TEMPOS

Scientific Background and Goals

JWST is revealing the low-metallicity galaxies that likely powered cosmic reionization at high redshift. These observations are revolutionizing our view of the early universe, but the community is under-prepared to interpret them because models of massive stars remain entirely theoretical and uncertain at the relevant low metallicities. FUV spectra from HST suggest that the winds and ionizing fluxes of O stars change substantially at low metallicity, but our understanding of this complex astrophysics is fundamentally limited by glaring gaps in the observational coverage of O-star parameter space.

Our major scientific goals are to empirically calibrate mass-loss models below 20% Solar metallicity and produce data-driven ionizing spectral templates suitable for modeling observations of metal-poor galaxies, including low-mass dwarf galaxies and high-redshift galaxies that contributed to the ionizing photon budget during the epoch of reionization.

Design of the COS observations

To ensure coverage of key diagnostic features and sufficient resolving power to detect weak absorption lines and take advantage of the information encoded in the structure of stellar and wind lines, we require that all stars in TEMPOS have observations in at least 2 COS gratings: G130M + (G160M or G140L). A target signal-to-noise ratio of at least 10 at the wavelengths of all important diagnostic lines was required for new TEMPOS observations to ensure strong detections.

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