Radial velocities of narrow emission line components in the spectra of T Tauri stars

TL;DR

This study investigates the radial velocity variations of narrow emission lines in T Tauri stars, revealing that observed line shifts are due to optical effects rather than actual gas motion, challenging previous assumptions.

Contribution

The paper demonstrates that line shifts in T Tauri stars are caused by optical thickness and Stark effects, not gas inflow, refining the understanding of emission line origins.

Findings

Line shifts are not due to gas inflow or motion.

Radial velocity curves show no phase shifts between lines.

Optical thickness and Stark effect explain line shifts.

Abstract

We studied rotational modulation of the radial velocities of narrow emission lines in four classical T Tauri stars. We found that the previously declared shift of the mean velocity of neutral and ionized helium lines relative to the mean radial velocity of the star is not associated with the inflow of accreted gas into the hotspot, since the radial velocity curves for lines with different velocity shifts should exhibit phase shifts relative to each other, while the observed phase shifts are absent within their uncertainties and do not correspond to the observed line velocity shifts. This means that the line shifts are not caused by the actual gas motion. For neutral helium lines, the shifts can be explained by the large optical thickness of the lines and the Stark effect at plasma parameters expected at the base of the accretion column of T Tauri stars.