Astronomical Science VISTA Variables in the Vía Láctea (VVV): Halfway Status and Results Maren Hempel1,2 I. Félix Mirabel36,37 12 Departamento de Física, Universidad Dante Minniti1,3 Lorenzo Monaco8 de La Serena, Chile István Dékány1 Christian Moni-Bidin38 13 Department of Astronomy, University of Roberto K. Saito1,4 Lorenzo Morelli39 Florida, Gainesville, USA Philip W. Lucas5 Nelson Padilla1 14 Universidade de São Paulo, Brazil Jim P. Emerson6 Tali Palma7 15 Facultad de Ciencias Astronómicas y Andrea V. Ahumada7,8,9 Maria Celeste Parisi7 Geofísicas, Universidad Nacional de Suzanne Aigrain10 Quentin Parker40,41 La Plata, Argentina Maria Victoria Alonso7 Daniela Pavani17 16 Space Telescope Science Institute, Javier Alonso-García1 Pawel Pietrukowicz42 Baltimore, USA Eduardo B. Amôres11 Grzegorz Pietrzynski24,43 17 Universidade Federal do Rio Grande do Rodolfo Angeloni1 Giuliano Pignata44 Sul, Porto Alegre, Brazil Julia Arias12 Marina Rejkuba8 18 Departamento de Física y Astronomía, Reba Bandyopadhyay13 Alejandra Rojas1 Facultad de Ciencias, Universidad de Rodolfo H. Barbá12 Alexandre Roman-Lopes12 Valparaíso, Chile Beatriz Barbuy14 Maria Teresa Ruiz19 19 Departamento de Astronomía, Univer- Gustavo Baume15 Stuart E. Sale1,18,45 sidad de Chile, Santiago, Chile Juan Carlos Beamin1 Ivo Saviane8 20 Institute for Astronomy, The University Luigi Bedin16 Matthias R. Schreiber18 of Edinburgh, UK Eduardo Bica17 Anja C. Schröder46,47 21 Joint Astronomy Centre, Hilo, USA Jordanka Borissova18 Saurabh Sharma18 22 Kavli Institute for Astronomy and Leonardo Bronfman19 Michael Smith48 Astrophysics, Peking University, China Giovanni Carraro8 Laerte Sodré Jr.14 23 Astrophysics Group, Imperial College Márcio Catelan1 Mario Soto12 London, UK Juan J. Clariá7 Andrew W. Stephens49 24 Departmento de Astronomía, Universi- Carlos Contreras1 Motohide Tamura50 dad de Concepción, Chile Nicholas Cross20 Claus Tappert18 25 Max Planck Institute for Astronomy, Christopher Davis21 Mark A. Thompson5 Heidelberg, Germany Richard de Grijs22 Ignacio Toledo51 26 Department of Astrophysics, University Janet E. Drew5,23 Elena Valenti8 of Oxford, UK Cecilia Fariña15 Leonardo Vanzi52 27 Department of Physics, University of Carlos Feinstein15 Walter Weidmann7 Cincinnati, USA Eduardo Fernández Lajús15 Manuela Zoccali1 28 School of Physics & Astronomy, Univer- Stuart Folkes5,18 sity of Leeds, UK Roberto C. Gamen15 29 Institute of Astronomy, University of Douglas Geisler24 1 Instituto de Astrofísica, Pontificia Cambridge, UK Wolfgang Gieren24 Universidad Católica de Chile, Chile 30 Jodrell Bank Centre for Astrophysics, Bertrand Goldman25 2 The Milky Way Millennium Nucleus, The University of Manchester, UK Oscar González8 Santiago, Chile 31 NASA-Ames Research Center, Moffett Andrew Gosling26 3 Vatican Observatory, Italy Field, USA Guillermo Gunthardt12 4 Universidade Federal de Sergipe, Depar- 32 Instituto de Astrofísica de Canarias, Sebastian Gurovich7 tamento de Física, Cristóvão, Brazil La Laguna, Tenerife, Spain Nigel C. Hambly20 5 Centre for Astrophysics Research, 33 Department of Physics, Texas Tech Margaret Hanson27 Science and Technology Research University, Lubbock, USA Melvin Hoare28 Institute, University of Hertfordshire, 34 Istituto di Astrofisica Spaziale e Fisica Mike J. Irwin29 Hatfield, UK Cosmica di Bologna, Italy Valentin D. Ivanov8 6 Astronomy Unit, School of Physics and 35 Rochester Institute of Technology, Andrés Jordán1 Astronomy, Queen Mary University of Rochester, USA Eamonn Kerins30 London, UK 36 Service d’Astrophysique – IRFU, Karen Kinemuchi31 7 Observatorio Astronómico de Córdoba, CEA-Saclay, Gif sur Yvette, France Radostin Kurtev18 Argentina 37 Instituto de Astronomía y Física del Andy Longmore20 8 ESO Espacio, Buenos Aires, Argentina Martin López-Corredoira32 9 Consejo Nacional de Investigaciones 38 Instituto de Astronomía, Universidad Tom Maccarone33 Científicas y Técnicas, Buenos Aires, Católica del Norte, Antofagasta, Chile Eduardo Martín32 Argentina 39 Dipartimento di Astronomia, Universitá Nicola Masetti34 10 School of Physics, University of Exeter, di Padova, Italy Ronald E. Mennickent24 UK 40 Department of Physics, Macquarie Uni- David Merlo7 11 SIM, Faculdade de Ciências da versity, Sydney, Australia Maria Messineo35 Universidade de Lisboa, Portugal 24 The Messenger 155 – March 2014 41 Australian Astronomical Observatory, 1.1 by 1.5 degree field of view, ideal for Epping, Australia surveys covering many hundreds of 42 Nicolaus Copernicus Astronomical square degrees. The large field of view in Center, Warsaw, Poland combination with the spatial resolution P93+ P85 360 hr (18.6%) 300 hr (15.6%) 43 Warsaw University Observatory, of 0.339 arcseconds per pixel make Warsaw, Poland VISTA/VIRCAM an ideal instrument to 44 Departamento de Ciencias Físicas, observe the most crowded and extincted Universidad Andres Bello, Santiago, regions of the Milky Way, i.e. the central P87 Chile regions of the Bulge and the mid-plane 292 hr (15.1%) 45 Rudolf Peierls Centre for Theoretical regions of the Galactic Disc. The feasible P91 Physics, Oxford, UK observing period for the VVV survey is 550 hr (28.5%) 46 SKA/KAT, Cape Town, South Africa limited to six months, between February P89 47 Hartebeesthoek Radio Astronomy and October, requiring careful scheduling 275 hr (14.3%) Observatory, Krugersdorp, South of the individual observing periods. P90 Africa 152 hr ( 7.9 %) 48 The University of Kent, Canterbury, UK The first main phase of the survey, 49 Division of Optical and Infrared Astron- consisting of the YZJHKs multi-colour omy, National Astronomical Observa- observations, was assigned to the first Figure 1. Observing schedule for the VVV survey in tory of Japan, Tokyo, Japan semester of the survey (Period 85, 2010) comparison with the total allotted observing time of 50 1929 hours. Note, that ca. 50% of the P91 observa- Gemini Observatory, Hawaii, USA to obtain a first overview of the survey tions were delayed due to poor weather. The remain- 51 ALMA Observatory, Santiago Chile area (described in Section 2). The vast ing 360 hours will be distributed over Period 93 52 Departamento de Ingeniería Eléctrica, majority of the observations however form (2014) and the following years. Pontificia Universidad Católica de Chile, the variability campaign, which started in Santiago, Chile parallel with the multi-colour observations Already, after the first two observing in Period 85, but then occupied all the fol- periods, despite the modest amount of lowing observing periods. For the variabil- data (see Figure 1) it has become obvious The VISTA Variables in the Vía Láctea ity campaign, VVV was allotted 300 hours that the data reduction, analysis and (VVV) survey is one of six near-infrared in 2010 (including multi-colour observa- even data storage/transfer are daunting ESO public surveys, and is now in its tions), 292 hours in 2011, 275 hours in tasks. These considerations affected fourth year of observing. Although far 2012 and 702 hours in 2013 (split between not only the survey team, conducting a from being complete, the VVV survey Periods 90 and 91). The remaining 360 wide range of science projects, final qual- has already delivered many results, hours of the survey will be used not only to ity control, preparation of observations some directly connected to the intended gather additional data for the variability and the public data release, but also the science goals (detection of variable survey (see below), but also to aid the Cambridge Astronomical Survey Unit stars, microlensing events, new star ongoing proper motion study on the Solar (CASU), in charge of the pipeline reduc- clusters), others concerning more exotic Neighbourhood and in searching for tion of all data, as well as ESO, perform- objects, e.g., novae. Now, at the end of microlensing events in a selected Bulge ing the observations, the first level of the fourth observing period, and com- area. The long-term status of the VVV sur- quality control and the final data release. prising roughly 50% of the proposed vey, especially in combination with other observations, the status of the survey, data (e.g., 2MASS and WISE) make it very as well some of results based on the suitable to conduct proper motion studies, Multi-colour photometry VVV data, are presented. which are the subject of a later section. The multi-colour observations in the five The following observations were sched- broadband filtersY , Z, J, H and Ks com- Introduction uled for each period (Minniti et al., 2010): menced in March 2010 and were con- – P85 (April–October 2010): YZJHKs cluded by September 2011. Starting with The Visible and Infrared Survey Tele- and additional Ks-band observations the J-, H- and Ks-band data only, an scope for Astronomy (VISTA, Emerson & for the whole survey area; unprecedented first multi-colour view on Sutherland, 2010) has been operated by – P87 (April–October 2011): Ks-band the inner region of the Milky Way Bulge ESO for four years. Observations began observations of the complete survey composed of 84 million stellar sources with Science Verification in September area; was presented by Saito et al. (2012a; see 2009, and this was followed by the six – P89 (April–October 2012): main varia- also the ESO Release 12421), followed by public surveys, one of which is VISTA bility campaign on the Bulge area; the study of Soto et al. (2013) of 88 mil- Variables in the Via Láctea (see Minniti et – P90 (November 2012 – March 2013): lion stellar sources in the southern Galac- al., 2010; Saito et al., 2010; Catelan