Investigating the asymmetry of young stellar outflows: Combined MUSE-X-shooter study of the Th 28 jet^★

¹ Academica Sinica Institute of Astronomy and Astrophysics, No 1. Sec. 4, Roosevelt Rd., Taipei 10617, 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
⁷ INAF – Osservatorio Astronomico di Roma, Via di Frascati 33, 00078 Monte Porzio Catone, Italy
⁸ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁹ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, D02 XF86 Dublin, Ireland

^★★ Corresponding author; amurphy@asiaa.sinica.edu.tw

Received: 20 June 2024
Accepted: 23 August 2024

Abstract

Context. Characterising stellar jet asymmetries is key to setting robust constraints on jet launching models and improving our understanding of the underlying mechanisms behind jet launching.

Aims. We aim to characterise the asymmetric properties of the bipolar jet coming from the Classical T Tauri Star Th 28.

Methods. We combined data from integral field spectroscopy with VLT/MUSE and high-resolution spectra from VLT/X-shooter to map the optical emission line ratios in both jet lobes. We carried out a diagnostic analysis of these ratios to compare the density, electron temperature, and ionisation fraction within both lobes. The mass accretion rate was derived from the emission lines at the source and compared with the mass outflow rate derived for both lobes, using the estimated densities and measured [O I]λ6300 and [S II]λ6731 luminosities.

Results. The blue-shifted jet exhibits a significantly higher electron temperature and moderately higher ionisation fraction than the red-shifted jet. In contrast to previous studies, we also estimated higher densities, denoted as n_H , in the blue-shifted jet by a factor of ~2. These asymmetries are traced to within 1″ (160 au) of the source in the line ratio maps. We find Ṁ_acc = 2.4 × 10⁻⁷ M_⊙ yr⁻¹, with an estimated obscuration factor of ~54 due to grey scattering around the star. Estimated values of Ṁ_out range between 0.66 and 13.7 × 10⁻⁹ M_⊙ yr⁻¹ in the blue-shifted jet and 5–9 × 10⁻⁹ M_⊙ yr⁻¹ in the red-shifted jet.

Conclusions. The emission line maps and diagnostic results suggest that the jet asymmetries originate close to the source and are likely to be intrinsic to the jet. Furthermore, the combined dataset offers access to a broad array of accretion tracers. In turn, this enables a more accurate estimation of the mass accretion rate, revealing a value of Ṁ_acc that is higher by a factor >350 than would otherwise be determined.