Max Planck Institute for Astronomy - Annual Report 2005

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64 III. Scientific Work z [AU] 1 0 −1 800 600 1000 1�10 –14 800 400 0 0.5 1.0 r [AU] 1.5 2.0 Fig. III.2.1: A dust torus is illuminated by a central source. The dotted lines indicate the density distribution of the dust. The colors illustrate the temperature distribution (bright � hot) determined with the »diffusion plus ray-tracing« algorithm. The corresponding lines of constant temperature are drawn as solid lines. For comparison, the dashed line shows the result from the more accurate continuum radiative transfer. The local error of the sound velocity in this test was always below 5 %. A Bit Closer to the Ideal Case: Inverse 3D Radiative Transfer When images of an object are available it would be desirable for the interpretation of the observational results to directly calculate a density and temperature distribution from the telescope images. However, the calculation of the radiation field for a given distribution is so complex that an inversion is possible only for very simply structured objects. For modeling telescope images one therefore has to rely on multiple iterations, varying the density and temperature distribution. A glance at the spatially 600 600 resolved dust distributions around young stars suffices to realize that filamentary or ellipsoidal distributions have to be assumed in almost all cases. And for these, modeling is virtually out of question because it takes too long to calculate a configuration. Scientists at MPIA, together with colleagues from Bordeaux and Potsdam, succeeded in calculating the first 3D-model of a condensation in the molecular cloud near rho Ophiuchi. This starless core is a good example of the initial stage of star formation where a protostar is forming by gravitational collapse of the core. For the core IsocaM maps at 7 and 15 µm wavelength were available, where it is visible in absorption against the infrared radiation of the background region as a complex structure divided in two main clumps. In a map obtained with the IraM-30-mtelescope in the long-wavelength mm-region, however, the core was detectable by emission of cold dust. The complex geometry of the distribution precluded a simple modeling with a 1D- or 2D-model. So 30 clumps with a three-dimensional Gaussian density distribution were used that were variable in their position, their axial ratio and their overall density. With the help of the optimizing algorithm »simulated annealing« the clumps were shifted and deformed in such a way that the measured absorption in the mid-infrared range at a given background radiation was exactly reproduced. However, the distribution of the clumps along the line of sight and their shapes could not be obtained by this alone. But since the dust emission in the mm-range is sensitive to the particular shape of the core it could be used to infer the missing 3D-information. For the calculation of the mm-emission the scientists made use of the fact that the temperature witin the core mainly depends on the mean optical depth of the radiation entering from the outside. This dependence varied with the translation and distortion of the clumps by less than 1 K in temperature and could be calculated before the actual modeling within the so-called T-tau method by using a 3D-program for the transfer of continuum radiation. The density distribution determined this way shows many local maxima, with a compact southern absolute maximum. Comparison with hydrodynamic simulations, which also allow for turbulent motions, shows that such maxima can be of transient nature and may disappear on the dynamical timescale of the turbulence. But because of the high density and compactness of the southern maximum it can be expected not to dissolve and even to collapse. Complex structures as often found in star formation regions have many free parameters which have to be determined by comparison with observations. The new inverse 3D-radiative-transport-method, however, is based on a simultaneous modeling of several maps containing several thousand pixels and is therefore well-defined. The development of three-dimensional models is also a natural consequence of the fact that many observations show a clearly resolved three-dimensional structure where conventional one-and two-dimensional models fail.
An important aspect of the modeling are the properties of the absorbing and emitting dust particles, which are assumed to be constant. Especially in cool molecular clouds, however, the particles could grow by coagulation thereby changing their optical properties. Besides the shape, the chemical composition of the dust grains (the thickness of possible ice mantles, e.g.) has still to be determined and is subject of current research. Future models will have to take into account such a differentiation. What Do Molecular Lines Tell Us about Star Formation? The common feature of the prestellar cores and disks is that they are well shielded from ionizing interstellar or stellar radiation, leading to low internal temperatures. Under such conditions many complex molecular species can be formed and survive, most notably CO, CS, N 2 H + . R [AU] 300 200 100 0 100 8 2 4 200 300 R [AU] 6 Z log nH2 [1/cm 9 3 ] III.2 Radiative Transfer – Link between Simulation and Observation 65 Stellar UV radiation 8 7 6 5 4 3 2 1 Each molecule rotates and emits radiation at certain radio frequencies. The energy state of the rotation can be changed by collisions with other species, like H 2 , or by interactions with photons. The radio emission of a hundred molecules has been detected in space so far. Using an antenna or antenna array with a good spectral and spatial resolution, we can image these objects in various molecular lines in detail. Molecular line observations allow physical condition and chemical composition of prestellar cores and circumstellar disks to be constrained. The major difficulty here is that the main component of the medium, H 2 , which constitutes about 80 percent of the mass, is not easily observable. Therefore, we have to rely on other indirect methods to determine the physical structure of prestellar objects and disks, namely, using observations of molecular lines and thermal continuum dust emission. The Fig. III.2.2: Sketch of the AB Aur system (top) and the model distributions of the density (left bottom) and temperature (right bottom) in the disk. Unshaded part of the envelope R [AU] Disk 300 200 100 0 Shaded part of the envelope 70 70 100 90 Interstellar UV radiation 90 200 R [AU] R 300 70 T kin [K] 180 160 140 120 100 80 60 40 20
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Max Planck Institute for Astronomy
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Max Planck Institute for Astronomy
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Contents Preface ..................
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6 I. General I.1 Scientific Goals U
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8 I. General massive protostars and
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10 I. General achieve higher angula
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12 I. General The institute is co-l
Page 16 and 17: 14 I. General Point Source sensitiv
Page 18 and 19: 16 I. General Edinburgh Groningen D
Page 20 and 21: 18 II. Highlights II.1 Light Echoes
Page 22 and 23: 20 II. Highlights 10 arcsec Fig. II
Page 24 and 25: 22 II. Highlights AB Dor C AB Dor A
Page 26 and 27: 24 II. Highlights II.3 The First He
Page 28 and 29: 26 II. Highlights II.4 Planetesimal
Page 30 and 31: 28 II. Highlights azimuthal directi
Page 32 and 33: 30 II. Highlights ticles fall faste
Page 34 and 35: 32 II. Highlights ANTU Seyfert 2 ga
Page 36 and 37: 34 II. Highlights cretion disk, one
Page 38 and 39: 36 II. Highlights 8.5 �m 2.3 ly 0
Page 40 and 41: 38 II. Highlights II.6 Massive Star
Page 42 and 43: 40 II. Highlights log M� /pc2 �
Page 44 and 45: 42 II. Highlights II.7 Observations
Page 46 and 47: 44 II. Highlights log IR luminosity
Page 48 and 49: 46 II.8 Dynamics, Dust, and Young S
Page 50 and 51: 48 II. Highlights and we see a temp
Page 52 and 53: 50 III. Selected Research Areas III
Page 54 and 55: 52 III. Scientific Work Fig. III.1.
Page 56 and 57: 54 III. Scientific Work the Data Ar
Page 58 and 59: 56 III. Scientific Work The Field o
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Page 74 and 75: 72 III.3 The Galaxy-Dark Matter Con
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Page 84 and 85: 82 III. Scientific Work DDO 53 HO I
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Page 90 and 91: 88 IV. Instrumental Development All
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Page 112 and 113: 110 V. People and Events 1� 10�
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114 V. People and Events V.3 Furthe
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116 V. People and Events presented.
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118 V. People and Events The IMPRS
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120 V. People and Events Fig. V.5.2
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124 V. People and Events These oppo
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130 V. People and Events V.10 The P
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132 V. People and Events Abb. V.11.
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134 V. People and Events V.13 Four
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136 V. People and Events Lemke: I w
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138 V. People and Events Fig. V.13.
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140 V. People and Events V.14 Where
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142 V. People and Events against sp
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144 Staff Directors: Henning (Actin
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146 Working Groups Rainer Lenzen, H
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148 Cooperation with industrial Fir
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150 Conferences Conferences and Mee
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152 Conferences D. Lemke: JWST-miri
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154 Conferences/Service in Comitees
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156 Publications Szalay, I. Szapudi
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158 Publications Hamilton, C. M., W
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160 Publications Brinkmann, D. G. Y
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162 Publications Zheng, X. Z., F. H
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164 Publications of the wheel mecha
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166 Publications ASP Conf. Ser. 331
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The Max Planck Society The Max Plan
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Max Planck Institute for Astronomy - Annual Report 2005

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