Search results for "Outflow"
showing 10 items of 111 documents
Jet propagation through inhomogeneous media and shock ionization
2021
In this contribution we present the first numerical simulations of a relativistic outflow propagating through the inner hundreds of parsecs of its host galaxy, including atomic and ionised hydrogen, and the cooling effects of ionisation. Our results are preliminary, but we observe efficient shock ionization of atomic hydrogen in interstellar clouds. The mean density of the interstellar medium in these initial simulations is lower than that expected in typical galaxies, which makes cooling times longer and thus no recombination is observed inside the shocked region. The velocities achieved by the shocked gas in the simulations are in agreement with observational results, although with a wide…
The X-ray emission mechanism in the protostellar jet HH 154
2004
We study the mechanism causing the X-ray emission recently detected in protostellar jets, by performing a detailed modeling of the interaction between a supersonic jet originating from a young stellar object and the ambient medium, for various values of density contrast, ν, between the ambient density and the jet, and of Mach number, M; radiative losses and thermal conduction have been taken into account. Here we report a representative case which reproduces, without any ad hoc assumption, the characteristics of the X-ray emission recently observed in the protostellar jet HH 154. We find that the X-ray emission originates from a localized blob, consistent with observations, which moves with…
X-rays from protostellar jets: emission from continuous flows
2006
Recently X-ray emission from protostellar jets has been detected with both XMM-Newton and Chandra satellites, but the physical mechanism which can give rise to this emission is still unclear. We performed an extensive exploration of a wide space of the main parameters influencing the jet/ambient interaction. Aims include: 1) to constrain the jet/ambient interaction regimes leading to the X-ray emission observed in Herbig-Haro objects in terms of the emission by a shock forming at the interaction front between a continuous supersonic jet and the surrounding medium; 2) to derive detailed predictions to be compared with optical and X-ray observations of protostellar jets; 3) to get insight int…
The diagnostic potential of Fe lines applied to protostellar jets
2013
We investigate the diagnostic capabilities of the iron lines for tracing the physical conditions of the shock-excited gas in jets driven by pre-main sequence stars. We have analyzed the 300-2500 nm X-shooter spectra of two jets driven by the pre-main sequence stars ESO-Halpha 574 and Par-Lup 3-4. Both spectra are very rich in [FeII] lines over the whole spectral range; in addition, lines from [FeIII] are detected in the ESO-H\alpha 574 spectrum. NLTE codes along with codes for the ionization equilibrium are used to derive the gas excitation conditions of electron temperature and density, and fractional ionization. The iron gas-phase abundance is provided by comparing the iron lines emissivi…
On the Azimuthal Stability of Shock Waves around Black Holes
1998
Analytical studies and numerical simulations of time dependent axially symmetric flows onto black holes have shown that it is possible to produce stationary shock waves with a stable position both for ideal inviscid and for moderately viscous accretion disks. We perform several two dimensional numerical simulations of accretion flows in the equatorial plane to study shock stability against non-axisymmetric azimuthal perturbations. We find a peculiar new result. A very small perturbation seems to produce an instability as it crosses the shock, but after some small oscillations, the shock wave suddenly transforms into an asymmetric closed pattern, and it stabilizes with a finite radial extent…
An X-shooter survey of star forming regions: Low-mass stars and sub-stellar objects
2011
We present preliminary results of our X-shooter survey in star forming regions. In this contribution we focus on sub-samples of young stellar and sub-stellar objects (YSOs) in the Lupus star forming region and in the TW Hya association. We show that the X-shooter spectra are suitable for conducting several parallel studies such as YSO + disk fundamental parameters, accretion and outflow activity in the very low-mass (VLM) and sub-stellar regimes, as well as magnetic activity in young VLM YSOs, and Li abundance determinations. The capabilities of X-shooter in terms of wide spectral coverage, resolution and limiting magnitudes, allow us to assess simultaneously the accretion/outflow, magnetic…
New Technique for Aortic Valve Functional Annulus Reshaping Using a Handmade Prosthetic Ring
2011
Background Despite a wide development in aortic leaflets repair techniques, aortic valve annuloplastic procedures are still poorly investigated. We present our aortic valve annuloplastic system consisting of a handmade prosthetic ring with 2 components for reshaping the aortic annulus and sinotubular junction (STJ) and illustrates our surgical approach and clinical results. Methods Since February 2003, 45 patients with aortic valve regurgitation underwent aortic annuloplasty using the new ring. Mean patient age was 58 ± 16 years (range, 46 to 76 years). The ring has 2 components: a circular ring used to undersize the circumference of the aortoventricular junction and 3-crown-like shape ring…
Postoperative non-invasive assessment of pulmonary vascular resistance using Doppler echocardiography.
2011
Non-invasive monitoring of pulmonary vascular resistance (PVR) in postoperative cardiac surgery patients might be useful, particularly for management of pulmonary hypertension. For this purpose, we sought to assess Doppler echocardiography in the intensive care setting. In 73 patients, hemodynamics was measured using both, invasive gold standard (pulmonary artery catheter), and non-invasively by Doppler echocardiography. Four Doppler parameters: (1) tricuspid regurgitant velocity/time-velocity-integral of right ventricular outflow tract (TRV/VTI(RVOT)), (2) tricuspid annular systolic velocity (S'), (3) tricuspid annular strain, and (4) tricuspid annular strain rate, were compared with invas…
Laboratory disruption of scaled astrophysical outflows by a misaligned magnetic field
2021
The shaping of astrophysical outflows into bright, dense, and collimated jets due to magnetic pressure is here investigated using laboratory experiments. Here we look at the impact on jet collimation of a misalignment between the outflow, as it stems from the source, and the magnetic field. For small misalignments, a magnetic nozzle forms and redirects the outflow in a collimated jet. For growing misalignments, this nozzle becomes increasingly asymmetric, disrupting jet formation. Our results thus suggest outflow/magnetic field misalignment to be a plausible key process regulating jet collimation in a variety of objects from our Sun’s outflows to extragalatic jets. Furthermore, they provide…
X-ray emission mechanisms in protostellar jets
2005
Prompted by the recent detection of X-ray emission from Herbig-Haro objects, we studied the interaction between a supersonic jet originating from a young stellar object and the ambient medium; our aim is to investigate the mechanisms causing the X-ray emission. Our model takes into account the radiative losses from optically in plasmas and Spitzer's thermal conduction including saturation effects. We explored the parameter space defined by the density contrast between the ambient medium and the jet and by the Mach number, to infer the configurations which can give rise to X-ray emission. From the models, we derived the X-ray emission as it would be observed with Chandra/ACIS-I and XMM-Newto…