Generation of radiative knots in a randomly pulsed protostellar jet I. Dynamics and energetics

Astronomy and Astrophysics (Impact Factor: 5.08). 12/2009; DOI: 10.1051/0004-6361/200913595
Source: arXiv

ABSTRACT HH objects are characterized by a complex knotty morphology detected mainly along the axis of protostellar jets in a wide range of bands. Evidence of interactions between knots formed in different epochs have been found, suggesting that jets may result from the ejection of plasma blobs from the source. We aim at investigating the physical mechanism leading to the irregular knotty structure observed in jets in different bands and the complex interactions occurring among blobs of plasma ejected from the stellar source. We perform 2D axisymmetric HD simulations of a randomly ejected pulsed jet. The jet consists of a train of blobs which ram with supersonic speed into the ambient medium. The initial random velocity of each blob follows an exponential distribution. We explore the ejection rate parameter to derive constraints on the physical properties of protostellar jets by comparison of model results with observations. Our model takes into account radiative losses and thermal conduction. We find that the mutual interactions of blobs ejected at different epochs and with different speed lead to a variety of plasma components not described by current models. The main features characterizing the random pulsed jet scenario are: single high speed knots, showing a measurable proper motion in nice agreement with observations; irregular chains of knots aligned along the jet axis and possibly interacting with each other; reverse shocks interacting with outgoing knots; oblique shocks produced by the reflection of shocks at the jet cocoon. All these structures concur to determine the morphology of the jet in different bands. We also find that the thermal conduction plays a crucial role in damping out HD instabilities that would develop within the cocoon and that contribute to the jet breaking. Comment: 10 pages, 10 figures, accepted for publication in A&A

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: X-ray emission from about ten protostellar jets has been discovered and it appears as a feature common to the most energetic jets. Although X-ray emission seems to originate from shocks internal to jets, the mechanism forming these shocks remains controversial. One of the best studied X-ray jet is HH 154 that has been observed by Chandra over a time base of about 10 years. We analyze the Chandra observations of HH 154 by investigating the evolution of its X-ray source. We show that the X-ray emission consists of a bright stationary component and a faint elongated component. We interpret the observations by developing a hydrodynamic model describing a protostellar jet originating from a nozzle and compare the X-ray emission synthesized from the model with the X-ray observations. The model takes into account the thermal conduction and radiative losses and shows that the jet/nozzle leads to the formation of a diamond shock at the nozzle exit. The shock is stationary over the period covered by our simulations and generates an X-ray source with luminosity and spectral characteristics in excellent agreement with the observations. We conclude that the X-ray emission from HH 154 is consistent with a diamond shock originating from a nozzle through which the jet is launched into the ambient medium. We suggest that the physical origin of the nozzle could be related to the dense gas in which the HH 154 driving source is embedded and/or to the magnetic field at the jet launching/collimation region.
    The Astrophysical Journal 05/2011; · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Protostars are actively accreting matter and they drive spectacular, dynamic outflows, which evolve on timescales of years. X-ray emission from these jets has been detected only in a few cases and little is known about its time evolution. We present a new Chandra observation of L1551 IRS 5's jet in the context of all available X-ray data of this object. Specifically, we perform a spatially resolved spectral analysis of the X-ray emission and find that (a) the total X-ray luminosity is constant over almost one decade, (b) the majority of the X-rays appear to be always located close to the driving source, (c) there is a clear trend in the photon energy as a function of the distance to the driving source indicating that the plasma is cooler at larger distances and (d) the X-ray emission is located in a small volume which is unresolved perpendicular to the jet axis by Chandra. A comparison of our X-ray data of the L1551 IRS 5 jet both with models as well as X-ray observations of other protostellar jets shows that a base/standing shock is a likely and plausible explanation for the apparent constancy of the observed X-ray emission. Internal shocks are also consistent with the observed morphology if the supply of jet material by the ejection of new blobs is sufficiently constant. We conclude that the study of the X-ray emission of protostellar jet sources allows us to diagnose the innermost regions close to the acceleration region of the outflows.
    Astronomy and Astrophysics 05/2011; 530. · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Context. HH 444 is one of the first Herbig-Haro (HH) jets discovered within a photoionized region. Aims: We re-analyze the Halpha and red [S II] HST images of HH 444, and calculate the width of the jet as a function of distance from the source. We compare the Halpha image with predictions from variable ejection velocity jet models. Methods: The determination of the jet's width is done with a non-parametric, wavelet analysis technique. The axisymmetric, photoionized jet simulations are used to predict Halpha maps that can be directly compared with the observations. Results: Starting with a thin jet (unresolved at the resolution of the observations), we are able to produce knots with widths and morphologies that generally agree with the Halpha knots of HH 444. This agreement is only obtained if the jet axis is at a relatively large, ~45° angle with respect to the sky. This agrees with previous spectroscopic observations of the HH 444 bow shock, which imply a relatively large jet axis/plane of the sky angle. Conclusions: We conclude that the general morphology of the chain of knots close to V510 Ori (the HH 444 source) can be explained with a variable ejection velocity jet model. For explaining the present positions of the HH 444 knots, however, it is necessary to invoke a more complex ejection velocity history than a single-mode, periodic variability.
    Astronomy and Astrophysics 01/2010; 517. · 5.08 Impact Factor

Full-text (2 Sources)

Available from
Jun 2, 2014