8 research outputs found
GRAVITY: getting to the event horizon of Sgr A*
We present the second-generation VLTI instrument GRAVITY, which currently is
in the preliminary design phase. GRAVITY is specifically designed to observe
highly relativistic motions of matter close to the event horizon of Sgr A*, the
massive black hole at center of the Milky Way. We have identified the key
design features needed to achieve this goal and present the resulting
instrument concept. It includes an integrated optics, 4-telescope, dual feed
beam combiner operated in a cryogenic vessel; near infrared wavefront sensing
adaptive optics; fringe tracking on secondary sources within the field of view
of the VLTI and a novel metrology concept. Simulations show that the planned
design matches the scientific needs; in particular that 10 microarcsecond
astrometry is feasible for a source with a magnitude of K=15 like Sgr A*, given
the availability of suitable phase reference sources.Comment: 13 pages, 11 figures, to appear in the conference proceedings of SPIE
Astronomical Instrumentation, 23-28 June 2008, Marseille, Franc
Merging history of three bimodal clusters
We present a combined X-ray and optical analysis of three bimodal galaxy
clusters selected as merging candidates at z ~ 0.1. These targets are part of
MUSIC (MUlti--Wavelength Sample of Interacting Clusters), which is a general
project designed to study the physics of merging clusters by means of
multi-wavelength observations. Observations include spectro-imaging with
XMM-Newton EPIC camera, multi-object spectroscopy (260 new redshifts), and
wide-field imaging at the ESO 3.6m and 2.2m telescopes. We build a global
picture of these clusters using X-ray luminosity and temperature maps together
with galaxy density and velocity distributions. Idealized numerical simulations
were used to constrain the merging scenario for each system. We show that A2933
is very likely an equal-mass advanced pre-merger ~ 200 Myr before the core
collapse, while A2440 and A2384 are post-merger systems ~ 450 Myr and ~1.5 Gyr
after core collapse, respectively). In the case of A2384, we detect a
spectacular filament of galaxies and gas spreading over more than 1 h^{-1} Mpc,
which we infer to have been stripped during the previous collision. The
analysis of the MUSIC sample allows us to outline some general properties of
merging clusters: a strong luminosity segregation of galaxies in recent
post-mergers; the existence of preferential axes --corresponding to the merging
directions-- along which the BCGs and structures on various scales are aligned;
the concomitance, in most major merger cases, of secondary merging or accretion
events, with groups infalling onto the main cluster, and in some cases the
evidence of previous merging episodes in one of the main components. These
results are in good agreement with the hierarchical scenario of structure
formation, in which clusters are expected to form by successive merging events,
and matter is accreted along large--scale filaments
GRAVITY: microarcsecond astrometry and deep interferometric imaging with the VLTI
We present the adaptive optics assisted, near-infrared VLTI instrument GRAVITY for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. With its two fibers per telescope beam, its internal wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will not only push the sensitivity far beyond what is offered today, but will also advance the astrometric accuracy for UTs to 10 muas. GRAVITY is designed to work with four telescopes, thus providing phase referenced imaging and astrometry for 6 baselines simultaneously. Its unique capabilities and sensitivity will open a new window for the observation of a wide range of objects, and --- amongst others --- will allow the study of motion within a few times the event horizon size of the Galactic Center black hole
GRAVITY: microarcsecond astrometry and deep interferometric imaging with the VLT
We present the AO assisted, near-infrared VLTI instrument GRAVITY for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. With its two fibers per telescope beam, its internal wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will not only push the sensitivity far beyond what is offered today, but will also advance the astrometric accuracy for UTs to 10 muas. GRAVITY is designed to work with four telescopes, thus providing phase referenced imaging and astrometry for 6 baselines simultaneously. Its unique capabilities and sensitivity will open a new window for the observation of a wide range of objects, and---amongst others---will allow the study of motions within a few times the event horizon size of the Galactic Center black hole
Science with GRAVITY, the NIR interferometric imager
10-m class telescopes have brought a wealth of breakthroughs in Galactic Center science. They have allowed tantalizing results such as the measurement of orbits of stars coming close to relativistic velocities and energetic outbursts in the emission from Sgr A*. To get more details in the flaring activity of Sgr A* and trace truly relativistic orbits, a spatial resolution of a few milliarcseconds only is required. For this purpose, we are currently designing GRAVITY, a second generation instrument for the VLT Interferometer