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. Mohanty, D. critical review from G. Chabrier of differ- VLM stars and BDs was emphasised in Jaffe and M. Gully Santiago). The current ent theoretical scenarios of VLM star many talks (e.g., by L. Hartman and millimetre observations do not yet allow and BD formation and the confrontation A. Natta). Recent studies also suggest us to resolve the disc sizes and place with recent observations of the initial outflow, accretion variability and disc strong constraints on the ejection mod- mass function (IMF). The large number of properties similar to those of more mas- els, but it is expected that ALMA will accumulating observational studies tar- sive pre-main sequence stars. These soon allow these constraints to be lifted. geting the IMF in various star-forming findings, although generally consistent Brown dwarf discs are also an interest- regions was then summarised in a sec- with the idea that objects as low as ing case study to test disc evolution theo- ond review talk by K. Luhman, suggesting ~ 50 MJup can form in a similar fashion to ries in a very low density regime. In that the low-mass IMF shows in general more massive stars, cannot yet rule ­particular, probing grain growth in very very little, if any, variation. On the other out different formation channels (ejection low-mass discs, such as those found hand, the measured IMF is subject to from multiple systems or fragmenting around BDs, will allow us to put strong substantial biases as a consequence of discs) starting to play a more significant constraints on dust evolution models. different observational approaches, role in the low-mass and brown dwarf The rapid and ubiquitous dust grain evo- such as the use of different stellar evolu- regimes. lution observed in discs around solar and tionary models to convert the observed slightly subsolar-mass stars are not pre- magnitudes to (sub)stellar masses, dif­ The key role of high sensitivity and dicted in the BD regime, but ALMA will ferent spectral classification schema, or ­simultaneous broadband spectroscopy soon tell us whether these predictions are the restriction of the analysis to photo- with instruments like X-shooter at the verified or not (talk by L. Testi). metric data alone. VLT was pointed out as an important step to understanding the complex interplay Several observational results based on between discs, accretion and outflow in Early evolution of very low-mass stars recently completed or ongoing wide-field these objects (talk by J. M. Alcalá). The and brown dwarfs imaging surveys, such as UKIDSS/GCS statistical analysis of the accretion sig­ or VISTA/Orion, in various star-forming natures in large population studies is Finally, during the last day of the work- regions showed the detection of numer- starting to show evidence for different shop an overall picture of the early evolu- ous candidate VLM objects impressively, timescales depending on the mass of the tionary stages of very low-mass stars down to the lowest-mass T-type dwarfs central stars (talks by A. Natta and C. F. and brown dwarfs was laid out in talks by (talks by N. Deacon, N. Lodieu, C. Alves Manara). The intriguing discovery of a I. Baraffe and L. Spezzi. As opposed to de Oliveira, K. Muzic and J. J. Downes). population of very long-lived accretors in the assumption of steady mass accretion Evidence was presented that shows the regions around very massive clusters limited to the protostellar stage, as in no difference in the spatial distribution of in the Magellanic Clouds and in the inner ­previous pre-main sequence evolutionary stars, VLM stars, BDs and planetary- regions of the Galaxy was also presented models, new models now consider epi- mass objects (talks by A. Bayo, K. Pena (talk by G. De Marchi). sodic and significant mass accretion Ramirez). The typical ratio of low-mass rates also during the early phases of pre- stars to brown dwarfs is 4–5 (P. Dawson) main sequence evolution (talks by Baraffe with some scatter from one star-forming and S. Offner). Episodic accretion acts region to another. However, the explicit on the internal structure of very low-mass shape of the substellar IMF is still under stars and brown dwarfs, making them discussion. During the workshop the more compact (smaller radii) and hence essential concern was raised that the appear less luminous, i.e. older, in the faintest (i.e. usually the lowest mass) Hertzsprung–Russell diagram. objects detected in most of the surveys

(< 13 MJup) are only photometric candi- New average lifetimes for different evolu- dates, and spectroscopic follow-up is tionary phases were constrained from urgently required. It was also pointed out Spitzer’s Cores to Discs and Gould Belt by various speakers that the true (low- surveys resulting in a revised Class 0 life- mass) end of the IMF has not yet been time estimate of ~ 1/5 of the Class I found. lifetime (~ 0.44 Myr), while the classical Figure 2. Stamp depicting a young brown dwarf T Tauri phase (Class II) represents the with an outflow, issued by the Republic of Ireland dominant phase during the pre-main Post to celebrate the International Year of Astronomy in 2009, was shown several times at the meeting. sequence evolution of low-mass stars

The Messenger 146 – December 2011 43 Astronomical News Petr-Gotzens M., Testi L., Workshop on “Very Low-mass Stars and Brown Dwarfs”

(talk by L. Spezzi). As spectroscopic In summary, the workshop stimulated port before, during and after the meeting. ­confirmation of a low effective tempera- a very successful exchange of ideas and The workshop gratefully acknowledges ture is often the final proof for a candidate new results, and was very well received the receipt of financial support from ESO, substellar mass object, it is essential to by the participants. The success of the the LMU/Excellence Cluster and from build up spectral libraries for the lowest- workshop and its smooth and efficient MPE. Most of the talks and posters are mass objects. Some large sample spec- practical organisation would have not available from the workshop webpage1. troscopic projects, as well as detailed been possible without the dedicated observations of individual objects, have work of ESO students and fellows (Joana been carried out, or are currently under- Ascenso, Giacomo Beccari, Eli Bressert Links way, as mentioned in talks by S. Antoni- and Sebastian Daemgen) and Christina 1 Workshop webpage: http://www.eso.org/sci/ ucci, J. Patience and J. Bochanski. Stoffer, who all provided excellent sup- meetings/2011/vlms2011.html

Brazilian Teachers and Students Visit Paranal and ALMA

Michael West1 Figure 1. Teachers and students from the Brazilian Louis Cruls Astronomy Club during 1 ESO their visit to Paranal.

With Brazil poised to become the first non-European member of ESO, new opportunities exist to strengthen ties between the Brazilian astronomical com- munity and ESO.

At the invitation of ESO’s Director Gen- eral, a group of ten Brazilian teachers and students travelled to Chile in August 2011. All are members of the Louis Cruls Astronomy Club from the city of Campos in Rio de Janeiro state, and were led by Professor Marcelo Souza of Universi- dade Estadual do Norte Fluminense and with the support of Dr José Monserrat Filho, Advisor for International Coopera- tion from the Brazilian Space Agency.

Accompanied by the head of the Office for Science in Chile, the group visited the ALMA and Paranal sites during the week of 21–27 August. Seeing the ALMA array and the VLT up close was a dream come Brazil’s first astronaut, Marcos Pontes, opportunity to visit the ESO and ALMA true for this enthusiastic group of amateur has inspired millions of young Brazilians facilities in Chile, today’s student mem- astronomers. Other highlights of the visit to consider scientific careers. “Brazil bers of the Louis Cruls Astronomy Club included an opportunity to chat with the has a very bright future in science and may be inspired to become tomorrow’s ESO astronomer and fellow countryman, technology,” he said, “but for this to professional astronomers and engineers Claudio Melo, and to get an insider’s look come true, you have to have young peo- in Brazil. at the VLT and ALMA operations. ple working in this area.” Thanks to the

44 The Messenger 146 – December 2011