The VMC survey

XVII. Proper motions of the Small Magellanic Cloud and the Milky Way globular cluster 47 Tucanae^⋆

¹ Universität Potsdam, Institut für Physik und Astronomie, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
e-mail: mcioni@aip.de
² Leibnitz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ University of Hertfordshire, Physics Astronomy and Mathematics, College Lane, Hatfield AL10 9AB, UK
⁴ ICRAR, M468, University of Western Australia, 35 Stirling Hwy, 6009 Crawley, Western Australia, Australia
⁵ INAF, Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁶ Kavli Intitute for Astronomy & Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, 100871 Beijing, PR China
⁷ Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, 100871 Beijing, PR China
⁸ Institute of Astronomy, University of Cambridge, Madingley, Road, Cambridge, CB3 0HA, UK
⁹ European Southern Observatory, Karl-Schwarzschild-Str. 2 , 85748 Garching bei München, Germany
¹⁰ European Southern Observatory, 3107 Ave. Alonso de Córdova, Vitacura, Santiago, Chile
¹¹ INAF, Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
¹² Lennard-Jones Laboratories, School of Physical and Geographical Sciences, Keele University, ST5 5BG, UK
¹³ Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina
¹⁴ Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Rivadavia 1917, C1033AAJ, Buenos Aires, Argentina

Received: 20 July 2015
Accepted: 27 October 2015

Abstract

Aims. In this study we use multi-epoch near-infrared observations from the VISTA survey of the Magellanic Cloud system (VMC) to measure the proper motions of different stellar populations in a tile of 1.5 deg² in size in the direction of the Galactic globular cluster 47 Tuc. We obtain the proper motion of the cluster itself, of the Small Magellanic Cloud (SMC), and of the field Milky Way stars.

Methods. Stars of the three main stellar components are selected according to their spatial distributions and their distributions in colour−magnitude diagrams. Their average coordinate displacement is computed from the difference between multiple K_s-band observations for stars as faint as K_s = 19 mag. Proper motions are derived from the slope of the best-fitting line among ten VMC epochs over a time baseline of ~1 yr. Background galaxies are used to calibrate the absolute astrometric reference frame.

Results. The resulting absolute proper motion of 47 Tuc is (μ_αcos(δ), μ_δ) = (+7.26 ± 0.03, −1.25 ± 0.03) mas yr^-1. This measurement refers to about 35 000 sources distributed between 10′ and 60′ from the cluster centre. For the SMC we obtain (μ_αcos(δ), μ_δ) = (+1.16 ± 0.07, −0.81 ± 0.07) mas yr^-1 from about 5250 red clump and red giant branch stars. The absolute proper motion of the Milky Way population in the line of sight (l = 305.9, b = −44.9) of this VISTA tile is (μ_αcos(δ), μ_δ) = (+10.22 ± 0.14, −1.27 ± 0.12) mas yr^-1 and has been calculated from about 4000 sources. Systematic uncertainties associated with the astrometric reference system are 0.18 mas yr^-1. Thanks to the proper motion we detect 47 Tuc stars beyond its tidal radius.