Kavli Affiliate: Gregory J. Herczeg
| First 5 Authors: Julia Roman-Duval, William J. Fischer, Alexander W. Fullerton, Jo Taylor, Rachel Plesha
| Summary:
Specifically selected to leverage the unique ultraviolet capabilities of the
Hubble Space Telescope, the Hubble Ultraviolet Legacy Library of Young Stars as
Essential Standards (ULLYSES) is a Director’s Discretionary program of
approximately 1000 orbits – the largest ever executed – that produced a UV
spectroscopic library of O and B stars in nearby low metallicity galaxies and
accreting low mass stars in the Milky Way. Observations from ULLYSES combined
with archival spectra uniformly sample the fundamental astrophysical parameter
space for each mass regime, including spectral type, luminosity class, and
metallicity for massive stars, and the mass, age, and disk accretion rate for
low-mass stars. The ULLYSES spectral library of massive stars will be critical
to characterize how massive stars evolve at different metallicities; to advance
our understanding of the production of ionizing photons, and thus of galaxy
evolution and the re-ionization of the Universe; and to provide the templates
necessary for the synthesis of integrated stellar populations. The massive star
spectra are also transforming our understanding of the interstellar and
circumgalactic media of low metallicity galaxies. On the low-mass end, UV
spectra of T Tauri stars contain a plethora of diagnostics of accretion, winds,
and the warm disk surface. These diagnostics are crucial for evaluating disk
evolution and provide important input to assess atmospheric escape of planets
and to interpret powerful probes of disk chemistry, as observed with ALMA and
JWST. In this paper we motivate the design of the program, describe the
observing strategy and target selection, and present initial results.
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