The Wide-field Spectroscopic Telescope (WST)

WST will be the crucial spectroscopic complement to Rubin's photometric LSST. WST is an innovative 10-m class wide-field telescope that allows simultaneous operation of a multi-object spectrograph (MOS) fed by ~20,000 low-resolution and ~2,000 high-resolution fibers across a very large field-of-view (3+ sq. degree) and an unprecedented (9 sq. arcmin) panoramic integral field spectrograph (IFS). Featuring both higher resolution and larger collecting area than 4MOST, a factor of several increase in fiber number, and an IFS 9 times the area of MUSE, WST will lead to breakthrough results across most areas of astrophysics, including the physics of the dark Universe, the first stars and galaxies, cosmic reionisation, the baryon cycle, the stellar populations of the Local Group, and the characterization of exoplanet host stars.

Crucially, a time-domain mindset is built into WST from the start, meaning that transient and time-variable phenomena are considered on par with cosmological, extragalactic, and Galactic science cases. In particular, WST will target synergies with multi-messenger astrophysics and be strongly influenced by time-domain surveys carried out in the meantime, notably ESA's Gaia mission and Rubin's LSST. 

Here, I will give an overview of WST as a facility and the current priorities identified by the time-domain working group. These include telescope-level ToOs to identify and characterize the electromagnetic counterparts of merging neutron stars, fiber-level ToOs for transient follow-up, AGN reverberation mapping, synoptic studies of stellar variability, and Solar system science, among others. The ability to issue alerts will render WST a veritable time-domain machine with crucial abilities in the Rubin era and beyond.