X-Shooting ULLYSES: Massive Stars at Low Metallicity

TL;DR

The XShootU project combines UV, optical, and near-infrared spectra of low-metallicity massive stars to improve parameter determination and enhance understanding of early stellar populations, aiding JWST data interpretation.

Contribution

It provides high-quality, multi-wavelength spectra and analysis tools for low-metallicity massive stars, integrating UV and optical data for comprehensive stellar characterization.

Findings

Enhanced accuracy in stellar parameter determination.

Improved understanding of mass-loss rates at low metallicity.

Resource for interpreting early universe stellar populations.

Abstract

The Hubble Space Telescope has devoted 500 orbits to observing 250 massive stars with low metallicity in the ultraviolet (UV) range within the framework of the ULLYSES program. The X-Shooting ULLYSES (XShootU) project enhances the legacy value of this UV dataset by providing high-quality optical and near-infrared spectra, which are acquired using the wide-wavelength-coverage X-shooter spectrograph at ESO's Very Large Telescope. XShootU emphasises the importance of combining UV with optical spectra for the consistent determination of key stellar parameters such as effective temperature, surface gravity, luminosity, abundances, and wind characteristics including mass-loss rates as a function of metallicity. Since uncertainties in these parameters have implications across various branches of astrophysics, the data and modelling generated by the XShootU project are poised to significantly advance our understanding of massive stars at low metallicity. This is particularly crucial for confidently interpreting JWST data of the earliest stellar generations, making XShootU a unique resource for comprehending individual spectra of low-metallicity stars.