Guest blog post by George Seabroke, RVS Payload Expert, on behalf of the team commissioning the RVS instrument.
The Radial Velocity Spectrometer (RVS) is one of three instruments onboard Gaia (see Figure 1). It is designed to measure the line-of-sight velocity component of Gaia stars (radial velocity, RV) to complement Gaia astrometry, which measures the transverse velocity component (parallax converts proper motions to transverse velocity). Combining the radial and transverse velocities gives the 3D space velocity of Gaia stars, allowing Gaia to produce not only a map of where Gaia stars are but how they are moving.
Figure 1: Photographs of RVS components (insets) overlaid on a photograph of the Gaia Payload Module at Astrium in Toulouse. Credits: Astrium, except top left (ESA/Gaia/DPAC/Airbus DS), bottom left (ESA) and top right (Selex Galileo, Italy). Composite designed by George Seabroke, MSSL.
The accuracy that Gaia astrometry is aiming for can only be achieved above the Earth’s atmosphere. The RV accuracy that RVS is aiming for (a few km/s for bright stars) can be achieved from the ground: however, the ground-based RV follow-up of the 118,200 Hipparcos stars managed about 20,000 stars in 15 years (a remarkable effort at the time!). Therefore it ...