High-velocity Bipolar Outflow Research Articles

The Extraordinary Outburst in the Massive Protostellar System NGC 6334I-MM1: Flaring of the Water Masers in a North–South Bipolar Outflow Driven by MM1B

Abstract We compare multi-epoch sub-arcsecond Very Large Array imaging of the 22 GHz water masers toward the massive protocluster NGC 6334I observed before and after the recent outburst of MM1B in (sub)millimeter continuum. Since the outburst, the water maser emission toward MM1 has substantially weakened. Simultaneously, the strong water masers associated with the synchrotron continuum point source CM2 have flared by a mean factor of 6.5 (to 4.2 kJy) with highly blueshifted features (up to 70 km s−1 from the LSR) becoming more prominent. The strongest flaring water masers reside 3000 au north of MM1B and form a remarkable bow shock pattern whose vertex coincides with CM2 and tail points back to MM1B. Excited OH masers trace a secondary bow shock located ∼120 au downstream. Atacama Large Millimeter Array images of CS (6–5) reveal a highly collimated north–south structure encompassing the flaring masers to the north and the nonflaring masers to the south seen in projection toward the MM3-UCHII region. Proper motions of the southern water masers over 5.3 years indicate a bulk projected motion of 117 km s−1 southward from MM1B with a dynamical time of 170 years. We conclude that CM2, the water masers, and many of the excited OH masers trace the interaction of the high-velocity bipolar outflow from MM1B with ambient molecular gas. The previously excavated outflow cavity has apparently allowed the radiative energy of the current outburst to propagate freely until terminating at the northern bow shock where it strengthened the masers. Additionally, water masers have been detected toward MM7 for the first time, and a highly collimated CS (6–5) outflow has been detected toward MM4.

THE MASSIVE PROTOSTELLAR CLUSTER NGC 6334I AT 220 au RESOLUTION: DISCOVERY OF FURTHER MULTIPLICITY, DIVERSITY, AND A HOT MULTI-CORE

ABSTRACT We present Very Large Array and Atacama Large Millimeter/submillimeter Array imaging of the deeply embedded protostellar cluster NGC 6334I from 5 cm to 1.3 mm at angular resolutions as fine as 0.″17 (220 au). The dominant hot core MM1 is resolved into seven components at 1.3 mm, clustered within a radius of 1000 au. Four of the components have brightness temperatures >200 K, radii ∼300 au, minimum luminosities ∼104 L ⊙, and must be centrally heated. We term this new phenomenon a “hot multi-core.” Two of these objects also exhibit compact free–free emission at longer wavelengths, consistent with a hypercompact H ii region (MM1B) and a jet (MM1D). The spatial kinematics of the water maser emission centered on MM1D are consistent with it being the origin of the high-velocity bipolar molecular outflow seen in CO. The close proximity of MM1B and MM1D (440 au) suggests a proto-binary or a transient bound system. Several components of MM1 exhibit steep millimeter spectral energy distributions indicative of either unusual dust spectral properties or time variability. In addition to resolving MM1 and the other hot core (MM2) into multiple components, we detect five new millimeter and two new centimeter sources. Water masers are detected for the first time toward MM4A, confirming its membership in the protocluster. With a 1.3 mm brightness temperature of 97 K coupled with a lack of thermal molecular line emission, MM4A appears to be a highly optically thick 240 L ⊙ dust core, possibly tracing a transient stage of massive protostellar evolution. The nature of the strongest water maser source CM2 remains unclear due to its combination of non-thermal radio continuum and lack of dust emission.

Submillimeter array observations of NGC 2264-C: molecular outflows and driving sources

We present 1.3mm Submillimeter Array (SMA) observations at $\sim$3$^{\prime\prime}$ resolution towards the brightest section of the intermediate/massive star forming cluster NGC 2264-C. The millimetre continuum emission reveals ten 1.3mm continuum peaks, of which four are new detections. The observed frequency range includes the known molecular jet/outflow tracer SiO (5-4), thus providing the first high resolution observations of SiO towards NGC 2264-C. We also detect molecular lines of twelve additional species towards this region, including CH$_3$CN, CH$_3$OH, SO, H$_2$CO, DCN, HC$_3$N, and $^{12}$CO. The SiO (5-4) emission reveals the presence of two collimated, high velocity (up to 30kms$^{-1}$ with respect to the systemic velocity) bi-polar outflows in NGC 2264-C. In addition, the outflows are traced by emission from $^{12}$CO, SO, H$_2$CO, and CH$_3$OH. We find an evolutionary spread between cores residing in the same parent cloud. The two unambiguous outflows are driven by the brightest mm continuum cores, which are IR-dark, molecular line weak, and likely the youngest cores in the region. Furthermore, towards the RMS source AFGL 989-IRS1, the IR-bright and most evolved source in NGC 2264-C, we observe no molecular outflow emission. A molecular line rich ridge feature, with no obvious directly associated continuum source, lies on the edge of a low density cavity and may be formed from a wind driven by AFGL 989-IRS1. In addition, 229GHz class I maser emission is detected towards this feature.

Kinematics of the nucleus of the radio galaxy M 87

The superfine structure of the active region of the radio galaxy M 87 has been investigated at millimeter and centimeter wavelengths. A disk, a core, a jet, and a counterjet have been identified. The disk is inclined to the plane of the sky at an angle of 60◦ toward the jet. We show that the surrounding thermal plasma inflows onto the disk, is transferred in a spiral to the center, and is ejected, carrying away an excess angular momentum as it is accumulated. The remainder falls to the forming central massive body. The temperature of the plasma as it is transferred increases to relativistic values; the ejection velocity increases to 0.02c. The nozzle diameter decreases as the axis is approached. The central high-velocity bipolar outflow is surrounded by low-velocity components, tubes. The interaction of the rotating flow with the ambient medium collimates and accelerates the flows. Ring currents whose tangential directions are observed as parallel chains of components are generated in the flows. The ring currents of the disk and jets produce aligned magnetic fields. The ejection of the jet and counterjet plasma flows is equiprobable; the motion is along the field in one case and opposite to the field in the other case, causing an acceleration or deceleration. The velocity of the high-velocity jet is a factor of 1.7 higher than the counterjet velocity. The acceleration compensates for the losses of relativistic electrons observed at distances exceeding those corresponding to their radiative cooling time. The hydrodynamic instability of the flow ejection causes precession, the formation of a conical helical flow structure with an increasing pitch. The reaction of the flows curves the disk and the helix axes. The spectra of compact fragments in the high-velocity bipolar outflow have lowfrequency cutoffs determined by reabsorption and absorption in the thermal plasma of the screen. The cutoff frequencies in the spectra increase as the center is approached and pass into the millimeter wavelength range. The screen thickness reaches 0.05 pc; the electron density is 104–105 cm−3. The magnetic fields of the bipolar outflow fragments are 50 mG ≤ B ≤ 500 mG at the nozzle exit and B ≈ 200 μG in the remote part at ρ ≥ 0.25 mas. The rotation measure toward the core center is RM ≈ 104 rad m−2. The sign of the rotation measure in the remote part of the bipolar outflow determined by the helical shape is reversed. The longitudinal magnetic field of the screen toward the central part of the core is BII ≈ 10 μG and falls at the edges of the active region to BII ≈ 2 μG.

A spider-like outflow in Barnard 5 - IRS 1: the transition from a collimated jet to a wide-angle outflow?

We present line and continuum observations made with the Submillimeter Array (SMA) of the young stellar object Barnard 5 - IRS1 located in the Perseus molecular cloud. Our $^{12}$CO(2-1) line observations resolve the high-velocity bipolar northeast-southwest outflow associated with this source. We find that the outflowing gas shows different structures at three different velocity regimes, in both lobes, resulting in a spider-like morphology. In addition to the low-velocity, cone-like (wide-angle) lobes that have previously been observed, we report the presence of intermediate-velocity parabolic shells emerging very close to the Class I protostar, as well as high velocity molecular bullets that appear to be associated to the optical/IR jet emanating from this source. These compact high-velocity features reach radial velocities of about 50 km s$^{-1}$ away from the cloud velocity. We interpret the peculiar spider-like morphology is a result of the molecular material being entrained by a wind with both a collimated jet-like component and a wide-angle component. We suggest the outflow is in a transitional evolutionary phase between a mostly jet-driven flow and an outflow in which the entrainment is dominated by the wide-angle wind component. We also detect 1300 $\mu$m continuum emission at the position of the protostar, which likely arises from the dusty envelope and disk surrounding the protostar. Finally, we report the detection of $^{13}$CO(2-1) and SO(6$_5$-5$_4$) emission arising from the outflow and the location of the young stellar object.

OUTFLOW, INFALL, AND PROTOSTARS IN THE STAR-FORMING CORE W3-SE

We report new results on outflow and infall in the star forming cores W3-SE SMA-1 and SMA-2 based on analysis of $\sim2.5\arcsec$ resolution observations of the molecular lines HCN(3-2), HCO$^+$(3-2), N$_2$H$^+$(3-2) and CH$_3$OH(5$_{2,3}-4_{1,3}$) with the Submillimeter Array. A high-velocity bipolar outflow originating from the proto-stellar core SMA-1 was observed in the HCN(3-2) line, with a projected outflow axis in position angle 48$\arcdeg$. The detection of the outflow is confirmed from other molecular lines. An inverse P-Cygni profile in the HCN(3-2) line toward SMA-1 suggests that at least one of the double cores accretes matters from the molecular core. A filamentary structure in the molecular gas surrounds SMA-1 and SMA-2. Based on the SMA observations, our analysis suggests that the double pre-stellar cores SMA-1 and SMA-2 result from fragmentation in the collapsing massive molecular core W3-SE, and it is likely that they are forming intermediate to high-mass stars which will be new members of a star cluster in the W3-SE region.

THE HIGH-VELOCITY MOLECULAR OUTFLOWS IN MASSIVE CLUSTER-FORMING REGION G10.6–0.4

We report the arcsecond resolution SMA observations of the $^{12}$CO (2-1) transition in the massive cluster forming region G10.6-0.4. In these observations, the high velocity $^{12}$CO emission is resolved into individual outflow systems, which have a typical size scale of a few arcseconds. These molecular outflows are energetic, and are interacting with the ambient molecular gas. By inspecting the shock signatures traced by CH$_{3}$OH, SiO, and HCN emissions, we suggest that abundant star formation activities are distributed over the entire 0.5 pc scale dense molecular envelope. The star formation efficiency over one global free-fall timescale (of the 0.5 pc molecular envelope, $\sim10^{5}$ years) is about a few percent. The total energy feedback of these high velocity outflows is higher than 10$^{47}$ erg, which is comparable to the total kinetic energy in the rotational motion of the dense molecular envelope. From order-of-magnitude estimations, we suggest that the energy injected from the protostellar outflows is capable of balancing the turbulent energy dissipation. No high velocity bipolar molecular outflow associated with the central OB cluster is directly detected, which can be due to the photo-ionization.

THREE-DIMENSIONAL MAGNETOHYDRODYNAMICAL SIMULATIONS OF GRAVITATIONAL COLLAPSE OF A 15 M ☉ STAR

We introduce our newly developed two different, three dimensional magneto hydrodynamical codes in detail. One of our codes is written in the Newtonian limit (NMHD) and the other is in the fully general relativistic code (GRMHD). Both codes employ adaptive mesh refinement and, in GRMHD, the metric is evolved with the "Baumgarte-Shapiro-Shibata-Nakamura" formalism known as the most stable method at present. We did several test problems and as for the first practical test, we calculated gravitational collapse of a $15M_\odot$ star. Main features found from our calculations are; (1) High velocity bipolar outflow is driven from the proto-neutronstar and moves through along the rotational axis in strongly magnetized models; (2) A one-armed spiral structure appears which is originated from the low-$|T/W|$ instability; (3) By comparing GRMHD and NMHD models, the maximum density increases about $\sim30%$ in GRMHD models due to the stronger gravitational effect. These features agree very well with previous studies and our codes are thus reliable to numerical simulation of gravitational collapse of massive stars.

SMA CO (2-1) Observations of CG 30: A Protostellar Binary System with a High-Velocity Quadrupolar Molecular Outflow

We present interferometric observations in the12CO (2-1) line and at 1.3 mm dust continuum of the low-mass protostellar binary system in the cometary globule CG 30, using the Submillimeter Array. The dust continuum images resolve two compact sources (CG 30N and CG 30S), with a linear separation of ~8700 AU and total gas masses of ~1.4 and ~0.6 M☉, respectively. With the CO images, we discover two high-velocity bipolar molecular outflows, driven by the two sources. The two outflows are nearly perpendicular to each other, showing a quadrupolar morphology. The northern bipolar outflow extends along the southeast (redshifted, with a velocity up to ~23 km s−1) and northwest (blueshifted, velocity up to ~30 km s−1) directions, while the southern pair has an orientation from southwest (blueshifted, velocity up to ~13 km s−1) to northeast (redshifted, velocity up to ~41 km s−1). The outflow mass of the northern pair, driven by the higher mass source CG 30N, is ~9 times larger than that of the southern pair. The discovery of the quadrupolar molecular outflow in the CG 30 protobinary system, as well as the presence of other quadrupolar outflows associated with binary systems, demonstrate that the disks in (wide) binary systems are not necessarily co-aligned after fragmentation.

Forming an early O-type star through gas accretion?

We present high angular resolution (∼3) and sensitive 1.3 mm continuum, cyanogen (CN) and vinyl cyanide (C 2 H 3 CN) line observations made with the Submillimeter Array (SMA) toward one of most highly obscured objects of the W51 IRS2 region, W51 North. We find that the CN line exhibits a pronounced inverse P-Cygni profile indicating that the molecular gas is falling into this object with a mass accretion rate between 4 and 7 x 10 -2 M ⊙ yr -1 . The C 2 H 3 CN traces an east-west rotating molecular envelope that surrounds either a single obscured (proto)star with a kinematic mass of 40 M ⊙ or a small central cluster of B-type stars and that is associated with a compact high velocity bipolar outflow traced by H 2 O masers and SiO molecular emission. We thus confirm that the W51 North region is part of the growing list of young massive star forming regions that have been associated with infalling motion and with high mass accretion rates (∼10 -2 -10 -4 M ⊙ yr -1 ), strengthening the evidence that massive stars can form with very high accretion rates sufficient to quench the formation of a UCHII region.

The Massive Bipolar Outflow in IRAS 20110+3321

Mapping observations were made towards IRAS 20110+3321 using theNobeyama 45 m and the Delingha 13.7 m radio telescopes. The highangular resolution (~21′′) image with the 45 m telescope showsthat there is a high-velocity bipolar molecular outflow in this region,which is in the NW–SE direction with a collimation factor of ~ 2.2.The outflow has significantly higher mass loss rate and mechanicalluminosity than those from low mass YSOs, indicating that the outflow isdriven by the IRAS source. A dense massive core was detected by mappingC18O (J = 1−0) line in the area with the 13.7 m telescope. TheIRAS source lies within the core but slightly offsets from its emissionpeak.

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.

High-Velocity Bipolar Outflow and Disklike Envelope in the Carbon Star V Hydrae

Using the partially completed Submillimeter Array with five antennas, we have observed the CO J = 2-1 and 3-2 emission from the envelope surrounding the carbon star V Hya. The high angular resolution (2''-4'') maps show that V Hya is powering a bipolar molecular jet with an extreme velocity of 70-185 km s-1. The axis of this high-velocity jet is perpendicular to the major axis of the flattened disklike envelope, which is expanding with a velocity of ~16 km s-1. There is a third kinematic component, a medium-velocity wind with a deprojected velocity of 40-120 km s-1 moving along the disk plane. Both the high-velocity jet and the medium-velocity wind have a dynamical timescale of a few hundred years. The flattened structure and the collimated jet observed in V Hya suggest that the formation of asymmetrical structure proceeds while the central star is still in the asymptotic giant branch phase.

A highly collimated, extremely high velocity outflow in Taurus

We present the first case of a highly collimated, extremely high velocity bipolar outflow in Taurus. It is powered by the low-luminosity (0.4 L_sun) source IRAS 04166+2706 and contains gas accelerated up to 50 km/s with respect to the ambient cloud both toward the blue and the red (uncorrected for projection). At the highest velocities, the outflow collimation factor exceeds 20, and the gas displays a very high degree of spatial symmetry. This very fast gas presents multiple maxima, and most likely arises from the acceleration of ambient material by a time-variable jet-like stellar wind. When scaled for luminosity, the outflow parameters of IRAS 04166 are comparable to those of other extremely high velocity outflows like L1448, indicating that even the very quiescent star-formation mode of Taurus can produce objects powering very high energy flows (L_mec/L_* > 0.15).

New high-velocity bipolar outflows in S39 and IRAS 06306 + 0232

New high-velocity bipolar outflows in S39 and IRAS 06306 + 0232

Star formation in the bright rimmed globule IC 1396N

We report mm-wave multiline and continuum observations of IC 1396N, a conspicuous bright, rimmed globule excited by the O6.5 star HD 206267 in the Cep OB2 association. Single-dish high resolution observations in CO and CS lines reveal the cometary structure of the globule with unprecedented detail. The globule head contains a dense core of 0.2 pc, whereas the tail, pointing away from the exciting star, has a total length of 0.8 pc. Two high velocity bipolar outflows have been identied in the CO maps: the rst one is located around the position of a strong IRAS source in the head of the globule, and the second one, which was previously unknown, is located in the northern region. The outflows emerge from high density clumps which exhibit strong line emission of CS, HCO + , and DCO + . Within these clumps, the sources driving the outflows have been identied thanks to mm-wave continuum observations. The globule head harbors two YSOs separated by about 10 4 AU. SiO line observations of the central outflow unveals a highly collimated structure with four clumps of sizes0: 1p c, which are located along the outflow axis and suggest episodic events in the mass loss process from the central star. Kinetic temperatures of50 100 K and hydrogen densities of fews 10 6 cm 3 have been estimated in the shocked regions traced by the strong SiO emission. The jet is also exposed to view by the means of interferometric HCO + observations that conrms that it is very narrow (0:02 pc wide). The detection of blue- and redshifted CO emission along the globule rim suggests that IC 1396N is in a transient phase, undergoing one of the expansions or compressions predicted by theoretical models describing the evolution of cometary globules. Moreover, the CO data, together with near IR observations reported elsewhere, indicate that the star forming process is occurring also in the northern part of IC 1396N, at 0.5 pc from the central CS peak. The present observations provide evidence that several star-forming sites can develop even in a moderately massive globule like IC 1396N.

Discovery of a Remarkable Point-Symmetric Proto–Planetary Nebula: [ITAL]Hubble Space Telescope[/ITAL] Imaging of IRAS 04296+3429

We present images of the proto‐planetary nebula (PPN) IRAS 0429613429 (hereafter I04296) taken with the Hubble Space TelescopeWide Field Planetary Camera 2 in two wide-band filters centered at 0.56 and 0.81mm. We find that this object, which belongs to a class of carbon-rich PPNs with a peculiar 21 mm dust emission feature, has a striking point-symmetric morphology, with a pair of long, well-collimated lobes oriented at about 707 to an equatorial elliptical “disklike” structure. Although dense disklike regions have been inferred from the presence of dark lanes separating the bipolar lobes of post‐asymptotic giant branch (AGB) objects, I04296 is the first to show a bounded disk directly in scattered light. The lobes and the disk appear embedded in a roughly round, faint halo with a radius at least as large as 2 0 .8. The bipolar lobes probably result from the interaction of a collimated high-velocity bipolar outflow with the spherical progenitor AGB circumstellar envelope, which is seen as the halo. The internal structure of the lobes suggests that the bipolar outflow changes its direction with time. A simple single-scattering model of a spherical inverse-square density envelope with a dust mass-loss rate of yr provides a good fit to the scattered light in the halo at both wavelengths. The collimated 28 21 4 # 10 M, lobes and point-symmetric structure in I04296 provide strong support for the jet-driven formation of aspherical planetary nebulae.

A Jet–driven, Extreme High‐Velocity Outflow Powered by a Cold, Low‐Luminosity Protostar near NGC 2023

We have discovered an extreme high-velocity bipolar CO outflow in the vicinity of NGC 2023, with total outflow velocities of ~200 km s-1. At very high velocities this outflow is jetlike with an opening angle ≤4°, while it shows a separate outflow lobe at low velocities. The outflow is bipolar and exhibits a clear mirror symmetry, which suggests that the source powering the outflow is episodic or precessing. The dynamical timescales for the outflow are ≤3000 yr. We identify the source driving the CO jet with a deeply embedded low-luminosity submillimeter double source (separation ~23''), where the primary component lies on the symmetry axis of the outflow and has all the signatures of a protostellar object. Analysis of molecular data and (sub)millimeter photometry suggests that the driving source is cold and compact, with a luminosity of lesssim10 L☉ and a total mass of 1.8-4.6 M☉. It has no near-IR counterpart, it drives an extremely young outflow, and it emits a large fraction of its luminosity in the submillimeter regime. Both millimeter sources have low dust emissivity, β ~ 0.8-1.3, similar to what is found for other class 0 objects, while the surrounding molecular cloud core appears to have a β ~ 2.0, the canonical value for normal interstellar dust in the submillimeter regime.

High-velocity molecular outflows hear massive young stellar objects

By mapping the (CO)-C-12 J = 1-0 lines in IRAS 05391-0217, 06114 + 1745 and 06291 + 0421, three new high-velocity bipolar molecular outflows are found. Parameters of these outflows are derived, which suggest that they are massive and energetic outflows with total kinetic energies of about 10(36) J and mass loss rates about 10(-5) H./a. The driving sources are identified by analyzing the positions, intensities and color temperatures of the associated infrared sources. These outflows are most likely driven by single sources which correspond to massive young stellar objects. In the se regions H2O masers have been detected located near the embedded infrared sources, which indicates that their exciting mechanism may be correlated with that of the CO outflows. The relationship between the parameters of outflows anti central sources shows that high-velocity outflow and thermal radiation of a star are two basic correlated but different features in the evolution of young stars.

An Excited H2Disk and the Core Structure of the Extraordinary Bipolar Planetary Nebula KjPn 8

A disk of excited H2v=1 → 0 S(1) (2.122 μm) emission has been found in the core of the extraordinary bipolar planetary nebula KjPn 8. This surrounds the central, extended, and clumpy thermal radio emission (VLA) and near-infrared (J, H, and K' bands) source. The H2 disk is found to be contained within a previously found expanding CO disk, and they share the same orientation. The plane of the H2 disk is perpendicular to the high-velocity bipolar outflows. The 4'' diameter core of KjPn 8 has also been observed for 37 on-source hours at a wavelength of 6 cm with the MERLIN radio interferometer with an angular resolution of 005. The data have been combined with 4 hr of VLA-A observations at the same wavelength but where the resolution is 05. The most remarkable feature of these radio observations is the possible presence of a weak radio source embedded in the center of the H2 disk. It is thought plausible that this point source may be direct emission from the powerful, ionized wind of the central star that now drives this nebulosity.