[Paper Review] Hydrodynamical simulations of the jet in the symbiotic star MWC 560 I. Structure, emission and synthetic absorption line profiles

M. Stute, M. Camenzind+1 more|ArXiv.org|Sep 3, 2004

Astrophysics and Star Formation Studies23 references6 citations

TL;DR

This study uses hydrodynamical simulations with and without radiative cooling to model the pulsed jet in the symbiotic star MWC 560, focusing on jet structure, emission, and synthetic absorption line profiles. The key finding is that while adiabatic models qualitatively reproduce the broad, detached absorption component in observed spectra, they overestimate gas temperatures, and higher jet densities or improved cooling mechanisms are needed to match observed low-ionization line strengths.

ABSTRACT

We performed hydrodynamical simulations with and without radiative cooling of jet models with parameters representative for the symbiotic system MWC 560. For symbiotic systems we have to perform jet simulations of a pulsed underdense jet in a high density ambient medium. We present the jet structure resulting from our simulations and calculate emission plots which account for expected radiative processes. In addition, our calculations provide expansion velocities for the jet bow shock, the density and temperature structure in the jet, and the propagation and evolution of the jet pulses. In MWC 560 the jet axis is parallel to the line of sight so that the outflowing jet gas can be seen as blue shifted, variable absorption lines in the continuum of the underlying jet source. Based on our simulations we calculate and discuss synthetic absorption profiles. Based on a detailed comparison between model spectra and observations we discuss our hydrodynamical calculations for a pulsed jet in MWC 560 and suggest improvements for future models.

Motivation & Objective

• To model the jet structure and dynamics in the symbiotic binary MWC 560 using hydrodynamical simulations with and without radiative cooling.
• To investigate how pulsed jet outflows evolve in a high-density ambient medium typical of symbiotic systems.
• To calculate synthetic absorption line profiles from simulated gas distributions and compare them with observed spectroscopic data.
• To assess the diagnostic potential of jet absorption lines for probing jet acceleration and evolution in astrophysical jets.
• To identify limitations in current models, particularly regarding gas temperature and ionization state, and suggest improvements.

Proposed method

• Hydrodynamical simulations were performed using a grid of eight adiabatic models and one radiative cooling model to simulate pulsed underdense jets in a high-density ambient medium.
• The simulations tracked jet propagation, pulse evolution, bow shock expansion, and density/temperature structures over time.
• Emission plots were generated to visualize jet morphology and radiative processes, including shock heating and cooling.
• Synthetic absorption line profiles were computed by projecting the radial velocity distribution of gas along the line of sight, assuming the jet axis is nearly parallel to the observer.
• Model parameters such as pulse velocity, density, and duration were varied to explore their effects on the resulting line profiles.
• The simulations were extended to 50 AU to assess jet evolution, with plans to extend further to avoid artificial truncation of the ambient medium.

Experimental results

Research questions

• RQ1 How do hydrodynamical simulations of pulsed jets in MWC 560 reproduce the observed broad, detached absorption components in the spectrum?
• RQ2 What role does radiative cooling play in determining the temperature and ionization state of jet gas, and how does it affect synthetic absorption line profiles?
• RQ3 Why are the high-velocity components in synthetic profiles weaker than observed, and what model adjustments (e.g., higher density) could resolve this discrepancy?
• RQ4 How does the jet transition from underdense to overdense as it propagates, and what impact does this have on kinematics and observed line profiles?
• RQ5 To what extent can adiabatic simulations serve as a proxy for radiative cooling models in predicting the projected velocity distribution of jet gas?

Key findings

• The adiabatic simulations successfully reproduce the general shape and velocity width of the broad, detached absorption component observed in MWC 560, matching the mean radial velocity and profile structure.
• Despite good agreement in velocity structure, the adiabatic models produce gas temperatures that are too high to explain the observed low-ionization Ca ii lines, indicating a need for more efficient cooling.
• The inclusion of radiative cooling reduces gas temperatures but still fails to fully reproduce the observed ionization levels, suggesting that higher jet densities or additional cooling processes are required.
• The simulated high-velocity components are significantly weaker than observed, pointing to insufficient gas density in the jet pulses as a key limitation.
• The synthetic absorption profiles show discrete components due to rectangular pulse profiles, indicating that smoother pulse shapes (e.g., Gaussian) might better match observations.
• The simulations suggest that extending the computational domain beyond 50 AU is necessary to avoid artificial truncation of the ambient medium, which currently distorts the density structure near the jet's end.