Abstract
Abstract The Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) Director’s Discretionary Program of low-mass pre-main-sequence stars, coupled with forthcoming data from Atacama Large Millimeter/submillimeter Array and James Webb Space Telescope, will provide the foundation to revolutionize our understanding of the relationship between young stars and their protoplanetary disks. A comprehensive evaluation of the physics of disk evolution and planet formation requires understanding the intricate relationships between mass accretion, mass outflow, and disk structure. Here we describe the Outflows and Disks around Young Stars: Synergies for the Exploration of ULLYSES Spectra (ODYSSEUS) Survey and present initial results of the classical T Tauri Star CVSO 109 in Orion OB1b as a demonstration of the science that will result from the survey. ODYSSEUS will analyze the ULLYSES spectral database, ensuring a uniform and systematic approach in order to (1) measure how the accretion flow depends on the accretion rate and magnetic structures, (2) determine where winds and jets are launched and how mass-loss rates compare with accretion, and (3) establish the influence of FUV radiation on the chemistry of the warm inner regions of planet-forming disks. ODYSSEUS will also acquire and provide contemporaneous observations at X-ray, optical, near-IR, and millimeter wavelengths to enhance the impact of the ULLYSES data. Our goal is to provide a consistent framework to accurately measure the level and evolution of mass accretion in protoplanetary disks, the properties and magnitudes of inner-disk mass loss, and the influence of UV radiation fields that determine ionization levels and drive disk chemistry.
Highlights
The Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES)1 Director’s Discretionary Program offers a once-in-a-lifetime opportunity to deepen our understanding of the connection between accreting young stars and their planet-forming disks
We present a first look at the results for the classical T Tauri stars (CTTS) CVSO 109 in order to demonstrate the analysis we will undertake with ODYSSEUS for the entire ULLYSES sample
Since CVSO 109A dominates the light at the TiO2 wavelength (7043–7061 ̊A, see Figure 2), we would expect the resulting spectral type to be closer to M0 than M1 for the nominal spectral types assigned in Table 3; given the spectral type uncertainty reported there and in the relation in Reid et al (1995), our analysis of the high-resolution McDonald spectra is fully consistent with the resolved spectral types determined from the Hubble Space Telescope (HST)/Space Telescope Imaging Spectrometer (STIS) spectra measured above and from the unresolved UVES spectra measured by Manara et al (2021)
Summary
The Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) Director’s Discretionary Program offers a once-in-a-lifetime opportunity to deepen our understanding of the connection between accreting young stars and their planet-forming disks. Far- and near-ultraviolet (FUV and NUV) spectroscopy provides unique and powerful spectral diagnostics of young stars and innermost disk regions, conveying crucial information to help answer some of the fundamental questions about CTTS accretion flows, mass and angular momentum transport in the disk, and disk irradiation (see review by Schneider et al 2020). ODYSSEUS will provide a uniform, systematic analysis of the ULLYSES data, including the application of new, rigorous models for accretion shocks and winds, as well as extraction and interpretation of the complex forest of FUV lines. These analyses are interconnected, with interpretations that rely upon one another and upon a consistent set of star and disk properties. We begin by introducing the background for FUV observations of accretion (§1.1), outflows (§1.2), and irradiated disks (§1.3), to place our results in context
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