A Multi-wavelength, Multi-epoch Monitoring Campaign of Accretion Variability in T Tauri Stars from the ODYSSEUS Survey. I. HST FUV and NUV Spectra

Kavli Affiliate: Gregory J. Herczeg

| First 5 Authors: John Wendeborn, Catherine C. Espaillat, Sophia Lopez, Thanawuth Thanathibodee, Connor E. Robinson

| Summary:

The Classical T Tauri Star (CTTS) stage is a critical phase of the star and
planet formation process. In an effort to better understand the mass accretion
process, which can dictate further stellar evolution and planet formation, a
multi-epoch, multi-wavelength photometric and spectroscopic monitoring campaign
of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was carried out in 2021 and
2022/2023 as part of the Outflows and Disks Around Young Stars: Synergies for
the Exploration of ULYSSES Spectra (ODYSSEUS) program. Here we focus on the HST
UV spectra obtained by the HST Director’s Discretionary Time UV Legacy Library
of Young Stars as Essential Standards (ULLYSES) program. Using accretion shock
modeling, we find that all targets exhibit accretion variability, varying from
short increases in accretion rate by up to a factor of 3 within 48 hours, to
longer decreases in accretion rate by a factor of 2.5 over the course of 1
year. This is despite the generally consistent accretion morphology within each
target. Additionally, we test empirical relationships between accretion rate
and UV luminosity and find stark differences, showing that these relationships
should not be used to estimate the accretion rate for individual target. Our
work reinforces that future multi-epoch and simultaneous multi-wavelength
studies are critical in our understanding of the accretion process in low-mass
star formation.

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