What is WEAVE?

WEAVE is a wide-field, fibre-fed multi-object spectrograph mounted at the prime focus of the 4.2-metre William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory on La Palma, in the Canary Islands. It was built by an international consortium with partners in the UK, the Netherlands, Spain, France, Italy, Germany, Sweden, Mexico, Hungary and the United States, and it started science operations in 2023.

The instrument can place about 1,000 optical fibres across a two-degree field of view. The fibres feed a two-arm spectrograph that covers the whole optical range from 3660 to 9590 Å in one exposure. A dichroic at 5900 Å splits the light into a blue arm and a red arm, and each arm is read out by two 6k × 6k low-fringing CCDs. There are two resolution settings, low (R ≈ 5,000) and high (R ≈ 20,000), so WEAVE can serve very different science cases, from large stellar surveys to detailed studies of galaxy kinematics.

Three observing modes

CAMCEAD's role in WEAVE

CAMCEAD, at the Institute of Astronomy in Cambridge, runs the complete WEAVE data flow, from preparing survey observations for the telescope to delivering products to the archive. This includes the WEAVE Automatic Submission Platform (WASP), the Operational Repository and its data access protocol (WOR/WDAP), the Core Processing System (CPS, Level 1) and the Advanced Processing System (APS, Level 2). The team also contributes to the WEAVE Archive System (WAS) and hosts contributed software.

The pipelines run in two places. WASP, WOR/WDAP and CPS run on CAMCEAD's own computing and storage at the Institute of Astronomy, while APS (L2) runs on the IRIS National Cloud Facility, on an OpenStack Kubernetes cluster that CAMCEAD manages.

How the data flows

The Operational Repository (OR) is the centre of WEAVE data operations. Survey preparation, telescope operations, pipeline processing, provenance tracking and archive publication are all coordinated through it.

WASP: WEAVE Automatic Submission Platform

WASP is where survey science teams hand their plans over to WEAVE operations. It runs on CAMCEAD's own computing and storage and covers every step from survey design to observing blocks the telescope can execute: submitting catalogues, checking them against the WEAVE data model, planning each trimester, generating observing blocks (OBs), and sending FITS target catalogues and XML observing blocks to the Observation Control System (OCS) at the WHT.

WOR and WDAP: running the operations

The WEAVE Operational Repository (WOR) keeps track of the state and provenance of all WEAVE data and manages the workflows. It is hosted on CAMCEAD's own computing and storage at the Institute of Astronomy. WDAP, the WEAVE Data Access Protocol, is the secure, recipe-driven interface that WASP, the WHT, CPS, APS and WAS all use to exchange data with the OR in both directions. Every product transfer, change of state, data-model check and provenance record goes through it.

CPS: Core Processing System (Level 1)

CPS turns raw WHT observations into calibrated spectra and data cubes that are ready for science. It runs on CAMCEAD's own computing and storage and processes all three observing modes (MOS, LIFU and mIFU) with a heavily parallelised, recipe-driven pipeline. Its outputs are calibrated 1D spectra for every fibre, IFU data cubes for the LIFU and mIFU, stacked products at OB and target level, quality control reports, and the calibration data that APS needs.

APS: Advanced Processing System (Level 2)

APS takes the calibrated L1 data and produces measurements, maps and catalogues for science. Unlike CPS, it runs on the IRIS National Cloud Facility, on an OpenStack Kubernetes cluster managed by CAMCEAD with about 1,400 vCPUs, 8 GPUs, 5 TB of RAM and 2 PB of Ceph storage. The cluster scales up and down as needed, which suits large jobs such as redshift fitting, spectral analysis and classification across all the WEAVE surveys.

The APSOB common reader prepares L1 FITS files from every observing mode. The science modules are Redrock (redshifts and object classification), FERRE (stellar parameters and chemical abundances), RVS (radial velocities), pPXF and EMI-pPXF (stellar kinematics and emission lines) and LS (emission-line measurements). The PyAPS pipeline is the framework that runs these modules inside APS. Galactic and extragalactic data are processed in separate branches, and the results include redshifts, stellar parameters, kinematics, IFU emission-line maps and science catalogues.

From telescope to archive

Every night the raw data from the WHT on La Palma is transferred to Cambridge, where CAMCEAD takes over. The diagram below follows the data from raw frames through CPS, validation in the OR and APS processing in the cloud, and finally to the WEAVE Archive System (WAS) in the Canary Islands. It also shows typical data volumes at each stage.

Infrastructure