A Multi-wavelength, Multi-epoch Monitoring Campaign of Accretion Variability in T Tauri Stars from the ODYSSEUS Survey. III. Optical Spectra

TL;DR

This study presents a multi-epoch optical spectral monitoring of four T Tauri stars, revealing significant variability in accretion processes and emission lines, and highlighting the complexities in using empirical line luminosity relationships to estimate accretion rates.

Contribution

It provides detailed insights into accretion variability in CTTSs and evaluates the reliability of empirical line luminosity relationships in dynamic accretion environments.

Findings

Magnetospheric truncation radius varies between 2.5-5 R*

Significant variability observed in Halpha, Hbeta, and Hgamma lines

Empirical relationships estimate accretion rates within 0.5 dex on average

Abstract

Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multi-epoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous HST UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5-5 R* across all of our observations. There is also significant variability in all emission lines studied, particularly Halpha, Hbeta, and Hgamma. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability.