2 research outputs found
Astrometry with the Keck-Interferometer: the ASTRA project and its science
The sensitivity and astrometry upgrade ASTRA of the Keck Interferometer is
introduced. After a brief overview of the underlying interferometric
principles, the technology and concepts of the upgrade are presented. The
interferometric dual-field technology of ASTRA will provide the KI with the
means to observe two objects simultaneously, and measure the distance between
them with a precision eventually better than 100 uas. This astrometric
functionality of ASTRA will add a unique observing tool to fields of
astrophysical research as diverse as exo-planetary kinematics, binary
astrometry, and the investigation of stars accelerated by the massive black
hole in the center of the Milky Way as discussed in this contribution.Comment: 22 pages, 10 figures (low resolution), contribution to the
summerschool "Astrometry and Imaging with the Very Large Telescope
Interferometer", 2 - 13 June, 2008, Keszthely, Hungary, corrected authorlis
First faint dual-field phase-referenced observations on the Keck interferometer
Ground-based long baseline interferometers have long been limited in
sensitivity by the short integration periods imposed by atmospheric turbulence.
The first observation fainter than this limit was performed on January 22, 2011
when the Keck Interferometer observed a K=11.5 target, about one magnitude
fainter than its K=10.3 limit. This observation was made possible by the Dual
Field Phase Referencing instrument of the ASTRA project: simultaneously
measuring the real-time effects of the atmosphere on a nearby bright guide
star, and correcting for it on the faint target, integration time longer than
the turbulence time scale are made possible. As a prelude to this
demonstration, we first present the implementation of Dual Field Phase
Referencing on the interferometer. We then detail its on-sky performance
focusing on the accuracy of the turbulence correction, and on the resulting
fringe contrast stability. We conclude with a presentation of early results
obtained with Laser Guide Star AO and the interferometer.Comment: 10 pages, 12 figures, Proc. SPIE 201