PLATOSpec: a precise spectrograph in support of space missions

TL;DR

PLATOSpec presents a blue-sensitive, high-resolution ($R=70{,}000$) echelle spectrograph mounted on the ESO 1.5-m La Silla telescope, designed to deliver RV precisions of about $3$–$5$ m s$^{-1}$ for efficient ground-based vetting of PLATO/Ariel targets and concurrent studies of stellar variability. The paper details the instrument’s hardware (front end, calibration unit, spectrograph), calibration modes (Simultaneous ThAr and iodine cell), a ceres+-based data-reduction workflow, and vipER iodine processing, and it showcases initial science verification across exoplanet mass determinations, RM spin-orbit measurements, line-profile analyses, and activity in young stars. It demonstrates PLATOSpec’s versatility for candidate screening, mass measurements, and variability surveys, with robust data-flow and archiving plans including a move to the ESO archive in 2026. Collectively, PLATOSpec provides a practical, automation-friendly platform to support upcoming space missions by enabling rapid, ground-based characterization and long-baseline stellar studies using blue-sensitive spectroscopy on a modest-aperture telescope.

Abstract

The upcoming space missions that will characterize exoplanets, such as PLATO and Ariel, will collect huge amounts of data that will need to be complemented with ground-based observations. The aim of the PLATOSpec project is to perform science with an echelle spectrograph capable of measuring precise radial velocities. The main focus of the spectrograph will be to perform the initial screening and validation of exoplanetary candidates, in addition to study stellar variability. It will be possible to determine the physical properties of large exoplanets. The PLATOSpec blue-sensitive spectrograph, with a spectral range of 380 to 700\,nm and a resolving power of R=70,000, is installed on the 1.5-m telescope at the ESO La Silla Observatory in Chile. Initial results show that the radial-velocity limit given by the wavelength calibration is about 2-3 m/s. Tests on bright F-K main-sequence standard stars reveal a scatter of about 5 m/s over a few hours. The scatter over a few months is slightly higher. We demonstrate the capabilities of PLATOSpec on the mass determination of WASP-79 b and the spin-orbit alignment of WASP-62\,b via the Rossiter-McLaughlin effect. We show its possible usage on variable star research as demonstrated on the false-positive exoplanetary candidate TIC 238060327, which is proven a binary star. Investigation of line-profile variations of the roAp star alpha Cir shows that PLATOSpec can also be used for the surface mapping. Finally, we present new results on the active star UY Pic in the PLATO southern field. Our results show that PLATOSpec is a versatile spectrograph with great precision.

Figures (18)

• Figure 1: Light path from the telescope to the spectrograph (FbS) via the front end and the fiber linking the calibration unit to the spectrograph (Fb1) and the front end (Fb2).
• Figure 2: Light path in the front end. At the bottom, a set of mirrors reflects light to the guiding camera, while a movable mirror (blue triangle in the beam from the telescope) can reflect light from the calibration unit to the spectrograph through the single scientific fiber. The front end includes also an iodine cell (IC) that can be moved in the beam if requested.
• Figure 3: The calibration unit consists of two ThAr lamps and, for simultaneous calibration, a flat lamp (FF) with an additional UV-LED (LED) source and an iodine cell (Iod). It is connected by another optical fiber to the front end (Fb2) and by other fiber (Fb1) to the spectrograph.
• Figure 4: Optical design of the elements of the spectrograph.
• Figure 5: Sample of optimal measurements used for the efficiency determination. The median value of 9% is represented by the blue dashed line.