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The Formation and Early Evolution of Very Low-Mass Stars and Brown Dwarfs Held at ESO Headquarters, Garching, Germany, 11–14 October 2011

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The Formation and Early Evolution of Very Low-Mass Stars and Brown Dwarfs Held at ESO Headquarters, Garching, Germany, 11–14 October 2011 Astronomical News and spectroscopic surveys identifying the at the ELTs, together with encouraging emphasised the power of emerging coun- first galaxies, rare quasars, supernovae some explicitly high-risk projects. It was tries and public outreach for investments and gamma-ray bursts. noted that is very important to retain a in astronomical research and that diver- broad range of facilities, including sity in facilities and astronomical capabili- A lively discussion arose on data policy 4-metre- and 8-metre-class telescopes, ties should be retained together with and data mining for surveys and ELTs. to be used as survey facilities, to pro- large-scale projects. Ellis reminded us Most participants agreed that proprietary mote small projects, and to train young that we cannot plan the future in detail time should be at the minimum level but astronomers. All the long-term flagship and so optimism, versatility and creativity sufficient to guarantee intellectual owner- projects should try to involve more stu- remain the key attributes for success. ship and a satisfactory progress of the dents and young researchers, allowing surveys and the ELTs. Others proposed them to attend science working com- All the presentations and the conference to have the data public from the begin- mittees, and communicating the outcome picture are available at the conference ning. In order to facilitate data mining, it of the major high-level decisional meet- website: http://www.eso.org/sci/meetings/ was proposed that all data provided by ings to them. Furthermore, it was pro- 2011/feedgiant. the surveys and the ELTs should be Vir- posed that at least one young astrono- tual Observatory compliant from the out- mer should be included in each of the set. Another interesting discussion was ELT science committees. More resources References about ELTs sharing their development should be allocated to provide for longer Diolaiti, E. 2010, The Messenger, 140, 28 efforts through common documentation, term contracts to leave young astrono- Marchis, F., Spencer, J. R. & Lopes, M. C. 2005, in complementary instrumentation capa- mers more time to develop new and cre- Io after Galileo, eds. R. M. C. Lopes and J. R. bilities, sharing information on site moni- ative ideas. Spencer, Springer, p.287 toring and sharing observing time. Thatte, N. 2010, The Messenger, 140, 26 Richard Ellis, in summarising the confer- The third part of the discussion dealt with ence, highlighted the opportunity to Links how to retain diversity and how to involve establish a better coordination of facili- 1 young people in the era of flagship pro- ties, instrumentations and programmes More about the World Café format at: http://www. theworldcafe.com/ jects. Astronomers agreed that a large and that we should further strengthen fraction of open time should be available these collaborations in the future. He also Report on the ESO/MPE/MPA/ExcellenceCluster/LMU Joint Astronomy Workshop The Formation and Early Evolution of Very Low-mass Stars and Brown Dwarfs held at ESO Headquarters, Garching, Germany, 11–14 October 2011 Monika Petr-Gotzens1 sions. In this report we provide a tion of VLM stars and BDs. We report Leonardo Testi1 brief summary of some of the areas on the ESO/MPE/MPA/LMU/Excellence- discussed at the workshop. Cluster joint workshop dedicated to recent theoretical and observational 1 ESO advances made in the field of study of the Very low-mass (VLM) stars (< 0.4 MA) formation and early evolution of brown and brown dwarfs (BDs) are faint objects dwarfs and very low-mass stars. The topics discussed at the workshop with low effective temperatures which are ranged from the structure and frag- difficult to detect due to their low lumi- It was demonstrated in several talks < mentation of molecular clouds to the nosities (~ 0.01 LA). On the other hand, that, with the help of new and powerful formation of individual very low-mass these objects are the major constituents ground- and space-based facilities objects, their multiplicity, physical of the stellar population of any galaxy and (e.g., VISTA and Herschel respectively), structure, mass distribution and early outnumber higher-mass stars by factors we are starting to discover young VLM evolution. Each topic was introduced of hundreds to thousands. Current wide stars and BDs and their precursors in by two reviews on the status of our area surveys in nearby molecular clouds, numbers large enough to allow statistical theoretical and observational under- from optical to far-infrared wavelengths, analyses of their properties. In addition, standing of the field, followed by pres- provide exciting new information on the detailed studies of individual objects and entations of new results and discus- process of the formation and early evolu- small samples are now effectively being The Messenger 146 – December 2011 41 Astronomical News Petr-Gotzens M., Testi L., Workshop on “Very Low-mass Stars and Brown Dwarfs” carried out with large optical/infrared telescopes and millimetre arrays (e.g., VLT/X-shooter and ALMA). On the theo- retical side, the latest modelling results were discussed and confronted with the observations. Approximately 120 par- ticipants came together in Garching (see Figure 1) for lively discussions in five sessions on the dedicated topics sum- marised below. Structure of molecular clouds: Formation and properties of cores Substantial progress in understanding the formation of pre-stellar cores has been made thanks to the Gould Belt sur- vey of nearby molecular clouds per- formed with the Herschel Space Obser- vatory. The emerging picture is of the important role of filaments as the prime places for pre-stellar core formation (review talks by P. Myers and P. Andre). The typical structure of a filament, based on the analysis of more than 100 fila- ments in different molecular clouds, is that of a narrow, steep density profile with Figure 1. Group picture of the workshop participants tends to inhibit disc fragmentation. This a characteristic width of roughly 0.1 par- in the entrance hall of ESO Headquarters. problem could be overcome if radiative secs. Observational evidence was pre- feedback is episodic, with long periods of sented for the formation of a pre-stellar luminosity Class 0 sources with quiescence. The detection and physical < core from velocity-coherent gas flows L ~ 0.8 LA appear under-abundant characterisation of very low luminosity along the filament directions (talk by A. in a large survey of protostars in the objects (VeLLOs) remains an observational Hacar). It was further argued that pre- Orion star-forming region (talk by W. challenge, but a few candidates were stellar cores are formed from the frag- Fischer). presented (in talks by M. Dunham and T. mentation of the densest parts of the fila- Huard). Progress in this respect is ments and that filament fragmentation expected to be made soon with ALMA, forms the basis of the (sub)stellar initial From cores to stellar systems: Fragmen- which provides excellent sensitivities mass function by setting the mass distri- tation, properties and multiplicity of pro- at submillimetre wavelengths and at high bution of pre-stellar cores. It was also tostars spatial resolution. shown that Herschel observations of the Perseus and Serpens clouds suggest In this session several models for the for- The observed properties of low-mass that the spatial density distribution of pre- mation of VLM stars and BDs were re­­ protostars/proto brown dwarfs are clearly stellar cores is scale-free, a result con- viewed and discussed by M. Bate, A. a key to understanding their formation. sistent with the spatial density distribution Boss, S. Basu and D. Stamatellos. New Protostellar/brown dwarf multiplicity was of young stellar objects in nearby molec- numerical simulations, including radia- discussed by several speakers (G. ular clouds (talk by E. Bressert). These tive feedback from protostars, show Duchene, A. Kraus, P. Viana Almeida and findings support the ideas of the existence reduced core fragmentation and produce R. Parker). It has been established of a column density threshold for the much fewer BDs than in previous simu- over the last couple of years that the bi­­ formation of cores and stars and that the lations. Very low-mass stars and BDs nary frequency declines with primary global properties of the outcome of the may also be formed in fragmenting mas- mass, a trend that continues down into star formation process in nearby clouds sive circumstellar discs involving sub- the substellar regime. For the youngest is closely linked to the fragmentation pro- sequent ejections from these discs. Ejec- objects, it seems that there is a lack of cess of molecular clouds. tions are frequent events and may 100–500 AU separation Class I binaries happen even at early evolutionary stages, (not specific to a particular primary mass However, the unambiguous identification leading to ejected low-mass clumps. range), while a high fraction is observed of the precursors of BDs and VLM stars However, it was pointed out that massive at larger separations. Also, Class 0 ob­­ remains elusive: very low luminosity pre- discs around Class 0 sources are not jects show a low binary frequency at sep- stellar cores remain undetected; and low observed and that radiative feedback arations < 2000 astronomical units (AU). 42 The Messenger 146 – December 2011 Revealing and understanding the low- The circum(sub)stellar environment: Sensitive surveys seem to suggest that mass end of the stellar initial mass func- Discs, outflows and accretion processes circumstellar discs around VLM stars tion and BDs are at least as common as in T The large body of evidence for a “T Tauri- Tauri stars, and their properties appear The third session was introduced by a like” phase in the early evolution of to be similar (talks by S.
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