30 research outputs found
GYES, a multifibre spectrograph for the CFHT
We have chosen the name of GYES, one of the mythological giants with one
hundred arms, offspring of Gaia and Uranus, for our instrument study of a
multifibre spectrograph for the prime focus of the Canada-France-Hawaii
Telescope. Such an instrument could provide an excellent ground-based
complement for the Gaia mission and a northern complement to the HERMES project
on the AAT. The CFHT is well known for providing a stable prime focus
environment, with a large field of view, which has hosted several imaging
instruments, but has never hosted a multifibre spectrograph. Building upon the
experience gained at GEPI with FLAMES-Giraffe and X-Shooter, we are
investigating the feasibility of a high multiplex spectrograph (about 500
fibres) over a field of view 1 degree in diameter. We are investigating an
instrument with resolution in the range 15000 to 30000, which should provide
accurate chemical abundances for stars down to 16th magnitude and radial
velocities, accurate to 1 km/s for fainter stars. The study is led by
GEPI-Observatoire de Paris with a contribution from Oxford for the study of the
positioner. The financing for the study comes from INSU CSAA and Observatoire
de Paris. The conceptual study will be delivered to CFHT for review by October
1st 2010.Comment: Contributed talk at the Gaia ELSA conference 2010, S\`evres 7-11 June
2010, to be published on the EAS Series, Editors: C. Turon, F. Arenou & F.
Meynadie
Spectroscopic survey of the Galaxy with Gaia I. Design and performance of the Radial Velocity Spectrometer
The definition and optimisation studies for the Gaia satellite spectrograph,
the Radial Velocity Spectrometer (RVS), converged in late 2002 with the
adoption of the instrument baseline. This paper reviews the characteristics of
the selected configuration and presents its expected performance. The RVS is a
2.0 by 1.6 degree integral field spectrograph, dispersing the light of all
sources entering its field of view with a resolving power R=11 500 over the
wavelength range [848, 874] nm. The RVS will continuously and repeatedly scan
the sky during the 5 years of the Gaia mission. On average, each source will be
observed 102 times over this period. The RVS will collect the spectra of about
100-150 million stars up to magnitude V~17-18. At the end of the mission, the
RVS will provide radial velocities with precisions of ~2 km/s at V=15 and
\~15-20 km/s at V=17, for a solar metallicity G5 dwarf. The RVS will also
provide rotational velocities, with precisions (at the end of the mission) for
late type stars of sigma_vsini ~5 km/s at V~15 as well as atmospheric
parameters up to V~14-15. The individual abundances of elements such as Silicon
and Magnesium, vital for the understanding of Galactic evolution, will be
obtained up to V~12-13. Finally, the presence of the 862.0 nm Diffuse
Interstellar Band (DIB) in the RVS wavelength range will make it possible to
derive the three dimensional structure of the interstellar reddening.Comment: 17 pages, 9 figures, accepted for publication in MNRAS. Fig. 1,2,4,5,
6 in degraded resolution; available in full resolution at
http://blackwell-synergy.com/links/doi/10.1111/j.1365-2966.2004.08282.x/pd
Spectroscopic survey of the Galaxy with Gaia- I. Design and performance of the Radial Velocity Spectrometer
The definition and optimization studies for the Gaia satellite spectrograph, the 'radial velocity spectrometer' (RVS), converged in late 2002 with the adoption of the instrument baseline. This paper reviews the characteristics of the selected configuration and presents its expected performance. The RVS is a 2.0 x 1.6 degree integral field spectrograph, dispersing the light of all sources entering its field of view with a resolving power R = lambda/Deltalambda = 11 500 over the wavelength range [848, 874] nm. The RVS will continuously and repeatedly scan the sky during the 5-yr Gaia mission. On average, each source will be observed 102 times over this period. The RVS will collect the spectra of about 100-150 million stars up to magnitude V similar or equal to 17-18. At the end of the mission, the RVS will provide radial velocities with precisions of similar to2 km s(-1) at V = 15 and similar to15-20 km s(-1) at V = 17, for a solar-metallicity G5 dwarf. The RVS will also provide rotational velocities, with precisions (at the end of the mission) for late-type stars of sigma(upsilonsin) similar or equal to (i) similar or equal to 5 km s(-1) at V similar or equal to 15 as well as atmospheric parameters up to V similar or equal to 14-15. The individual abundances of elements such as silicon and magnesium, vital for the understanding of Galactic evolution, will be obtained up to V similar or equal to 12-13. Finally, the presence of the 862.0-nm diffuse interstellar band (DIB) in the RVS wavelength range will make it possible to derive the three-dimensional structure of the interstellar reddenin
Spectroscopic survey of the Galaxy with Gaia- I. Design and performance of the Radial Velocity Spectrometer
The definition and optimization studies for the Gaia satellite spectrograph, the âradial velocity spectrometer' (RVS), converged in late 2002 with the adoption of the instrument baseline. This paper reviews the characteristics of the selected configuration and presents its expected performance. The RVS is a 2.0 Ă 1.6 degree integral field spectrograph, dispersing the light of all sources entering its field of view with a resolving power R=λ/Îλ= 11â500 over the wavelength range [848, 874] nm. The RVS will continuously and repeatedly scan the sky during the 5âyr Gaia mission. On average, each source will be observed 102 times over this period. The RVS will collect the spectra of about 100-150 million stars up to magnitude Vâ 17-18. At the end of the mission, the RVS will provide radial velocities with precisions of âŒ2 km sâ1 at V= 15 and âŒ15-20 km sâ1 at V= 17, for a solarâmetallicity G5 dwarf. The RVS will also provide rotational velocities, with precisions (at the end of the mission) for lateâtype stars of Ïvsin iâ 5 km sâ1 at Vâ 15 as well as atmospheric parameters up to Vâ 14-15. The individual abundances of elements such as silicon and magnesium, vital for the understanding of Galactic evolution, will be obtained up to Vâ 12-13. Finally, the presence of the 862.0ânm diffuse interstellar band (DIB) in the RVS wavelength range will make it possible to derive the threeâdimensional structure of the interstellar reddenin
X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope
X-shooter is the first 2nd generation instrument of the ESO Very Large
Telescope(VLT). It is a very efficient, single-target, intermediate-resolution
spectrograph that was installed at the Cassegrain focus of UT2 in 2009. The
instrument covers, in a single exposure, the spectral range from 300 to 2500
nm. It is designed to maximize the sensitivity in this spectral range through
dichroic splitting in three arms with optimized optics, coatings, dispersive
elements and detectors. It operates at intermediate spectral resolution
(R~4,000 - 17,000, depending on wavelength and slit width) with fixed echelle
spectral format (prism cross-dispersers) in the three arms. It includes a
1.8"x4" Integral Field Unit as an alternative to the 11" long slits. A
dedicated data reduction package delivers fully calibrated two-dimensional and
extracted spectra over the full wavelength range. We describe the main
characteristics of the instrument and present its performance as measured
during commissioning, science verification and the first months of science
operations.Comment: accepted for publication in A&
Comparison of several RVS FP/CCD configurations: Gaia Report to ESA (RVS-DK-002)
International audienc
Comparison of several RVS FP/CCD configurations: Gaia Report to ESA (RVS-DK-002)
International audienc
Atom Interferometry with Top-Hat Laser Beams
International audienceThe uniformity of the intensity and the phase of laser beams is crucial to high-performance atom interferometers. Inhomogeneities in the laser intensity profile cause contrast reductions and systematic effects in interferometers operated with atom sources at micro-Kelvin temperatures and detrimental diffraction phase shifts in interferometers using large momentum transfer beam splitters. We report on the implementation of a so-called top-hat laser beam in a long-interrogation-time cold-atom interferometer to overcome the issue of inhomogeneous laser intensity encountered when using Gaussian laser beams. We characterize the intensity and relative phase profiles of the top-hat beam and demonstrate its gain in atom-optic efficiency over a Gaussian beam, in agreement with numerical simulations. We discuss the application of top-hat beams to improve the performance of different architectures of atom interferometers
Imaging capabilities of hypertelescopes with a pair of micro-lens arrays
We verify the imaging performance of hypertelescopes on
the sky, using a new scheme for pupil densification. To avoid
seeing limitations, we used a miniature version with a 10 cm
aperture containing 78 sub-apertures of 1 mm size, arrayed
periodically as a square grid. The pupil densification is achieved
with a pair of micro-lens arrays, where each pair of facing lenses
behaves like a tiny demagnifying telescope. We have tested the
direct snapshot performance with laboratory-simulated multiple
stars and observed the binary star Castor (α Gem). We
measured a separation of 3.8ÂŽÂŽâand a magnitude difference
of 0.85 which is in agreement with current orbital data. This
verified the theoretical expectations for hypertelescopes in terms
of field of view and fluxes and qualified the new optical
implementation for future arrays at the scale of meters and
beyond