Highlight - Plenary Talk

Thursday, 21 September 2017, 12:00   (HS1)

First Science Results of the GRAVITY interferometer

O. Pfuhl1, F. Eisenhauer1, G. Perrin2, K. Perraut3, C. Straubmeier4, W.Brandner5, A. Amorim6, and the GRAVITY collaboration
1 Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany
2 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 92195 Meudon Cedex, France
3 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
4 1. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
5 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6 CENTRA and Universidade de Lisboa - Faculdade de Ciencias, Campo Grande, 1749-016 Lisboa, Portugal

GRAVITY is a recently deployed instrument, which coherently combines the light of the European Southern Observatory (ESO) Very Large Telescope Interferometer. The instrument exploits the tremendous 130 m resolving power and 200 m2 collective area of the VLTI. GRAVITY uses a novel design of fiber-fed integrated optics beam combination, high resolution spectroscopy, phase- tracking, laser metrology and dual-beam operation. GRAVITY opens the techniques of phase-referenced imaging and narrow-angle astrometry to optical interferometry.
We present some key science results, which have been obtained during the first year of operation. This includes milli-arcsec scale imaging of the Galactic Center supermassive black hole and its fast orbiting star S2; few \rm \muas differential spectro-astrometry of the high mass X-ray binary BP Cru and the active galactic nucleus of PDS 456; high accuracy visibility observations and imaging of the resolved stars \xi Tel and 24 Cap.
GRAVITY has shifted the limits of optical interferometry in terms of sensitivity and accuracy by orders of magnitude. During the commissioning we demonstrated real-time phase stabilisation on stars as faint as \rm m_K \approx10 mag, phase-referenced interferometry of objects as faint as \rm m_K\approx 18 mag, visibility accuracies better than 0.25% and a spectro-astrometric precision of better than ten micro-arcseconds (\rm \muas). The experimental dual-beam astrometry mode shows residuals as low as 50 \rm \mu as when following objects over several months. The demonstrated performance represents a game-changer in optical interferometry, which leads to exciting new science prospects.