scholarly journals VELOCITY SEGREGATION IN A CLUMP-LIKE OUTFLOW WITH A NON-TOP HAT VELOCITY CROSS-SECTION

2021 ◽  
Vol 57 (2) ◽  
pp. 269-277
Author(s):  
A. Castellanos-Ramírez ◽  
A. C. Raga ◽  
J. Cantó ◽  
A. Rodríguez-González ◽  
L. Hernández-Martínez
Keyword(s):  
Star Formation ◽  
Simple Model ◽  
Radial Velocity ◽  
Cross Section ◽  
High Velocity ◽  
Planetary Nebulae ◽  
Young Stars ◽  
Working Surface ◽  
Star Formation Regions ◽  
Analytic Models

High velocity clumps joined to the outflow source by emission with a “Hubble law” ramp of linearly increasing radial velocity vs. distance are observed in some planetary nebulae and in some outflows in star formation regions. We propose a simple model in which a “clump” is ejected from a source over a period τ0, with a strong axis to edge velocity stratification. This non-top hat cross section results in the production of a highly curved working surface (initially being pushed by the ejected material, and later coasting along due to its inertia). From both analytic models and numerical simulations we find that this working surface has a linear velocity vs. position ramp, and therefore reproduces in a qualitative way the “Hubble law clumps” in planetary nebulae and outflows from young stars.

scholarly journals Physical Processes in Nebular Shells and the Interpretation of Nebular Spectra

1983 ◽  
Vol 103 ◽  
pp. 219-227
Author(s):  
J. Patrick Harrington
Keyword(s):  
Charge Transfer ◽  
Simple Model ◽  
Stellar Wind ◽  
High Velocity ◽  
Planetary Nebulae ◽  
Geometrical Parameters ◽  
Stellar Winds ◽  
Physical Processes ◽  
Rapid Cooling ◽  
Particle Distributions

Computed models are now recognized as useful tools for interpretation of the spectra of planetary nebulae. However, even the most detailed models need geometrical parameters such as filling factors which are poorly determined by observations. Some effects may be seen more clearly by modeling the stratification than by just using total fluxes. A simple model for NGC 6720 is presented which reproduces the behavior of (Ne III) λ3869 observed by Hawley and Miller (1977), clearly showing the effects of charge transfer. The behavior of C II λ4267 remains puzzling. Finally, we comment on the interaction of high velocity stellar winds with nebular shells. Non-equilibrium particle distributions at the contact between the shocked stellar wind and the nebula may result in the rapid cooling of the shocked gas.

scholarly journals CO J = 3-2 and 4-3 Observations of Molecular Clouds

1987 ◽  
Vol 115 ◽  
pp. 172-172
Author(s):  
Glenn J. White ◽  
Ruth Rainey ◽  
Lorne Avery ◽  
Peter Phillips ◽  
Matthew Griffin ◽  
...  
Keyword(s):  
Star Formation ◽  
High Velocity ◽  
Molecular Clouds ◽  
Queen Mary College ◽  
Heterodyne Receiver ◽  
Relative Abundances ◽  
Star Formation Regions

We report on extensive submillimetre wavelength observations in the CO J = 3-2 and 4-3 lines towards a sample of star formation regions. The observations have been obtained using the Queen Mary College Submillimetre Heterodyne Receiver at the UKIRT 3.8 m telescope. The data include observations and maps of NGC 2024, S88, W3, S140, CRL2591, NGC 2264, K3-50, G35.2-0.74, ρ Oph A, M17, W51, S68, S106, NGC 1333, DR21 and W49. Several new bipolar flow sources have been detected in NGC 2024, S88 and NGC 2264. Comparisons between the spectra in the CO J = 1-0, 2-1, 3-2 and 4-3 transitions will be discussed in terms of their excitation, in particular for the gas in the high velocity line wings, where we have attempted to estimate the densities and relative abundances of the flow material.

High-Velocity H 2 O Masers Associated Massive Star Formation Regions

2001 ◽  
Vol 18 (12) ◽  
pp. 1663-1665 ◽  
Author(s):  
Xu Ye ◽  
Jiang Dong-Rong ◽  
Zheng Xing-Wu ◽  
Gu Min-Feng ◽  
Yu Zhi-Yao ◽  
...  
Keyword(s):  
Star Formation ◽  
High Velocity ◽  
Massive Star ◽  
Massive Star Formation ◽  
Star Formation Regions

High-Velocity Molecular Gas from High-Mass Star Formation Regions

1996 ◽  
Vol 457 ◽  
pp. 267 ◽  
Author(s):  
D. S. Shepherd ◽  
E. Churchwell
Keyword(s):  
Star Formation ◽  
High Velocity ◽  
High Mass ◽  
Molecular Gas ◽  
Mass Star ◽  
Star Formation Regions

A search for high-velocity gas in massive star formation regions

1998 ◽  
Vol 22 (4) ◽  
pp. 459-462
Author(s):  
Yue-fang Wu ◽  
Yue-xing Li ◽  
Li-feng Zheng
Keyword(s):  
Star Formation ◽  
High Velocity ◽  
Massive Star ◽  
Massive Star Formation ◽  
Star Formation Regions

scholarly journals The Most Luminous Star Formation Regions in the Galaxy

1987 ◽  
Vol 115 ◽  
pp. 143-143 ◽  
Author(s):  
D. T. Jaffe ◽  
R. Genzel ◽  
D. A. Harper ◽  
A. I. Harris ◽  
P.T.P. Ho
Keyword(s):  
Star Formation ◽  
High Velocity ◽  
Massive Star ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Broad Band ◽  
Physical Conditions ◽  
Velocity Flow ◽  
The Galaxy ◽  
Star Formation Regions

We present new far-IR and submillimeter broad-band and spectroscopic results on the dense and very luminous cores of massive star formation regions. The best-studied region, W51, contains one core around the source IRS2 and another around W51 MAIN. Our earlier submillimeter continuum mapping has shown that these two cores are very massive (2-4 × 104 M⊙) and have average densities of nH2 ∼ 105 over their inner parsec. New far-IR maps show that both cores are very luminous (L(MAIN) ∼2 × 106 L⊙; L(IRS2) ∼4x106 L⊙). Observations of the (1,1) and (2,1) transitions of NH3, indicate high kinetic temperatures (200-400 K) for the quiescent gas in the inner several arc seconds (0.1 pc) of both cores. Spectroscopy of the 370 μm J = 7 → 6 and 163 μm J = 16 → 15 transitions of CO toward the cores allows us to characterize the hot high velocity material seen previously on the H2O maser transitions and not readily visible in the low J transitions of CO. The high velocity flow in IRS2 is ∼ 60 times more massive than the very similar outflow in the ∼ 30 times less luminous Orion/KL core. The mass loss rate is ∼ 30 times greater than in Orion. Additional observations of W49 allow us to draw a few general conclusions about the most luminous star formation regions in our galaxy: (1) The luminous cores are 102-103 more massive than the Orion core with the same density. (2) Outflows and warm regions in these cores have physical conditions similar to those in their less luminous counterparts but far more mass is involved in the flows.

Jets from young stars: estimates of their physical parameters

1986 ◽  
Vol 64 (4) ◽  
pp. 407-413 ◽  
Author(s):  
Reinhard Mundt
Keyword(s):  
High Velocity ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Physical Parameters ◽  
Stellar Objects ◽  
Working Surface ◽  
Mass Fluxes ◽  
Emission Line Spectrum ◽  
Characteristic Values ◽  
Mach Numbers

On the basis of existing observational data, the characteristic values of the physical parameters of jets from young stellar objects are estimated. The results of these estimates are as follows: velocities = 200–400 km/s, Mach numbers = 10–40, hydrogen-number densities = 15–150 cm−3, and mass fluxes = 10−10–10−7 [Formula: see text]. The derived Mach numbers imply reasonable jet temperatures (≈ 104 K), being consistent with the observed emission-line spectrum. The estimated jet densities are in agreement with the idea that some high-velocity Herbig–Haro objects (v ≈ 200 km/s) represent the working surface of a freely expanding jet boring through the outer, tenuous parts of a molecular cloud.

scholarly journals Mechanisms for the Production of Bipolar Flows and Jets in Star Formation Regions

1992 ◽  
Vol 45 (4) ◽  
pp. 513 ◽  
Author(s):  
GV Bicknell
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Pressure ◽  
Young Stars ◽  
Rotating Magnetic Field ◽  
Neutral Wind ◽  
Neutral Winds ◽  
Star Formation Regions ◽  
Mass Ejection ◽  
Pressure Driven

Two types of mass ejection are associated with the formation of young stars: poorly collimated bipolar flows and well collimated jets. Some mechanisms which have been suggested for the driving of these flows are reviewed. These include centrifugally driven magnetised winds, magnetic pressure driven winds and bubbles driven by ionised or neutral winds. The idea that the bipolar flows are bubbles driven by a neutral wind seems attractive on both theoretical and observational grounds but the source of the neutral wind-disk or star-is uncertain. It is possible that the jets are driven by magnetic pressure or by a rapidly rotating magnetic field close to the star. However, no definitive theory exists at the present time.

scholarly journals Rationale for the Joint Discussion

2002 ◽  
Vol 12 ◽  
pp. 135-139
Author(s):  
Peter S. Conti ◽  
Edwin B. Churchwell
Keyword(s):  
Star Formation ◽  
Stellar Dynamics ◽  
Young Stars ◽  
Accretion Discs ◽  
Stellar Winds ◽  
Mass Star ◽  
Lyman Continuum ◽  
Low Mass ◽  
Star Formation Regions ◽  
Birth Processes

AbstractThis Joint Discussion (JD) will consider the birth processes of massive stars. While similar phenomena (e.g., accretion discs, outflows, etc.) are found in low mass star formation, additional physics must be considered given the ionization of the interstellar environment by Lyman continuum photons, stellar winds from the hot star(s), and their deeper gravitational potentials. This JD will bring together experts from several disparate astronomical communities: stellar astrophysics, interstellar medium, radio astronomy, and stellar dynamics. The concept is to contrast observations of very young stars and star formation regions over various wavelengths with theoretical expectations.

scholarly journals HH 34: The bow shock of a jet

1987 ◽  
Vol 122 ◽  
pp. 175-176
Author(s):  
Th. Bührke ◽  
R. Mundt
Keyword(s):  
Radial Velocity ◽  
Electron Density ◽  
High Velocity ◽  
Shock Structure ◽  
Bow Shock ◽  
Complex Velocity ◽  
Ccd Imaging ◽  
Working Surface ◽  
Lower Excitation ◽  
Hh Object

Deep CCD imaging of HH 34 in H∝ shows that the HH-object has a bow shock-like structure, of which the wings can be traced over about 1 arcmin ( pc). A knotty jet is pointing towards the apex of the bow shock structure. Long-slit spectroscopy reveals that 1) the jet has approximately a constant radial velocity and electron density. 2). The spectrum of the jet is of a much lower excitation than that of HH 34. 3) HH 34 has a complex velocity and line excitation structure. The extended bow shock is interpreted by a jet of which the working surface is propagating with high velocity (≈ 200 km/s) through a partially ionized medium.

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