Chromosome Studies an &lt;i&gt;Trillium kamtschaticum&lt;/i&gt; Pall VIII

Matsuura, Hajime; Haga, Tutomu

doi:10.1508/cytologia.10.382

Cited by 22 publications

(13 citation statements)

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“…Dyson, Hartquist & Biro 1993; Dyson et al 2006). Examples of resolved tails include those in NGC 7293 (the Helix nebula; O'Dell, Henney & Ferland 2005; Hora et al 2006; Matsuura et al 2007), the complex substructure of knots and wakes seen in the Orion Molecular Cloud OMC1 (e.g. Allen & Burton 1993; Schultz et al 1999; Tedds, Brand & Burton 1999; Kaifu et al 2000; Lee & Burton 2000) and the radial protrusions from the bipolar nebula surrounding the supermassive star η Carinae (Weis, Duschl & Chu 1999; Currie et al 2000; Redman, Meaburn & Holloway 2002).…”

Section: Discussionmentioning

confidence: 99%

The turbulent destruction of clouds - I. Ak-ε treatment of turbulence in 2D models of adiabatic shock-cloud interactions

Pittard

Falle

Hartquist

et al. 2009

Monthly Notices of the Royal Astronomical Society

162

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The interaction of a shock with a cloud has been extensively studied in the literature, where the effects of magnetic fields, radiative cooling and thermal conduction have been considered. In many cases, the formation of fully developed turbulence has been prevented by the artificial viscosity inherent in hydrodynamical simulations. This problem is particularly severe in some recent simulations designed to investigate the interaction of a flow with multiple clouds, where the resolution of individual clouds is necessarily poor. Furthermore, the shocked flow interacting with the cloud has been assumed to be completely uniform in all previous single‐cloud studies. In reality, the flow behind the shock is also likely to be turbulent, with non‐uniform density, pressure and velocity structure created as the shock sweeps over inhomogeneities upstream of the cloud (as seen in recent multiple cloud simulations). To address these twin issues we use a subgrid compressible k–ε turbulence model to estimate the properties of the turbulence generated in shock–cloud interactions and the resulting increase in the transport coefficients that the turbulence brings. A detailed comparison with the output from an inviscid hydrodynamical code puts these new results into context. Despite the above concerns, we find that cloud destruction in inviscid and k–ε models occurs at roughly the same speed when the post‐shock flow is smooth and when the density contrast between the cloud and intercloud medium, χ≲ 100. However, there are increasing and significant differences as χ increases. The k–ε models also demonstrate better convergence in resolution tests than inviscid models, a feature which is particularly useful for multiple‐cloud simulations. Clouds which are over‐run by a highly turbulent post‐shock environment are destroyed significantly quicker as they are subject to strong ‘buffeting’ by the flow. The decreased lifetime and faster acceleration of the cloud material to the speed of the ambient flow leads to a reduction in the total amount of circulation (vorticity) generated in the interaction, so that the amount of vorticity may be self‐limiting. Additional calculations with an inviscid code where the post‐shock flow is given random, grid‐scale, motions confirm the more rapid destruction of the cloud. Our results clearly show that turbulence plays an important role in shock–cloud interactions, and that environmental turbulence adds a new dimension to the parameter space which has hitherto been studied.

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Section: Discussionmentioning

confidence: 99%

The turbulent destruction of clouds - I. Ak-ε treatment of turbulence in 2D models of adiabatic shock-cloud interactions

Pittard

Falle

Hartquist

et al. 2009

Monthly Notices of the Royal Astronomical Society

162

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“…We construct a grid of CK models with different core densities ( n K ), density profiles, dust‐to‐gas ratios ( M d / M g ) and distances from the central star ( R K ). We obtain models with n K between 10 5 and 10 6 cm −3 (Huggins et al 1992; Meaburn et al 1998; Matsuura et al 2007). We assume that the density profile has an increase from n D to n K over a given distance Δ R .…”

Section: Modelsmentioning

confidence: 99%

“…Analyses of the emission of these structures suggest that they are significantly denser than the gas around them. While the typical diffuse gas density is around 10 2 –10 4 cm −3 (Kwok 2000; Osterbrock & Ferland 2006), in the CKs the density is around 10 5 –10 6 cm −3 (Huggins et al 1992; Meaburn et al 1998; Matsuura et al 2007). The origin of the CKs is still uncertain.…”

Section: Introductionmentioning

confidence: 99%

“…There is no evidence that the H 2 emission in CKs is produced by shocks (Huggins et al 2002; O’Dell et al 2005; Matsuura et al 2007, 2008). On the other hand, as mentioned above, the emission of the CKs seems to be linked to the central star radiation field (O’Dell et al 2005, 2007).…”

Section: Introductionmentioning

confidence: 99%

“…We use our models to study the CKs in the Helix nebula (NGC 7293). The Helix is one of the nearest PNe (219 pc), and high‐resolution images resolved the structure of the CKs (O’Dell et al 2004; Meixner et al 2005; Hora et al 2006; Matsuura et al 2007, 2008, 2009). The detailed observations allow us to test the model.…”

Section: Introductionmentioning

confidence: 99%

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Modelling the warm H2 infrared emission of the Helix nebula cometary knots

Aleman

Zijlstra

Matsuura

et al. 2011

Monthly Notices of the Royal Astronomical Society

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Molecular hydrogen emission is commonly observed in planetary nebulae. Images taken in infrared H2 emission lines show that at least part of the molecular emission is produced inside the ionized region. In the best studied case, the Helix nebula, the H2 emission is produced inside cometary knots (CKs), comet‐shaped structures believed to be clumps of dense neutral gas embedded within the ionized gas. Most of the H2 emission of the CKs seems to be produced in a thin layer between the ionized diffuse gas and the neutral material of the knot, in a mini‐photodissociation region (mini‐PDR). However, PDR models published so far cannot fully explain all the characteristics of the H2 emission of the CKs. In this work, we use the photoionization code Aangaba to study the H2 emission of the CKs, particularly that produced in the interface H+/H0 of the knot, where a significant fraction of the H2 1–0 S(1) emission seems to be produced. Our results show that the production of molecular hydrogen in such a region may explain several characteristics of the observed emission, particularly the high excitation temperature of the H2 infrared lines. We find that the temperature derived from H2 observations, even of a single knot, will depend very strongly on the observed transitions, with much higher temperatures derived from excited levels. We also proposed that the separation between the Hα and [N ii] peak emission observed in the images of CKs may be an effect of the distance of the knot from the star, since for knots farther from the central star the [N ii] line is produced closer to the border of the CK than Hα.

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Effect of Environment Upon Chromosomal Pairing of Some Species and Hybrids of Poa

Grun

1952

American J of Botany

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Chromosome Studies an <i>Trillium kamtschaticum</i> Pall VIII

Cited by 22 publications

References 0 publications

The turbulent destruction of clouds - I. Ak-ε treatment of turbulence in 2D models of adiabatic shock-cloud interactions

The turbulent destruction of clouds - I. Ak-ε treatment of turbulence in 2D models of adiabatic shock-cloud interactions

Modelling the warm H2 infrared emission of the Helix nebula cometary knots

Effect of Environment Upon Chromosomal Pairing of Some Species and Hybrids of Poa

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