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Constraining the Parameters of AGN Jets - Comparisons with Herbig-Haro Jets  [PDF]
Silvano Massaglia
Physics , 2003,
Abstract: Comparing the properties AGN and Herbig-Haro jets can be a useful exercise for understanding the physical mechanisms at work in collimated outflows that propagate in such different environments. In the case of Herbig-Haro jets, the presence of emission lines in the spectra and the continuous evolution of the observation techniques greatly favor our knowledge of the physical parameters of the jets instead, for AGN jets, the process of constraining the jet parameters is hampered by the nature of the emission from these objects that is non-thermal. I will discuss how one cannot directly constrain the basic parameters of extragalactic jets by observations but must treat and interpret the data either by statistical means or by comparing observed and simulated morphologies in order to gain some indications on the values of these parameters.
Irradiated Herbig-Haro Jets in the Orion Nebula and Near NGC 1333  [PDF]
John Bally,Bo Reipurth
Physics , 2000, DOI: 10.1086/318258
Abstract: We report the discovery of a dozen Herbig-Haro jets illuminated by the Lyman continuum and/or softer far-ultraviolet radiation fields of nearby high mass stars. Five irradiated outflows lie in the outer parts of the Orion Nebula and seven lie near the reflection nebula NGC 1333 in the Perseus molecular cloud. We propose that the UV radiation field has eroded residual material left over from the formation of these young source stars. Many of the irradiated jets exhibit unusual C-shaped bending. In the outskirts of the Orion Nebula, most irradiated jets bend away from the core of the nebula. On the other hand, in NGC 1333, the C-shaped jets bend back towards the cluster center. Jet bending in the Orion Nebula may be dominated by either the outflow of material from the nebular core or by the rocket effect pushing on the irradiated portion of a mostly neutral jet beam. But in NGC 1333, jet bending may indicate that the source stars have been ejected from the cluster core. Many irradiated jets are asymmetric with one beam much brighter than the other. When fully photo-ionized, irradiated jets may provide unique insights into the physical conditions within outflows powered by young stars, permitting the determination of the density and location of stellar ejecta even in the absence of shocks. We present a model for the photo-ionization of these outflows by external radiation fields and discuss possible mechanisms for producing the observed asymmetries. We demonstrate that the UV radiation field may alter the amount of cloud material entrained by the jet. We also report the discovery of some large scale bow shocks which face the core of the Orion Nebula and which surround visible young stars. These wind-wind collision fronts provide further evidence for a large scale mass flow originating near the nebular core.
The Physics of turbulent and dynamically unstable Herbig-Haro jets  [PDF]
Lorenzo Zaninetti
Physics , 2009, DOI: 10.1007/s10509-009-0255-8
Abstract: The overall properties of the Herbig-Haro objects such as centerline velocity, transversal profile of velocity, flow of mass and energy are explained adopting two models for the turbulent jet. The complex shapes of the Herbig-Haro objects, such as the arc in HH34 can be explained introducing the combination of different kinematic effects such as velocity behavior along the main direction of the jet and the velocity of the star in the interstellar medium. The behavior of the intensity or brightness of the line of emission is explored in three different cases : transversal 1D cut, longitudinal 1D cut and 2D map. An analytical explanation for the enhancement in intensity or brightness such as usually modeled by the bow shock is given by a careful analysis of the geometrical properties of the torus.
Kinematics of Herbig-Haro Objects and Jets in the Orion Nebula  [PDF]
Margarita Rosado,Eduardo de la Fuente,Lorena Arias,Alejandro Raga,Ettiane Le Coarer
Physics , 2001, DOI: 10.1086/323303
Abstract: We have surveyed the inner 5' of the Orion Nebula by means of Halpha and [NII] Fabry-Perot imaging spectroscopy to present a kinematical study of the Herbig-Haro objects in the nebula. The objects studied in this work are HH 202, 203, 204, 529, 269 and other associated features. For HH 202 we find new features that, because of their high velocities (up to 100 km/seg) indicate the presence of an outflow that probably is a HH flow not catalogued previously. HH 202 could be only a part of this larger outflow. Large internal motions are found in the fainter regions of HH 203-204, as well as evidence of transverse density gradients that could account for the asymmetry in the brightness distribution of HH 204. We report for the first time a high blueshifted velocity (-118 km/seg) associated with HH 204, and show that the apex of HH 204 is indeed the zone of maximum velocity, in agreement with bow shock models. We also studied the radial velocity field of HH 269 finding features associated with the HH object. From our studies, we find kinematic evidence that suggests that HH 203-204 and HH 202 are part of a big (aprox. 0.55 pc) bipolar HH outflow.
HST/ACS H-alpha Imaging of the Carina Nebula: Outflow Activity Traced by Irradiated Herbig-Haro Jets  [PDF]
Nathan Smith,John Bally,Nolan R. Walborn
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.16520.x
Abstract: We report the discovery of new Herbig-Haro (HH) jets in the Carina Nebula, and we discuss the protostellar outflow activity of a young OB association. These are the first results of an HST/ACS H-alpha imaging survey of Carina. Adding to the one previously known example (HH666), we detect 21 new HH jets, plus 17 new candidate jets, ranging in length from 0.005 to 3 pc. We derive jet mass-loss rates ranging from 8e-9 to 1e-6 Msun/yr, but a comparison to the distribution of jet mass-loss rates in Orion suggests that we may be missing a large fraction of the jets below 1e-8 Msun/yr. A key qualitative result is that even some of the smallest dark globules with sizes of 0.01pc are active sites of ongoing star formation because we see HH jets emerging from them, and that these offer potential analogs to the cradle of our Solar System because of their proximity to dozens of imminent supernovae that will enrich them with radioactive nuclides like 60Fe. HST images reveal proplyd structures in the core of the Tr14 cluster, only 0.1-0.2 pc from several O-type stars. Many examples of bent jets serve as "wind socks"; strong photoevaporative flows can shape the jets, competing with the direct winds and radiation from massive stars. Finally, even allowing for a large number of jets that may escape detection, we find that HH jets are negligible to the global turbulence of the surrounding region, which is driven by massive star feedback.
Herbig-Haro Jets Emerging from a Neutral Cloud into a H II region  [cached]
A. C. Raga,B. Reipurth
Revista mexicana de astronomía y astrofísica , 2004,
Abstract: Presentamos simulaciones numéricas de un flujo Herbig-Haro que sale de una nube densa hacia una región H II. Este tipo de "salidas" de nubes densas han sido observadas recientemente en varias regiones de formación estelar, y aquí exploramos las propiedades de estos flujos variando algunos de los parámetros libres del modelo. Presentamos series temporales de la temperatura, densidad, fracción de ionización y de la emisión en H. Encontramos que la emisión en H de los flujos está mayormente controlada por el flujo incidente de fotones ionizantes, en lugar de por las propiedades intrínsecas del flujo.
The outflow history of two Herbig-Haro jets in RCW 36: HH 1042 and HH 1043  [PDF]
L. E. Ellerbroek,L. Podio,L. Kaper,H. Sana,D. Huppenkothen,A. de Koter,L. Monaco
Physics , 2012, DOI: 10.1051/0004-6361/201220635
Abstract: Jets around low- and intermediate-mass young stellar objects (YSOs) contain a fossil record of the recent accretion and outflow activity of their parent star-forming systems. We aim to understand whether the accretion/ejection process is similar across the entire stellar mass range of the parent YSOs. To this end we have obtained VLT/X-shooter spectra of HH 1042 and HH 1043, two newly discovered jets in the massive star-forming region RCW 36. HH 1042 is associated with the intermediate-mass YSO 08576nr292. Over 90 emission lines are detected in the spectra. High-velocity (up to 220 km/s) blue- and redshifted emission from a bipolar flow is observed in typical shock tracers. Low-velocity emission from the background cloud is detected in nebular tracers, including lines from high ionization species. We applied combined optical and infrared spectral diagnostic tools in order to derive the physical conditions (density, temperature, and ionization) in the jets. The measured mass outflow rates are Mjet ~ 10^-7 Msun/yr. We measure a high accretion rate for HH 1042 (Macc ~ 10^-6 Msun/yr) and Mjet/Macc ~ 0.1, comparable to low-mass sources and consistent with models for magneto-centrifugal jet launching. The knotted structure and velocity spread in both jets are interpreted as fossil signatures of a variable outflow rate. The mean velocities in both lobes of the jets are comparable, but the variations in Mjet and velocity in the two lobes are not symmetric, suggesting that the launching mechanism on either side of the accretion disk is not synchronized. For HH 1042, we have constructed an interpretative physical model with a stochastic or periodic outflow rate and a description of a ballistic flow as its constituents. The knotted structure and velocity spread can be reproduced qualitatively with the model, indicating that the outflow velocity varies on timescales on the order of 100 yr.
Wide Field Surveys of Herbig-Haro Objects  [PDF]
Jun Yan,Hongchi Wang,Min Wang,Licai Deng,Ji Yang,Jiansheng Chen
Physics , 1997,
Abstract: We report our new results from wide-field surveys of Herbig-Haro (HH) objects in the nearby star forming regions. The surveys covered approximately 56 degree in Perseus, Taurus, Orion, Monoceros, and other regions. Using refined techniques, we discovered in total 68 HH objects, of which 32 were in Perseus, 4 in Taurus, 13 in Orion, 18 in Monoceros, and 1 in S287 regions. The newly discovered HH objects demonstrate a great variety of morphological structures, including 5 jets, 7 arcs, 12 cirri or cirrus groups, 13 patches, and many knots. These objects provide a new comprehensive database for the study of HH objects in the regions of recent star formation.
Numerical simulations of radiative magnetized Herbig-Haro jets: the influence of pre-ionization from X-rays on emission lines  [PDF]
Ovidiu Tesileanu,Andrea Mignone,Silvano Massaglia,Francesca Bacciotti
Physics , 2011, DOI: 10.1088/0004-637X/746/1/96
Abstract: We investigate supersonic, axisymmetric magnetohydrodynamic (MHD) jets with a time-dependent injection velocity by numerical simulations with the PLUTO code. Using a comprehensive set of parameters, we explore different jet configurations in the attempt to construct models that can be directly compared to observational data of microjets. In particular, we focus our attention on the emitting properties of traveling knots and construct, at the same time, accurate line intensity ratios and surface brightness maps. Direct comparison of the resulting brightness and line intensity ratios distributions with observational data of microjets shows that a closer match can be obtained only when the jet material is pre-ionized to some degree. A very likely source for a pre-ionized medium is photoionization by X-ray flux coming from the central object.
The deceleration of Giant Herbig-Haro Flows  [PDF]
Elisabete M. de Gouveia Dal Pino
Physics , 2000, DOI: 10.1086/320065
Abstract: It has been recently discovered that spatially separated Herbig-Haro objects, once considered unrelated, are linked within a chain that may extend for parsecs in either direction of the embedded protostar forming a "giant Herbig-Haro jet". Presently, several dozen of these giant flows have been detected and the best documented example, the HH~34 system, shows a systematic velocity decrease with distance on either side of the source. In this paper, we have modeled giant jets by performing fully three-dimensional simulations of overdense, radiatively cooling jets modulated with long-period (P $\sim$ several hundred years) and large amplitude sinusoidal velocity variability at injection ($\Delta v \sim$ mean jet flow velocity). Allowing them to travel over a distance well beyond the source, we have found that multiple travelling pulses develop and their velocity indeed falls off smoothly and systematically with distance. This deceleration is fastest if the jet is pressure-confined, in which case the falloff in velocity is roughly consistent with the observations. The deceleration occurs as momentum is transferred by gas expelled sideways from the traveling pulses. The simulation of a pressure-confined, steady-state jet with similar initial conditions to those of the pulsed jet shows that the flow in this case experiences $acceleration$. This result is thus an additional indication that the primary source of deceleration in the giant flows $cannot$ be attributed to braking of the jet head against the external medium.
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