Outflow Axis Research Articles

A CO ( J = 3-2) Outflow Survey of the Elias 29 Region

We present a 5' × 5' integrated intensity map of 12CO (J = 3-2) emission from the ρ Ophiuchi cloud core that traces low-luminosity outflow emission from two protostars: Elias 29 and, most likely, LFAM 26. The morphology of the outflow from Elias 29 is bipolar and has a curved axis that traces the S-shaped symmetry seen in H2 emission. The outflow from LFAM 26 is a new detection and oriented in the east-west direction near the plane of the sky with most of the blueshifted emission being absorbed by intervening clouds. The outflow axis of this object also appears to intersect a knot of H2 emission previously attributed to Elias 29. LFAM 26 is a low-luminosity source (Lbol = 0.06 L☉), which, in combination with the observed outflow, makes it a candidate very low luminosity object (VeLLO). We derive lower limits to the gas column densities and energetics for both outflows. The mechanical luminosities for Elias 29 and LFAM 26 are 6.4 and 10.3 × 10-3 L☉, respectively.

Near-infrared polarimetry and modelling of the dusty young planetary nebula IRAS 19306+1407

We present near-infrared polarimetric images of the dusty circumstellar envelope (CSE) of IRAS 19306+1407, acquired at the United Kingdom Infrared Telescope (UKIRT) using the UKIRT 1-5 μm Imager Spectrometer (UIST) in conjunction with the half-waveplate module IRPOL2. We present additional 450- and 850-μm photometry data obtained with the Sub-millimetre Common-User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT), as well as archived Hubble Space Telescope (HST) F606W- and F814W-filter images. The CSE structure in polarized flux at J and K bands shows an elongation north of north-east and south of south-west with two bright scattering shoulders north-west and south-east. These features are not perpendicular to each other and could signify a recent 'twist' in the outflow axis. We model the CSE using an axisymmetric light scattering (ALS) code to investigate the polarization produced by the CSE, and an axisymmetric radiation transport (DART) code to fit the spectral energy distribution. A good fit was achieved with the ALS and DART models using silicate grains, 0.1-0.4 μm with a power-law size distribution of a -3.5 , and an axisymmetric shell geometry with an equator-to-pole ratio of 7:1. The spectral type of the central star is determined to be B 11 supporting previous suggestions that the object is an early planetary nebula. We have constrained the CSE and interstellar extinction as 2.0 and 4.2 mag, respectively, and have estimated a distance of 2.7 kpc. At this distance, the stellar luminosity is ∼4500 L ⊙ and the mass of the CSE is ∼0.2 M ⊙ . We also determine that the mass loss lasted for ∼5300 yr with a mass-loss rate of ∼3.4 x 10 -5 M ⊙ yr -1 .

Millimeter Imaging of the HH 270 Protostellar Core and Outflow

The HH 270 region was observed in the C18O and the 13 CO J = 1 → 0 lines with angular resolutions ranging from 3'' to 10''. The dense molecular core containing the centimeter continuum source VLA 1 has a mass of ~1.6 M☉. As the 13CO image shows that the dense core is elongated in the direction perpendicular to the outflow axis, the core may be flattened and viewed nearly edge-on. The 13CO spectrum shows a blue-skewed line profile when the imaging is done at a high resolution, suggesting that the infall motion becomes kinematically important on a small scale, within ~2000 AU from the center. The molecular outflow does not show a large line width, and the outflow axis may be close to the plane of the sky. Archival near-IR images reveal that there is a nebulosity associated with VLA 1, and that VLA 1 and HH 270 IRS are separate objects. Comparison of the near-IR and optical images with an accurate positional alignment shows that VLA 1 is the driving source of the HH 270 flow. If HH 270 IRS is not a background star, the HH 270 core may contain a binary system with inhomogeneous spectral classes: VLA 1 may be a Class 0 protostar, and HH 270 IRS may be a young stellar object with a hotter spectral energy distribution.

Outflows from the high-mass protostars NGC 7538 IRS1/2 observed with bispectrum speckle interferometry

NGC 7538 IRS1 is a high-mass (approx. 30 M_sun) protostar with a CO outflow, an associated UCHII region, and a linear methanol maser structure, which might trace a Keplerian-rotating circumstellar disk. The directions of the various associated axes are misaligned with each other. We investigate the near-infrared morphology of the source to clarify the relations among the various axes. K'-band bispectrum speckle interferometry was performed at two 6-meter-class telescopes -- the BTA 6m telescope and the 6.5m MMT. Complementary IRAC images from the Spitzer Space Telescope Archive were used to relate the structures detected with the outflow at larger scales. High-dynamic range images show fan-shaped outflow structure in which we detect 18 stars and several blobs of diffuse emission. We interpret the misalignment of various outflow axes in the context of a disk precession model, including numerical hydrodynamic simulations of the molecular emission. The precession period is approx. 280 years and its half-opening angle is 40 degrees. A possible triggering mechanism is non-coplanar tidal interaction of an (undiscovered) close companion with the circumbinary protostellar disk. Our observations resolve the nearby massive protostar NGC 7538 IRS2 as a close binary with separation of 195 mas. We find indications for shock interaction between the outflow activities in IRS1 and IRS2. Indications of outflow precession have been discovered to date in a number of massive protostars, all with large precession angles 20--45 degrees. This might explain the difference between the outflow widths in low- and high-mass stars and add support to a common collimation mechanism.

Star Formation in the Northern Cloud Complex of NGC 2264

We have made continuum and spectral line observations of several outflow sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope (HHT) and ARO 12 m millimeter-wave telescope. This study explores the kinematics and outflow energetics of the young stellar systems observed and assesses the impact star formation is having on the surrounding cloud environment. Our data set incorporates 12CO (3-2),13CO (3-2), and 12CO (1-0) observations of outflows associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS 25 and 27, respectively, in the northern cloud complex. Complementary 870 μm continuum maps were made with the HHT 19 channel bolometer array. Our results indicate there is a weak ≤0.5% coupling between outflow kinetic energy and turbulent energy of the cloud. An analysis of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining their dynamical integrity except where outflowing material directly interacts with the core, such as along the outflow axes.

Variability of the NGC 1333 IRAS 4A Outflow: Molecular Hydrogen and Silicon Monoxide Images

The NGC 1333 region was observed in the H2 1-0 S(1) line. The H2 images cover a 5' × 7' region around IRAS 4. Numerous H2 emission features were detected. The northeast-southwest bipolar outflow driven by IRAS 4A was studied by combining the H2 images with SiO maps published previously. The SiO-H2 outflows are continuous on the southwestern side but show a gap on the northeastern side. The southwestern outflow lobe curves smoothly, and the position angle increases with the distance from the driving source. The base and the outer tip of the northeastern outflow lobe are located at positions opposite to the corresponding parts of the southwestern lobe. This point symmetry suggests that the outflow axis may be drifting or precessing clockwise in the plane of the sky and that the cause of the axis drift may be intrinsic to the outflow engine. The axis drift model is supported by the asymmetric lateral intensity profile of the SiO outflow. The axis drift rate is ~0011 yr-1. The middle part of the northeastern outflow does not exactly follow the point symmetry because of the superposition of two different kinds of directional variability: the axis drift of the driving source and the deflection by a dense core. The axis drift model provides a good explanation for the large deflection angle of the northeastern outflow. Other H2 emission features around the IRAS 4 region are discussed briefly. Some of them are newly found outflows, and some are associated with outflows already known before.

Tracing the base of protostellar wind(s) towards the high-mass star forming region AFGL 5142: VLA continuum and VLBA H$_\mathsf{2}$O maser observations

We have conducted phase-reference multi-epoch observations of the 22.2 GHz water masers using the Very Long Baseline Array (VLBA) and a multi-frequency study of the continuum emission using the Very Large Array (VLA) towards the high-mass star forming region (SFR) AFGL 5142. 29 maser features were identified and most of them were persistent over the four observing epochs, allowing absolute proper motions to be determined. The water maser emission comes from two elongated structures (indicated as Group I and Group II), with the measured proper motions aligned along the structures’ elongation axes. Each group consists of two (blue- and red-shifted) clusters of features separated by a few hundreds and thousands of AU respectively for Group I and Group II. The maser features of Group II have both positions and velocities aligned along a direction close to the axis of the outflow traced by HCO + and SiO emission on angular scales of tens of arcsec. We predict that the maser emission arises from dense, shocked molecular clumps displaced along the axis of the molecular outflow. The two maser clusters of Group I are oriented on the sky along a direction forming a large angle (60 ◦ ) with the axis of the jet/outflow traced by Group II maser features. We have detected a compact (8.4 and 22 GHz) continuum source (previously reported at 4.9 and 8.4 GHz) that falls close to the centroid of Group I masers, indicating that the source ionizing the gas is also responsible for the excitation of the water masers. The kinematic analysis indicates that the Group I masers trace outflowing rather than rotating gas, discarding the Keplerian disk scenario proposed in a previous paper for Group I. Since the axis joining the two maser clusters of Group II does not cross the position of the continuum source, Group II masers might be excited by an (undetected) massive YSO, distinct from the one (pinpointed by the VLA continuum emission) responsible for the excitation of the Group I masers. Our results give support to models of accretion and jet ejection related to the formation of high-mass stars.

First results from a VLBA proper motion survey of H$_\mathsf{2}$O masers in low-mass YSOs: the Serpens core and RNO 15-FIR

This article reports first results of a long-term observational program aimed to study the earliest evolution of jet/disk systems in low-mass YSOs by means of VLBI observations of the 22.2 GHz water masers. We report here data for the cluster of low-mass YSOs in the Serpens molecular core and for the single object RNO~15-FIR. Towards Serpens SMM1, the most luminous sub-mm source of the Serpens cluster, the water maser emission comes from two small (< 5 AU in size) clusters of features separated by ~25 AU, having line of sight velocities strongly red-shifted (by more than 10 km/s) with respect to the LSR velocity of the molecular cloud. The two maser clusters are oriented on the sky along a direction that is approximately perpendicular to the axis of the radio continuum jet observed with the VLA towards SMM1. The spatial and velocity distribution of the maser features lead us to favor the interpretation that the maser emission is excited by interaction of the receding lobe of the jet with dense gas in the accretion disk surrounding the YSO in SMM1. Towards RNO~15-FIR, the few detected maser features have both positions and (absolute) velocities aligned along a direction that is parallel to the axis of the molecular outflow observed on much larger angular scales. In this case the maser emission likely emerges from dense, shocked molecular clumps displaced along the axis of the jet emerging from the YSO. The protostar in Serpens SMM1 is more massive than the one in RNO~15-FIR. We discuss the case where a high mass ejection rate can generate jets sufficiently powerful to sweep away from their course the densest portions of circumstellar gas. In this case, the excitation conditions for water masers might preferably occur at the interface between the jet and the accretion disk, rather than along the jet axis.

SiO J = 5-4 in the HH 211 Protostellar Jet Imaged with the Submillimeter Array

We have mapped the SiO J = 5-4 line at 217 GHz from the HH 211 molecular outflow with the Submillimeter Array (SMA). The high-resolution map (16 × 09) shows that the SiO J = 5-4 emission comes from the central narrow jet along the outflow axis with a width of ~08 (~250 AU) FWHM. The SiO jet consists of a chain of knots separated by 3''-4'' (~1000 AU), and most of the SiO knots have counterparts in shocked H2 emission seen in a new, deep VLT near-infrared image of the outflow. A new, innermost pair of knots have been discovered at just ±2'' from the central star. The line ratio between the SiO J = 5-4 data and the upper limits from the SiO J = 1-0 data of Chandler & Richer suggests that these knots have a temperature in excess of 300-500 K and a density of (0.5-1) × 107 cm-3. The radial velocity measured for these knots is ~30 km s-1, comparable to the maximum velocity seen in the entire jet. The high temperature, high density, and velocity structure observed in this pair of SiO knots suggest that they are closely related to the primary jet launched close to the protostar.

Submillimeter Emission from the Hot Molecular Jet HH 211

We observed the HH 211 jet in the submillimeter continuum and the CO(3-2) and SiO(8-7) transitions with the Submillimeter Array. The continuum source detected at the center of the outflow shows an elongated morphology, perpendicular to the direction of the outflow axis. The high-velocity emission of both molecules shows a knotty and highly collimated structure. The SiO(8-7) emission at the base of the outflow, close to the driving source, spans a wide range of velocities, from -20 up to 40 km s^{-1}. This suggests that a wide-angle wind may be the driving mechanism of the HH 211 outflow. For distances greater than 5 (1500 AU) from the driving source, emission from both transitions follows a Hubble-law behavior, with SiO(8-7) reaching higher velocities than CO(3-2), and being located upstream of the CO(3-2) knots. This indicates that the SiO(8-7) emission is likely tracing entrained gas very close to the primary jet, while the CO(3-2) is tracing less dense entrained gas. From the SiO(5-4) data of Hirano et al. we find that the SiO(8-7)/SiO(5-4) brightness temperature ratio along the jet decreases for knots far from the driving source. This is consistent with the density decreasing along the jet, from (3-10)x10^6 cm^{-3} at 500 AU to (0.8-4)x10^6 cm^{-3} at 5000 AU from the driving source.

Outflow and Infall in Star‐forming Region L1221

We have mapped the 3.3 mm continuum, CO, HCO+, N2H+, and CS emission around a nearby Class I source, IRAS 22266+6845, in the L1221 cometary dark cloud. L1221 is a complicated star-forming region. It hosts three infrared sources: a close binary consisting of an east source and a west source around the IRAS source position and a southeast source ~45'' to the southeast (T. Bourke 2004, private communication). The east source is identified as the IRAS source. Continuum emission is seen around the east and southeast sources, probably tracing the dust around them. No continuum emission is seen toward the west source, probably indicating that there is not much dust there. An east-west molecular outflow is seen in CO, HCO+, and CS originated from around the binary. It is bipolar with an east lobe and a west lobe, both appearing as a wide-opening outflow shell originated from around the binary. It is likely powered by the east source, which shows a southeast extension along the outflow axis in the K' image. A ringlike envelope is seen in N2H+ around the binary surrounding the outflow waist. It is tilted with the major axis perpendicular to the outflow axis. The kinematics is well reproduced by a thin-disk model with both infall and rotation, and a column density peak in a ring. The ringlike envelope is not rotationally supported, as the rotation velocity is smaller than the infall velocity.

Jets, structured outflows and energy injection in gamma-ray burst afterglows: numerical modelling

We investigate numerically the ability of three models (jet, structured outflow and energy injection) to accommodate the optical light-curve breaks observed in 10 gamma-ray burst (GRB) afterglows (980519, 990123, 990510, 991216, 000301c, 000926, 010222, 011211, 020813 and 030226), as well as the relative intensities of the radio, optical and X-ray emissions of these afterglows. We find that the jet and structured outflow models fare much better than energy injection model in accommodating the multiwavelength data of the above 10 afterglows. For the first two models, a uniform circumburst medium provides a better fit to the optical light-curve break than a wind-like medium with a r -2 stratification. However, in the only two cases where the energy injection model may be at work, a wind medium is favoured (an energy injection is also possible in a third case, the afterglow 970508, whose optical emission exhibited a sharp rise, but not a steepening decay). The best-fitting parameters obtained with the jet model indicate an outflow energy of 2 × 10 50 to 6 x 11 50 ergs and a jet opening of 2 - 3°. Structured outflows with a quasi-uniform core have a core angular size of 0.°7-1° and an energy per solid angle of 0.5 x 10 53 to 3 x 10 53 erg sr -1 , surrounded by an envelope where this energy falls off roughly as θ -2 with angle from the outflow axis, requiring thus the same energy budget as jets. Circumburst densities are found to be typically in the range 0.1-1 cm -3 , for either model. We also find that the reverse shock emission resulting from the injection of ejecta into the decelerating blast wave at about 1 d after the burst can explain the slowly decaying radio light curves observed for the afterglows 990123, 991216 and 010222.

The Direct Detection of a (Proto)Binary/Disk System in IRAS 20126+4104

We report the direct detection of a binary/disk system towards the highmass (proto)stellar object IRAS20126+4104 at infrared wavengths. The presence of a multiple system had been indicated by the precession of the outflow and the double jet system detected earlier at cm-wavelengths. Our new K, L 0 & M 0 band infrared images obtained with the UKIRT under exceptional seeing conditions on Mauna Kea are able to resolve the central source for the rst time, and we identify two objects separated by 0.5 00 (850 AU). The K and L 0 images also uncover features characteristic of a nearly edge-on disk, similar to many low mass protostars with disks: two emission regions oriented along an outflow axis and separated by a dark lane. The peaks of the L 0 &M 0 band and mm-wavelength emission are on the dark lane, presumably locating the primary young star. The thickness of the disk is measured to be 850 AU for radii < 1000 AU. Approximate limits on the NIR magnitudes of the two young stars indicate a high-mass system, although with much uncertainty. These results are a demonstration of the high-mass nature of the system, and the similarities of the star-formation process in the low-mass and high-mass regimes viz. the presence of a disk-accretion stage. The companion is located along the dark lane, consistent with it being in the equatorial/disk plane, indicating a disk-accretion setting for massive, multiple, star-formation. Subject headings: stars: formation { stars: massive { stars: binary { circumstellar matter { ISM: individual (IRAS20126+4104) { infrared: ISM

Subarcsecond Structure and Velocity Field of Optical Line‐emitting Gas in NGC 1052

We have obtained integral field spectra of the low-ionization emission-line region in the galaxy NGC 1052 by using the Kyoto Tridimensional Spectrograph II mounted on the Subaru Telescope. Our high signal-to-noise ratio data with precise template subtraction have revealed weaker features at the nucleus, including the [Fe III] and He II emission lines, as well as a broad component of the Hβ emission. The broad Hβ component suggests the existence of a broad-line region. The spatial structure and velocity field derived from the data cube suggest the existence of three main components: a high-velocity bipolar outflow, low-velocity disk rotation, and a spatially unresolved nuclear component. The outflow axis does not coincide with the disk rotation axis. The opening angle of the outflow decreases with velocity shift from the systemic velocity both in bluer and redder velocity channels. This is explained only if the outflow has intrinsically higher velocity components inside, i.e., in regions closer to the outflow axis. At both sides of the bipolar outflow, we find that the highest velocity components are detached from the nucleus. This gap can be explained by an acceleration of at least a part of the flow or the surrounding matter, or by bow shocks that may be produced by even higher velocity outflow components that are not yet detected. Along the edges of the outflow and extending east-northeast and west-southwest, there exist strong [O III] emission ridges. These are closely related to the radio jet-counterjet structure. The abrupt change in the velocity field of the ionized gas and a large [O ]/Hβ line flux ratio in this region suggest a strong interaction of the jets, and possibly also of some ridge components of the line-emitting gas, with the interstellar matter.

Outflow Interaction in the Late Stages of Star Formation

We have mapped the CO, HCO+, N2H+, and CS emission around a nearby T Tauri star, IRAS 16316-1540. A molecular outflow is seen in CO, HCO+, N2H+, and CS emission originating from the IRAS source, while an envelope is seen in N2H+ and HCO+ emission surrounding the IRAS source. The molecular outflow is bipolar with a southeastern (SE) lobe and a northwestern (NW) lobe. The structure and the kinematics of the SE lobe are well defined and can be explained with a simple kinematic model. In this model, the SE lobe is a U-shaped shell consisting of a wide-opening base mimicking the reflection nebula RNO 91 and a cylindrical shell with a constant radius mimicking the CO outflow shell. The wide-opening base is expanding toward the circumstellar envelope, while the cylindrical shell is expanding mainly laterally into the ambient medium. If the base of the SE lobe continues to expand at its current velocity, it will meet with the base of the NW lobe and disperse the circumstellar envelope in a few times 104 yr. The circumstellar envelope is elongated perpendicular to the outflow axis, extending to the northeast and southwest of the IRAS source. The envelope has differential rotation with the velocity increasing toward the source. It may result from material infalling toward the source carrying its angular momentum. The HCO+ emission near the source may arise from an unresolved inner ring of the envelope, showing two peaks with one on each side of the IRAS source and a position-velocity structure consistent with the rotation law derived from the N2H+ emission. The HCO+ emission in the outer part of the envelope likely traces the swept up envelope material, showing both the outflow motion and probably rotation.

Pushing the Envelope: The Impact of an Outflow at the Earliest Stages of Star Formation

We present new multiline and 3 mm continuum interferometer observations of the circumstellar environment within 2 × 104 AU of the class 0 protostar IRAS 05295+1247, the source of the RNO 43 outflow. The high-resolution molecular line and continuum images enable a thorough study of the circumstellar envelope, the molecular outflow, and its impact on the surroundings. We detect a highly collimated bipolar molecular outflow seen in the 12CO (1-0) map, which we interpret to be a new outflow episode, undetected in previous observations of the RNO 43 outflow. The medium-density gas of the outer circumstellar envelope, which is traced by the 13CO (1-0) emission, is accelerated over an extended volume and not confined to the narrow 12CO outflow axis. Our data also suggest that the outflow affects the chemical composition of the surroundings, enhancing the HCO+ (1-0) abundance along its edges. Most importantly, the kinetic energy injected by the outflow is sufficient to produce a velocity gradient in the dense inner circumstellar envelope traced by the C18O (1-0) and H13CO+ (1-0) emission. Such a strong perturbation to the envelope will clearly have an important effect on the mass-assembling process in IRAS 05295+1247.

A study of the Keplerian accretion disk and precessing outflow in the massive protostar IRAS 20126+4104

We report on interferometric observations at 3.2 and 1.3 mm of the massive young stellar object IRAS 20126+4104 obtained in the C 34 Sa nd CH 3OH lines and in the continuum emission. The C 34 S data confirm the existence of a Keplerian disk, as already suggested by various authors. However, the mass of the central object is ∼7 M� , significantly less than previous estimates. We believe that such a discrepancy is due to the fact that the rotation curve is affected not only by the star but also by the mass in the innermost regions of the disk itself: this leads to an overestimate of the stellar mass when low-density tracers are used to study the velocity field over regions larger than a few seconds of arc (i.e. a few 0.01 pc). On the basis of the line profiles we speculate that accretion onto the star might be still occurring through the disk. This seems consistent with current models of high-mass star formation which predict an accretion luminosity equal to that of IRAS 20126+4104 for a 7 Mprotostar. The CH3OH lines trace both the disk and the bipolar outflow previously detected in other molecules such as HCO + ,S iO, and H 2. New H2 images obtained at 2.2 µm confirm that the outflow axis is undergoing precession. We elaborate a simple model that suitably fits the data thus allowing derivation of a few basic parameters of the precession.

3-D kinematics of the HH 110 jet

We present new results on the kinematics of the jet HH 110. New proper motion measurements have been calculated from [SII] CCD images obtained with a time baseline of nearly fifteen years. HH 110 proper motions show a strong asymmetry with respect to the outflow axis, with a general trend of pointing towards the west of the axis direction. Spatial velocities have been obtained by combining the proper motions and radial velocities from Fabry-Pérot data. Velocities decrease by a factor ~3 over a distance of cm, much shorter than the distances expected for the braking caused by the jet/environment interaction. Our results show evidence of an anomalously strong interaction between the outflow and the surrounding environment, and are compatible with the scenario in which HH 110 emerges from a deflection in a jet/cloud collision.

Molecular Line Observations of IRAM 04191+1522

We have mapped the CO, HCO+, CS, and N2H+ emission around a low-luminosity Class 0 source IRAM 04191+1522 in the Taurus molecular cloud using the Berkeley-Illinois-Maryland Association array. A bipolar molecular outflow is seen in CO, HCO+, and CS emission originating from around the IRAM source, while a flattened envelope is seen in N2H+ emission surrounding the waist of the molecular outflow around the IRAM source. Outflow, rotation, and probably infall are seen around the Class 0 source, indicating a complicated context for star formation in the earliest stages. The N2H+ envelope is a thick clumpy torus with a tenuous outer part and a ringlike dense inner edge. The dense inner edge has a mean radius of 10'', or 1400 AU. The outer part of the torus exhibits differential rotation, and the infalling material appears to carry angular momentum inward toward the central source. The region surrounded by the inner edge of the torus may have a solid-body rotation. The envelope may result from the collapse of a rotating, magnetized toroid toward the central source. Outflow motion is seen in the outer part of the inner edge of the torus, probably due to an interaction with the molecular outflow. Two armlike structures are seen extending out from the inner edge in the torus. One of them is clearly seen with the velocity increasing roughly linearly with the distance. The HCO+ emission around the source may trace the central core around the source, showing a velocity structure connecting to that of the outer part of the torus. The molecular outflow is best seen in CO. It is bipolar with both a southwest and a northeast lobe. Two internal structures are seen along the main outflow axis within the lobes: (1) a strong CO emission at ~20'' to the northeast of the IRAM source, likely tracing an internal bow shock driven by a collimated, episodic jet and (2) a linear HCO+ structure of ~50'' length at low blueshifted velocity to the southwest of the IRAM source, requiring some interaction with a jet to be produced. In addition, a dense condensation is also seen in HCO+ and CS to the south of the IRAM source, likely representing a recent strong outflow interaction.

New Silhouette Disks with Reflection Nebulae and Outflows in the Orion Nebula and M43

We report the detection of several new circumstellar disks seen in silhouette against background nebular light in the outskirts of the Orion Nebula and the neighboring H II region M43. These were detected as part of our Hα survey of Orion with the Advanced Camera for Surveys on board the Hubble Space Telescope. Several of the disks show bipolar reflection nebulae, microjets, or pronounced temporal variability of their central stars. The relatively large fraction of bipolar reflection nebulae and microjets in our sample may be a selection effect caused by the faint nebular background far from the Trapezium. Two disks in our sample are large and particularly noteworthy: A nearly edge-on disk, d216-0939, is located several arcminutes northwest of M43 and resembles the famous HH 30 disk/jet system in Taurus. It drives the 0.15 pc long bipolar outflow HH 667 and exhibits a remarkable asymmetric reflection nebula caused by the tilt of the flared disk. With a diameter of ∼26 (1200 AU), d216-0939 is as large as the giant edge-on silhouette disk d114-426 in the core of the Orion Nebula. The large disk d253-1536 is located in a binary system embedded within an externally ionized giant proplyd in M43. The disk exhibits distortions that we attribute to tidal interactions with the companion star. The bipolar jet HH 668 emerges from the proplyd ionization front in a direction orthogonal to the disk and can be traced to the young star embedded within it. A bow shock lies 54'' south of this binary system along the outflow axis. Proper motions over a 1.4 yr baseline confirm that these emission knots are indeed moving away from d253-1536 with speeds as high as ∼330 km s-1 in the HH 668 microjet and slower motion farther from the star.