A Unified Model for Bipolar Outflows from Young Stars

Shang, Hsien; Allen, Anthony; Li, Zhi-Yun; Liu, Chun-Fan; Chou, Mei-Yin; Anderson, Jeffrey M.

doi:10.1086/506513

Cited by 95 publications

(115 citation statements)

References 61 publications

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“…These results support the scenario that the jet is surrounded by an unseen wide-angled wind, which interacts with the ambient gas and produces the bipolar cavity and also shocked H 2 emission. The presence of such a wide-angled wind indeed agrees with proposed magnetohydrodynamicallydriven wind models (see, e.g., Blandford & Payne 1982;Uchida & Shibata 1985;Shang et al 2006). Alternatively, Close et al (1997) suggest that the cavities associated with HL Tau could be produced by a precessing jet.…”

supporting

confidence: 84%

A Micro-Molecular Bipolar Outflow from HL Tauri

Takami¹,

Beck²,

Pyo³

et al. 2007

ApJ

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We present detailed geometry and kinematics of the inner outflow toward HL Tau observed using Near Infrared Integral Field Spectrograph (NIFS) at the Gemini-North 8 m Observatory. We analyzed H 2 2.122 mm emission and [Fe ii] 1.644 mm line emission as well as the adjacent continuum observed at a !0.2Љ resolution. The H 2 emission shows (1) a bubblelike geometry to the northeast of the star, as briefly reported in the previous paper, and (2) faint emission in the southwest counterflow, which has been revealed through careful analysis. The emission on both sides of the star shows an arc 1.0Љ away from the star, exhibiting a bipolar symmetry. Different brightnesses and morphologies in the northeast and southwest flows are attributed to absorption and obscuration of the latter by a flattened envelope and a circumstellar disk. The H 2 emission shows a remarkably different morphology from the collimated jet seen in [Fe ii] emission. The positions of some features coincide with scattering continuum, indicating that these are associated with cavities in the dusty envelope. Such properties are similar to millimeter CO outflows, although the spatial scale of the H 2 outflow in our image (∼150 AU) is strikingly smaller than the millimeter outflows, which often extend over 1000-10000 AU scales. The positionvelocity diagrams of the H 2 and [Fe ii] emission do not show any evidence for kinematic interaction between these flows. All results described above support the scenario that the jet is surrounded by an unseen wide-angled wind, which interacts with the ambient gas and produces the bipolar cavity and shocked H 2 emission.

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supporting

confidence: 84%

A Micro-Molecular Bipolar Outflow from HL Tauri

Takami¹,

Beck²,

Pyo³

et al. 2007

ApJ

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“…4.2) the envelope will quickly dissipate on timescales of <10 3 years (e.g., Shang et al 2006) and the wind would be much faster than what is observed at later evolutionary stages. The key ingredients that a successful model should reproduce are: (i) the excitation conditions and Fig.…”

Section: Physical Originmentioning

confidence: 94%

Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars usingHerschel-HIFI

Kristensen

Dishoeck

Benz

et al. 2013

A&A

109

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Aims. Herschel-HIFI spectra of H 2 O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise this component in terms of excitation conditions and physical origin. Methods. A velocity component with an offset of ∼10 km s −1 detected in spectra of the H 2 O 1 10 -1 01 557 GHz transition towards six low-mass protostars in the "Water in star-forming regions with Herschel" (WISH) programme is also seen in higher-excited H 2 O lines. The emission from this component is quantified and local excitation conditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH + , CH + , C + , OH) where the same component is uniquely detected. Results. The velocity component is detected in all six targeted H 2 O transitions (E up ∼ 50-250 K), as well as in CO 16-15 towards one source, Ser SMM1. Inferred excitation conditions imply that the emission arises in dense (n ∼ 5 × 10 6 -10 8 cm −3 ) and hot (T ∼ 750 K) gas. The H 2 O and CO column densities are 10 16 and 10 18 cm −2 , respectively, implying a low H 2 O abundance of ∼10 −2 with respect to CO. The high column densities of ions such as OH + and CH + (both 10 13 cm −2 ) indicate an origin close to the protostar where the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is 100 AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by a comparison with models of such shocks. Furthermore, one of the sources, IRAS 4A, shows temporal variability in the offset component over a period of two years which is expected from shocks in dense media. High-J CO gas detected with Herschel-PACS with T rot ∼ 700 K is identified as arising in the same component and traces the part of the shock where H 2 reforms. Thus, H 2 O reveals new dynamical components, even on small spatial scales in low-mass protostars.

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“…Such a picture has been discussed in terms of models of ''wide-angle winds'' or combinations of jets and wide-angle winds (Shu et al 1991;Shang et al 2006).…”

Section: Dispersalmentioning

confidence: 99%

Protostar Mass due to Infall and Dispersal

Myers

2008

Astrophysical Journal

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The mass of a protostar is calculated from the infall and dispersal of an isothermal sphere in a uniform background. For high contrast between peak and background densities and for short dispersal time t d , the accretion is ''self-limiting''; gas beyond the core is dispersed before it accretes, and the protostar mass approaches a time-independent value of low mass. For lower density contrast and longer dispersal time, the accretion ''runs away''; gas accretes from beyond the core, and the protostar mass approaches massive star values. The final protostar mass is approximately the initial gas mass whose free-fall time equals t d . This mass matches the peak of the IMF for gas temperature 10 K, peak and background densities 10 6 and 10 3 cm À3 , respectively, and t d comparable to the core free-fall time t core . The accretion luminosity exceeds 1 L for 0.1 Myr, as in the ''Class 0'' phase. For t d /t core ¼ 0:4 0:8 and temperature 7-50 K, selflimiting protostar masses are 0.08-5 M . These protostar and core masses have ratio 0:4 AE 0:2, as expected if the core mass distribution and the initial mass function have the same shape.

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A Unified Model for Bipolar Outflows from Young Stars

Cited by 95 publications

References 61 publications

A Micro-Molecular Bipolar Outflow from HL Tauri

A Micro-Molecular Bipolar Outflow from HL Tauri

Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars usingHerschel-HIFI

Protostar Mass due to Infall and Dispersal

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