Nonradial and nonpolytropic astrophysical outflows IX. Modeling T Tauri jets with a low mass-accretion rate

TL;DR

This paper models stellar jets from T Tauri stars using semi-analytical MHD solutions, showing how jets can brake star rotation and explaining why some stars have visible jets while others do not.

Contribution

It introduces a novel semi-analytical approach to model T Tauri stellar jets, linking jet properties to star braking and visibility, and explains the CTTS/WTTS dichotomy.

Findings

Jets can effectively brake star rotation at low accretion rates.

Jet visibility depends on boundary conditions and activity phases.

Different jet configurations explain observed star behaviors.

Abstract

Context: A large sample of T Tauri stars exhibits optical jets, approximately half of which rotate slowly, only at ten per cent of their breakup velocity. The disk-locking mechanism has been shown to be inefficient to explain this observational fact. Aims: We show that low mass accreting T Tauri stars may have a strong stellar jet component that can effectively brake the star to the observed rotation speed. Methods: By means of a nonlinear separation of the variables in the full set of the MHD equations we construct semi- analytical solutions describing the dynamics and topology of the stellar component of the jet that emerges from the corona of the star. Results: We analyze two typical solutions with the same mass loss rate but different magnetic lever arms and jet radii. The first solution with a long lever arm and a wide jet radius effectively brakes the star and can be applied to the visible jets of T Tauri stars, such as RY Tau. The second solution with a shorter lever arm and a very narrow jet radius may explain why similar stars, either Weak line T Tauri Stars (WTTS) or Classical T Tauri Stars (CTTS) do not all have visible jets. For instance, RY Tau itself seems to have different phases that probably depend on the activity of the star. Conclusions: First, stellar jets seem to be able to brake pre-main sequence stars with a low mass accreting rate. Second, jets may be visible only part time owing to changes in their boundary conditions. We also suggest a possible scenario for explaining the dichotomy between CTTS and WTTS, which rotate faster and do not have visible jets.