GEPI

From instrumental design
to scientific exploitation

Projects

International Projects

The team is involved in three observational projects: Gaia, WEAVE and MOONS, which are also three major international collaborations.

Gaia

Our team has been one of the most involved in Europe for the preparation of the Gaia space mission and then for the validation of its data. The first catalogue was published in 2017. The second in spring 2018, had a major scientific impact (1605 peer-reviewed articles in 2019, 605 in the first quarter of 2020). It contains the largest catalogue of precise stellar radial velocities, RVS/Gaia, ever produced ( 7 million radial velocities), published under the responsibility of the team (including Paola Sartoretti, head of Coordination Unit 6 of the Gaia consortium, the DPAC, responsibility previously assumed by David Katz). The next catalogue will be published in two parts (EDR3, December 2020, DR3, first semester 2022), it will contain about 30 million radial velocities. The publication of successive catalogues will continue until 2027. The team is also heavily involved in the scientific exploitation of Gaia data, and has participated in many of the most important discoveries made possible by the publication of DR2 in 2018. These include the study of the kinematics of the Galaxy in unprecedented detail and volume, the detection of the first major accretion of a satellite galaxy about 9 billion years ago, the formation of the galactic halo, and the discovery and characterisation of the most primitive stars in the galactic disc (probably formed very quickly after the Big Bang).

Spectroscopic surveys

The Gaia project is complemented by some ground-based spectroscopic surveys (WEAVE, MOONS, 4MOST), to obtain complementary radial velocities and detailed chemical abundances for stars for which these quantities were not measured by Gaia. These surveys will observe several million stars in the coming years.

WEAVE

The WEAVE project is a multi-object spectrograph installed at the William Herschel telescope (4.2m). It will be able to observe about 900 stars per exposure time at medium and high resolutions (R 5000 and 20000). The galactic archaeological part of the project consists in observing several million stars, at high and lower spectral resolutions, to study the stellar populations of the thin, thick discs and stellar halo. Half of the researchers of the team are engaged on WEAVE at the GEPI, Piercarlo Bonifacio in particular is the French PI of the project, and part of the spectrograph fibers have been assembled at the GEPI. The start of the WEAVE archaeology survey is expected in April 2021. This survey will provide high-resolution chemical abundances for 1.5 million stars and low-resolution surveys for more than a million stars, and will extend until 2025. This survey is the subject of an ANR project (accepted) that will start in 2021, between the Nice Observatory (PI) and the Strasbourg Observatory and our team.

MOONS

MOONS is a multi-object spectrograph that will be installed at the VLT in early 2022. Like WEAVE, MOONS is capable of observing about 900 stars at once, but its installation on an 8m, and its observation range, in the visible and near infrared, make it a unique tool for observing the dense regions of our Galaxy: the central parts of the Milky Way, globular clusters, or satellite galaxies of the Milky Way, Sagittarius and the Magellanic Clouds. A high-resolution galactic archaeology survey will thus make it possible to observe 0.5 million stars in the central 3 kpc of the Galaxy, several thousand stars in the nuclear part (up to 140pc), as well as at least twenty globular clusters. Several tens of thousands of stars will be observed in the Magellanic Clouds and the Sagittarius Galaxy. The team is involved in all these programmes.