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The Numerical Modelling Of Scenarios For The Herbig-Haro Object HH30

Lynch, Chris (2017) The Numerical Modelling Of Scenarios For The Herbig-Haro Object HH30. Doctor of Philosophy (PhD) thesis, University of Kent,. (KAR id:65784)

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Abstract

The classical T-Tauri star HH30 in Taurus-Auriga exhibits a well-collimated plume of hot, optically-emitting atomic and partially ionised Hydrogen, and also a colder, dense, wide-angle molecular Hydrogen ouflow. Observations suggest HH30 is a binary system system, surrounded by a circumbinary accretion disc. We investigated the propagation and interaction of dual atomic and molecular outflows from HH30, using a series of numerical simulations with parameters informed by observational campaigns. These 3-dimensional models were computed using the established Eulerian astrophysics code ZEUS-MP, with in-house modifications and an enhanced chemistry and cooling module. These simulations assumed off-domain launch and tracked the evolution of the jets over spatial scale of ~ 100 AU, and with a timescale ~ 100 - 200 years. The propagation in this region is of special interest, as this is where the greatest difference between the two scenarios is likely to emerge. Our work here differs from "classical" simulations of jet propagation by virtue of one or both outflow sources moving in an orbit.

Two competing scenarios were investigated, in which the morphology of the light-year scale outflow from HH30 is explained by different kinds of motion of the atomic outflow source, and in which the launch site of the molecular outflow differs. In both cases a velocity-pulsed atomic jet emerges from the more massive binary object. In the Orbital scenario, the orbital motion of the primary explains the morphology seen at large scale, while the molecular flow is launched from the secondary partner; in the Precessional scenario, precession of the primary dominates the morphology, while launch of the molecular flow is from the inner edge of the circumbinary disc. The binary orbit and inner depletion zone of the circumbinary disc differs between the scenarios, with the Precessional scenario having a much smaller orbit and correspondingly reduced inner depletion zone. Clearly identifiable structural differences emerge between the simulated models.

We compared the effects of the two different kinds of perturbing molecular outflow on the faster atomic jet; position, velocity, line mass per unit length, temperature and other variables, as a function of distance x (AU) from the binary source. Linear and quadratic fit functions were determined to facilitate comparison with observation. These quantify the expected behaviours of the atomic jet in the presence of the two different kinds of molecular flow. Where the fit function domains overlap direct comparisons may be drawn; where 26 < x < 42 AU, the average velocity as a function of distance is Vx(x) = (1.39×10^?1 ±2.15×10^?3)x + (246.82±1.29) km s^?1 in the Precessional model, while in the Orbital model we find Vx(x) = (?3.26 ± 0.26)x + (269.57 ± 6.75) km s^?1. In the region 10 < x < 60 AU, the Precessional model has temperature dependence T(x) = (64.53 ± 12.54)x + (3535 ± 330) K. Whilst in the same region of the Orbital model, T(x) = (401.99 ± 333.19)x + (4258.4 ± 1340.3) K.

Synthetic Mass-Velocity Spectra have been generated for our models, to investigate distinguishing features of these spectra in the presence of the two different types of molecular outflow. The shallow-angle spectra matching the aspect angle of HH30 itself are examined and the link between outflow scenario and time variability discussed. Spectra from the same dual outflow systems observed at different aspect angles to the sky plane are given, to provide a means to confirm these senarios in other HH30-like T-Tauri stars.

Using code written in-house to calculate emission using rate coefficients for photon production, we generated synthetic observations; spatially resolved images, velocity channel maps and position-velocity diagrams. The morphology of the synthetic images from the two scenarios when compared to HST R-band imaging of HH30 suggests that the Orbital case is unlikely, whilst the Precessional case is supported.

Item Type: Thesis (Doctor of Philosophy (PhD))
Thesis advisor: Smith, MIchael
Thesis advisor: Miao, Jingqi
Uncontrolled keywords: astrophysics; astronomy; computational numerical simulation; T-Tauri; HH30; protostar; protostellar; jet outflow; binary circumbinary mass-velocity; orbital precessional wiggle; ZEUS-MP SCIAMA
Divisions: Faculties > Sciences > School of Physical Sciences
SWORD Depositor: System Moodle
Depositing User: System Moodle
Date Deposited: 25 Jan 2018 10:30 UTC
Last Modified: 25 Jan 2020 04:10 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/65784 (The current URI for this page, for reference purposes)
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