Polar Cavity Research Articles

Structure and physical properties of the rapidly evolving dusty envelope of IRC + 10216 reconstructed by detailed two-dimensional radiative transfer modeling

We present the first detailed, two-dimensional radiative transfer model of the dusty envelope around the carbon star IRC + 10216. Our goal was to find a self-consistent model of the star and its envelope which takes into account as many observational constraints as possible. The model reproduces very well the entire beam-matched spectral energy distribution of IRC + 10216 from optical to centimeter wavelengths (at several phases of stellar luminosity), observed intensity profiles of the object at 1.25, 2.2, 10.5, 50, 100 ${\mu}$m, and 1.3 mm, a 10.5 ${\mu}$m lunar occultation intensity profile, our high-resolution $J, H$, K , and $H\!-\!K$ bispectrum speckle-interferometry images, and visibilities in $J, H, K, L, M$, and N bands. For the adopted distance of 130 pc, the model of IRC + 10216 implies that the object changes its luminosity between 13 000 and 5200 $L_{\odot}$, its effective temperature between 2800 and 2500 K, and its radius between 500 and 390 $R_{\odot}$. There is a dense non-spherical dust shell around the star, with outflow cavities at position angle PA${ \approx }$20°. The southern cavity with a full opening angle of 36° is tilted toward us by 40° from the plane of sky, causing the observed bipolar appearance of the object on a subarcsecond scale. If the envelope's outflow velocity of 15 km s -1 applies to the material making up the dense core, then just ${\sim }$15 years ago the star was losing mass at a rate of $9{ }10^{-5}$ $M_{\odot}$ yr -1 . Dust exists in the envelope of IRC + 10216 everywhere from the stellar photosphere up to a distance of 3 pc from the star. The total mass of the envelope lost by the central star is 3 $M_{\odot}$ and the dust-to-gas mass ratio is 0.004. The total optical depth $\tau_{V}$ toward the star in the visual is 40, in the polar cavities it is 10. The innermost parts of the envelope are optically thick even at 10.7 ${\mu}$m due to a strong resonance absorption of silicon carbide grains at that wavelength. In addition to SiC dust, the model contains inhomogeneous grains made of a mixture of SiC and incompletely amorphous carbon with thin [ Mg 0.5 Fe 0.5 ] S mantles. This is the simplest dust mixture required to fit all observations of IRC + 10216 and to correctly interpret the well-known 11.3 ${\mu}$m and 27 ${\mu}$m emission bands. The dust model found in this study can also be successfully applied to many other carbon stars exhibiting broad emission features in the 10.3-12.6 ${\mu}$m and 25-37 ${\mu}$m wavelength regions. An important and firm result of our modeling is that the brightest compact peak observed in IRC + 10216 is not the direct light from the underlying central star. In contrast to previous suggestions, the brightest southern component, labeled A in our high-resolution near-infrared images [CITE], is only the radiation emitted and scattered in the optically thinner southern cavity of the bipolar dense shell moving away from the central star. The carbon star is at the position of the fainter component B in our H and K images, which is 0 fraction of arcsecond21 away from A along the symmetry axis. Direct stellar light (component B) is not seen at all in the Hubble Space Telescope 0.8 ${\mu}$m and 1.1 ${\mu}$m images, being absorbed by the dense dusty material. The even fainter components C and D in the H and K images are probably due to smaller deviations of the dense shell from the spherical shape. IRC + 10216 seems to have entered a phase immediately before moving off the asymptotic giant branch and started developing asymmetries in its envelope.

Reaction of primary aromatic amines with alkyl carbonates over NaY faujasite: a convenient and selective access to mono-N-alkyl anilines.

At atmospheric pressure and at 130-160 degrees C, primary aromatic amines (p-XC6H4NH2, X = H, Cl, NO2) are mono-N-alkylated in a single step, with symmetrical and asymmetrical dialkyl carbonates [ROCOOR', R = Me, R' = MeO(CH2)2O(CH2)2; R = R' = Et; R = R' = benzyl; R = R' = allyl; R = Et, R' = MeO(CH2)2O(CH2)2], in the presence of a commercially available NaY faujasite. No solvents are required. Mono-N-alkyl anilines are obtained with a very high selectivity (90-97%), in good to excellent yields (68-94%), on a preparative scale. In the presence of triglyme as a solvent, the mono-N-alkyl selectivity is independent of concentration and polarity factors. The reaction probably takes place within the polar zeolite cavities, and through the combined effect of the dual acid-base properties of the catalyst.

QSIスキームを用いた流体解析法の適用性について

A computational method has been proposed for viscous incompressible flows with QSI (quintic spline interpolation) scheme. This method is based on general curvilinear coordinates and collocated grid arrangement, which allows us to deal with moving boundary problems. In order to confirm the validity of this computational method, it was was applied to the rectangular and polar cavity flows. In addition, it was also applied to small amplitude standing waves and free-surface flows within a cavity. As a result, it has been shown that the predicted results are in good agreement with the theory and other computational results and that the QSI scheme is effective to predict various fluid flows with sufficient accuracy.

The crystal structure of Escherichia coli class II fructose-1,6-bisphosphate aldolase in complex with phosphoglycolohydroxamate reveals details of mechanism and specificity

The structure of a class II fructose-1,6-bisphosphate aldolase in complex with the substrate analogue and inhibitor phosphoglycolohydroxamate (PGH) has been determined using X-ray diffraction terms to a resolution of 2.0 Å (1 Å = 0.1 nm). The crystals are trigonal, space group P3121 with a = b = 78.24 Å, c = 289.69 Å. The asymmetric unit is a homodimer of (α/β)8 barrels and the model has refined to give R-work 19.2 %, R-free (based on 5 % of the data) 23.0 %. PGH resembles the ene-diolate transition state of the physiological substrate dihydroxyacetone phosphate. It is well ordered and bound in a deep polar cavity at the C-terminal end of the (α/β)8 barrel, where it chelates the catalytic zinc ion using hydroxyl and enolate oxygen atoms. Trigonal bipyramidal coordination of the zinc ion is completed by three histidine residues. The complex network of hydrogen bonds at the catalytic centre is required to organise the position of key functional groups and metal ion ligands. A well-defined monovalent cation-binding site is observed following significant re-organisation of loop structures. This assists the formation of a phosphate-binding site on one side of the barrel that tethers PGH in the catalytic site. The positions of functional groups of substrate and putative interactions with key amino acid residues are identified. Knowledge of the complex structure complements the results of spectroscopic and site-directed mutagenesis studies, and contributes to our understanding of the mechanism and substrate specificity of this family of enzymes. A reaction mechanism distinct from that proposed for other class II aldolases is discussed. The results suggest that the class II aldolases should be sub-divided into two groups on the basis of both distinct folds and mechanism.

High-resolution bispectrum speckle interferometry and two-dimensional radiative transfer modeling of the Red Rectangle

We present the first diffraction-limited K-band image of the Red Rectangle with 76mas resolution, an H-band image with 75mas resolution, and an RG715 filter image (∼ 800nm wavelength) with 78mas resolution (corresponding to 25AU for a distance of 330pc). The H and K images were reconstructed from 6m telescope speckle data and the RG715 image from 2.2m telescope data using the speckle masking bispectrum method. At all wavelengths the images show a compact, highly symmetric bipolar nebula, suggesting a toroidal density distribution of the circumstellar material. No direct light from the central binary can be seen as it is obscured by a dust disk or circumbinary torus. Our first high-resolution H−K color image of the nebula shows a broad red plateau of H−K≈2m in the bright inner regions.The optical and near-infrared images and the available photometric continuum observations in a wide range of ultraviolet to centimeter wavelengths enabled us to model the Red Rectangle in detail using a two-dimensional radiative transfer code. Our model matches both the high-resolution images and the spectral energy distribution of this object very well, making the following picture much more certain. The central close binary system with a total luminosity of 3000L⊙ is embedded in a very dense, compact circumbinary torus which has an average number density 〈nH〉≈5×1012cm−3, an outer radius of the dense inner region of R≈30AU (91mas), and a ρ∝r−2 density distribution. The full opening angle of the bipolar outflow cavities in our model is 70°. By comparing the observed and theoretical images, we derived an inclination angle of the torus to the line of sight of 7°±1°.The radiative transfer calculations show that the dust properties in the Red Rectangle are spatially inhomogeneous. The modeling confirms that the idea of large grains in the long-lived disk around the Red Rectangle (Jura et al., 1997 [ApJ, 474, 741]) is quantitatively consistent with the observations. In our models, unusually large, approximately millimeter-sized grains dominate the emission of the compact, massive torus. Models with smaller average grain sizes can possibly be found in future studies, for instance, if it turns out that the radio spectrum is not mainly caused by continuum dust emission. Therefore, the large grains suggested by our models require further confirmation by both new observations and radiative transfer calculations. Assuming a dust-to-gas ratio ρd/ρg of 0.005, the dense torus mass is 0.25M⊙. The model gives a lower limit of 0.0018M⊙, for the mass of the large particles, which produce a gray extinction of A≈28m, towards the center. A much smaller mass of submicron-sized dust grains is presumably located in the polar outflow cavities, their conical surface layers, and in the outer low-density parts of the torus (where ρ∝r−4, in the region of 30AU≲r≲2000AU corresponding to 0.′′09–6′′).

A set of van der Waals and coulombic radii of protein atoms for molecular and solvent-accessible surface calculation, packing evaluation, and docking

We analyze the contact distance distributions between nonbonded atoms in known protein structures. A complete set of van der Waals (VDW) radii for 24 protein atom types and for crystal-bound water is derived from the contact distance distributions of these atoms with a selected group of apolar atoms. In addition, a set of Coulombic radii for polar atoms is derived from their contacts with water. The contact distance distributions and the two sets of radii are derived in a systematic and self-consistent manner using an iterative procedure. The Coulombic radii for polar atoms are, on average, 0.18 A smaller than their VDW radii. The VDW radius of water is 1.7 A, which is 0.3 A larger than its Coulombic radius. We show that both the VDW and the Coulombic radii of polar atoms are needed in calculating the molecular and solvent-accessible surfaces of proteins. The VDW radii are needed to generate the apolar portions of the surface and the Coulombic radii for the polar portions. The fact that polar atoms have two apparent sizes implies that a hydrophobic cavity has to be larger than a polar cavity in order to accommodate the same number of water molecules. Most surface area calculations have used only one radius for each polar atom. As a result, unreal cavities, grooves, or pockets may be generated if the Coulombic radii of polar atoms are used. On the other hand, if the VDW radii of polar atoms are used, the details of the polar regions of the surface may be lost. The accuracy of the molecular and the solvent-accessible surfaces of proteins can be improved if the radii of polar atoms are allowed to change depending on the nature of their contacting neighbors. The surface of a protein at a protein-protein interface differs from that in solution in that it has to be generated using at least two kinds of probes, one representing a typical apolar atom and the other a typical polar atom. This observation has important implications for docking, which relies on surface complementarity at the interface.

A set of van der Waals and coulombic radii of protein atoms for molecular and solvent‐accessible surface calculation, packing evaluation, and docking

We analyze the contact distance distributions between nonbonded atoms in known protein structures. A complete set of van der Waals (VDW) radii for 24 protein atom types and for crystal-bound water is derived from the contact distance distributions of these atoms with a selected group of apolar atoms. In addition, a set of Coulombic radii for polar atoms is derived from their contacts with water. The contact distance distributions and the two sets of radii are derived in a systematic and self-consistent manner using an iterative procedure. The Coulombic radii for polar atoms are, on average, 0.18 Å smaller than their VDW radii. The VDW radius of water is 1.7 Å, which is 0.3 Å larger than its Coulombic radius. We show that both the VDW and the Coulombic radii of polar atoms are needed in calculating the molecular and solvent-accessible surfaces of proteins. The VDW radii are needed to generate the apolar portions of the surface and the Coulombic radii for the polar portions. The fact that polar atoms have two apparent sizes implies that a hydrophobic cavity has to be larger than a polar cavity in order to accommodate the same number of water molecules. Most surface area calculations have used only one radius for each polar atom. As a result, unreal cavities, grooves, or pockets may be generated if the Coulombic radii of polar atoms are used. On the other hand, if the VDW radii of polar atoms are used, the details of the polar regions of the surface may be lost. The accuracy of the molecular and the solvent-accessible surfaces of proteins can be improved if the radii of polar atoms are allowed to change depending on the nature of their contacting neighbors. The surface of a protein at a protein–protein interface differs from that in solution in that it has to be generated using at least two kinds of probes, one representing a typical apolar atom and the other a typical polar atom. This observation has important implications for docking, which relies on surface complementarity at the interface. Proteins 32:111–127, 1998. © 1998 Wiley-Liss, Inc.

The Structure of the Prototype Bipolar Protoplanetary Nebula CRL 2688 (Egg Nebula): Broadband, Polarimetric, and H[TINF]2[/TINF] Line Imaging with NICMOS on the [ITAL]Hubble Space Telescope[/ITAL

High-resolution near-infrared (1.65-2.1 μm) images and 2 μm polarimetric images of the inner 195 × 193 region of the bipolar protoplanetary nebula CRL 2688, taken with the newly installed Near-Infrared Camera and Multiobject Spectrometer (NICMOS) aboard the Hubble Space Telescope (HST), are reported. The NICMOS images reveal a wealth of structure also seen in HST Wide Field Planetary Camera 2 images but not detected in previous, ground-based near-infrared imaging studies. In particular, we detect a system of concentric arcs centered on, and twin searchlight beams emanating from, the obscured central star. The images also show two sharply bounded spindle-shaped polar cavities with point-symmetric structure, and the 2.122 μm H2 S(1) v = 1-0 emission-line image clearly resolves the sharp interface between the high-velocity outflow that produces these polar cavities and the surrounding slow outflow that forms the extended nebula. The H2 image also resolves the bright equatorial H2 emission into distinct components and elucidates their detailed morphologies. We have discovered, within the dark lane that bifurcates the bipolar lobes of CRL 2688, a compact source of unpolarized light. Our imaging polarimetry shows that this source is not the post-asymptotic giant branch star that illuminates the nebula; we conclude that the compact source is a companion star.

High-Resolution Near-Infrared Imaging of the Orion 114−426 Silhouette Disk

We present the first high-resolution near-infrared images of the edge-on silhouette circumstellar disk, Orion 114-426, made using NICMOS on the Hubble Space Telescope. Images taken against the bright nebular background of the ionized hydrogen Paα line at 1.87 μm show the major axis of the disk to be approximately 20% smaller than at 0.6 μm, from which we deduce the structure of the edge of the disk. Continuum images of diffuse polar lobes above and below the plane of the disk show a morphology and evolution with wavelength consistent with predictions for reflection nebulae in a diffuse envelope with large polar cavities, surrounding a thin, massless, Keplerian disk, centered on an otherwise hidden central star. We make use of our observations and reasonable assumptions about the underlying disk structure to show that the disk mass is at least 10 M⊕ and plausibly ≥5 × 10−4 M☉.

Characterization of Low-Barrier Hydrogen Bonds. 6. Cavity Polarity Effects on the Formic Acid−Formate Anion Model System. An ab Initio and DFT Investigation

High-level ab initio molecular orbital and density functional theory calculations incorporating cavity polarity effects via the use of self-consistent reaction field (SCIPCM) simulations reveal that the short, strong hydrogen bond formed between a formic acid molecule and a formate anion is significantly, but nowhere near completely, weakened by the presence of an extremely polar cavity. These results suggest that even if an enzyme active site were to present an environment as polar as aqueous water, the formation of a low-barrier, or short-strong, hydrogen bond would still be some 8 kcal/mol more favorable than the corresponding neutral, traditional, weak hydrogen bondlike the one formed between two formic acid molecules. The short, strong hydrogen bond formed between a formic acid and a formate anion is clearly much more sensitive to the effects of its environment than is a typical weak traditional hydrogen bond. However, even in the most polar of cavities, the calculated hydrogen bond energy for formic...

Applicability of the Free Energies of Solvation for the Prediction of Ecotoxicity: Study of Chlorophenols

Free energies of solvation of chlorophenols were calculated in two solvents: water and n-hexadecane from the AMSOL program. These free energies of solvation are the sum of two terms: polarization free energies (ΔG ENP) and cavity, dispersion, solvent structure free energies (G° CDS). This study shows, in the case of chlorophenols, that a direct relation exists between one of the two components for the calculation of free energy (G°CDS) in water and in n-hexadecane, and the ecotoxicity values for five biological systems. We point out the interest of using these new descriptors in QSAR study.

The transmembrane 7-alpha-bundle of rhodopsin: distance geometry calculations with hydrogen bonding constraints

A 3D model of the transmembrane 7-alpha-bundle of rhodopsin-like G-protein-coupled receptors (GPCRs) was calculated using an iterative distance geometry refinement with an evolving system of hydrogen bonds, formed by intramembrane polar side chains in various proteins of the family and collectively applied as distance constraints. The alpha-bundle structure thus obtained provides H bonding of nearly all buried polar side chains simultaneously in the 410 GPCRs considered. Forty evolutionarily conserved GPCR residues form a single continuous domain, with an aliphatic "core" surrounded by six clusters of polar and aromatic side chains. The 7-alpha-bundle of a specific GPCR can be calculated using its own set of H bonds as distance constraints and the common "average" model to restrain positions of the helices. The bovine rhodopsin model thus determined is closely packed, but has a few small polar cavities, presumably filled by water, and has a binding pocket that is complementary to 11-cis (6-s-cis, 12-s-trans, C = N anti)-retinal or to all-trans-retinal, depending on conformations of the Lys296 and Trp265 side chains. A suggested mechanism of rhodopsin photoactivation, triggered by the cis-trans isomerization of retinal, involves rotations of Glu134, Tyr223, Trp265, Lys296, and Tyr306 side chains and rearrangement of their H bonds. The model is in agreement with published electron cryomicroscopy, mutagenesis, chemical modification, cross-linking, Fourier transform infrared spectroscopy, Raman spectroscopy, electron paramagnetic resonance spectroscopy, NMR, and optical spectroscopy data. The rhodopsin model and the published structure of bacteriorhodopsin have very similar retinal-binding pockets.

The Radiative Impact of FU Orionis Outbursts on Protostellar Envelopes

We present preliminary results of an investigation into the radiative impact of FU Orionis outbursts on protostellar envelopes. In the thermal accretion disk instability model, the inner portion of the disk is inflated in such a way as to funnel most of the outburst luminosity along the poles of the system. A multidimensional radiative transfer code is employed to derive the thermal equilibrium structure of the surrounding protostellar envelope and the backheated accretion disk during outburst. The radiation emitted during outburst is modeled as a combination of a self-luminous accretion disk and a central point source. We compare the relative heating of circumstellar material due to (1) an isotropic point source and (2) an anisotropic point source in which the emitted radiation is confined to a 30° cone about the polar axis. The isotropic point source creates a spherical dust cavity, while the anisotropic source naturally results in a cavity which is hourglass-shaped. Repeated outbursts may ultimately be responsible for the large-scale polar cavities commonly inferred to exist around young stellar objects. We also show that due to the anisotropy of the radiation expected during outburst, disk annuli within a few au will be shielded from the radiation of the outburst.

The Transport of Thermal Radiation in a Protostellar Envelope

view Abstract Citations (16) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Transport of Thermal Radiation in a Protostellar Envelope Chick, Kenneth M. ; Pollack, James B. ; Cassen, Patrick Abstract We present a discrete ordinate solution for gray radiation transport in axisymmetric protostellar envelopes, for the purpose of defining the patterns of interstellar-grain survival during the formation of the solar system. The gray transfer problem is nonlinear because the opacity depends on temperature, with discontinuities at temperatures where various species of dust vaporize. The standard lambda iteration techniques that are required for accurate solutions to the transfer equation tend to be nonconvergent under these conditions. We show that accuracy can be achieved through a relaxation method. We first compare the thermal profiles in spherically symmetric envelopes computed by the discrete ordinate solution with those predicted by the diffusion approximation. The more accurate discrete ordinate solutions tend to yield steeper temperature gradients, and the central vaporized cavity around the protostar is larger than that given by the diffusion approximation. The transport solution is then applied to an axisymmetric model envelope in which the cloud is flattened due to rotation, and in which a wind evacuates the polar regions of the cloud. The resulting cavity beams the emergent intensity in the polar direction. When the cloud is uniformly opaque, the polar cavity enhances the diffusive escape of radiation and globally reduces temperatures in the cloud. Modeled temperature profiles are used to predict the radial distances at which various dust species survive infall in the cloud. The results indicate that survival boundaries range from within 1 AU for the most refractory solids, to several AU for volatile organics, and that water ice is excluded from within 20-30 AU of the protostar during the collapse phase. We compare dust vaporization due to heating in the cloud with destruction in the accretion shock; based on the test case, heating in the cloud during collapse is potentially more destructive. Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177117 Bibcode: 1996ApJ...461..956C Keywords: METHODS: NUMERICAL; RADIATIVE TRANSFER; SOLAR SYSTEM: FORMATION; STARS: PRE-MAIN-SEQUENCE; STARS: ATMOSPHERES full text sources ADS |

Steady state fluorescence studies of the complexes between pyrene and per-6-O-tert-butyldimethylsilyl α-, β- and γ-cyclodextrins

The complexation of pyrene by α-, β- and γ-cyclodextrins (CDs), persubstituted at the 6 position by tert-butyldimethylsilyl groups, has been investigated using steady state fluorescence spectroscopy. The α-CD derivative does not, as would be expected from steric considerations, form complexes. The β- and γ-CD derivatives form 1:1 host–guest complexes which show high association constants in 90:10 H2O–DMF solution [i.e.β-CD(SiR)7, 4.85 × 105 M–1;γ-CD(SiR)8, 4.91 × 105 M–1]. Analysis of the polarity of the microenvironment by means of the I/III peak ratios shows a more polar cavity in the case of γ-CD(SiR)8. The concentration dependence of I/III suggests that a weak supramolecular complex γ-CD(SiR)8–pyrene-n·DMF, may exist.

A simplified marker and cell method for unsteady flows on non‐staggered grids

AbstractThe SMAC (simplified marker and cell) time‐advancing method for solving the unsteady incompressible Navier‐Stokes equations on non‐staggered grids is developed in generalized co‐ordinate systems. The primitive variable formulation uses Cartesian velocities and pressure, all defined at the centre of the control volume, as the dependent variables. A special elliptic flux correction at the faces of the finite volume is utilized in discretizing the continuity equation to suppress pressure oscillations. The test flows considered are a polar cavity flow starting from rest and the flow around a circular cylinder. The numerical results are compared with experimental results and results obtained by the well‐known SIMPLEC and PISO methods. The comparisons show that the elliptic flux correction technique works well in suppressing pressure oscillations and that the SMAC method is more efficient than the SIMPLEC and PISO methods for both steady and unsteady flows.

Gain-dependent polarization properties of vertical-cavity lasers

We show that the partitioning of power into the two orthogonal eigen polarizations of infra-red gain-guided vertical cavity lasers depends upon the relative spectral overlap of the nondegenerate polarization cavity resonances with the laser gain spectrum. Furthermore, at the condition where the polarization resonances and the peak laser gain are aligned, abrupt switching of power between the eigen polarizations is observed as the gain sweeps through the polarization resonances. The gain-dependence of the polarization requires spectral splitting between the eigen polarizations, which is found to be strongly influenced by local strain. The polarization of the fundamental and higher-order spatial modes can be selected and maintained for all InGaAs vertical-cavity lasers in a wafer simply by employing a 20 nm or greater blue-shift offset of the peak laser gain relative to the cavity resonances. >

A hybrid adaptive gridding procedure for three-dimensional flow problems

A hybrid adaptive gridding procedure which combines both the local refinement method and the global grid moving method is devised. The grid moving method is employed to obtain the initial adaptive solution. The local refinement method is then applied on the large error regions of this initial adaptive solution. The large error regions are flagged by using the weight function approach. The effectiveness of using an adaptive initial solution instead of a uniform grid initial solution is assessed. Use of the weight function as an error indicator is discussed in the computation of the model problems. It is found that an adaptive initial solution reduces the sizes of the large error regions. This can save effort in the later solution refinement. Use of the weight function as an indicator can reduce the effort required for error estimation. The procedure is first verified in the computation of the model equations which have exact solutions. The procedure is then applied to the computation of three-dimensional, steady, laminar flow problems which requires the solutions of the Navier-Stokes equations. The flow problems are a polar cavity flow, a natural convection flow in an enclosure and a curved tube flow. Numerical efficiencies ranging from 30 to 40 are obtained in the model equations. Those for the flow problems are about 20–30. The proposed procedure is most suitable for flows whose high gradient regions are localized in a limited portion of the domain. The most attractive feature of the procedure is its ease of application of practical flow problems.

The embedded young stars in the Taurus-Auriga molecular cloud. II - Models for scattered light images

We describe NIR imaging observations of embedded young stars in the Taurus-Auriga molecular cloud. We find a large range in J-K and H-K colors for these class I sources. The bluest objects have colors similar to the reddest T Tauri stars in the cloud; redder objects lie slightly above the reddening line for standard ISM dust and have apparent K extinctions of up to 5 mag. Most of these sources also show extended NIR emission on scales of 10-20 arcsec which corresponds to linear sizes of 1500-3000 AU. The NIR colors and nebular morphologies for this sample and the magnitude of linear polarization in several sources suggest scattered light produces most of the NIR emission in these objects. We present modeling results that suggest mass infall rates that agree with predictions for cold clouds and are generally consistent with rates estimated from radiative equilibrium models. For reasonable dust grain parameters, the range of colors and extinctions require flattened density distributions with polar cavities evacuated by bipolar outflows. These results support the idea that infall and outflow occur simultaneously in deeply embedded bipolar outflow sources. The data also indicate fairly large centrifugal radii and large inclinations to the rotational axis for a typical source.

A Hybrid Adaptive Gridding Procedure for Recirculating Fluid Flow Problems

A hybrid adaptive gridding procedure combining the concepts of both local grid refinement and global grid moving has been developed for time-independent recirculating flow problems. The procedure starts with the global grid moving method which provides an initial adaptive solution. Base on this initial solution, large error regions are flagged and local refinement is then applied on the large error regions. The methods for error estimation and interface treatment are discussed. The procedure is assessed in a one-dimensional convection-diffusion equation, a driven polar cavity flow, and a laminar backward-facing step flow. Efficiencies of the various approaches are evaluated. Specifically, in the test problems, the hybrid adaptive grid solution requires less than one-tenth of the CPU time of that of the uniform fine grid solution to achieve the same accuracy, The procedure can be conveniently extended to three-dimensional, irregular geometry flow problems.