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Parameter Study In Disk Jet Systems: Authors: Tzeferacos Petros 1, Ferrari Attilio 1, Mignone Andrea 1,2, Bodo Gianluigi 2, Massaglia Silvano 1, Zanni Claudio 3 1 Dipartimento di Fisica Generale, Universita’ degli Studi di Torino,Italy 2 INAF/Osservatorio Astronomico di Torino,Italy 3 Laboratoire de l’Observatoire de Grenoble,France 5th JetSet school, Galway, DIAS, Ireland, 12.01.2008 : A Focus on Equipartition

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Overview Introduction Numerical Setup/Parameters Results Conclusions

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Constrains on YSOs YSO Jets YSO Jets Well Collimated Magnetically driven Length 0.1-10 pc Age ~10 5 yr Temperature ~ 10 3 - 10 4 0 K Velocity ~ 100-300 km s -1 dM/dt ~ 10 -9 - 10 -7 M sun yr -1 (Bally & Reipurth, 2002) Central Object &Disk The majority are low mass stars (<5 M sun ) Surrounded by accretion disks (rad~10 2 -10 3 AU) dM acc /dt ~10 -8 -10 -6 M sun yr -1 t survival ~ 10 6 -10 7 yr (Siess et al. 1998) (Siess et al. 1998)

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Initial conditions (tabulating the disk) Radial Self Similarity at the equator (Blandford & Payne.1982) Assume equatorial symmetry (r axis) Assume axisymmetry (z axis) Fill the domain from bottom to top solving the equilibrium equations for both directions, using a second order approximation Over impose a static hot corona in equilibrium with the disk’s surface

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boundary conditions (equatorial & axial symmetry, open boundaries) We define at the borders of the domain and the sink the behavior of primitive variables R,Z axis → equatorial & axial symmetry The “open” boundaries assume outflow condition (zero gradient) for all variables except for V phi and the magnetic field Ghost zones of the sink region are treated as the respective boundaries of the domain Uniform Resolution [256,768] Pluto Code (Mignone et al. 2007)

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Parameters Normalization of the MHD equations yields 7 non-dimensional parameters that can be chosen arbitrarily (almost !!! ) Normalization of the MHD equations yields 7 non-dimensional parameters that can be chosen arbitrarily (almost !!! ) } Calculated at z=0 } m : initial field inclination (Blandford & Payne criterion) α m : resistivity parameter (Shakura & Sunyaev. 1973) f : cooling function (currently all ohmic heating is radiated away) δ : corona to disk density ratio χ m : anisotropy parameter Case 0 Case 1 Case 2 Case 3 Case 4 Case 5 μ0.10.3130.30.3 α11110.10.1 χmχmχmχm33331003

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← Magnetic field lines (on the background is displayed the logarithm of density) Poloidal current → Case1

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Evolved outflow & magnetic field case0 case1 case2 case3 case4 case5 (μ study) (anisotropy) (μ study) (anisotropy)

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acceleration of the outflow, crossing the critical surfaces case0 case1 case2 case3 The alfvenic surface is crossed only for values small values of μ ) at least within the computation- al box. The alfvenic surface is crossed only for values small values of μ ) at least within the computation- al box. Only in cases 0,1 the outflow becomes super fast Only in cases 0,1 the outflow becomes super fast

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acceleration mechanism (ІB phi І /B p ) case0 case1 case2 case3 (only grad Bphi) (only co-rotation) (only grad Bphi) (only co-rotation) magnetically driven! The ratio between Bφ and Bp gives a good perspective of the dominant mechanism |Bφ| /Bp<1 →co- rotation, centrifugal acceleration |Bφ| /Bp>1 →gradient of Bφ along the field lines is the main accelerating mechanism In all: Magneto- centrifugal acceleration

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case0case1case2case3case4case5 2Mj/Μa 0.190.270.36 (0.99) 0.560.38 ξ0.080.110.15 (~1) 0.280.18 Mj0.0070.0130.010(0.013)0.0110.017 Macc0.0740.0940.049(0.029)0.0430.089 Ejection efficiency In all cases we calculated the final ratio 2 (dMej/dt) / (dMacc/dt) as well as the ejection index ξ In all cases but case3 we have a plateau in the time evolution of the ratio The ejection index increases as the plasma beta decreases Low diffusivity cases show elevated indexes in comparison to case1

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* A well known signature of the magneto-centrifugal acceleration mechanism is the transformation of magnetic (poynting flux) to kinetic * This is shown in cases 1,2 from the poynting over kinetic flux ratio that is high near the disk drops by 1-2 orders of magnitude (less than unity) at higher altitudes Energy transformation along the outflow

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>We have super alfvenic outflows for cases 0,1,2,4,5 and the final velocity reached is of the expected order of magnitude (~100-150 Km s -1 )*. Only cases 0, 1 become superfast in the domain. > The acceleration mechanism is magneto-centrifugal, mainly megnetic pressure for low μ and co-rotation for high μ. > The outflow collimates through hoop stress (no artificial collimation) > Accretion rates are of the order of 10 -8 M sun y -1 whereas ejection rates are ~10 -9 M sun y -1 * > Mass ejection efficiency increases with μ. Conclusions

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> Significant increase in the ejection efficiency is observed for for low a configurations (in agreement with Zanni et al. 2007) > The highly anisotropic / low resistivity configuration settles in a steady outflow configuration (as predicted in Casse & Ferreira 2000a) > Straying away from equipartition brings either distorted magnetic field topologies (weak collimation) or inefficient acceleration (inability to cross critical surfaces) > Returning current sheet at the innermost region of the disk as well as some artificial heating due to dissipation in the disk’s surface produces elevated mass loading thus it is explained the higher values of ξ. Conclusions

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Go raibh maith agat (presumably “thank you”) for your attention!

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Reference [1] Zanni, C., Ferrari, A., Rosner, R., et al., 2007, A&A, 469, 811 [2] Mignone, A., Bodo, G., Massaglia, S., et al., 2007, ApJS, 170, 228 [3] Ferreira, J. & Pelletier, G., 1995, A&A, 295, 807 [4] Ferreira, J., 1997, A&A, 319, 340 [5] Casse, F. & Ferreira, J. 2000a, A&A, 353, 1115 [6] Ferrari, A., 1998, ARA&A, 36,539 [7] Ferrari, A., 2004, Ap&SS, 293, 15 [8] Blandford, R.D. & Payne, D.G., 1982, MNRAS, 199, 883 [9] Pudritz, R.E., Oyed, R., Fendt, C. & Brandenburg, A., 2006, in “Protostarts and Planets V”, B. Reipurth, D. Jewitt and K. Keil (eds.), University Arizona Press, Tucson, p. 277 [10] Shakura, N.I. & Sunyaev, R.A., 1973, A&A, 24, 337 [11] Powell, K.G., Roe P.L., Linde, T.J., Gombosi, T.I. & DeZeew, D.L., 1999, JCP, 154, 284

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