Molecular hydrogen jets and outflows in the Serpens South filamentary cloud

Context. Proper motion measurements provide unique and powerful means to identify the driving sources of mass outflows, which are of particular importance in regions with complex star formation activity and deeply embedded protostars. They also provide the necessary kinematic information to study the dynamics of mass outflows, the interaction between outflows and the ambient medium, and the evolution of outflows with the age of the driving sources. Aims. We aim to take a census of molecular hydrogen emission line objects (MHOs) in the Ophiuchi molecular cloud and to make the first systematic proper motion measurements of these objects in this region. The driving sources are identified based on the measured proper motions, and the outflow properties are characterized. The relationship between outflow properties and the evolutionary stages of the driving sources are also investigated. Methods. Deep H 2 near-infrared imaging is performed to search for molecular hydrogen emission line objects. Multi-epoch data are used to derive the proper motions of the features of these objects, and the lengths and opening angles of the molecular hydrogen outflows. Results. Our imaging covers an area of 0.11 deg 2 toward the L1688 core in the Ophiuchi molecular cloud. In total, six new MHOs are discovered, 32 previously known MHOs are detected, and the proper motions for 86 features of the MHOs are measured. The proper motions lie in the range of 14 to 247 mas/yr, corresponding to transversal velocities of 8 to 140 km s -1 with a median velocity of about 35 km s -1 . Based on morphology and proper motion measurements, 27 MHOs are ascribed to 21 driving sources. The molecular hydrogen outflows have a median length of 0.04 pc and random orientations. We find no obvious correlation between H 2 jet length, jet opening angle, and the evolutionary stage of the driving sources as defined by their spectral indices. We find that the fraction of protostars (23%) that drive molecular hydrogen outflows is similar to the one for Class II sources (15%). For most molecular hydrogen outflows, no obvious velocity variation along the outflow has been found. Conclusions. In Ophiuchus the frequency of occurrence of molecular hydrogen outflows has no strong dependency on the evolutionary stage of the driving source during the evolution from the protostellar stage to the classical T Tauri stage.

We present the results of a narrow-band near-infrared imaging survey for Molecular Hydrogen emission-line Objects (MHOs) toward 26 regions containing high-mass protostellar candidates and massive molecular outflows. We have detected a total of 236 MHOs, 156 of which are new detections, in 22 out of the 26 regions. We use H2 2.12 μm/H2 2.25 μm flux ratios, together with morphology, to separate the signatures of fluorescence associated with photo-dissociation regions (PDRs) from shocks associated with outflows in order to identify the MHOs. PDRs have typical low flux ratios of ∼1.5–3, while the vast majority of MHOs display flux ratios typical of C-type shocks (∼6–20). A few MHOs exhibit flux ratios consistent with expected values for J-type shocks (∼3–4), but these are located in regions that may be contaminated with fluorescent emission. Some previously reported MHOs have low flux ratios, and are likely parts of PDRs rather than shocks indicative of outflows. We identify a total of 36 outflows across the 22 target regions where MHOs were detected. In over half these regions, MHO arrangements and fluorescent structures trace features present in CO outflow maps, suggesting that the CO emission traces a combination of dynamical effects, which may include gas entrained in expanding PDRs as well as bipolar outflows. Where possible, we link MHO complexes to distinct outflows and identify candidate driving sources.

We uncover the H2 flows in the Corona Australis molecular cloud and in\nparticular identify the flows from the Coronet cluster. Near-infrared H2 v=1--0\nS(1), 2.12micron-line, narrow-band imaging survey of the R CrA cloud core was\ncarried out. We identify the best candidate-driving source for each outflow by\ncomparing the flow properties, available proper motions, and the\nknown/estimated properties of the driving sources. We also adopted the\nthumbrule of outflow power as proportional to source luminosity and inversely\nproportional to the source age to reach a consensus.\n Results: Continuum-subtracted, narrow-band images reveal several new\nMolecular Hydrogen emission-line Objects (MHOs). Together with previously known\nMHOs and Herbig-Haro objects we catalog at least 14 individual flow components\nof which 11 appear to be driven by the RCrA aggregate members. The flows\noriginating in the Coronet cluster have lengths of ~0.1-0.2 pc. Eight out of\nnine submillimeter cores mapped in the Coronet cluster region display embedded\nstars driving an outflow component. Roughly 80% of the youngest objects in the\nCoronet are associated with outflows. The MHO flows to the west of the Coronet\ndisplay lobes moving to the west and vice-versa, resulting in nondetections of\nthe counter lobe in our deep imaging. We speculate that these counterflows may\nbe experiencing a stunting effect in penetrating the dense central core.\n Conclusions:Although this work has reduced the ambiguities for many flows in\nthe Coronet region, one of the brightest H2 feature (MHO2014) and a few fainter\nfeatures in the region remain unassociated with a clear driving source. The\nflows from Coronet, therefore, continue to be interesting targets for future\nstudies.\n

We present a catalogue of Molecular Hydrogen emission-line Objects (MHOs) in outflows from young stars, most of which are embedded. All objects are identified in the near-infrared lines of molecular hydrogen, all reside in the Milky Way, and all are associated with jets or molecular outflows from young stars. Objects in both low and high-mass star forming regions are included. This catalogue complements the existing database of Herbig-Haro objects; indeed, for completeness, HH objects that are detected in H2 emission are included in the MHO catalogue.

We have performed an unbiased deep near-infrared survey toward the Aquila molecular cloud with a sky coverage of ~1 deg2. We identified 45 molecular hydrogen emission-line objects(MHOs), of which only 11 were previously known. Using the Spitzer archival data we also identified 802 young stellar objects (YSOs) in this region. Based on the morphology and the location of MHOs and YSO candidates, we associate 43 MHOs with 40 YSO candidates. The distribution of jet length shows an exponential decrease in the number of outflows with increasing length and the molecular hydrogen outflows seem to be oriented randomly. Moreover, there is no obvious correlation between jet lengths, jet opening angles, or jet H2 1-0 S(1) luminosities and spectral indices of the possible driving sources in this region. We also suggest that molecular hydrogen outflows in the Aquila molecular cloud are rather weak sources of turbulence, unlikely to generate the observed velocity dispersion in the region of survey.

We have discovered 12 new molecular hydrogen emission-line objects (MHOs) in\nthe vicinity of the candidate massive young stellar object Mol 121, in addition\nto five that were previously known. H2 2.12-micron/H2 2.25-micron flux ratios\nindicate another region dominated by fluorescence from a photo-dissociation\nregion (PDR), and one region that displays an anomalously low H2 2.12-micron/H2\n2.25-micron flux ratio (<1) and coincides with a previously reported deeply\nembedded source (DES). Continuum observations at 3 mm reveal five dense cores;\nthe brightest core is coincident with the DES. The next brightest cores are\nboth associated with cm continuum emission. One of these is coincident with the\nIRAS source; the other lies at the centroid of a compact outflow defined by\nbipolar MHOs. The brighter of these bipolar MHOs exhibits [Fe II] emission and\nboth MHOs are associated with CH3OH maser emission observed at 95 GHz and 44\nGHz. Masses and column densities of all five cores are consistent with\ntheoretical predictions for massive star formation. Although it is impossible\nto associate all MHOs with driving sources in this region, it is evident that\nthere are several outflows along different position angles, and some\nunambiguous associations can be made. We discuss implications of observed H2\n2.12-micron/H2 2.25-micron and [Fe II] 1.64-micron/H2 2.12-micron flux ratios\nand compare the estimated total H2 luminosity with the bolometric luminosity of\nthe region. We conclude that the outflows are driven by massive young stellar\nobjects embedded in cores that are likely to be in different evolutionary\nstages.\n

(abbreviated) We used HAWK-I at the ESO VLT to produce a near-infrared survey\nof the Carina Nebula that is deep enough to detect the full low-mass stellar\npopulation. The results of a recent deep X-ray survey are used to distinguish\nbetween young stars in Carina and background contaminants. We find that the\nages of the low-mass stars (derived from color-magnitude diagrams of the\ninvidual cluster in the Carina Nebula) agree with previous age estimates for\nthe massive stars. About 3200 of the X-ray selected stars have masses >= 1\nMsun; this number is in good agreement with extrapolations of the field IMF\nbased on the number of high-mass stars and shows that there is no deficit of\nlow-mass stars. The near-infrared excess fractions for the stellar populations\nin Carina are lower than typical for other, less massive clusters of similar\nage, suggesting a faster timescale of circumstellar disk dispersal than in the\nmore quiescent regions, most likely due to the very high level of massive star\nfeedback. Narrow-band images reveal six molecular hydrogen jets. However, none\nof the optical HH objects shows molecular hydrogen emission, suggesting that\nthe jet-driving protostars are located very close to the edges of the globules\nin which they are embedded. This adds strong support to the scenario that their\nformation was triggered by the advancing ionization fronts.\n

Molecular jets have been discovered in large numbers, spread throughout star formation regions. They can usually be traced back to embedded driving protostars. We here investigate a squadron of such molecular hydrogen jets in the DR21/W75N region through echelle spectroscopy of the near infrared v=1-0 S(1) emission line centred at 2.122 microns. We detect 79 components, a number of which possess radial velocities in excess of 80 km/s. The majority of the components exhibit blue shifts.The regions closer to DR21 exhibit more blueshifted components suggesting that extinction is important across individual flows and is higher near DR21. We provide a classification scheme for the resulting collection of position-velocity diagrams, including other published data. One prominent class is associated with pairs of shocks well separated in radial velocity. We use hydrodynamic simulations with molecular cooling and chemistry to show that these are associated with Mach discs and bow shocks. We also employ a steady-state bow shock model to interpret other revealing position-velocity diagrams. We consider mechanisms which can generate vibrationally-excited hydrogen molecules moving at speeds well beyond the breakdown speed permitted for shock excitation. We conclude that the molecules have formed within the jets well before being excited by internal shocks triggered by impacts with the ambient clouds. We also note the relatively high number of high blueshifted radial velocity components and argue that these must be associated with high-density molecular jets from Class 0 protostars which are obscured unless we are selectively viewing within a conical cavity containing the jet.

We present the analysis of 35.5 deg2 of images in the 1–0 S(1) line of H2 from the UK Widefield Infrared Survey for H2 (UWISH2) towards Cassiopeia and Auriga. We have identified 98 Molecular Hydrogen emission-line Objects (MHOs) driven by Young Stellar Objects, 60 per cent of which are bipolar outflows and all are new discoveries. We estimate that the UWISH2-extended emission object catalogue contains fewer than 2 per cent false positives and is complete at the 95 per cent level for jets and outflows brighter than the UWISH2 detection limit. We identified reliable driving source candidates for three quarters of the detected outflows, 40 per cent of which are associated with groups and clusters of stars. The driving source candidates are 20 per cent protostars, the remainder are Classical T-Tauri Stars. We also identified 15 new star cluster candidates near MHOs in the survey area. We find that the typical outflow identified in the sample has the following characteristics: the position angles are randomly orientated; bipolar outflows are straight within a few degrees; the two lobes are slightly asymmetrical in length and brightness; the length and brightness of the lobes are not correlated; typical time gaps between major ejections of material are 1–3 kyr, hence FU-Ori or EX-Ori eruptions are most likely not the cause of these, but we suggest MNors as a possible source. Furthermore, we find that outflow lobe length distributions are statistically different from the widely used total length distributions. There are a larger than expected number of bright outflows indicating that the flux distribution does not follow a power law.

Context. In recent years, a new hot topic has emerged in the star and planet formation field, namely, the interaction between the circumstellar disk and its birth cloud. The birth environments of young stars leave strong imprints on the star itself and their surroundings. In this context, we present a detailed analysis of the rich circumstellar environment around the young Herbig Ae/Be star T CrA. Aims. Our aim is to understand the nature of the stellar system and the extended circumstellar structures, as seen in scattered light images. Methods. We conducted our analysis on the basis of a set of combined archival data and new adaptive optics images at a high contrast and high resolution. Results. The scattered light images reveal the presence of a complex environment around T CrA, composed of a bright, forward-scattering rim of the disk's surface that is seen at very high inclinations, along with a dark lane of the disk midplane, bipolar outflows, and streamer features that are likely tracing infalling material from the surrounding birth cloud onto the disk. The analysis of the light curve suggests that the star is a binary with a period of 29.6 yr, confirming previous assertions based on spectro-astrometry. The comparison of the scattered light images with the ALMA continuum and 12CO (2–1) line emission shows that the disk is in Keplerian rotation and the northern side of the outflowing material is receding, while the southern side is approaching the observer. The overall system lies on different geometrical planes. The orbit of the binary star is perpendicular to the outflows and is seen edge on. The disk is itself seen edge-on, with a position angle of ~7°. The direction of the outflows seen in scattered light is in agreement with the direction of the more distant molecular hydrogen emission-line objects (MHOs) associated with the star. Modeling of the spectral energy distribution using a radiative transfer scheme is in good agreement with the proposed configuration, as well as the hydrodynamical simulation performed using a smoothed particle hydrodynamics code. Conclusions. We find evidence of streamers of accreting material around T CrA. These streamers connect the filament, along which T CrA is forming along with the outer parts of the disk, suggesting that the strong misalignment between the inner and outer disk is due to a change in the direction of the angular momentum of the material accreting on the disk during the late phase of star formation. This impacts the accretion taking place in the components of the binary, favoring the growth of the primary with respect the secondary, in contrast to the case of aligned disks.

view Abstract Citations (162) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a Molecular Hydrogen Jet near IC 348 McCaughrean, Mark J. ; Rayner, John T. ; Zinnecker, Hans Abstract We present near-infrared images of a newly discovered molecular hydrogen jet (HH 211) near the young stellar cluster IC 348 in the Perseus dark cloud complex. A wide-field true-color JHK' image locates HH 211 relative to the embedded source IC 348 IR, and a high-resolution image taken in the H2 upsilon = 1 - 0 S(1) line at 2.122 micrometers delineates the shock-excited gas. The jet is very young, with a dynamical age of less than 1000 yr. We suggest that the H2 emission arises in a turbulent sheath around the true jet, leading to an unusual symmetric limb-brightened appearance. This boundary layer is probably where ambient molecular material is being entrained to form a coincident bipolar CO outflow. We discuss possible models for the knots in HH 211, including internal working surfaces in an episodic outflow and crossing shocks in a recollimating jet. The exciting source of the jet and outflow was detected at lambda greater than or = 350 micrometers, and our observations imply that the exciting source is a young star deeply embedded in a dense NH3 core, perhaps an edge-on circumstellar disk. The HH 211 system of jet, molecular outflow, and embedded exciting source is the first discovered through near-infrared imaging. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/187664 Bibcode: 1994ApJ...436L.189M Keywords: Hydrogen; Interstellar Gas; Jet Flow; Molecular Clouds; Molecular Flow; Star Clusters; Star Formation; Stellar Envelopes; Rosat Mission; Stellar Luminosity; Astrophysics; STARS: CIRCUMSTELLAR MATTER; INFRARED: ISM: CONTINUUM; INFRARED: ISM: LINES AND BANDS; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; STARS: FORMATION full text sources ADS | data products SIMBAD (39)

view Abstract Citations (56) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Twin Herbig-Haro Jets and Molecular Outflows in L1228 Bally, John ; Devine, David ; Fesen, Robert A. ; Lane, Adair P. Abstract We present new optical, near-infrared, and millimeter wavelength observations of the dark cloud L1228 located in the Cepheus Flare. There are at least two active young stellar objects within a 2' diameter region in the L1228 cloud core that drive two separate Herbig-Haro (HH) outflows, a molecular hydrogen jet, and associated CO outflows. The red nebulous object RNO 129 (HH 198), located 1 north of the L1228 cloud core, is a Herbig-Haro flow from a T Tauri star located near the eastern end of the HH object. The Herbig-Haro object HH 199 is associated with a large molecular outflow (L1228A) centered on a low-luminosity (4 Lsun) young stellar object IRAS 20582+7724, the brightest infrared source in this cloud core. The brightest visual wavelength components, HH 199R1 and R2, lie about 8' to the southwest of the IRAS source, where the redshifted lobe of the CO outflow may be breaking out of the molecular cloud. A chain of faint blueshifted (V ≍-40 to -150 km s-1) HH objects, HH 199B1 through HH 199B6, lies to the northeast of the IRAS source toward the blueshifted lobe of the L1228A CO outflow. The projected distance between HH 199R2 and HH 199B6 is about 20' or nearly 2 pc. Near the center of this outflow, a chain of knots bright in the 2.122 microns wavelength 5(1) line of molecular hydrogen extends for about 1' along a nearly east-west axis on both sides of IRAS 20582+7724. This axis differs from that of the L1228A/HH 199 outflow by about 40°. We consider a model in which the jet from IRAS 20582+7724 varies in its ejection direction. At present, the outflow as traced by the H_{2 }jet appears to be impacting dense C3H_{2 }emitting clumps east and west of the IRAS source. A redshifted CO ridge extends 10' to the west of the IRAS source at the same orientation as the H2 jet, but a more prominent northeast-southwest ridge extends along the HH 199 optical axis from HH 199B6 in the northeast, through the IRAS source, to HH 199R2 in the southwest. A periodic blueshifted (V ≍ -40 to -150 km s-1) chain of Herbig-Haro objects, HH 200, is superimposed on the redshifted lobe of the L1228A outflow. It is associated with the low-velocity blueshifted CO lobe of a second outflow, L1228B. The source of this jet is an embedded T Tauri star located 1'S northwest of IRAS 20582+7724. There is a faint HH object 9' to the northeast of the source of the HH 200 jet, directly opposite the location of the bright bow shock at the end of the blueshifted lobe of the HH 200 jet. This lobe may mark the location of an invisible counterjet HH 200 has a projected length of over 18' corresponding to 1.8 pc (assuming a distance of 300 pc to L1228), and it shows quasi-periodic knot spacing of roughly 1' corresponding to a projected spacing of 0.09 pc. At a flow velocity of 300 km s-1, and an assumed outflow inclination angle of 45°, this spacing may be a result of episodes of enhanced mass loss occurring roughly every 500 years. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176486 Bibcode: 1995ApJ...454..345B Keywords: INFRARED: ISM: LINES AND BANDS; ISM: INDIVIDUAL ALPHANUMERIC: L1228; ISM: JETS AND OUTFLOWS; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (26)

The environs of interstellar space in which star formation takes place involve high-velocity gas flows. Channelled by embryonic dust toroids, these gas flows culminate in energy-losing shock processes at the interface with the ambient interstellar cloud. The excitation of molecular hydrogen transitions in this gas provides one means of observing these shocked regions and their relation to the well-known indicators of star formation such as the Herbig Haro objects and T Tauri stars. In an attempt to understand the relationship of the recently discovered complex of Herbig Haro objects in Orion1 to the IR sources in this region, we have carried out a survey of the molecular hydrogen S(1) line distribution. These observations have led to the discovery of a previously unsuspected structure of finger-like filaments of H2 emission extending radially outwards from a common centre at IRC9.

We present deep H$_2$ images of planetary nebulae obtained with the CHFTIR camera of the Canada-France-Hawaii Telescope. Molecular hydrogen emissions are seen in the equatorial torus, bipolar lobes, as well as in extended haloes. Radial equatorial jets are also detected in a number of bipolar nebulae.

The role of magnetic fields in the early stages of star formation is not well constrained. In order to discriminate between different star formation models, we analyze 3D magnetohydrodynamic simulations of low-mass cores and explore the correlation between magnetic field orientation and outflow orientation over time. We produce synthetic observations of dust polarization at resolutions comparable to millimeter-wave dust polarization maps observed by the Combined Array for Research in Millimeter-wave Astronomy and compare these with 2D visualizations of projected magnetic field and column density. Cumulative distribution functions of the projected angle between the magnetic field and outflow show different degrees of alignment in simulations with differing mass-to-flux ratios. The distribution function for the less magnetized core agrees with observations finding random alignment between outflow and field orientations, while the more magnetized core exhibits stronger alignment. We find that fractional polarization increases when the system is viewed such that the magnetic field is close to the plane of the sky, and the values of fractional polarization are consistent with observational measurements. The simulation outflow, which reflects the underlying angular momentum of the accreted gas, changes direction significantly over over the first ∼0.1 Myr of evolution. This movement could lead to the observed random alignment between outflows and the magnetic fields in protostellar cores.