The accretion-ejection connection in the asymmetric Th 28 jet revealed by MUSE-NFM^★

¹ Academia Sinica Institute of Astronomy and Astrophysics, No. 1. Sec. 4, Roosevelt Rd., Taipei 106319, Taiwan
² Department of Experimental Physics, Maynooth University, Maynooth, Co Kildare, Ireland
³ INAF—Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
⁵ ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁶ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany

^★★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 22 December 2025
Accepted: 23 January 2026

Abstract

Context. Mass loss through stellar jets is closely tied to the process of accretion through the disk. Understanding mass loss phenomena such as episodic ejections and outflow asymmetries can shed light on the mechanism of jet launching and its connection to both mass accretion and the evolution of the protoplanetary disk.

Aims. We aim to determine the mass outflow rates close to the base of the asymmetric jets launched by the Classical T Tauri Star Th 28 and to identify signatures of variable mass accretion and ejection in this source.

Methods. We used new VLT/MUSE Narrow Field Mode observations of Th 28 to map the jet structures within 6" of the source at an effective angular resolution of 0.' 12 provided by the combination of the adaptive optics correction and image deconvolution. We investigated the emission line profiles and flux ratios and used a diagnostic analysis of the optical forbidden emission lines (FELs) to estimate the electron density, ionisation fraction, electron temperature, and shock velocities in both jet lobes within 200 au of the star. The mass outflow rates in each lobe were obtained using the derived total densities and FEL luminosities and compared with the mass accretion rate.

Results. We identified several new knots in both jet lobes that were ejected in the previous 10 years. These indicate ejections on a timescale of 3-6 years, which is significantly more frequent than previously estimated. In both lobes, we find comparable mass outflow rates close to the jet base, with average values of Ṁ_out = 1-3 × 10⁻⁸ M_⊙ yr⁻¹. We find that the mass accretion rate has approximately doubled between 2014 and 2023, and we estimate Ṁ_acc = 2.11 × 10⁻⁷ M_⊙ yr⁻¹. Analysis of the redshifted jet mass outflow rate shows a similar increase of a factor of two, indicating that the ratio of mass outflow to accretion remains constant.

Conclusions. Th 28 has undergone a significant rise in mass accretion rate since the previous epoch, which may be linked to the most recently ejected knot pair detected in each side of the jet. These observations show that the mass outflow rate remains a constant fraction of the mass accretion. A moderately lower mass outflow rate is found in the faster blueshifted lobe, supporting the possibility that momentum ejection is conserved on each side of the jet. The evidence of frequent knot ejections indicates that this source is a good target for further monitoring to study the accretion-ejection connection.