Spectroscopic anatomy of a meteor with the very large telescope (ESO)

A meteor spectrum was recorded serendipitously with the ESO Very Large Telescope during a long exposure in long-slit spectroscopic mode with the instrument FORS1. The -8 magnitude fireball crossed the narrow (1 arcsec × 7 arcmin) slit during the observation of a high z supernova in normal service mode operation on May 12, 2002. The spectrum covers the range of 637 1050 nm, where the meteor’s air plasma emissions from N[SUB]2[/SUB], N and O dominate. The meteor trail appears moreover resolved along the slit but we conclude that this is because the meteor at 100 km altitude was out of focus for the VLT. The plasma excitation temperature varies only from about 4300 to 4365 K across the trail, based on the ratio of atomic and molecular nitrogen emissions. This is in agreement with the fact that the trail is not actually spatially resolved. Finally, carbon atom emission is not detected in the relatively unexplored range above 900 nm

Euclid. II. The VIS Instrument

International audienceThis paper presents the specification, design, and development of the Visible Camera (VIS) on the ESA Euclid mission. VIS is a large optical-band imager with a field of view of 0.54 deg^2 sampled at 0.1" with an array of 609 Megapixels and spatial resolution of 0.18". It will be used to survey approximately 14,000 deg^2 of extragalactic sky to measure the distortion of galaxies in the redshift range z=0.1-1.5 resulting from weak gravitational lensing, one of the two principal cosmology probes of Euclid. With photometric redshifts, the distribution of dark matter can be mapped in three dimensions, and, from how this has changed with look-back time, the nature of dark energy and theories of gravity can be constrained. The entire VIS focal plane will be transmitted to provide the largest images of the Universe from space to date, reaching m_AB>24.5 with S/N >10 in a single broad I_E~(r+i+z) band over a six year survey. The particularly challenging aspects of the instrument are the control and calibration of observational biases, which lead to stringent performance requirements and calibration regimes. With its combination of spatial resolution, calibration knowledge, depth, and area covering most of the extra-Galactic sky, VIS will also provide a legacy data set for many other fields. This paper discusses the rationale behind the VIS concept and describes the instrument design and development before reporting the pre-launch performance derived from ground calibrations and brief results from the in-orbit commissioning. VIS should reach fainter than m_AB=25 with S/N>10 for galaxies of full-width half-maximum of 0.3" in a 1.3" diameter aperture over the Wide Survey, and m_AB>26.4 for a Deep Survey that will cover more than 50 deg^2. The paper also describes how VIS works with the other Euclid components of survey, telescope, and science data processing to extract the cosmological information