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Spatially Resolved Imaging of the Jet and Low Velocity Wind Component from the Classical T Tauri Star RU Lupi


Core Concepts
The first spatially resolved images of the jet and low velocity wind component from the strongly accreting classical T Tauri star RU Lupi are presented, providing new insights into the structure and collimation of these outflow components.
Abstract

The key findings from this study are:

  1. The jet is imaged for the first time, showing an asymmetric morphology with a possible red-shifted counterpart. The jet extends to double the minimum distance suggested by previous spectro-astrometric studies.

  2. The full opening angle of the jet is larger than typically measured for other young stellar objects, potentially due to the presence of an unresolved shock feature.

  3. The low velocity component (LVC) is also imaged for the first time, revealing that it is wider than the jet in the [O I] λ6300 and [S II] λ6731 emission lines. This supports the interpretation that the LVC traces an MHD disk wind.

  4. The mass outflow rate in the [O I] λ6300 LVC is estimated to be very low, only ~0.02% of the mass accretion rate. This suggests the LVC does not significantly contribute to angular momentum removal, in contrast with model predictions for MHD winds.

  5. The height of the [O I] λ6300 LVC emitting region is measured for the first time, providing a key parameter for estimating the mass outflow rate.

Overall, these spatially resolved observations provide new insights into the structure and collimation of the jet and wind components from RU Lupi, a strongly accreting classical T Tauri star. The results highlight the power of integral field spectroscopy for advancing our understanding of outflow launching and angular momentum regulation in young stellar systems.

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Stats
The mass accretion rate of RU Lupi is estimated to be 1.6 × 10^-7 M_sun/yr. The mass outflow rate in the [O I] λ6300 low velocity component is estimated to be 2.6 × 10^-11 M_sun/yr. The mass outflow rate in the [O I] λ6300 jet component is estimated to be 3.6 - 4.7 × 10^-9 M_sun/yr.
Quotes
"The mass loss rate value puts the efficiency of the outflow component traced by the NC at < 0.1% while models suggest that that Mdot_out ≈ Mdot_acc for the wind, if it dominates angular momentum removal." "The height of the [O I] λ6300 wind emitting region, a key parameter for the derivation of the mass loss rate, is estimated for the first time at ~35 au."

Deeper Inquiries

How do the properties of the molecular wind, as traced by CO emission, compare to the atomic wind traced by [O I] and what implications does this have for our understanding of the outflow launching mechanism?

The properties of the molecular wind traced by CO emission and the atomic wind traced by [O I] reveal significant differences that have important implications for our understanding of the outflow launching mechanism in classical T Tauri stars like RU Lupi. The CO emission, which is indicative of a molecular wind, has been reported to have a mass loss rate approximately two orders of magnitude higher than that of the atomic wind traced by [O I] λ6300, which is estimated at (2.6 \times 10^{-11} M_{\odot} \text{yr}^{-1}). This stark contrast suggests that the molecular wind may carry a substantial amount of mass and energy away from the star, potentially playing a more critical role in the overall outflow dynamics. The low mass loss rate of the atomic wind implies that it may not be the primary mechanism for angular momentum removal, as models suggest that for effective angular momentum regulation, the mass loss rate of the wind should be comparable to the mass accretion rate. In RU Lupi, the mass accretion rate is significantly higher at (1.6 \times 10^{-7} M_{\odot} \text{yr}^{-1}), indicating that the atomic wind traced by [O I] does not contribute significantly to angular momentum removal. This leads to the conclusion that the molecular wind, which is likely more abundant and carries more mass, could be the dominant outflow component responsible for regulating the accretion process and angular momentum in the system.

What role could the asymmetry observed in the jet play in the overall angular momentum regulation of the system, and how might this asymmetry arise?

The observed asymmetry in the jet of RU Lupi could play a significant role in the overall angular momentum regulation of the system. Asymmetries in outflows can indicate variations in the density and magnetic field structure of the surrounding medium, which can affect the dynamics of the outflow. In the case of RU Lupi, the brighter north-western side of the jet compared to the south-eastern side suggests that one side may be expanding into a denser medium, which could enhance the outflow's momentum on that side. This differential expansion could lead to a more efficient removal of angular momentum from the accretion disk, as the denser medium may provide a greater resistance to the outflow, allowing for more effective collimation and acceleration of the jet. The asymmetry may arise from several factors, including the influence of the magnetic field, which can create preferential pathways for the outflow, or from the interaction of the outflow with the surrounding environment, such as the accretion disk or nearby material. Additionally, variations in the mass accretion rate or the distribution of angular momentum in the disk could lead to asymmetric outflow dynamics. Understanding these asymmetries is crucial, as they may provide insights into the mechanisms of angular momentum transfer and the efficiency of mass ejection processes in young stellar objects.

Given the low efficiency of the atomic wind traced by [O I], what other observational signatures could be used to identify the dominant mechanism for angular momentum removal in this system?

To identify the dominant mechanism for angular momentum removal in the RU Lupi system, especially given the low efficiency of the atomic wind traced by [O I], several other observational signatures could be explored. One promising avenue is the study of molecular outflows, particularly those traced by CO or H₂ emissions. These molecular lines can provide insights into the mass loss rates and kinematics of the outflow, which are critical for understanding their role in angular momentum regulation. Additionally, high-resolution observations of the dust continuum emission from the surrounding disk could reveal the structure and dynamics of the disk itself, allowing for a better understanding of how the disk interacts with the outflows. Observations of the disk's rotation and any potential warping or asymmetries could indicate how angular momentum is being transferred between the disk and the outflow. Spectro-astrometric techniques could also be employed to measure the spatial distribution of emission lines in the outflow, providing information on the velocity structure and density of the outflowing material. This could help distinguish between different outflow components and their contributions to angular momentum removal. Finally, multi-wavelength observations, including X-ray and UV emissions, could provide additional context regarding the energetic processes at play in the system. These emissions can be indicative of the interaction between the stellar radiation and the surrounding material, which may influence the dynamics of both the accretion and outflow processes. By combining these various observational signatures, a more comprehensive understanding of the mechanisms governing angular momentum removal in RU Lupi can be achieved.
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