Bipolar Flows Research Articles

Rotation measures of extragalactic radio sources viewed through the molecular clouds Cepheus A and L1551

VLA data on polarized sources in 11 high-velocity molecular flow regions at C-and L-band frequencies with 50 MHz resolution are analyzed to derive the Faraday rotation measures (RM) of the magnetic fields associated with the flows. The survey revealed the L1551 field, which has a strong source behind the molecular flow, and Cep A, where numerous polarized sources are located near the flow. The calculations of the RM were based on least squares analyses of the polarized intensity, position angle and total intensity maps. Differences were calculated in the RMs for different lines of sight in order to determine the causes of variations in the electron densities and magnetic fields within the clouds. The magnetic field within the L1551 flow was estimated to be 0.1 mG, indicating the presence of significant shock ionization at relative velocities exceeding 50 km/sec. Further observational techniques that may be employed to increase the understanding of the physical characteristics of bipolar flows are discussed. 31 references

Hydrodynamic ejection of intrinsically bipolar flows

A general mechanism is presented for generating pressure-driven winds, which are intrinsically bipolar, from objects undergoing disk accretion. The energy liberated in a boundary-layer shock as disk matter impacts the central object makes the vertical density structure of the boundary layer go out of hydrostatic equilibrium by large factors. The resultant expansion in the direction of the density gradient, i.e., perpendicular to the disk, converts accretion energy into P dV work and is shown to be capable of ejecting a fraction β ~ 10−2–10−1 of the accreted mass from the system. The ejection of these flows, accelerated within [Formula: see text], can account for the jets observed from pre-main-sequence stars and cataclysmic variables. Unless an analogous boundary-layer shock develops during accretion onto massive black holes, however, this mechanism does not seem to be applicable to jets from galaxies.

Formation of Bipolar Flows in Star Forming Regions by Stellar Winds

Formation of Bipolar Flows in Star Forming Regions by Stellar Winds

Jets From Young Stars

AbstractRecent optical observations have shown that many young stars are capable of generating highly-collimated bipolar flows. Such flows are evident from narrow emission-line jets extending over 0.01-1 pc and having opening angles of a few degrees. Their measured radial velocities reach values of up to 400 km/s. For most known jets the “driving stars” are T Tauri stars or IR-sources of low to moderate luminosity (1-100 L⊙) . The typical velocities, Mach numbers, particle densities, and mass fluxes of these jets are estimated to be 200-400 km/s, 10-40, 15-150 cm−3, and 10−10−10−7 M⊙/yr, respectively. The estimated mass fluxes and velocities are consistent with our present knowledge of T Tauri star wind properties.The emission-line spectra of the jets are the same as observed in Herbig-Haro (HH) objects. Furthermore, the brightest parts of some jets (hot spots) are known as HH objects, having often been discovered many years before their associated jet. Thus, both phenomena are highly related and in both cases the emission lines are very probably formed in the cooling regions of shock waves with velocities of 50-100 km/s. There are a variety of mechanisms, which can in principal excite internal (oblique) Shockwaves in these jets. Examples of likely excitation mechanisms are fluid dynamical instabilities or pressure gradients in the ambient medium.A model is proposed in which HH objects are representing the locations of the most strongly radiating (internal)shock waves in these jets. For those HH objects being located at the end of the jet the observational data strongly suggest that they are tracing the working surface of the jet. This idea is consistent with the observed proper motions of these HH objects, the typical densities near the edges of their associated molecular clouds, and with the jet parameter given above. For a more detailed discussion of these jets the reader is refered to the review articles listed below.

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)

Hydrodynamic ejection of bipolar flows from objects undergoing disk accretion - T Tauri stars, massive pre-main-sequence objects, and cataclysmic variables

Hydrodynamic ejection of bipolar flows from objects undergoing disk accretion - T Tauri stars, massive pre-main-sequence objects, and cataclysmic variables

Interactions between pre-main-sequence objects and molecular clouds. II - PV Cephei

CO observations reveal a bipolar flow associated with the peculiarpre-main-sequence object PV Cephei. The axis of this flow is roughly aligned with the symmetry axis of GM 29, the cometary nebula illuminated by PV Cephei. The total mass in high-velocity gas is 0.8--2.6 M/sub sun/; its expansion age is (0.5--1.5) x 10/sup 5/ years. If driven by a 400 km s/sup -1/ stellar wind, a mass loss rate of (0.4--2.0) x 10/sup -6/ M/sub sun/ yr/sup -1/ is required to drive this flow. The optical morphology of GM 29 provides strict constraints on the size of any collimating disk in the PV Cephei system. Implications of these observations for models of cometary nebulae and bipolar flows are discussed.

Observations of H2 emission from molecular clouds and Herbig-Haro objects

Using a CVF spectrometer with a spectral resolution of approx.2%, we have searched a group of molecular clouds, HH sources, and related objects for emission in the v = 1 ..-->.. 0 S(1) line of H/sub 2/ at lambda/sub 0/ = 2.122 ..mu..m. Included in this survey were H/sub 2/O masers with high-velocity components as well as CO hotspots with broad radio emission lines indicative of high-speed molecular flows. Generally our 3sigma detection limit for the integrated S(1) line flux corresponded to 7 x 10/sup -20/W cm/sup -2/ in our 34'' diameter beam. We present results for six sources that we detected and mapped in the S(1) line (NGC 1333, HH 12, NGC 2071, S255, S140, and Cep A), and we report limits for another 18 regions that were searched but not detected (e.g., L1551). In the H/sub 2/ sources that were mapped, we observed line emission over an extended area >0.2 pc in diameter. For NGC 1333 and Cep A, whose high velocity CO gas appears to be channeled into bipolar flows, we detected H/sub 2/ emission from the blueshifted CO lobe but not from the redshifted radio lobe. If the redshifted gas lies relatively deeper within the molecularmore » cloud, then differential 2 ..mu..m extinction from dust within the cloud might be sufficient to reduce the H/sub 2/ emission from this part of the flow below our detection limit. By comparison with the Orion H/sub 2/ source, the surface brightness and luminosity in the S(1) line of the regions detected in this survey are weaker by an order of magnitude or more.« less

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.

Analysis of ooplasmic flows and their structural basis during cleavage ofPimpla turionellae L. (Hymenoptera) : III. Time lapse analysis of the development of centrifuged eggs

Films ofPimpla eggs in which three different density gradients were produced (Nuss, 1974) made it possible to analyse the dynamic conditions that form the basis for the correct course of cleavage, of ooplasm movements and the distribution of energids. The results of sublethal stresses on the eggs led to the postulate that there is a system of factors which are arranged in a cylindrical wall in the central plasm flowing system, linked with the marginal streaming in opposite direction (Bruhns, 1974). Centrifuged eggs developing normally do not show any visible change in longitudinal streaming or in energid migration, as a result of the different stratification after spinning or after swinging at a short distance as well further from the rotational axis. Ooplasmic movements can take place independently of the arrangement of shiftable constituents visible in the light microscope. From the means of cleavage aberrations that result from centrifugation three components of the supporting and moving system can be distinguished. 1. The submicroscopic longitudinal flowing mechanism can not be shifted in a lateral direction within the egg by density gradients. It corresponds to the potential cylindrical system of factors which is either hindered or able to be restired after accelerations above 5800 g but which is destroyed when the whole egg is stressed at 10000 g. In this case, the eggs do not show any longitudinal flowings and their ingredients shift according to the gravitational forces. The flowing mechanism helps to, also supporting the normal egg architecture. After the egg has been activated, during the mixing motion and the formation of periplasm the flowing mechanism has to be completed in structure and put in working order for the unipolar flows. In centrifuged eggs, the initial region of the fountain flow may be shifted along the egg axis or it may not be distinctly visible, nevertheless normal larvae appear. 2. When the whole egg architecture has been overstressed, polar caps do not appear and those already formed during the unipolar flows are lost. This contraction of ooplasm may happen not, missing independently of the flowing mechanism, so that we have to postulate a specialmechanism of ooplasmic contraction. It should be found near the egg surface. The annular ooplasm contractions which appear later in cleavage might be in synergistic connexion with the bipolar fountain flows. 3. The flowing mechanism and the mechanism of contraction can function independently of the presence of energids. On the other hand the energids are able to migrate independently of flows. An essentialmechanism of energid migration might be the "migration aster" (Wolf, 1973); by its means the nucleus is transported and its cytoplasmic island can be extended. The redistribution begins just where energids migrate, multiply and from new cytoplasmic islands, i.e. where ooplasm is converted. In a caudal half of the egg without fountain flow the nergids are able to go in all directions and to reach the egg surface directly way. 4. The distinct formation of an anterior (Fz), a medium (Dz) and a posterior initial region (Bz) of ooplasm flows in centrifuged eggs is discussed. The unipolar flows appear to be necessary to lead the pronuclei into the cleavage center (Fz). Energid migration which is activated, is limited to a small region of converted ooplasm which is transported as a whole by transfer flow into differentiation center (Dz). If energids remain along this route the cephalic fountain does not appear: meanwhile the caudal one transports the energids from theDz towards the caudal end of the egg. The flowing mechanism must be a barrier to migration asters so that they are not able to extend in a radial direction. But also towards the poles they are coordinated to form a streaming front, for in eggs with damaged energid systems, corresponding flow resistance regions are formed. In consequence of the longitudinal flowing mechanism the cleavage energids, when migrating in a radial direction, react at about the same time as the marginal plasm and form nucleoli. Because normal larvae hatch from eggs with an aberrant course of cleavage, energids in the central plasm must be isopotent.