Time-dependent Ejection Velocity Research Articles

Numerical Models of Externally Irradiated Herbig–Haro Objects

Abstract We use 3D radiation–hydrodynamic simulations to study the effects of an external photoionization source on the structure of a Herbig–Haro (HH) jet launched from a young stellar object. Different ionizing photon rates are considered as well as a time-dependent ejection velocity and density. From our numerical results, synthetic Hα emission maps are computed in order to study how the external ionizing source affects the observed morphology of the jet and counterjet. We find that, as expected, the outflow has jet/counterjet and side-to-side asymmetries (with brighter Hα emission toward the external photoionizing source). We find that, for a variable ejection velocity, jet morphologies similar to different observed externally irradiated jets can be straightforwardly obtained. Models of jets with a variable ejection density (and constant outflow velocity) produce morphologies that are not seen in observed HH jets and are, therefore, not justified by the presently available observations.

Evolution from Spherical AGB Wind to Multipolar Outflow in Pre-planetary Nebula IRAS 17150−3224

Abstract We have mapped the pre-planetary nebula IRAS 17150−3224 in the 350 GHz continuum and CO J = 3–2 line at an angular resolution of ∼0.″09 using the Atacama Large Millimeter/submillimeter Array. A continuum source is detected at the center of the nebula, elongated along the equatorial plane, likely tracing a dusty torus around the central source. Continuum emission is also detected on both sides of the central continuum source in the equatorial plane, probably resulting from interactions of collimated fast winds (CFWs) with envelope material in the equator. CO emission is detected along the optical lobe. Although the optical lobe appears as bipolar, the CO map shows that it is actually a quadrupolar outflow consisting of two overlapping bipolar outflows. Two additional younger bipolar outflows are also detected in CO, one at the lower latitude and the other along the equatorial plane. In the CO position–velocity maps, blueshifted absorption stripes are detected in the outflow emissions, due to absorption by a series of shells produced by a series of asymptotic giant branch (AGB) wind ejections. By modeling the morphology and kinematics of the AGB wind and outflows, we find that the AGB wind could have ended ∼1300 yr ago, the quadrupolar outflow was ejected ∼350 yr ago, and the two additional bipolar outflows were ejected ∼280 and 200 yr ago, respectively. The outflows could be produced either by bullets coming from an explosion, or by a precessing CFW with a time-dependent ejection velocity.

3D hydrodynamical models of point-symmetric planetary nebulae: the special case of H 1-67

We present 3D hydrodynamical simulations of a precessing jet with a time-dependent ejection velocity or a time-dependent ejection density, interacting with a circumstellar medium given by a dense, anisotropic, and slow AGB wind, forming a torus. We explore a set of configurations with different values for the precession angle and number of ejections. The temporal evolution of these models is analised at times up to 1500 or 1800 yr. From our hydrodynamical models, we obtain position-velocity diagrams (PV diagrams) in the [NII]{\lambda}6583 line to be compared with high resolution observations of the planetary nebula H1-67. From spectral data this object shows high-velocity jets and a point-symmetric morphology. With our synthetic PV diagrams we show that a precessing jet with a time-dependent ejection velocity or a time-dependent ejection density reproduce the point-symmetric morphological structure for this nebula if the precession cone angle is larger than 30$^{\circ}$. Our synthetic PV diagrams can be used to understand how the S-like morphology, also presented by other planetary nebulae, is formed. For H1-67 we found a heliocentric velocity of -8.05 km s^-1 and height below the galactic plane of -451.6 pc.

MAGNETOHYDRODYNAMIC EFFECTS ON PULSED YOUNG STELLAR OBJECT JETS. I. 2.5D SIMULATIONS

In this paper we explore the dynamics of radiative axisymmetric MHD jets at high resolution using AMR methods. The goal of the study is to determine both the dynamics and emission properties of such jets. To that end we have implemented microphysics enabling us to produce synthetic maps of H$\alpha$ and [S II]. The jets are pulsed either sinusoidally or randomly via a time-dependent ejection velocity which leads to a complicated structure of internal shocks and rarefactions as has been seen in previous simulations. The high resolution of our simulations allows us to explore in great detail the effect of pinch forces (due to the jet's toroidal magnetic field) within the "working surfaces" where pulses interact. We map the strong H$\alpha$ emission marking shock fronts and the strong [S II] emission inside cooling regions behind shocks as observed with high-resolution images of jets. We find that pinch forces in the stronger field cases produce additional emission regions along the axis as compared with purely hydrodynamic runs. These simulations are a first step to understanding the full 3-D emission properties of radiative MHD jets.

New light on the multiple jets of CRL 618

Context. Proto-planetary nebulae (pPNe) are thought to represent the transitory phase of the late stages of low- to intermediate-mass stars. Most pPNe show a bipolar or multipolar geometry. The process(es) that transforms the spherical asymptotic giant branch (AGB) ejecta into a bipolar/multipolar geometry is not known in detail. Interactions between stars in a binary system are suspected to cause the departure from spherical symmetry. Aims. We aim to determine whether the existence of a binary source that ejects a wind (from the primary) and a bipolar precessing jet with a time-dependent ejection velocity (from the orbiting companion) could produce the morphology and kinematics of the wellknown multipolar pPN CRL 618. Methods. We applied an anisotropic wavelet analysis to the [S ii] Hubble Space Telescope (HST) images of CRL 618 to determine the charateristic sizes of various small-scale structures across and along the optical jets of CRL 618. From the archival [S ii] HST images of CRL 618 with a 10.7 yr time base, we carried out proper-motion measurements of the emission structures observed in the lobes of CRL 618. We computed six 3D numerical simulations of a precessing, time-dependent ejection velocity jet launched from a hypothetical companion star of a binary system. Results. We found the proper motions to be well aligned with the jet axis with tangential velocities ranging from 60 to 430 km s −1 . The tangential velocity is a monotonically increasing function of the distance to the central source. We found that our numerical simulations reproduce the morphology and proper-motion measurements of CRL 618 when we considered a trend of decreasing jet velocity with time to reproduce the tangential velocity vs. distance dependence. Conclusions. From the comparison we made between the structure and proper motions observed in CRL 618 and predictions from 3D jet simulations, we found that the size and morphology of the lobes and the proper motion behavior of CRL 618 can be explained in terms of a well-collimated bipolar ejection, a precession of the outflow axis, an approximately periodic time-variability of the outflow velocity (with a period of ∼15 yr), and a long-term trend of decreasing outflow velocities from dynamical timescales of 50 yr towards more recent times.

DIFFUSE IONIZING RADIATION WITHIN HH JETS

We present numerical hydrodynamical simulations of a time-dependent ejection velocity precessing jet. The parameters used in our models correspond to a high excitation Herbig-Haro object, such as HH 80/81. We have included the transfer of ionizing radiation produced within the shocked regions of the jet. The radiative transfer is computed with a ray-tracing scheme from all the cells with an emissivity above a certain threshold. We show the development of a radiative precursor, and compare the morphology with a model without the diffuse radiation. Our simulations show that the morphology of the Hα emission is affected considerably if the diffuse ionizing radiation is accounted for. The predicted Hα position-velocity diagram (i.e., spatially resolved emission line profiles) from a model with the transfer of ionizing radiation has a relatively strong component at velocity, corresponding to the radiative precursor. Qualitatively similar zero velocity components are observed in HH 80/81 and in the jet from Sanduleak's star in the Large Magellanic Cloud.

A ballistic model for a precessing and orbiting jet with a time-dependent ejection velocity

Fil: Velazquez, Pablo F.. Universidad Nacional Autonoma de Mexico. Instituto de Ciencias Nucleares; Mexico

Multipolar young planetary nebulae modelled as a precessing and orbiting jet with time-dependent ejection velocity

We have carried out 3D hydrodynamic simulations of precessing, variable ejection velocity bipolar jets in order to model multipolar protoplanetary (or planetary) nebulae. For these nebulae, we assume a binary source, with an asymptotic giant branch primary star which ejects an isotropic wind, and a companion which ejects the bipolar jet system. We find that it is possible to relate the large-scale morphological characteristics of these nebulae (lobe size, semi-aperture angle, number of observed lobes) to some of the parameters of the binary system, such as the ratio between the orbital and precession periods, the ratio between the masses of the binary components and the major axis of the elliptical orbit. Our results show that synthetic nebulae with well-defined lobe morphologies (resembling many of the observed multipolar planetary nebulae) are obtained from our models.

Shaping proto-planetary nebulae by binary systems

AbstractWe present the results of 3D hydrodynamic simulations aimed to explore the binary scenario for shaping bipolar, point- and mirror-symmetric proto-Planetary Nebulae. We consider a jet launched by the secondary star of a binary system, located at the center of the PPN, which propagates within a circumstellar medium swept previously up by the wind of the giant companion. As a result of the presence of the companion star, the accretion disk around the jet source is likely to precess. We have carried out 3D hydrodynamical simulations with the YGUAZÚ-A code including the combination of an orbital motion plus a precession. Our results show that to produce a multipolar nebula, it is necessary to have a precessing jet in a binary system with a time-dependent ejection velocity.

Time-dependent ejection velocity model for the outflow of Hen 3-1475

We present 2D axisymmetric and 3D numerical simulations of the proto-planetary nebula Hen 3-1475, which is characterized by a remarkably highly collimated optical jet, formed by a string of shock-excited knots along the axis of the nebula. It has recently been suggested that the kinematical and morphological properties of the Hen 3-1475 jet could be the result of an ejection variability of the central source (Riera et al. [CITE]). The observations suggest a periodic variability of the ejection velocity superimposed on a smoothly increasing ejection velocity ramp. From our numerical simulations, we have obtained intensity maps (for different optical emission lines) and position-velocity diagrams, in order to make a direct comparison with the HST observations of this object. Our numerical study allows us to conclude that a model of a precessing jet with a time-dependent ejection velocity, which is propagating into an ISM previously perturbed by an AGB wind, can succesfully explain both the morphological and the kinematical characteristics of this proto-planetary nebula.

The time-dependent ejection velocity histories of HH 34 and HH 111

The southern lobe of HH 34 and the western lobe of HH 111 show remarkable similarities. Both objects have a chain of well aligned knots, ending in well defined bow shocks (HH 34S and HH 11 IV, respectively). In this paper, we derive the past ejection velocity histories from previously published radial velocity measurements of the HH 34 and HH 111 jets. This is done under the assumption that the flows are ballistic. From these reconstructed ejection velocity variabilities, we compute axisymmetric gasdynamic simulations of the two flows, and find that we do obtain large working surfaces at the positions of the HH 34S and HH 11 IV bow shocks for the time at which these objects are being observed. This appears to be quite definite proof that these bow shocks are indeed the result of an ejection velocity time-variability. Also, there is the observational fact that the HH 34S bow shock is huge, being wider than HH 11 IV by a factor of ∼3. We find that we can reproduce this difference in size by choosing an appropriate value for the density of the ambient medium. Finally, from our small sample of two reconstructed ejection velocity variability histories, we attempt to make some statements about the general nature of these variabilites, and their implications on the possible ejection/collimation mechanisms.

Analytic and Numerical Models for the Knots along the HH 111 Jet

We consider a model for HH 111 as a jet ejected with a sawtooth, time-dependent ejection velocity. Such a variability is suggested by the position-velocity (PV) diagrams obtained from Hubble Space Telescope observations. We calculate both analytic and numerical models describing the flow resulting from such an ejection velocity time variability. Analytically, we calculate the flow for the limiting cases of massless working surfaces (i.e., those that efficiently eject mass sideways into the cocoon of the jet) and mass-conserving working surfaces, and we find that the numerically computed flow lies between these two limits. From the numerical simulations, we compute PV diagrams that can be directly compared with the corresponding observations. We find a surprisingly good agreement, which can be seen as a partial confirmation of the interpretation of the knots along HH 111 as the result of a time dependence in the ejection. Also, we show that a sawtooth functional form for the ejection velocity variability appears to be particularly appropriate for modeling the detailed radial velocity structure of the knots along HH 111.

Knots in stellar jets from time-dependent sources

view Abstract Citations (115) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Knots in Stellar Jets from Time-dependent Sources Raga, A. C. ; Kofman, Lev Abstract An analytical model is presented that describes the time evolution of a highly supersonic jet of small opening angle ejected from a time-dependent source. This model is used to explore the possibility that the aligned knots observed along astrophysical (and in particular, stellar) jets might be the result of 'internal working surfaces' produced in the jet flow as a result of a time-dependent ejection velocity. This model allows very concrete predictions of the shock velocities, H-alpha luminosities and characteristic masses of the knots in a stellar jet. A comparison is made between these predictions and previously existing observations of the HH 34 outflow (which has a very well-defined, jetlike structure), and good agreement is found between theoretical predictions and observations. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/171008 Bibcode: 1992ApJ...386..222R Keywords: Herbig-Haro Objects; Jet Flow; Pre-Main Sequence Stars; Stellar Mass Ejection; Stellar Structure; Stellar Winds; H Alpha Line; Interstellar Gas; Shock Wave Propagation; Stellar Models; Time Dependence; Astrophysics; ISM: JETS AND OUTFLOWS; SHOCK WAVES; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (1)