Bipolar CO Research Articles

Aperture synthesis CS(2-1) observations of a young stellar object GL 490 - Accretion flow in gas disk

view Abstract Citations (14) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture Synthesis CS(2--1) Observations of a Young Stellar Object GL 490: Accretion Flow in Gas Disk Nakamura, Akiko ; Kawabe, Ryohei ; Kitamura, Yoshimi ; Ishiguro, Masato ; Murata, Yasuhiro ; Ohashi, Nagayoshi Abstract Aperture synthesis CS(J = 2-1) observations of the disk structure of the dense molecular gas around the young stellar object GL 490 are performed with 4-arcsec resolution using the Nobeyama Millimeter Array. The gas is found to have a noncircular velocity of about (1-1.5) km/s/sin i (i = inclination angle of the disk) and a mass of about 10 solar masses inside an 8500 AU region of the disk. According to the disk orientation indicated from one-sided cone-shaped optical and IR nebulocities, and the bipolar CO outflow, the noncircular motion is interpreted as inflow. The accretion time scale of the gas is estimated to be about 30,000 yr and the mass accretion rate to be 0.0003 solar mass/yr. Publication: The Astrophysical Journal Pub Date: December 1991 DOI: 10.1086/186247 Bibcode: 1991ApJ...383L..81N Keywords: Accretion Disks; Infrared Sources (Astronomy); Interstellar Gas; Molecular Gases; Star Formation; Infrared Astronomy; Millimeter Waves; Radio Astronomy; Stellar Mass Accretion; Synthetic Apertures; Astrophysics; INTERSTELLAR: MOLECULES; INFRARED: SOURCES; STARS: FORMATION; STARS: INDIVIDUAL ALPHANUMERIC: GL 490 full text sources ADS | data products SIMBAD (1)

U-shaped outflow in the LYNDS 1221 dark cloud - an example of interaction of outflows with ambient molecular clouds

Molecular line observations of the dark cloud L1221 in the J = 1-0 transitions of CO, 13 CO, C 18 O, HCO + , HCN, and CS with angular resolutions of 17″-2.7' are presented. A bipolar CO outflow associated with IRAS 22266+6845 have been discovered. The outflow shows a remarkably bent U-shaped structure. The present observations show rather clear evidence for interaction of the outflow with the ambient molecular gas; the ambient gas shows density depression and velocity shift just toward the blue lobe of the outflow. This fact indicates the acceleration and exclusion of the ambient gas by the outflow.

Interferometric observations of the 1-0 transition of HCO(+) toward NGC 7538 IRS 1

Interferometric observations of the molecular cloud toward the compact H II region IRS 1 in NGC 7538 in the 1-0 line of HCO(+) are reported. Employing a resolution of 8.5 arcsec, a highly elongated molecular cloud oriented at position angle 52 deg is found, perpendicular to the axis of the bipolar CO outflow. In perfect alignment with the blueshifted lobe in CO, strong blueshifted line wings are detected in HCO(+). The origin of the flow is at the center of the HCO(+) cloud, 15 arcsec to the south of IRS 1, which is clearly not the source that powers this outflow. So far no other indication of star formation has been detected at this position. 8 references.

The geometry of anisotropic CO outflows

A simple geometrical model for the space motions of the bipolar high-velocity CO outflows in regions of recent, active star formation is proposed. It is assumed that the velocity field of the neutral gas component can be represented by large-scale uniform motions. From observations of the spatial distribution and from the characteristics of the line shape of the high-velocity molecular gas emission the geometry of the line-emitting regions can be inferred, i.e., the direction in space and the collimating angle of the flow. The model has been applied to regions where a check on presently obtained results is provided by independent optical determinations of the motions of Herbig-Haro objects associated with the CO flows. These two methods are in good agreement and, furthermore, the results obtained provide convincingly strong evidence for the physical association of CO outflows and Herbig-Haro objects. This also supports the common view that a young stellar central source is responsible for the active phenomena observed in its environmental neighborhood. It is noteworthy that within the framework of the model the determination of the flow geometry of the high-velocity gas from CO measurements is independent of the distance to the source and, furthermore, can be done atmore » relatively low spatial resolution. 32 references.« less

High Velocity Gas Flows Associated with h2 Emission Regions - how are they Related and what Powers Them

view Abstract Citations (126) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-velocity gas flows associated with H2 emission regions : how are they related and what powers them ? Fischer, J. ; Sanders, D. B. ; Simon, M. ; Solomon, P. M. Abstract We report on an investigation of high-velocity molecular material near the vibrationally excited H2 emission regions in the objects DR 21, W75 N, NGC 7538, OMC-2, NGC 6334/Peak V, and the Herbig-Haro Object 2. The 12CO(J = 1-0) and 13CO(J = 1-0) transitions were used as tracers of the high-velocity molecular flows. All the H2 sources are associated with bipolar CO high-velocity flows. We also present a new highspatial-resolution map (11") of the DR 21 H2 region. The spatial relationship of the high-velocity gas and the vibrationally excited gas, together with the similarity of the energies involved in the two molecular components, is convincing evidence to support the scenario in which the H2 emission traces the cooling gas that has been shocked by outflowing gas. Although radiation pressure could be responsible for driving the flows in OMC-2 and NGC 7538, it is unlikely to be the driving mechanism in DR 21 and W75 N. Similarly, H II region expansion does not appear to be the driving mechanism for any of the outflows. Publication: The Astrophysical Journal Pub Date: June 1985 DOI: 10.1086/163256 Bibcode: 1985ApJ...293..508F full text sources ADS | data products SIMBAD (7)

Polarimetry of infrared sources in bipolar CO flows

view Abstract Citations (74) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polarimetry of infrared sources in bipolar CO flows. Sato, S. ; Nagata, T. ; Nakajima, T. ; Nishida, M. ; Tanaka, M. ; Yamashita, T. Abstract The results of polarimetry at 2.3 microns for nine infrared sources associated with high-velocity molecular outflow are reported. All the sources show large linear polarization ranging from 4 percent to more than 20 percent. The position angles of infrared polarization are perpendicular to the direction of bipolar molecular outflow and are parallel to the major axis of the associated molecular disk/torus. A possible mechanism for the polarization is scattering by anisotropic dust clouds surrounding the infrared sources. The infrared polarizations have a tendency to be orthogonal to the optical interstellar polarizations in the vicinity of the sources. Publication: The Astrophysical Journal Pub Date: April 1985 DOI: 10.1086/163109 Bibcode: 1985ApJ...291..708S Keywords: Carbon Monoxide; Gas Flow; Infrared Astronomy; Molecular Clouds; Polarimetry; Radio Sources (Astronomy); Bipolarity; Linear Polarization; Nebulae; Optical Polarization; Astrophysics full text sources ADS | data products SIMBAD (16) NED (1)

An infrared study of the bipolar outflow region GGD 12-15

Infrared observations from 1 to 100 microns are presented for the region associated with a bipolar CO outflow source near the nebulous objects GGD 12 to 15. A luminous far-infrared source was found associated with a radio-continuum source in the area. This object appears to be a compact HII region around a nearly main-sequence BO star. A faint 20 micron source was also discovered at the position of an H2O maser 3O deg northwest of the HII region. This object appears to be associated with but not coincident with a 2 micron reflection nebula. This structure serves as evidence for a non-spherically symmetric, possibly disk-like dust distribution around the exciting star for the maser. This object probably powers the bi-polar CO outflow although its luminosity is less than 10% that of the star which excites the compact HII region. A number of other 2 micron sources found in the area are probably members of a recently formed cluster.

Jets in Molecular Clouds

There is now growing evidence that the cosmic jet phenomenon manifests itself in a remarkable way in regions of active star formation embedded in dense molecular clouds. The first indications for oppositely directed, supersonic outflows from young stars were provided by molecular line observations (most notably of CO) which detected spatially separated regions of redshifted and blueshifted emission in association with embedded infrared sources. About twenty sources of this kind have been identified so far, and more are continuously being discovered; they typically have radii ∼1018cm, velocities ∼10–50 km s−1, dynamical ages ∼104yr, and energies ∼1046-1047erg s−1(see Bally and Lada 1983 for a review). Statistical arguments indicate that energetic outflows of this type are probably a common feature in stellar evolution, and that they occur in both massive and low-mass stars. Direct evidence that the outflows in many cases are highly collimated was subsequently provided by the detection of high-velocity Herbig-Haro objects (optical emission clumps with typical masses ∼10−5M⊙) along the axes of the bipolar CO lobes. Proper-motion measurements are now available for a number of these objects (e.g., Herbig and Jones 1981), and they invariably reveal that the velocity vectors (of typical magnitudes 200–400 km s−1) point away from the central star. The clumps are often found to consist of many sub-condensations which move independently with disparate speeds, but which nevertheless travel in the same general direction with an angular spread ≲ 10°. Finally, radio continuum observations (e.g., Cohen et al. 1982) and deep CCD images (e.g., Mundt and Fried 1983) have shown that the collimation of the outflows is already well established on scales of ≲ 1015cm.

Ammonia observations of the Herbig-Haro objects HH24-27

The region centred on HH25 has been mapped in the J = 1, K = 1 inversion line of ammonia, with spatial and velocity resolutions of 2.2 arcmin and 0.43 km s−1 respectively. The ammonia emission covers the known centres of activity HH24–26, including the recently observed bipolar CO outflows. Its spatial distribution relative to the outflows probably implies a disc structure (of mass |$\sim70-210M_\odot$|⁠), with the bipolar outflow perpendicular to the faces of the disc. The derived particle density of |$\sim(1-3)\times10^4$| cm−3 is in reasonable agreement with values deduced from other molecular lines. The abundance ratio of ammonia is estimated to be |$N_{\text{NH}_3}/N_{\text H_2} \sim 1 \times 10^{-8}$|⁠.

Detection of bipolar CO outflow in Orion

view Abstract Citations (121) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of bipolar CO outflow in Orion. Erickson, N. R. ; Goldsmith, P. F. ; Snell, R. L. ; Berson, R. L. ; Huguenin, G. R. ; Ulich, B. L. ; Lada, C. J. Abstract The Multiple Mirror Telescope was used as a phase coherent array to map the CO J = 3-2 emission from the central 1 arcmin region of the Orion molecular cloud. The angular resolution was 26 arcsec and the absolute pointing accuracy was better than 5 arcsec. The peak radiation temperature of the high-velocity gas is approximately 75 K, and the characteristic size of the emission region is 30-40 arcsec. The centroid of the high-velocity emission is located roughly 10 arcsec northeast of IRc2. The peaks in the emission strength of the redshifted and blueshifted high-velocity CO are offset with the redshifted emission peaking east and the blueshifted emission peaking north of IRc2. The axis of the high-velocity CO emission is aligned with the two maxima of the 2 micron H2 emission suggesting that the CO is participating in the same bipolar outflow. Publication: The Astrophysical Journal Pub Date: October 1982 DOI: 10.1086/183897 Bibcode: 1982ApJ...261L.103E Keywords: Astronomical Maps; Carbon Monoxide; Emission Spectra; Interstellar Gas; Molecular Clouds; Orion Nebula; Angular Resolution; Antenna Arrays; Astronomical Spectroscopy; Phase Coherence; Red Shift; Telescopes; Astrophysics full text sources ADS | data products SIMBAD (3)

THE CASE FOR ANISOTROPIC MASS LOSS FROM T TAURI STARS.

ABSTRACT Observational evidence and theoretical arguments are assembled in favor of directed, rather than isotropic, mass flows from T Tauri stars. These arguments include the structure of T Tauri nebulosities, radio continuum maps of the stars, the motions of Herbig-Haro objects away from their exciting T Tauri stars, bipolar CO flows, and particularly the spatial coincidence of an optical jet and radio emission associated with an embedded, probably T Tauri star in the dark cloud L1551.