Max Planck Institute for Astronomy - Annual Report 2005

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52 III. Scientific Work Fig. III.1.2: Mosaic image of the glowing gas of the interstellar medium of the Large Magellanic Cloud taken for the Magellanic Cloud Emission Line Survey (MCELS). This image, which covers the central 8 by 8 degrees of the LMC, is a color composite of observations taken in five wavelength emission from the HII regions at the loci of associations is related to these massive stars, since they affect the ISM of their environment through their strong stellar winds and ionizing radiation, which can be observed in the ultraviolet wavelengths. The Initial Mass Function The star formation process is determined by the conversion of gas to stars with the outcome of stars with a range of masses. It is of great significance to quantify the relative numbers of stars in different mass ranges and to identify systematic variations of the stellar mass distri- bands: emission lines of hydrogen (H α ), doubly-ionized oxygen ([O III]), singly-ionized sulfur ([S II]), and red and green continuum bands. Over 1.500 individual images have been combined for the mosaic. Credit: C. Smith, S. Points, the MCELS Team and Noao/aura/NSF. bution with different star-forming conditions, which will allow us to understand the physics involved in assembling each of the mass ranges. The distribution of stellar masses in a given volume of space in a stellar system at the time of their formation is known as the stellar Initial Mass Function (IMF). Together with the time modulation of the star formation rate, the IMF characterizes the stellar content of a galaxy as a whole (Kroupa 2002, Science, 295, 82). The IMF may be characterized by the logarithmic derivative Γ (Scalo 1986, Fundam. Cosmic Phys. 11, 1): G � d log x(log m) ––––––––––––– . d lg m
Here, �(log m) is the IMF, which is constructed by counting stellar masses in equal logarithmic intervals, and Γ is its slope, which can be derived from the linear regression between log �(log m) and log m. A reference value for the IMF slope Γ, as found by Salpeter (1955, ApJ, 121, 161) for the solar neighborhood and stars with masses between 0.4 and 10 M 0 , is Γ � – 1.35. The Massive Initial Mass Function Ground-based investigations of a large sample of associations in the MCs led to the conclusion that for massive stars, the IMF in these systems is more or less the same, and it has a slope which varies around a value of Γ � – 1.5 � 0.1 (Massey et al. 1995, ApJ, 454, 151). This value is not very different from the IMF slopes of typical young compact LMC clusters for the same mass range (e.g. Gouliermis et al. 2004, A&A, 416, 137). Thus, the IMF of massive stars in young stellar systems appears more or less to be universal, with a typical slope, which does not differ significantly from the reference value found by Salpeter. On the other hand, the IMF of massive stars in the field away from any stellar system in both the LMC and SMC appears to be steep with slope Γ � – 4, the same value as for the Milky Way field. In general, the IMF for massive stars shows variations from one region of the galaxy to the other, which clearly suggest that environmental conditions most likey significantly affect the IMF in the high-mass regime. A characteristic example is the case of the LMC association LH 95 (Gouliermis et al. 2002, A&A, 381, 862), where a gradient of the IMF slope was observed in the sense that the IMF of stars with masses between 3 and 10 M 0 becomes steeper outwards from the center of the system (Fig. III.1.3). This suggests that there is a clear distinction between the population Fig. III.1.3: The Mass Function of all main-sequence stars located in the region of the association LH 95. The mass function for all the stars within the association (distance less than 1.2 arc minutes from its center) is shown in the left plot. The field population is included. The corresponding mass function of stars in the surrounding field is shown in the central plot. The lack of stars more massive than 10 M � in the latter makes the mass log [� (/log M/kpc 2 )] 5 4 3 2 � = –1.76 � 0.20 0.4 LH 95 III.1 Star Formation in the Magellanic Clouds 53 of the system, its surrounding field and the general field of the LMC. In addition, there are stellar associations which exhibit slopes of the massive IMF quite different from each other with values varying between Γ � – 1 and – 2 (Parker et al. 1998, AJ, 116, 180).This variability presumably originates in the differences in the star formation process from one region to the other. The IMF Toward the Low-Mass Regime The picture of the stellar content of stellar associations in the MCs from ground-based observations is limited above 2 M 0 . Information on the low-mass stellar membership and the corresponding IMF in these systems is still incomplete. Considering that the MCs, being very close, are the only extra-galactic targets where stars of sub-solar masses can be observed with the advanced instruments available today, this gap has only recently started to be filled with our research based on observations with the HubblE Space Telescope (HST). Our results open up a new debate by addressing important questions such as: (1) Are there any low-mass stars in stellar associations and, if yes, then what is the low-mass slope of the IMF in these systems? (2) What would be the lowest mass that can be observed? Is there any specific low-mass cutoff in the IMF of associations in the MCs? (3) What is the functional form of the low-mass IMF in the MCs? Is there a flattening of the IMF for sub-solar masses? and therefore (4) Has the IMF got a constant slope or not through the whole mass range detected? and finally (5) What is the low-mass slope of the IMF in the general field and what are the differences to those of young stellar systems? Is there any dependence/relation of the IMF slope on/to the environment, in which star formation does it take place? Data from space observations of the MCs is available in function steeper. This exemplifies the radial dependence of the mass function slope, which becomes steeper outwards. The plot on the right shows the IMF of the main sequence stars in the association, after the contribution of stars, which belong to the field has been subtracted. This IMF is comparable to a typical Salpeter IMF. Adapted from Gouliermis et al. (2002). LH 95 (field) � = –2.94 � 0.15 � = –1.59 � 0.30 LH 95 (field subtracted) 0.8 1.2 1.6 0.4 0.8 1.2 1.6 0.4 0.8 1.2 1.6 log M
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Max Planck Institute for Astronomy
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Page 5: Contents Preface ..................
Page 8 and 9: 6 I. General I.1 Scientific Goals U
Page 10 and 11: 8 I. General massive protostars and
Page 12 and 13: 10 I. General achieve higher angula
Page 14 and 15: 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 56 and 57: 54 III. Scientific Work the Data Ar
Page 58 and 59: 56 III. Scientific Work The Field o
Page 60 and 61: 58 III. Scientific Work lower than
Page 62 and 63: 60 III. Scientific Work
Page 64 and 65: 62 III. Scientific Work Fig. III.1.
Page 66 and 67: 64 III. Scientific Work z [AU] 1 0
Page 68 and 69: 66 III. Scientific Work line observ
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Page 72 and 73: 70 III. Scientific Work Column dens
Page 74 and 75: 72 III.3 The Galaxy-Dark Matter Con
Page 76 and 77: 74 III. Scientific Work redshift su
Page 78 and 79: 76 III. Scientific Work Mocking the
Page 80 and 81: 78 III. Scientific Work tion rate o
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Page 84 and 85: 82 III. Scientific Work DDO 53 HO I
Page 86 and 87: 84 III. Scientific Work Fig. III.4.
Page 88 and 89: 86 III. Scientific Work tribution o
Page 90 and 91: 88 IV. Instrumental Development All
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102 IV. Instrumental Development IV
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104 IV. Instrumental Development Fi
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106 IV. Instrumental Development IV
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108 IV. Instrumental Development jo
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110 V. People and Events 1� 10�
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112 V. People and Events V.2 Open H
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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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