Multiple Bow Shocks Research Articles

The HH30 edge-on T Tauri star

Context. The disk-outflow connection is thought to play a key role in extracting excess angular momentum from a forming protostar. HH30 is a rare and beautiful example of a pre-main sequence star exhibiting a flared edge-on disk, an optical jet, and a CO molecular outflow, making this object a case study for the disk-jet-outflow paradigm. Aims. We aim to clarify the origin of the small-scale molecular outflow of HH30 and its link and impact on the accretion disk. Methods. We present ALMA 0.25″ angular resolution observations of the circumstellar disk and outflow around the T Tauri star HH30 in the dust continuum at 1.33 mm and of the molecular line transitions of 12CO(2–1) and 13CO(2–1). We performed a disk subtraction from the 12CO emission, from which we analysed the outflow properties in detail in the altitudes z ≲ 250 au. We fit the transverse position-velocity diagrams across the 12CO outflow to derive the ring positions and projected velocity components (including rotation). We use the results of these fits to discuss the origin of the CO outflow. Results. The 1.3 mm continuum emission shows a remarkable elongated morphology along PA = 31.2∘ ± 0.1∘ that has a constant brightness out to a radius of r = 75 au. The emission is marginally resolved in the transverse direction, implying an intrinsic vertical width ≤24 au and an inclination to the line-of-sight i ≥ 84.8∘. The 13CO emission is compatible with emission from a disk in Keplerian rotation, in agreement with the previous findings. The monopolar outflow, detected in 12CO, arises from the north-eastern face of the disk from a disk radius r ≤ 22 au and extends up to 5″ (or 700 au) above the disk plane. We derive a lower limit to the total mass of the CO cavity/outflow of 1.7 × 10−5 M⊙. The CO cavity morphology is that of a hollow cone with semi-opening angle ∼35∘. The derived kinematics are consistent with gas flowing along the conical surface with constant velocity of 9.3 ± 0.7 km s−1. We detect small rotation signatures (Vϕ sin i ∈ [0.1; 0.5] km s−1) in the same sense as the underlying circumstellar disk. From these rotation signatures we infer an average specific angular momentum of the outflow of 38 ± 15 au km s−1 at altitudes z ≤ 250 au. We also report the detection of small amplitude wiggling (1.2∘) of the CO axis around an average inclination to the line of sight of i = 91∘. Conclusions. The derived morphology and kinematics of the CO cavity are compatible with expectations from a slow disk wind, originating either through photo-evaporation or magneto-centrifugal processes. Under the steady assumption, we derive launching radii in the range 0.5–7 au. In that scenario, we confirm the large minimum mass flux of 9 × 10−8 M⊙ yr−1 for the CO wind. The wind would therefore extract a significant amount of the accreted mass flux through the disk and would likely play a crucial role in the disk evolution. If the CO flow originates from a steady-state disk wind, our ALMA observations rule out the 18 au binary orbital scenario previously proposed to account for the wiggling of the optical jet and favour instead a precession scenario in which the CO flow originates from a circumbinary disk around a close (separation ≤ 3.5 au) binary. Alternatively, the CO outflow could also trace the walls of a stationary cavity created by the propagation of multiple bow shocks. Detailed numerical simulations are under way to fully test the entrainment hypothesis.

Solar Wind Properties During Juno's Approach to Jupiter: Data Analysis and Resulting Plasma Properties Utilizing a 1‐D Forward Model

AbstractThe Jovian Auroral Distributions Experiment ion sensor (JADE‐I) on board the National Aeronautics and Space Administration's Juno mission measured solar wind ions for ≈40 days prior to the spacecraft's arrival at Jupiter, simultaneous with numerous telescope observations of the Jovian aurora. JADE‐I is a thermal plasma time‐of‐flight instrument designed to measure Jovian auroral and magnetospheric ions. This study provides a solar wind parameter data set for the approach phase that may be used in coordinated studies with remote measurements of the Jovian aurora, to compare with models that propagate solar wind conditions from Earth and to apply to Jovian bow shock or magnetopause models. While multiple bow shock crossings were predicted during Juno's approach, there was only one observed suggesting a compressed magnetosphere that was shrinking as Juno approached. However, the calculated ram pressure at the bow shock was near the median value of those 40 days, rather than being in an upper percentile.

CSO CO (2–1) and Spitzer IRAC observations of a bipolar outflow in high-mass star-forming region IRAS 22506+5944

We present Caltech Submillimeter Observatory CO (2–1) and Spitzer IRAC observations toward IRAS 22506+5944, which is a 104 L⊙ massive star-forming region. The CO (2–1) maps show an east-west bipolar molecular outflow originating from the 3 mm dust continuum peak. The Spitzer IRAC color-composite image reveals a pair of bow-shaped tips which are prominent in excess 4.5μm emission and are located at the leading fronts of the bipolar outflow, providing compelling evidence for the existence of bow-shocks as the driving agents of the molecular outflow. By comparing our CO (2–1) observations with previously published CO (1–0) data, we find that the CO (2–1)/(1–0) line ratio increases from low (∼5 kms−1) to moderate (∼8–12 kms−1) velocities, and then decreases at higher velocities. This is qualitatively consistent with the scenario that the molecular outflow is driven by multiple bow-shocks. We also revisit the position-velocity diagram of the CO (1–0) data, and find two spur structures along the outflow axis, which are further evidence for the presence of multiple jet bowshocks. Finally, power-law fittings to the mass spectrum of the outflow gives power law indexes more consistent with the jet bow-shock model than the wide-angle wind model.

Solar wind control of the terrestrial magnetotail as seen by STEREO

AbstractAt the beginning of 2007 the twin STEREO spacecraft provided a unique opportunity to study the global solar wind control of the terrestrial magnetotail under typical solar activity minimum conditions. The STEREO‐B (STB) spacecraft flew in the vicinity of the far terrestrial magnetotail, while the STEREO‐A (STA) spacecraft was located in front of the Earth performing measurements in the undisturbed solar wind. In February, the STB spacecraft was located in the magnetosheath most of the time but experienced several incursions into the distant magnetotail. Comparison of STA and STB observations determines unambiguously whether solar wind events such as energetic particle enhancements observed by STB are of pure solar origin or due to the influence of the terrestrial magnetosphere. During this time period in 2007, there were solar minimum conditions with alternating fast and slow solar wind streams that formed corotating interaction regions, which were the dominating source of magnetospheric disturbances encountering the Earth almost every week. Under these conditions, STB experienced multiple bow shock and magnetopause crossings due to the induced highly dynamic behavior of the terrestrial magnetotail and detected bursts of tailward directed energetic ions in the range of 110–2200 keV accompanied by suprathermal electrons of ~700–1500 eV, which were not seen in the undisturbed solar wind by STA. The corotating interaction regions triggered these energetic particle enhancements, and we demonstrate their magnetosphere‐related origin. Even after leaving the magnetosheath in March 2007, STB continued to observe antisunward directed energetic ion bursts until May up to a distance of ~ 800 RE behind Earth, the largest distance to which solar wind and magnetospheric interaction has been observed. These results show that Earth is a very significant source of energetic particles in its local interplanetary environment.

Simultaneous measurements of Martian plasma boundaries by Rosetta and Mars Express

We present the first two-spacecraft near-simultaneous observations of the Martian bow shock (BS), magnetic pileup boundary (MPB) and photo-electron boundary (PEB) obtained by the plasma instruments onboard Rosetta and Mars Express during the Rosetta Mars flyby on February 25, 2007. Our observations are compared with shape models for the BS and MPB derived from previous statistical studies. The MPB is found at its expected position but the BS for this event is found significantly closer to the planet than expected for the rather slow and moderately dense solar wind. Cross-calibration of the density measurements on the two spacecraft gives a density profile through the magnetosheath, indicating an increasing solar wind flux during the Rosetta passage which is consistent with the multiple BS crossings at the Rosetta exit.

Three decades of bow shock observations by IMP 8 and model predictions

During almost three decades of operation, the IMP 8 satellite collected an extensive amount of both plasma and magnetic field measurements. The entire data set has been searched for all Earth's bow shock crossings observed by IMP 8. We have recorded total 11,455 single and multiple bow shock crossings and for 5870 of the crossings complete upstream interplanetary magnetic field and solar wind parameters, measured by the same spacecraft, were available allowing us to test empirical models predicting the bow shock position as a function of upstream parameters. The chosen models were F79, NS91, FR94, CL95, P95 and V01 (Planet. Space Sci. 27(9) (1979) 1151; J. Atmos. Terr. Phys. 53 (1991) 1049; J. Geophys. Res. 99(A9) (1994) 17,681; J. Geophys. Res. 100(A9) (1995) 17,173; J. Geophys. Res. 100(A5) (1995) 7907; Earth Planets Space 53 (2001) 1001). This study investigates these models’ accuracy not only for average upstream conditions but also for unusual conditions and as a result points out some deficiencies of these models. We demonstrate that most of the models underestimate bow shock distance for low Mach numbers and/or high magnitudes of IMF components.

The bow shock velocity from two-point measurements in frame of the interball project

The bow shock is a highly dynamic boundary controlled by steady and transient variations in solar wind parameters. It has been found that both shape and position of this boundary are determined mainly by the dynamic pressure and by the upstream Mach number of the incoming solar wind. Intervals of multiple bow shock crossings, often lasting over intervals from minutes to hours, are currently interpreted in terms of bow shock motions with respect to the observing spacecraft. In the present paper, we examine the bow shock velocity based on several series as well as several single bow shock crossings observed by two closely separated spacecraft (MAGION-4/INTERBALL-1). Our estimations of the bow shock velocity typically ranges from several tens of kilometers per second to approx. 120 km/s. These results correspond to those previously published for quasiperpendicular shocks but our set contains both quasiparallel and quasiperpendicular shocks. An analysis shows that about 80% of crossings can be explained by radial expansion/compression of the bow shock surface. The timing of the rest of events requires another mechanisms for explanation.

Kinematics of Optical Outflows in the Orion Nebula. I. The Giant Outflow HH 400 and the Irradiated Jet HH 502

We present narrowband filter and high-resolution, velocity-resolved Fabry-Perot images of outflows in the southern portion of the Orion Nebula. HH 400 is a giant, low-velocity, redshifted bow shock located about 10' south of the core of the Orion Nebula. Its axis of symmetry passes close to the Trapezium cluster 1.5 pc to the north. The most likely point of origin is a young stellar object in the OMC-1 cloud core. HH 400 may be the remnant of a parsec-scale bipolar outflow powered by one of the young stars forming within this region. The radial velocity of gas in the limb-brightened rim of HH 400 is low, with redshifted speeds ranging from 8 to 20 km s-1 with respect to the emission from the Orion Nebula. The shape of the bow indicates that it lies close to the plane of the sky. For an inclination angle of 30° to the plane of the sky and assuming that the plasma is flowing mostly along the axis of symmetry, the visible gas at the rim of HH 400 has a mean velocity of about 30 km s-1, a mass of about 3 × 10-2 M⊙, and a dynamical age of about 5 × 104 yr, assuming the source lies in the OMC-1 cloud core. The estimated mass flux in the HH 400 bow is about 10-6 M⊙ yr-1. The bent bipolar irradiated jet HH 502 is superposed on the western rim of HH 400. We resolve the spatial and velocity structure of the jet and its multiple bow shocks. The jet consists of a chain of photoionized segments separated by wide gaps; bow shocks lie at the leading edges of these jet segments. The mean radial velocities of the jet segments decrease with increasing distance from the source. The large radial velocity dispersions of the gas at the tips of the HH 502 internal working surfaces and the small spreading angles of the HH 502 jet segments, combined with their low radial velocities, indicate that this flow lies close to the plane of the sky. Assuming that the jet is fully ionized, that it spreads at the Mach angle, and that the internal sound speed in the photoionized gas is about 10 km s-1, the jet must have a space velocity of about 400 km s-1. Finally, we present velocity-resolved images of the bow shocks in HH 540, a flow that may originate from the large protoplanetary disk 181-826. Several additional high-velocity features identified in the Fabry-Perot data trace additional jets and outflows in this portion of the Orion Nebula.

Interaction between an interplanetary magnetic cloud and the Earth's magnetosphere: Motions of the bow shock

An interplanetary magnetic cloud (IMC) is an important solar‐terrestrial connection event. It is an ideal object for the study of solar‐terrestrial relations and space weather because the Earth's space environment can be affected considerably during an IMC passage. An IMC was observed to pass the Earth during October 18–20, 1995. Wind recorded its interplanetary characteristics at ∼ 175 RE upstream of the Earth's bow shock, and ∼ 45 min later, Geotail, being near the nominal location of the dawn bow shock, detected IMC‐related multiple bow shock crossings. Using simultaneous measurements from Wind and Geotail, we analyzed, with a semiempirical bow shock model with two parameters, the bow shock motion caused by the interaction of the IMC with the magnetosphere during the passage. We also compared the bow shock motion predicted by the model, and hence the predicted Geotail bow shock crossings, with Geotail observations of the actual crossings. The results showed that the observed multiple bow shock crossings, which were obviously due to temporal variations of the upstream solar wind, can be well explained by the model‐predicted bow shock motion.

Cepheus A East: Unraveling the Mysteries

New infrared images of Cep A East are presented that show two regions of shock-excited line emission from separate bipolar flows. We identify the dominant sources powering the outflows and argue that the results support a multiple outflow model (Narayanan & Walker) as opposed to a quadrupolar outflow scenario. The images include near-infrared broadband ( [2.158 μm], L'' [3.81 μm], and M' [4.67 μm]) and spectral line ([Fe II] emission line at 1.644 μm and H2 1-0 S[1] line at 2.122 μm) observations, as well as continuum emission, at 1.644 μm and 2.122 μm. Considering our data and other results, we present a unified, self-consistent picture of the disk and shock structure. The northern emission region appears to be the result of the ablation of a dense molecular clump (coincident with HW 6) in the path of a diverting jet from YSO HW 2 and subsequent multiple bow shocks with prompt entrainment arising from the interaction of the jet with the molecular cloud Cep A-2. The southern line emission region near HW 7 resembles the artillery shell bow shocks found in Orion and is most likely a J-type shock caused by a jet from another YSO, possibly HW 3(d)ii.

The location of the Jovian bow shock and magnetopause: Galileo initial results

The Galileo spacecraft observed multiple bow shock crossings and a single magnetopause crossing on its inbound approach to Jupiter in November 1995. We compare these observations to those obtained on previous missions, taking account of variable solar wind pressure and the disk-like shape of the magnetosphere. We find that the subsolar magnetopause location varies with solar wind dynamic pressure to the −0.22 power in contrast to the terrestrial −0.167 power. This difference is well known, and has been attributed to the presence of hot plasma and centrifugal stretching in the Jovian magnetodisk that lessens the pressure gradients in the outer magnetosphere. Our analysis also reveals for the first time that the magnetopause boundary of magnetosphere exhibits polar flattening, as has been previously inferred from the stretched magnetic field lines seen within the magnetosphere. The bow shock is not so asymmetric in shape. Finally,, we find that Galileo observed expanded boundaries early on its inbound pass, perhaps in part due to hotspot activity at Io in the fall of 1995 prior to the Galileo encounter. Observations within the magnetosphere are consistent with externally driven motion of the boundaries.

HST Observations of the HH 47 and HH 111 Stellar Jets

AbstractThe superb spatial resolution made possible by the WFPC2 imager on the Hubble Space Telescope has opened a new era in the study of shocks in stellar jets. This paper summarizes the results of imaging surveys of two of the brightest and best resolved stellar jets, HH 111 and HH 47. The new HST images show that the jets appear quite different in the Ha and [S II] lines; Ha concentrates in distinctive filaments while [S II] tends to be clumpier and more widespread. Filamentary Hα emission should trace the location of the shock fronts if the preshock gas is neutral, because a significant fraction of the incident H gas becomes excited collisionally before becoming ionized in moderate velocity shocks.Both HH 111 and HH 47 exhibit multiple bow shocks along the channel of the jet, and in some cases we observe the classical double shock structure of a bow shock/Mach disk expected within the working surface of a jet. The jet material is considerably denser than that of the ambient gas. Ejection angles vary a few degrees with time, giving some jets a ‘wiggling’ appearance. However, motion along the jet appears to be radial; there is no convincing evidence for azimuthal motion in the radial velocity data. Multiple bow shocks observed along the jets probably arise from unsteady accretion of a protostellar disk onto the central object.

Energetics, Collimation and Propagation of Galactic Protostellar Outflows

Formation of jets in low-mass protostellar objects and young pre-main sequence stars is ultimately related to the existence of some gaseous disk around a rapidly rotating central object. This configuration has deep parallels to extragalactic systems such as radio galaxies and quasars. Rotating black holes are still thought to be the prime-mover behind the activity detected in centers of galaxies, while, in the case of protostellar jets, rapidly rotating stars and disks are responsible for the ejection of bipolar outflows. In both cases, magnetic fields are invoked for the acceleration, the collimation and propagation of these outflows. The ultimate rooting of these fields is still under debate. We discuss models where winds injected into rapidly rotating magnetospheres of the central object drive the outflows. From these considerations it follows that the jets of young stellar objects can only be produced magnetically and that their progagation is determined by their magnetic properties. Such jets have low Mach numbers ≃ 2 and their instabilities are dominated by the pinch mode. Knots closest to the source are attributed to compression by the time-dependent pinches. Multiple bow shocks occur on longer time-scales (a few thousand years) and are attributed to variations in the magnetospheric structure of the star, or the disk.

Giant Bow Shock Pairs Associated with Herbig-Haro Jets

Two pairs of giant (linear size ~1 pc) bow shock structures have been discovered, each located symmetrically about HH 1/2 and HH 124. Their Herbig-Haro (HH) nature has been examined by narrowband CCD imaging on and off [S II] λλ6717, 6731 and/or slit spectroscopy. Multiple bow shocks associated with a few HH objects such as HH 34 are known, and are interpreted as evidence for recurrent outflow activity of the exciting sources. The giant bow shocks associated with HH 1/2 or HH 124 provide further beautiful examples of this phenomenon and, with dynamical ages of about 10,000 yr in both pairs, extend the timescale of HH activity by an order of magnitude.

Multiple outflow episodes from protostars: Three-dimensional models of intermittent jets

view Abstract Citations (57) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiple Outflow Episodes from Protostars: Three-dimensional Models of Intermittent Jets de Gouveia dal Pino, Elisabete M. ; Benz, Willy Abstract Short abstract: We present fully 3-D simulations of supersonic, radiatively cooling intermittent jets with intermediate and long variability periods (that is, periods of the order of or longer than, the dynamical time scale of the jet). Variations of intermediate period elucidate the formation and evolution of chains of internal regularly spaced radiative shocks, which in this work are identified with the observed emission knots of protostellar jets. Variations of long period elucidate the formation of multiple bow shock structures separated by long trails of diffuse gas, which resemble those observed in systems like HH111 and HH46/47. The time variability of the outflow is probably associated with observed irruptive events in the accretion process around the protostars. In our simulations, the outflow variations are produced by periodically turning on the outflow with a highly supersonic velocity and periodically turning off it to a low velocity regime. In the case of velocity variations of intermediate period, we find, as in previous work, that the shock structures form a train of regularly spaced emitting features which move away from the source with a velocity close to that of the outflow, have high radial motions, and produce low intensity spectra, as required by the observations. As they propagate downstream, the shocks widen and dissipate due to the expulsion of material sideways to the cocoon by the high pressure gradients of the postshock gas. This fading explains the most frequent occurence of knots closer to the driving source. In the case of the long period velocity variability, our simulations have produced a pair of bow-shock-like structures separated by a trail almost Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/174811 arXiv: arXiv:astro-ph/9405035 Bibcode: 1994ApJ...435..261D Keywords: Astronomical Models; Interstellar Matter; Magnetohydrodynamic Flow; Plasma Jets; Pre-Main Sequence Stars; Shock Waves; Stellar Mass Ejection; Supersonic Jet Flow; Jet Flow; Mathematical Models; Shock Wave Interaction; Three Dimensional Models; Astrophysics; HYDRODYNAMICS; ISM: INDIVIDUAL ALPHANUMERIC: HH 46/47; ISM: INDIVIDUAL ALPHANUMERIC: HH 111; STARS: PRE--MAIN-SEQUENCE; Astrophysics E-Print: accepted by ApJ, LaTex file, 33 pages full text sources arXiv | ADS | data products SIMBAD (3)

Submillimetre and near-infrared observations of L1448: a curving Formula jet with multiple bow shocks

A high-resolution (0.6 arcsec pixel −1 ), narrow-band, H 2 v=1-0 S(1) image of the high-velocity CO outflow in L1448 reveals a remarkable jet-like structure. The coincidence of this H 2 jet with the CO bipolar outflow implies a close association between the two phenomena. The H 2 jet comprises a series of knots, and three bow-shaped features equally spaced along the jet length, which we associate with the sporadic nature of this outflow. K-band imaging of the source also shows a conical reflection nebula extending towards the H 2 jet structure, whilst maps in HCO + J=3-2 and CS J=5-4 show two peaks, one towards the source of the H 2 jet and CO outflow, and the other towards the infrared source IRS 3 situated to the north of this region

Evidence of high excitation in the Herbig-Haro 111 jet

We obtained long slit spectrophotometric observations in the blue spectral region, 3600-5400 A, of the Herbig-Haro (HH) 111 jet in Orion. Our purpose was to search for the high excitation [O III] 5007 A line and medium-to-high excitation [O II] 3727/29 A lines in the internal condensations or knots of the jet. We found [O III], which indicates shock velocities ≥80 km s −1 , and strong [O II] in condensation L. The morphology and excitation of this condensation gives more support to a multiple bow shock structure in HH 111, and therefore, strengthens the case for a time variability of its source. Strong emission in [O II] was also found in most of the bright condensations, indicating shock velocities ≥40 km s −1 . Estimates of the extinction in Herbig-Haro 111 give values of E(B−V)∼1, a relatively large value for an optical HH object

Observations of entrainment and time variability in the HH 47 jet

view Abstract Citations (56) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Entrainment and Time Variability in the HH 47 Jet Hartigan, Patrick ; Morse, Jon A. ; Heathcote, Steve ; Cecil, Gerald Abstract We present new Fabry-Perot images of the HH 47 jet that show the first clear evidence for entrainment in a jet from a young star. The material in the jet moves faster down the axis of the flow and slower at the edges, similar to viscous flow in a pipe. The higher excitation lines occur along the edges of the jet, as expected if entrainment accelerates and heats the ambient material. We confirm previous observations of multiple bow shocks in this system. Together, time variability and entrainment produce much of the observed shock-excited gas in this object. Our data show that the 'wiggles' along the jet are not caused by jet material tied to a spiraling magnetic field, but instead result from time variability, variable ejection angles, or inhomogeneities in the flow. The gas entrained in the HH 47 jet may be atomic; our results do not provide direct evidence that stellar jets drive molecular outflows. Publication: The Astrophysical Journal Pub Date: September 1993 DOI: 10.1086/187011 Bibcode: 1993ApJ...414L.121H Keywords: Early Stars; Herbig-Haro Objects; Jet Flow; Molecular Flow; Bow Waves; Shock Waves; Viscous Flow; Astrophysics; ISM: KINEMATICS AND DYNAMICS; STARS: INDIVIDUAL ALPHANUMERIC: HH 46/47; STARS: PRE--MAIN-SEQUENCE; SHOCK WAVES full text sources ADS | data products SIMBAD (5)

Stellar jets with intrinsically variable sources

Models for high Mach number, isothermal, pressure-matched jets ejected from sources with variable velocities are presented. It is found that the relaxation of the assumption of a time-independent source allows the complex position-velocity diagrams and multiple bow shock structures observed in some stellar jets to be explained in a straightforward way. Analytic and numerical models are presented for jets with variable velocity sources. A comparison with previously published observations of the HH 46/47 jet is performed which shows how the velocity variations observed along a jet can be used to reconstruct the past time variability of the source. This technique is promising for future studies of the mechanism by which stellar jets are produced. 41 refs.