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has formed. Recent direct detections of the magnetic field configuration in the protostellar accretion disc FU Orionis confirm the idea that magnetic fields are wound up and pinched in such a disc (Donati et al., 2005). The lack of a strong collimated outflow from this object could be due to a strong magnetic braking effect which slows down the disc plasma. We proposed a follow-up observation of this protostar (Jean-Francois Donati being the principal investigator) with the ESPaDOnS instrument on the Canada-France-Hawaii Telescope (CFHT). Within the proposed 15 day observational period we hope to get clear Zeeman signatures which will reveal in unprecedented detail the magnetic field structure in this object. We also studied the influence of magnetic fields during the collapse of massive molecular cores (Banerjee & Pudritz, 2007). For a similar setup than described above but a higher core mass (M ∼ 170M⊙) we could show that outflows and jets can be launched by the same mechanism than in low-mass case (see Figure 7). Even if these outflows are not long lived, i.e. do not propagate far into the cloud, this has particular interesting implications for massive star formation: These outflows and jets will punch cavities into the infalling envelope. It is known that radiation, then emitted from the young massive star, will choose the way of least resistance and escape through the outflow carved cavities (Krumholz et al., 2005b). Krumholz et al. showed that these radiation funnels lower the radiation pressure exerted on the gas next to the funnels and the disc. Therefore, upper mass limits for massive stars derived from radiation pressure (e.g., Wolfire & Cassinelli, 1987) will be weakened or even removed by this mechanism. Another implication due to outflows and magnetic fields comes from the extraction of angular momentum. Disc winds extract angular momentum while physically removing gas with nonvanishing specific angular momentum from the disc. Magnetic fields exert torques on the disc if their field lines connect fast and slowly circulating gas at the same time (e.g., Pudritz, 2003). Typically, the disc fields connect to slower rotating gas further out (like in the case where the magnetic field is dragged inwards by the infalling gas) and the resulting torques spin down the disc. This in turn will increase accretion as gas with high specific angular momentum at the edge of the disc can settle deeper into the gravitational potential. By removing angular momentum from the disc magnetic fields and outflows can actually help to assemble massive stars quickly. In Banerjee & Pudritz (2006) we showed that the magnetic torque and the angular momentum loss by the disc wind are comparable to the angular momentum gain by the infalling gas. In Section 3.1 we discuss how we will extend and improve the work we did so far on studying outflows and jets. In particular, with the prospective sink particle approach we will be able to study these outflows for much longer dynamical time and more rational periods. Driving of Supersonic Turbulence Massive stars are formed in an environment of supersonic turbulence (e.g., Elmegreen & Scalo, 2004; Mac Low & Klessen, 2004; Ballesteros-Paredes et al., 2007). It is known that supersonic turbulence decays quickly and has to be continuously driven to maintain (e.g., Stone et al., 1998; Mac Low et al., 1998; Padoan et al., 1999). So far we do not have a conclusive mechanism which could serve as a driving source for the observed supersonic turbulence in molecular clouds. Many proposals have been made among are such which inject energy into the gas from inside the cloud. Norman & Silk (1980) firstly proposed that jets from YSOs could sufficiently stir up their environment. This is an interesting idea in the context of turbulence regulated star formation. Supersonic turbulence can, on small scales, prevent star formation because here it supports the gas against gravity. On large scales, it can compress enough gas in clumps and cores which can become supercritical 12
Figure 8: Summarises the main results form our study on jet-driven turbulence. The left panel shows probability density functions (PDFs) of the velocity distribution in the gas at different times (dimensionless units). The PDFs are normalised to the volume which is affected by the jet and can be interpreted as volume fractions which are occupied by a certain velocity interval. The jet itself, here Mach 10, is clearly visible in the peak at v/c = 10. Apart from it, almost non supersonic fluctuations are excited by the jet although it is driven continuously. Most of the fluctuations are highly sub-sonic and peak below v/c < 0.1. The reason is that supersonic fluctuations do not propagate far from its source and decay quickly in time as can be seen in the right panel. Here, we show the evolution of the kinetic energy for the supersonic (v > c) and subsonic (v < c) regime separately. After the driving force is shut off at t = 1.3 the supersonic part of the energy decays much faster than the subsonic part. From the evolution of the total energy it is also obvious that the energy is transfered from the supersonic to the subsonic regime. Graphs taken from Banerjee, Klessen, & Fendt (2007). and collapse under their own weight, therefore initiate star formation. If YSO jets could maintain supersonic turbulence on all scales star formation within a molecular cloud would be a self-regulating process. In a recent study we re-addressed the question of of jet-driven turbulence (Banerjee, Klessen, & Fendt, 2007). For this investigation we used again numerical two and three-dimensional simulations performed with the FLASH code. Here we model the supersonic jet as a momentum injection from one side of the simulation box. The jet diameter is only a small fraction of the side length of the simulation box which allows us to simulate the jet for many sound crossing times until the gas will leave the box (we use outflow boundary conditions). We can vary various parameters of the jet and the background properties. Among these are the jet speed, the density and pressure of jet, the duration of the jet, the strength and orientation of a background magnetic field, and we can set up clumps with which the jet interacts. If jets are the driving source of supersonic turbulence in molecular clouds they should entrain a large fraction of the surrounding gas and excite supersonic fluctuations in it. Supersonic jets running into a gaseous medium develop a bow shock at their tip which opening angle depends on the speed of the jet. The opening angle is smaller for faster jets and becomes very narrow for highly supersonic jets (vjet > 10c). It is mainly this bow shock which entrains the surrounding gas as long as the jet does not become unstable. But, the velocity in the bow shock region decreases with increasing distance from the jet axis and becomes subsonic shortly beyond the edge of the jet. Usually, instabilities develop at the edge of the jet. Due to shear flows Kelvin-Helmholtz instabilities can build up at the boundary layers between the moving jet and the non-moving surrounding gas. These instabilities are most prominent if the jet moves with transonic speeds, i.e. close to the sound velocity. For highly supersonic jets, as 13
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Page 8 and 9: Figure 2: Shows the evolution of th
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Page 18 and 19: • What is the influence of outflo
Page 20 and 21: Second year At the end of the first
Page 22 and 23: intensity field. Such approximation
Page 24 and 25: • Modelling of jets and outflows
Page 26 and 27: winds and disc-driven outflows. How
Page 28 and 29: 4. Requested Funding 4.1 Personnel
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Page 32 and 33: 8. Attachments a) Curricula vitae b
Page 34 and 35: Goldsmith, P. F. 2001, ApJ, 557, 73

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