre.


Jan Palous

 Astronomical Institute, Academy of Sciences of the Czech Republic

Expanding shells, massive star clusters and gas stripping of galaxies [T]



Richard Parker

Sheffield University

The Initial Binary Population in Star Clusters [T]


Recent work on constraining the initial binary fraction and separation distributions of M-dwarf binary systems in Orion-like clusters using N-body  simulations is presented. In addition, I describe current work to explain the observed characteristics of brown dwarf-brown dwarf binaries and M-dwarf-brown dwarf binary systems. I also detail the input physics and model set-up required to conduct efficient N-body simulations of such clusters.



Dieter Poelman

 University of St. Andrews

 Rotational line emission from water in protoplanetary disks [T]

 One of the most fundamental questions to date in modern astrophysics is how stars and planets form. Protoplanetary disk evolution and planet formation are closely entangled. Therefore, to understand their formation mechanisms, one first needs to develop a comprehensive picture of the physical and chemical conditions in protoplanetary disks. In this talk, I will present recent work in combining a thermal-chemical model of a typical T Tauri star disk with a molecular line radiative transfer program to investigate the diagnostic potential of the far-infrared lines of water. I discuss the observability of pure rotational water lines with the Herschel Space Observatory.




Basmah Riaz
Instituto de Astrofisica de Canarias

A study of a depply-embedded low-mass protostellar system in the B59 molecular cloud [P]



Ken Rice

Institute for Astronomy, University of Edinburgh

Using SPH, with realistic thermodynamics, for simulations of star and planet formation [T]


Smoothed Particle Hydrodynamics (SPH) is a highly versatile code that is very suitable for modelling systems with complex geometries.  In particular it has been very successful in simulations of the collapse of molecular clouds to form stars and the evolution of planet forming discs around young stars.  It has, however, often been criticised for not necessarily modelling all the physical processes particularly well.  In this talk I will discuss why this is indeed important and give some examples of recent work, using SPH that includes detailed thermodynamics and radiation transfer. 



Boyke Rochau

Max Planck Institute for Astronomy, Heidelberg, Germany

Starburst Cluster of the Milky Way [P]


Starburst clusters are spectacular young and dense stellar systems containing copious numbers of massive O-type and Wolf-Rayet stars. As Milky Way starburst clusters can be found either in spiral arms or in den Galactic center region, studies in general suffer from a significant amount of contamination by foreground and field stars. With high quality astrometric observations we can distinguish cluster members from field stars based on their proper motions. Multi epoch observations provide time-baselines of several years and subsequent high precision proper motion measurements used to identify cluster members and to derive a 2D velocity dispersion. It helps to shed light on the internal dynamics of these young and dense stellar systems. Here we focus on the NGC 3603 Young Cluster located in the Carina spiral arm. By analysing two epochs of HST/WFPC2 observations taken 10 years apart, we can trace proper motions with an accuracy comparable to the internal velocity dispersion. These observations will help us to improve our understanding of massive star formation in the Milky Way and, furthermore, these clusters can be used as templates for massive, extragalactic star formation as observed in e.g. the Antennae Galaxies.



Giuseppe Germano Sacco

INAF-Osservatorio Astronomico di Palermo

Hydrodynamic modeling of accretion shock on CTTSs [P]


We investigate the dynamics and the stability of shock-heated accreting material in classical T-Tauri stars and the role of the stellar chromosphere in determining the position and the thickness of the shocked region by performing one-dimensional simulations of the impact of an accretion flow on the chromosphere of a CTTS. Our model includes the effects of gravity, radiative losses from optically thin plasma, thermal conduction and a well tested detailed model of the stellar chromosphere. We present the results of a set of simulations  exploring the  domain of the physical parameters of the system, namely the density, the velocity and the heavy elements abundances.  We also present preliminary results of a 2D simulation.



 Vojtech Sidorin

Astronomical Institute of the Academy of Sciences of the Czech Republic

 Multiwavelength Study of Expanding H I Shells in the Milky Way [P]

CONTEXT. Our Galaxy, when viewed in the neutral hydrogen line, resembles a sponge. It is a turbulent environment with a plethora of holes, bubbles and filaments. Thousands of these holes and bubbles have been found so far but only a fraction of them are actually expanding (growing). These expanding structures are commonly refered as H I shells. H I shells are thought to be created by the stellar winds and supernovae explosions of OB associations. Alternative explanations are that they may be created by collisions of high-velocity clouds with the Galactic disc or by some violent event associated with gamma-ray bursts. H I shells are also thought to trigger star formation either via fragmentation of their borders or via expanding into a preexisting molecular cloud.

OUR RESEARCH. We have analyzed multiwavelength images of twelve H I shells in order to test the possible theories of the shells' origin and to look for areas of possible star formation triggered by the shells. On the poster, we present an example of the analysis of a shell in Orion. We also present a short summary of the research and introduce briefly our ongoing research.



Rowan J Smith

University of St-Andrews

Tracing the Evolution of Pre-Stellar Clumps [P]


We present an analysis of star-forming clumps of gas in an SPH simulation of a Giant Molecular Cloud. We identify gas clumps using their deep potential wells to ensure that the clumps are likely to form stars. Clumps identified using gravitational potential should be more reliable than density clumps as density distributions are noisy and clump boundaries hard to define. Moreover, there is a reasonable expectation that a potential clump is bound.  It is then possible to trace the evolution of the clumps forward in time and investigate the connection between the original clump mass and the resulting stellar mass. Is there a one-to-one connection, or do dynamical interactions complicate things?



 Loredana Spezzi

 Research and Scientific Support Department, European Space Agency (ESTEC)

 Probing the mass accretion process in the field of SN1987A [P]


Many efforts have been made in recent years to quantify the rate of mass accretion in disks around young stellar objects. The mass accretion rate is a key parameter for understanding disk structure and evolution, as well as planet formation and migration. In this contribute, we present the first results of a study of the stellar population in an area around the supernova SN1987A in the Large Magellanic Cloud. Our study is based on multiband HST+WFPC2 observations. We determine the mass accretion rate of pre-main sequence stars with no need for spectroscopic observations. The method relies solely on narrow-band (H_alpha) and broad-band photometry and can therefore be efficiently applied to star-forming regions extending over wide areas on the sky.



Dimitris Stamatellos

Cardiff University

The formation of brown dwarfs in discs: physics and numerics [T]

We suggest that stars like the Sun should sometimes form with massive (a few 0.1 Msun), extended (a few hundred AU) discs, and we show by means of radiative hydrodynamic simulations that the outer parts (>100 AU) of such discs are likely to fragment on a dynamical time-scale, forming low-mass objects: principally brown dwarfs, but also low-mass hydrogen-burning stars and planetary-mass objects. We will examine the conditions for disc fragmentation and the role of disc thermodynamics. Finally, we shall briefly discuss the properties of the objects produced by the mechanism of disc fragmentation, and show that the formation of low-mass objects by disc fragmentation explains the brown dwarf desert and the binary properties of low-mass stars and brown dwarfs.



Mario Tafalla

Observatorio Astronomico Nacional, Spain

Determining molecular abundances in starless cores [T]


Starless dense cores are the simplest sites of star formation, and their study can be used to determine the initial conditions and main physical processes that are involved in the birth of a star. For a number of years, the study of dense cores was plagued by conflicting results from observations made using different molecular tracers. A recent combination of detailed analysis and chemical modeling has demonstrated that most of the inconsistencies between observations resulted from  the cores having an inhomogeneous chemical composition caused by the depletion of most species onto the dust grains in the cold and dense interior of the cores. In this talk, I will show how observations of cores can be used to infer the chemical structure of dense cores, and how chemistry can be used to reconstruct the contraction history of the gas. I will also show how the core chemical structure has a profound effect on the observations, and how any model of core formation needs to include  a realistic chemical composition in order for its predictions be testable with observations.



Bernd Völkl

ITA Heidelberg

Radiative Cooling with FLASH [P]


We implement a method to account for radiative transfer effects (based on Stamatellos, Whitworth, Bisbas, Goodwin, 2007, A&A, 475, 37) in the hydrodynamics code FLASH. The method estimates a mean column density and a mean optical depth which then regulates the heating and cooling of each grid cell. We test the implementation on protostellar collapse scenarios. The results obtained are in good agreement with the literature.



Steffi Walch

Cardiff University

The Formation & Early Evolution of Protostellar Disks around Low-Mass Stars [T]

                 

Pre- and protostellar cores are highly obscured. As a result the  collapse phase of protostellar cores as well as the early embedded  stages of forming stars are only poorly understood. The missing pieces in the puzzle of low-mass star and disk formation  can only be replaced by ambitious numerical studies.

We present and compare high-resolution, 3D SPH simulations of  isolated molecular cloud core collapse conducted with VINE.  We model the initial cores as slightly supercritical Bonnor-Ebert spheres.  The observed amount of core angular momentum may be explained by regular  rotation or by sub-/transonic turbulence. Depending on each specific case one or the other model is in better agreement with observed velocity gradient  maps. Within this framework, the density and temperature evolution of the  forming star+disk system are in the center of this study.

We address the questions: 1) Are disks, which were formed from turbulent cores comparable to disks from  rigidly rotating cores concerning size and mass? 2) Is a disk's temperature evolution strongly influenced by the distribution  of the infalling gas? This would lead to a modified temperature structure in  an early evolutionary state of turbulent disk formation. 3) Are the fragmentation properties of subsonically turbulent cores essentially different from the properties of cores in rigid rotation?

We also discuss the influence of different treatments  of the SPH artificial viscosity on the disk fragmentation properties and on the redistribution of angular momentum during the simulation.



 Malcolm Walmsley

 Arcetri

 The competition between depletion and collapse [T]


Molecular depletion onto the surface of cold dust grains has been shown to be effective for most species at densities above  3 10^4 cm-3.  There are however exceptions to this such as the N-containing species N2H+ and NH3 and their deuterated counterparts.  It is not clear why there is this exception and moreover it is puzzling that the critical density for depletion is as high as the value of 3 10^4 cm-3 given above. Most recently moreover, there has been found evidence for some C-containing species (CN,HCN,HNC) at densities above 10^5 cm-3  in a couple of cases. These puzzles matter because one would like to use depletion as a measure of core age and this is difficult until one understands the chemistry in a collapsing core. Presently, our conclusion is that the dynamical timescales of well observed cores is unlikely to be much more than a free fall time.  I will summarise the present state of our misunderstanding.



Richard Wunsch

Cardiff University

Gravitational fragmentation of the expanding shell [T]


Due to their ionising radiation, stellar winds and supernova explosions, massive stars insert large amounts of energy into the interstellar medium. It leads to the formation of more or less spherical bubbles surrounded by dense cold shells of the swept up ambient medium. These shells may become gravitationally unstable and condense into new stars. We study the gravitational instability of the expanding shell on a highly idealised model of the momentum driven shell which helps us to avoid other hydrodynamic instabilities. We use the AMR code FLASH and the new tree-based gravity solver. We show that the perturbation growth rate as a function of wavelength depends on the external pressure which confines the shell. This results is in contradiction with the analytical theory based on the thin shell approximation.