Astronomical Science The VLT FLAMES Tarantula Survey Chris Evans1 7 School of Physics, University of Exeter, high quality survey of extragalactic William Taylor2 United Kingdom massive stars ever assembled, and Hugues Sana3 8 ESO is already providing exciting new Vincent Hénault-Brunet2 9 Harvard–Smithsonian Center for Astro­ insights into their evolution, multiplicity Tullio Bagnoli3 physics, Cambridge, USA and formation. Nate Bastian4 10 Department of Astronomy, University of Joachim Bestenlehner5 Vienna, Austria Alceste Bonanos6 11 Argelander­Institut für Astronomie der Massive stars and their descendants Eli Bressert7, 8, 9 Universität Bonn, Germany dominate the dynamics and chemical Ines Brott10 12 Department of Physics and Astronomy, enrichment of young star­forming gal­ Michael Campbell2 The Open University, Milton Keynes, axies, through their intense winds, radia­ Matteo Cantiello11 United Kingdom tion fields and dramatic deaths as core- Giovanni Carraro8 13 Departamento de Astronomia, Univer­ collapse supernovae. An overarching Simon Clark12 sidad de Chile, Santiago, Chile goal for studies of stellar evolution and Edgardo Costa13 14 Department. of Physics & Astronomy, resolved stellar populations is to develop Paul Crowther14 University of Sheffield, United Kingdom realistic tools to analyse integrated­light Alex de Koter3, 15 15 University of Utrecht, the Netherlands observations of distant star clusters Selma de Mink16, 17 16 Space Telescope Science Institute, and galaxies; if we can understand the Emile Doran14 Baltimore, USA properties and behaviour of the stars Philip Dufton18 17 Hubble Fellow on our own doorstep, we can be more Paul Dunstall18 18 Department of Physics & Astronomy, confident of an accurate interpretation of Miriam Garcia19, 20 Queen’s University Belfast, Northern unresolved populations far away. Mark Gieles21 Ireland, United Kingdom Götz Gräfener5 19 Instituto de Astrofísica de Canarias, Artemio Herrero19, 20 La Laguna, Tenerife, Spain Background and motivations Ian Howarth22 20 Departamento de Astrofísica, Universi­ Rob Izzard11 dad de La Laguna, Tenerife, Spain A vibrant area of research has been the Karen Köhler11 21 Insitiute of Astronomy, University of role of environment (metallicity) on the Norbert Langer11 Cambridge, United Kingdom evolution of massive stars, often focus­ Daniel Lennon23 22 Department of Physics & Astronomy, sing on the properties of individual stars Jesús Maíz Apellániz24 University College London, United in the nearby metal-poor Magellanic Nevena Markova25 Kingdom Clouds compared to their Galactic cous­ Paco Najarro26 23 European Space Agency, Space Tele­ ins. These efforts culminated in a previ­ Joachim Puls27 scope Science Institute, Baltimore, ous Large Programme, the VLT FLAMES Oscar Ramirez3 USA Survey of Massive Stars (FSMS), which Carolina Sabín-Sanjulián19, 20 24 Instituto de Astrofísica de Andalucía­ analysed tens of O­type stars and hun­ Sergio Simón-Díaz19, 20 CSIC, Granada, Spain dreds of early B­type stars, from ob ­ Stephen Smartt18 25 Institute of Astronomy with NAO, servations centred on open clusters in Vanessa Stroud12, 28 Smoljan, Bulgaria the Galaxy and in the Clouds (Evans et Jacco van Loon29 26 Centro de Astrobiología, CSIC­INTA, al., 2008). Jorick S. Vink5 Madrid, Spain Nolan Walborn16 27 Universitäts-Sternwarte München, A major result from the previous survey Germany was empirical evidence for weaker winds 28 Faulkes Telescope Project, University of in massive O­type stars at lower metal­ 1 United Kingdom Astronomy Technol­ Glamorgan, Wales, United Kingdom licities, in agreement with theoretical pre­ ogy Centre, STFC, Royal Observatory, 29 School of Physical & Geographical Sci­ dictions. This was a crucial test because Edinburgh, United Kingdom ences, Keele University, United Kingdom evolutionary models employ theoretical 2 Scottish Universities Physics Alliance, scaling laws to account for the loss of Institute for Astronomy, University of mass and angular momentum in metal­ Edinburgh, United Kingdom We introduce the VLT FLAMES Taran- poor stars. In lower metallicity systems 3 Astronomical Institute Anton tula Survey, an ESO Large Programme stars therefore require a larger initial mass Pannekoek, University of Amsterdam, from which we have obtained optical to progress to the Wolf–Rayet (W–R) the Netherlands spectroscopy of over 800 massive stars phase than in the Galaxy, and will lose 4 Excellence Cluster Universe, Garching, in the spectacular 30 Doradus region less angular momentum over their life­ Germany of the Large Magellanic Cloud. A key times. Consequences of this include 5 Armagh Observatory, Northern Ireland, feature is the use of multi-epoch obser- reduced feedback of material from their United Kingdom vations to provide strong constraints winds and potentially different types of 6 National Observatory of Athens, Greece on the binary fraction. This is the largest core-collapse explosions. The Messenger 145 – September 2011 33 Astronomical Science Evans C. et al., The VLT FLAMES Tarantula Survey The O­type stars span a wide range of A thriving stellar nursery to the Giraffe spectrograph. Three of mass (upwards of ~ 20 MA), effective the standard Giraffe settings were used: temperatures (~ 30 000 to 50 000 K) and The 30 Doradus nebula is more than just LR02 (3960–4564Å, R = 7000), LR03 wind properties, with a diverse range a beautiful extragalactic H II region — it (4499–5071Å, R = 8500), HR15N (6442– of morphological sub­groups. To under­ harbours one of the richest populations 6817Å, R = 16 000). This provided inter­ stand the most massive stars as a popu­ of massive stars in the local Universe and mediate resolution spectroscopy of the lation, including the evolutionary con­ is our only opportunity to resolve the blue optical lines commonly used in nections between those sub­groups, a components of a young, small­scale star­ classification and quantitative analysis of much larger, homogeneous sample burst. The nebula spans 15 arcminutes massive stars, combined with higher of high quality data was required. In par­ on the sky, equivalent to over 200 par­ resolution observations of the Hα line to ticular, rotationally-induced mixing is secs (pc) and comparable in scale to provide a diagnostic of the stellar wind thought to modify the surface chemistry regions of intense star formation observed intensity. These settings also include of massive stars on the main sequence, in high-redshift galaxies. The engine at important strong nebular lines (e.g., [O III] with the most dramatic enhancements its core is the dense stellar cluster R136, and [S II]), giving a useful tracer of the predicted for their nitrogen abundances. home to some of the most massive stars gas velocities along each line of sight. In This is an important test of evolutionary known (with masses in excess of 150 MA; addition, a small number of selected models, where the benefits of large sam­ Crowther et al., 2010). When combined targets were observed at greater spectral ples are highlighted by the puzzling with its well­constrained distance (by resolution with the fibre-feed to UVES results for some of the B­type stars from virtue of being in the LMC) and low fore­ (see Figure 1). the FSMS (e.g., Brott et al., 2011; and ref­ ground extinction, 30 Doradus provides erences therein). Moreover, the progres­ us with a unique laboratory in which to One of the primary motivations of the sion of increasing wind strength along compile a large spectroscopic sample of VFTS was to detect massive companions the evolutionary sequence of O–Of–Of/ massive stars. WN–WN types is not well known, yet these are the stars which truly dominate The VFTS observations primarily em ­ Figure 1. The FLAMES ARGUS integral field unit in terms of mechanical feedback and ion­ ployed the Medusa mode of FLAMES, in images (and extracted sources) overlaid on an HST WFC3 F555W image of R136. The location of ising photons. which 132 fibres are positioned within a Medusa and UVES targets in the central region are 25-arcminute field of view to feed targets also shown. To add to these factors, the catalyst for a new and ground­breaking survey was provided by recent results highlighting ARGUS the prevalence of binarity in massive stars MEDUSA (e.g., Sana & Evans, 2011). Parts of the UVES extragalactic community have begun to explore the consequences of this, with massive binaries argued to account for some of the integrated­light properties of low-redshift star-forming galaxies. How­ ever, an empirical description of the bi ­ N nary fraction of massive systems (and their distribution of mass ratios) has, to date, been poorly constrained in models of star formation and cluster evolution. The VLT FLAMES Tarantula Survey (VFTS; Evans et al., 2011) was conceived E to address these outstanding issues relating to the evolution, multiplicity and eventual fate of massive stars. By using the multi-object capability of FLAMES, 10ǥ combined with the light­gathering power of the VLT, we targeted the massive­ star population of the Tarantula Nebula (30 Doradus, NGC 2070), the largest star- forming complex in the Local Group of galaxies, located in the Large Magellanic Cloud (LMC). 34 The Messenger 145 – September 2011 the LMC. We now summarise three dis­ –68°56' coveries which highlight the huge poten­ tial of the VFTS data. Discovery of a very massive star outside –69°00' R136 There have been numerous narrowband imaging surveys in the Clouds to look for W–R stars and it is often presumed that we have a complete census of them. 04' However, the VFTS has discovered a new hydrogen­rich W–R star, VFTS 682, ) located 29 pc northeast of R136 (Fig­ 000 2 ure 3; Evans et al., 2011). The spectrum (J c of VFTS 682, classified as WN5h, resem­ De bles those of the very luminous stars in 08' the core of R136 (Crowther et al., 2010). No radial velocity shifts are seen between the individual epochs, suggesting that the star is single to a high level of confidence. From analysis of the spectra and availa­ 12' ble optical/infrared photometry the star appears to be very luminous, with log(L/ LA) = 6.5 ± 0.2 and with a current mass of ~ 150 MA (Bestenlehner et al., 2011).