Max Planck Institute for Astronomy - Annual Report 2007

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90 III. Selected Research Areas masses Westerlund 1 is the most massive starburst cluster identified in the Milky Way to date. Seeing-limited wide-field data obtained with the ESO NTT and SO F I cover an area of about 5 pc 5 pc centered on Westerlund 1. This is supplemented by adaptive optics high-resolution imaging of the cluster center obtained with NA C O at the ESO VLT. Starburst Clusters Going Bust – or are they Proto-Globular Clusters? Given a total stellar mass of at least several 10,000 solar masses, starburst clusters must have formed out of giant molecular clouds. Once the most massive stars appear on the main sequence, they rapidly ionize and disperse the remaining gas. Simulations by a number of research groups indicate that, in general, a star formation efficiency (SFE) of at least 30 percent is required for a stellar cluster to re-main bound, though under special circumstances a SFE as low as 10 percent might suffice for clusters to survive for a hundred million years. To answer the question whether any of the local starburst clusters constitutes a proto-globular cluster, observation of the cluster kinematics are required. Thus far 1d velocity dispersions derived from radial velocity measurements of a handful of the brightest cluster members in Arches and Westerlund 1 have been obtained, and – NGC3603 Young Cluster 1 Myr (Stolte et al. 2004) Arches 2 Myr (Stolte et al. 2005) Westerlund 1 3–5 Myr (Brandner et al. 2008) assuming virial equilibrium – employed to estimate an upper limit of the total mass in each of the two clusters. Of the Galactic starburst clusters shown in Fig. III.4.3, all plotted to the same physical scale, and ordered according to age from left to right, only NGC 3603 YC and Arches, the two youngest clusters in the sample, exhibit compact cores with half-mass radii of less than 0.5 pc, whereas the already slightly more evolved Westerlund 1 and Quintuplet clusters have half-mass radii of 1 pc. The two recently discovered red supergiant clusters with ages of around 10 Myr have still larger half-mass radii. For the spiral arm clusters, which are experiencing only weak tidal force fields, this could be evidence that dynamical evolution is accelerated by the gas expulsion. For the starburst clusters in the Galactic center region, strong tidal shear could result in rapid cluster dispersal. Thus there are hints that the current generation of Milky Way starburst clusters is not long-lived, and hence is different from proto-globular clusters. Fig. III.4.3: Five near-infrared images of Galactic starburst clusters are all shown to the same physical scale, ordered according to their age from left to right. The apparent increase in cluster size as measured by the half-mass radius with increasing age is suggestive of a rapid dynamical evolution (and dissolution in the general Galactic field) of the starburst clusters. Quintuplet 3–6 Myr (Figer et al. 1999) RSGC1 (UKIDSS/GPS) 7–12 Myr (Figer et al. 2006)
Outlook Recently, Stolte et al. (2008) compared multi-epoch high-resolution adaptive optics observations of Arches, and derived an upper limit on the two-dimensional velocity dispersion in agreement with the radial velocity measurements. They also discuss that astrometric follow-up observation should yield the true velocity dispersion of Arches. Ongoing multi-epoch astrometric monitoring of Milky Way starburst clusters will thus provide considerably improved constraints on the internal velocity dispersion, which in turn will be valuable for comparison with theoretical models. III.4 Starburst Clusters in the Milky Way 91 The next generation of high-precision astrometric instruments like gr av i t y for the eSo VLTI should reveal the kinematics of stars in the very cores of the starburst clusters, provide dynamical mass estimates for the most massive stars, and possibly even trace intermediate mass blackholes hidden in the very centers of these clusters. Wolfgang Brandner, Boyke Rochau, Felix Hormuth, in collaboration with Andrea Stolte (UCLA)
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Max Planck Institute for Astronomy
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Contents Preface ..................
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6 I. General I. General I.1 Scienti
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8 I. General Planet and Star Format
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10 I. General plementary. Ground-ba
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12 I. General High-fidelity imagers
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14 I. General Fig. I.6: Foreseen de
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16 I. General I.3 National and Inte
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18 I. General Edinburgh, University
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20 II. Highlights II.1 Youngest Ext
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22 II. Highlights radial velocity [
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24 II. Highlights II.2 A Search for
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26 II. Highlights F 1 [5] -2 0 2 4
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28 II. Highlights Number of Planets
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30 II. Highlights z [AU] z [AU] 1 0
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32 II. Highlights t =0 T orb t =1 T
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34 II. Highlights II.4 An Exoplanet
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36 II. Highlights F / F 12m 4 3 2
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38 II. Highlights the planet disapp
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Page 66 and 67: 64 III. Selected Research Areas III
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Page 120 and 121: 118 V. People and Events Dr. Gerner
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Page 138 and 139: 136 Staff Directors: Henning, Rix (
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140 Teaching Activities / Service i
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142 Further Activities / Compatibil
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144 Cooperation with Industrial Com
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146 Conferences StageS workshop, MP
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148 Conferences Ralf Launhardt: Wor
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150 Conferences Anna Pasquali: ASU
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152 Publications Apai, D., A. Bik,
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154 Publications Chen, X. P., R. La
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156 Publications of an unusual dwar
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158 Publications Moreau, J. A. Peac
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160 Publications Pontoppidan, K. M.
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162 Publications Garching-Bonn Deep
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164 Publications Zirm, A. W., A. va
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166 Publications Linz, H., R. Klein
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168 Publications Güdel, M.: The su
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A656 Eppelheim Patrick- Henry- Sied
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Max Planck Institute for Astronomy - Annual Report 2007

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