Star formation and the singular isothermal sphere

Whitworth, Anthony Peter; Bhattal, A. S.; Francis, N.; Watkins, S. J.

doi:10.1093/mnras/283.3.1061

Cited by 57 publications

(51 citation statements)

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“…The Shu (1977) collapse starts with a cloud core with an r −2 density profile, but observations of pre-stellar cores usually show an r −1.5 density profile instead (Alves et al 2001;Motte & André 2001;Harvey et al 2003;André et al 2004;Kandori et al 2005). Bonnor-Ebert (BE) spheres have such a density profile (Ebert 1955;Bonnor 1956), so they have been proposed as an alternative starting point for collapse models (Whitworth et al 1996). The collapse of a BE sphere results in different densities, velocities and temperatures than those obtained with the Shu collapse (Foster & Chevalier 1993;Matsumoto & Hanawa 2003;Banerjee et al 2004;Walch et al 2009), leading in turn to different crystalline silicate abundances.…”

Section: Discussion and Future Workmentioning

confidence: 99%

Sub-Keplerian accretion onto circumstellar disks

Visser¹,

Dullemond²

2010

A&A

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Context. Models of the formation, evolution and photoevaporation of circumstellar disks are an essential ingredient in many theories of the formation of planetary systems. The ratio of disk mass over stellar mass in the circumstellar phase of a disk is for a large part determined by the angular momentum of the original cloud core from which the system was formed. While full 3D or 2D axisymmetric hydrodynamical models of accretion onto the disk automatically treat all aspects of angular momentum, this is not so trivial for 1D and semi-2D viscous disk models. Aims. Since 1D and semi-2D disk models are still very useful for long-term evolutionary modelling of disks with relatively little numerical effort, we investigate how the 2D nature of accretion affects the formation and evolution of the disk in such models. A proper treatment of this problem requires a correction for the sub-Keplerian velocity at which accretion takes place. Methods. We develop an update of our semi-2D time-dependent disk evolution model to properly treat the effects of sub-Keplerian accretion. The new model also accounts for the effects of the vertical extent of the disk on the accretion streamlines from the envelope. Results. The disks produced with the new method are smaller than those obtained previously, but their mass is mostly unchanged. The new disks are a few degrees warmer in the outer parts, so they contain less solid CO. Otherwise, the results for ices are unaffected. The 2D treatment of the accretion results in material accreting at larger radii, so a smaller fraction comes close enough to the star for amorphous silicates to be thermally annealed into crystalline form. The lower crystalline abundances thus predicted correspond more closely to observed abundances than did earlier model predictions. We argue that thermal annealing followed by radial mixing must be responsible for at least part of the observed crystalline material.

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Section: Discussion and Future Workmentioning

confidence: 99%

Sub-Keplerian accretion onto circumstellar disks

Visser¹,

Dullemond²

2010

A&A

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“…Ward-Thompson et al 1994;Hirota, Ito & Yamamoto 2002;Enoch et al 2008;Gómez et al 2014;Pattle et al 2015), the underlying geometry of a starless core is unlikely to obey a Gaussian distribution, instead typically showing a flat central plateau and power-law wings (e.g. Alves, Lada & Lada 2001), which may be characterised using a Bonnor-Ebert geometry (Ebert 1955;Bonnor 1956) or a Plummer-like geometry (Plummer 1911;Whitworth et al 1996). However, the Gaussian model remains a very useful tool for character- Table 4.…”

Section: Modelmentioning

confidence: 99%

The JCMT Gould Belt Survey: first results from SCUBA-2 observations of the Cepheus Flare region

Pattle

Ward-Thompson

Kirk

et al. 2016

Mon. Not. R. Astron. Soc.

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We present observations of the Cepheus Flare obtained as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Legacy Survey (GBLS) with the SCUBA-2 instrument. We produce a catalogue of sources found by SCUBA-2, and separate these into starless cores and protostars. We determine masses and densities for each of our sources, using source temperatures determined by the Herschel Gould Belt Survey. We compare the properties of starless cores in four different molecular clouds: L1147/58, L1172/74, L1251 and L1228. We find that the core mass functions for each region typically show shallower-than-Salpeter behaviour. We find that L1147/58 and L1228 have a high ratio of starless cores to Class II protostars, while L1251 and L1174 have a low ratio, consistent with the latter regions being more active sites of current star formation, while the former are forming stars less actively. We determine that, if modelled as thermally-supported Bonnor-Ebert spheres, most of our cores have stable configurations accessible to them. We estimate the external pressures on our cores using archival 13 CO velocity dispersion measurements and find that our cores are typically pressure-confined, rather than gravitationally bound. We perform a virial analysis on our cores, and find that they typically cannot be supported against collapse by internal thermal energy alone, due primarily to the measured external pressures. This suggests that the dominant mode of internal support in starless cores in the Cepheus Flare is either non-thermal motions or internal magnetic fields.

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“…In the highly dynamic scenario the collapse of a prestellar core is far more likely to lead to fragmentation and the formation of multiple systems (e.g., Whitworth et al 1995;Turner et al 1995;Whitworth et al 1996;Klein et al 2001Klein et al , 2003Bate et al 2002aBate et al ,b, 2003Bonnell et al 2003;Delgado-Donate 2003, 2004Goodwin et al 2004a,b;Hennebelle et al 2003Hennebelle et al , 2004. This is because in the highly dynamic scenario prestellar cores are formed non-quasistatically and therefore (a) they are launched directly into the non-linear regime of gravitational collapse, and (b) they are likely to have retained some internal turbulence.…”

Section: Introductionmentioning

confidence: 99%

Simulating star formation in molecular cores

Goodwin¹,

Whitworth²,

Ward-Thompson³

2004

A&A

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127

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Abstract. We explore, by means of a large ensemble of SPH simulations, how the level of turbulence affects the collapse and fragmentation of a star-forming core. All our simulated cores have the same mass (5.4 M ), the same initial density profile (chosen to fit observations of L1544), and the same barotropic equation of state, but we vary (a) the initial level of turbulence (as measured by the ratio of turbulent to gravitational energy, α turb ≡ U turb /|Ω| = 0, 0.01, 0.025, 0.05, 0.10 and 0.25) and (b), for fixed α turb , the details of the initial turbulent velocity field (so as to obtain good statistics).

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Star formation and the singular isothermal sphere

Cited by 57 publications

References 0 publications

Sub-Keplerian accretion onto circumstellar disks

Sub-Keplerian accretion onto circumstellar disks

The JCMT Gould Belt Survey: first results from SCUBA-2 observations of the Cepheus Flare region

Simulating star formation in molecular cores

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