An infall model for the T Tauri phenomenon

Ulrich, R. K.

doi:10.1086/154840

Cited by 341 publications

(359 citation statements)

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“…For this purpose, they used a detailed emission model, coupled with an analytical model for the envelope, the cavity, and the disk. The envelope model is that of a rotating, collapsing sphere developed by Ulrich (1976), with a cavity in which the density is set to zero to mimic the outflows. The disk density is given by a power-law dependence in radius and a Gaussian dependence in height (see Enoch et al (2009) for more details).…”

Section: Comparison With Observationsmentioning

confidence: 99%

Protostellar disk formation and transport of angular momentum during magnetized core collapse

Joos

Hennebelle

Ciardi

2012

A&A

271

446

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Context. Theoretical studies of collapsing clouds have found that even a relatively weak magnetic field may prevent the formation of disks and their fragmentation. However, most previous studies have been limited to cases where the magnetic field and the rotation axis of the cloud are aligned. Aims. We study the transport of angular momentum, and its effects on disk formation, for non-aligned initial configurations and a range of magnetic intensities. Methods. We perform three-dimensional, adaptive mesh, numerical simulations of magnetically supercritical collapsing dense cores using the magneto-hydrodynamic code Ramses. We compute the contributions of all the relevant processes transporting angular momentum, in both the envelope and the region of the disk. We clearly define centrifugally supported disks and thoroughly study their properties. Results. At variance with earlier analyses, we show that the transport of angular momentum acts less efficiently in collapsing cores with non-aligned rotation and magnetic field. Analytically, this result can be understood by taking into account the bending of field lines occurring during the gravitational collapse. For the transport of angular momentum, we conclude that magnetic braking in the mean direction of the magnetic field tends to dominate over both the gravitational and outflow transport of angular momentum. We find that massive disks, containing at least 10% of the initial core mass, can form during the earliest stages of star formation even for mass-to-flux ratios as small as three to five times the critical value. At higher field intensities, the early formation of massive disks is prevented. Conclusions. Given the ubiquity of Class I disks, and because the early formation of massive disks can take place at moderate magnetic intensities, we speculate that for stronger fields, disks will form later, when most of the envelope will have been accreted. In addition, we speculate that some observed early massive disks may actually be outflow cavities, mistaken for disks by projection effects.

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Section: Comparison With Observationsmentioning

confidence: 99%

Protostellar disk formation and transport of angular momentum during magnetized core collapse

Joos

Hennebelle

Ciardi

2012

A&A

271

446

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“…For the model of the envelope structure we follow the ideas of Ulrich (1976). We thus implement a model for a rotating envelope resulting from infalling matter similar to Whitney et al (2003); Eisner et al (2005):…”

Section: The Envelopementioning

confidence: 99%

The circumstellar disc in the Bok globule CB 26

Sauter

Wolf²,

Launhardt

et al. 2009

A&A

107

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Context. Circumstellar discs are expected to be the nursery of planets. Grain growth within such discs is the first step in the planet formation process. The Bok globule CB 26 harbours such a young disc. Aims. We present a detailed model of the edge-on circumstellar disc and its envelope in the Bok globule CB 26. Methods. The model is based on HST near-infrared maps in the I, J, H, and K bands, OVRO and SMA radio maps at 1.1 mm, 1.3 mm and 2.7 mm, and the spectral energy distribution (SED) from 0.9 μm to 3 mm. New photometric and spectroscopic data from the Spitzer Space Telescope and the Caltech Submilimeter Observatory are also part of our analysis. Using the self-consistent radiative transfer code MC3D, the model we construct is able to discriminate between parameter sets and dust properties of both envelope and disc. Results. We find that the data are fit by a disc that has an inner hole with a radius of 45 ± 5 AU. Based on a dust model including silicate and graphite, the maximum grain size needed to reproduce the spectral millimetre index is 2.5 μm. Features seen in the nearinfrared images, dominated by scattered light, can be described as a result of a rotating envelope. Conclusions. Successful employment of ISM dust in both the disc and envelope hint that grain growth may not yet play a significant role for the appearance of this system. A large inner hole implies that CB 26 is a circumbinary disc.

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“…As is predicted from the present star formation theories, lowmass star models have an infalling envelope at a large distance from the central star and a rotating disk inside the envelope (Shakura & Sunyaev 1973;Ulrich 1976;Cassen & Moosman 1981;Pringle 1981;Terebey et al 1984). We assume a form that is often used in T Tauri models, and the mass density distribution ρ is given by…”

Section: Model Assumptionmentioning

confidence: 99%

Polarization disks in near-infrared high-resolution imaging

Murakawa

2010

A&A

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A polarization disk is a characteristic feature of optical and near-infrared (NIR) polarimetric images of young stellar objects (YSOs) and is regarded as convincing evidence that a dust disk is present. We analyze high-resolution linear polarization maps of a sample of low-mass YSO disk models by means of radiative transfer calculations to investigate the effects of the disk geometry and grain sizes on polarization properties. Our modeling assumes spherical grains with a power-law size distribution of n (a) ∝ a −3.5 ; 0.005 μm ≤ a ≤ a max and with a fixed a max of 0.25 μm for the outer envelope and a different a max for the disk. The parameters to examine are the disk height (i.e. the ratio of the disk height to the outer disk radius H of 0.1 to 1.0) and the dust sizes in the disk (i.e. a max of 0.25 to 1000.0 μm). In a near pole-on view, the polarization vectors are centro-symmetrically aligned even towards the disk, but the degree of polarization can be different from the envelope. We predict that the pole-on disk can be distinguished from the envelope. In contrast, the model images show a bipolar nebulosity and a polarization disk with a vector alignment in edge-on view. The polarization is low (<10%) for large grains or low H values and high (up to ∼80%) for small grains and high H values. In contrast, comparably constant polarizations (20-40%) are obtained in the optical. The wavelength dependence in low NIR polarization cases is often detected in many T Tauri stars, suggesting that grain growth or an advanced disk accretion is expected in these objects. The opposite trend in high NIR polarization cases, which is found in some low-mass protostars, is reproduced with spherical grain models. To understand our results, we developed a generalized scattering model, which is an extension of the vector alignment mechanism. In the lowmass star disk case, multiple-scattered light behaves as if it chooses paths of comparably low optical density region (e.g. the disk surface), avoiding a high density, equatorial region, which we call the roundabout effect. The single-scattered light does not reach the observer, and the double-scattered light contributes the most flux. However, the effect of the first scattering still appears in the final polarization status. The higher the disk height in our models, the closer to 90 • the scattering angle on the disk surface, resulting in a higher polarization. The variety of the wavelength dependence on the polarization is also an example of the roundabout effect. In the optical, only stray light passed through the envelope reaches the observer. Thus, the optical polarization is characterized by scattering by small grains in the envelope. On the other hand, since the NIR photons can pass through a somewhat inner part of the disk, the NIR polarization can still offer information on the dust and geometry of the disk. We expect that a polarization disk analysis in high-resolution data, such as the one we present, offers opportunities to investigate the grain growth and dust se...

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An infall model for the T Tauri phenomenon

Cited by 341 publications

References 0 publications

Protostellar disk formation and transport of angular momentum during magnetized core collapse

Protostellar disk formation and transport of angular momentum during magnetized core collapse

The circumstellar disc in the Bok globule CB 26

Polarization disks in near-infrared high-resolution imaging

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