Search results for "Jets [Galaxies]"
showing 10 items of 488 documents
Study of W Boson Production in Association with Beauty and Charm
2015
The associated production of a W boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and 2.0 fb[superscript -1] collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The W bosons are reconstructed using the W → μν decay and muons with a transverse momentum, p[subscript T], larger than 20 GeV in the pseudorapidity range 2.0 20 GeV and 2.2 20 GeV. The fraction of W + jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the W + b and W + c produ…
ESO-Hα 574 and Par-Lup 3-4 jets: Exploring the spectral, kinematical, and physical properties
2014
In this paper a comprehensive analysis of VLT / X-Shooter observations of two jet systems, namely ESO-H$\alpha$ 574 a K8 classical T Tauri star and Par-Lup 3-4 a very low mass (0.13~\Msun) M5 star, is presented. Both stars are known to have near-edge on accretion disks. A summary of these first X-shooter observations of jets was given in a 2011 letter. The new results outlined here include flux tables of identified emission lines, information on the morphology, kinematics and physical conditions of both jets and, updated estimates of $\dot{M}_{out}$ / $\dot{M}_{acc}$. Asymmetries in the \eso flow are investigated while the \para jet is much more symmetric. The density, temperature, and ther…
Generation of radiative knots in a randomly pulsed protostellar jet. II. X-ray emission
2010
Protostellar jets are known to emit in a wide range of bands, from radio to IR to optical bands, and to date also about ten X-ray emitting jets have been detected, with a rate of discovery of about one per year. We aim at investigating the mechanism leading to the X-ray emission detected in protostellar jets and at constraining the physical parameters that describe the jet/ambient interaction by comparing our model predictions with observations. We perform 2D axisymmetric hydrodynamic simulations of the interaction between a supersonic jet and the ambient. The jet is described as a train of plasma blobs randomly ejected by the stellar source along the jet axis. We explore the parameter spac…
X-RAY EMISSION FROM PROTOSTELLAR JET HH 154: THE FIRST EVIDENCE OF A DIAMOND SHOCK?
2011
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 nozz…
The Complex Morphology of the X-ray and Optical Emission from HH 154: The Pulsed Jet Scenario
2009
We study the optical and X-ray emission from protostellar jets, focusing, in particular, on the case of HH 154. This project consists of two different and complementary approaches: the development of hydrodynamical models of the jet/ambient interaction, and the analysis of multi-wavelength observations. Comparing the results derived from the simulations with the observations we can infer the physical mechanisms leading to the complex morphology of the X-rays source observed at the base of HH 154.
Generation of radiative knots in a randomly pulsed protostellar jet
2009
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 in…
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…
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…