388 research outputs found
Bivariate spline interpolation with optimal approximation order
Let be a triangulation of some polygonal domain f c R2 and let S9 (A) denote the space of all bivariate polynomial splines of smoothness r and degree q with respect to A. We develop the first Hermite-type interpolation scheme for S9 (A), q >_ 3r + 2, whose approximation error is bounded above by Kh4+i, where h is the maximal diameter of the triangles in A, and the constant K only depends on the smallest angle of the triangulation and is independent of near-degenerate edges and nearsingular vertices. Moreover, the fundamental functions of our scheme are minimally supported and form a locally linearly independent basis for a superspline subspace of Sr, (A). This shows that the optimal approximation order can be achieved by using minimally supported splines. Our method of proof is completely different from the quasi-interpolation techniques for the study of the approximation power of bivariate splines developed in [71 and [181
Mid-infrared interferometry of the massive young stellar object NGC3603 - IRS 9A
We present observations and models for one of these MYSO candidates, NGC3603
IRS 9A. Our goal is to investigate with infrared interferometry the structure
of IRS 9A on scales as small as 200AU, exploiting the fact that a cluster of O
and B stars has blown away much of the obscuring foreground dust and gas.
Observations in the N-band were carried out with the MIDI beam combiner
attached to the VLTI. Additional interferometric observations which probe the
structure of IRS 9A on larger scales were performed with an aperture mask
installed in the T-ReCS instrument of Gemini South. The spectral energy
distribution (SED) is constrained by the MIDI N-band spectrum and by data from
the Spitzer Space Telescope. Our efforts to model the structure and SED of IRS
9A range from simple geometrical models of the brightness distribution to one-
and two-dimensional radiative transfer computations. The target is resolved by
T-ReCS, with an equivalent (elliptical) Gaussian width of 330mas by 280mas
(2300 AU by 2000 AU). Despite this fact, a warm compact unresolved component
was detected by MIDI which is possibly associated with the inner regions of a
flattened dust distribution. Based on our interferometric data, no sign of
multiplicity was found on scales between about 200AU and 700AU projected
separation. A geometric model consisting of a warm (1000 K) ring (400 AU
diameter) and a cool (140 K) large envelope provides a good fit to the data. No
single model fitting all visibility and photometric data could be found, with
disk models performing better than spherical models. While the data are clearly
inconsistent with a spherical dust distribution they are insufficient to prove
the existence of a disk but rather hint at a more complex dust distribution.Comment: 8 pages, 11 figures. Accepted for publication in A&
Properties of active galactic star-forming regions probed by imaging spectroscopy with the Fourier transform spectrometer (FTS) onboard AKARI
We investigate the structure of the interstellar medium (ISM) and identify
the location of possible embedded excitation sources from far-infrared (FIR)
line and mid-infrared continuum emission maps. We carried out imaging
spectroscopic observations of four giant Galactic star-forming regions with the
Fourier Transform Spectrometer (FTS) onboard AKARI. We obtained [OIII] 88
micron and [CII] 158 micron line intensity maps of all the regions:
G3.270-0.101, G333.6-0.2, NGC3603, and M17. For G3.270-0.101, we obtained
high-spatial-resolution [OIII] 88 micron line-emission maps and a FIR continuum
map for the first time, which imply that [OIII] 88 micron emission identifies
the excitation sources more clearly than the radio continuum emission. In
G333.6-0.2, we found a local [OIII] 88 micron emission peak, which is
indicative of an excitation source. This is supported by the 18 micron
continuum emission, which is considered to trace the hot dust distribution. For
all regions, the [CII] 158 micron emission is distributed widely as suggested
by previous observations of star-forming regions. We conclude that [OIII] 88
micron emission traces the excitation sources more accurately than the radio
continuum emission, especially where there is a high density and/or column
density gradient. The FIR spectroscopy provides a promising means of
understanding the nature of star-forming regions.Comment: 14 pages with 15 figures, accepted for publication in Astronomy and
Astrophysic
Overlap of QRPA states based on ground states of different nuclei --mathematical properties and test calculations--
The overlap of the excited states in quasiparticle random-phase approximation
(QRPA) is calculated in order to simulate the overlap of the intermediate
nuclear states of the double-beta decay. Our basic idea is to use the
like-particle QRPA with the aid of the closure approximation and calculate the
overlap as rigorously as possible by making use of the explicit equation of the
QRPA ground state. The formulation is shown in detail, and the mathematical
properties of the overlap matrix are investigated. Two test calculations are
performed for relatively light nuclei with the Skyrme and volume delta-pairing
energy functionals. The validity of the truncations used in the calculation is
examined and confirmed.Comment: 17 pages, 15 figures, full paper following arXiv:1205.5354 and Phys.
Rev. C 86 (2012) 021301(R
Synthetic CO emission and the factor of young molecular clouds: a convergence study
The properties of synthetic CO emission from 3D simulations of forming
molecular clouds are studied within the SILCC-Zoom project. Since the time
scales of cloud evolution and molecule formation are comparable, the
simulations include a live chemical network. Two sets of simulations with an
increasing spatial resolution (d pc to d pc) are used to
investigate the convergence of the synthetic CO emission, which is computed by
post-processing the simulation data with the RADMC-3D radiative transfer code.
To determine the excitation conditions, it is necessary to include atomic
hydrogen and helium alongside H, which increases the resulting CO emission
by ~7-26 per cent. Combining the brightness temperature of CO and
CO, we compare different methods to estimate the excitation temperature,
the optical depth of the CO line and hence, the CO column density. An
intensity-weighted average excitation temperature results in the most accurate
estimate of the total CO mass. When the pixel-based excitation temperature is
used to calculate the CO mass, it is over-/underestimated at low/high CO column
densities where the assumption that CO is optically thick while
CO is optically thin is not valid. Further, in order to obtain a
converged total CO luminosity and hence factor, the 3D
simulation must have d pc. The evolves over time
and differs for the two clouds; yet pronounced differences with numerical
resolution are found. Since high column density regions with a visual
extinction larger than 3~mag are not resolved for d~pc, in this
case the H mass and CO luminosity both differ significantly from the higher
resolution results and the local is subject to strong noise. Our
calculations suggest that synthetic CO emission maps are only converged for
simulations with d pc.Comment: 23 pages, 22 figures, accepted for publication in MNRA
Probing the centre of the large circumstellar disc in M17
We investigated the nature of the hitherto unresolved elliptical infrared
emission in the centre of the ~20000 AU disc silhouette in M 17. We combined
high-resolution JHKsL'M' band imaging carried out with NAOS/CONICA at the VLT
with [Fe II] narrow band imaging using SOFI at the NTT. The analysis is
supported by Spitzer/GLIMPSE archival data and by already published SINFONI/VLT
Integral Field Spectroscopy data. For the first time, we resolve the elongated
central infrared emission into a point-source and a jet-like feature that
extends to the northeast in the opposite direction of the recently discovered
collimated H2 jet. They are both orientated almost perpendicular to the disc
plane. In addition, our images reveal a curved southwestern emission nebula
whose morphology resembles that of the previously detected northeastern one.
Both nebulae are located at a distance of 1500 AU from the disc centre. We
describe the infrared point-source in terms of a protostar that is embedded in
circumstellar material producing a visual extinction of 60 <= Av <= 82. The
observed Ks band magnitude is equivalent to a stellar mass range of 2.8 Msun <=
Mstar <= 8 Msun adopting conversions for a main-sequence star. Altogether, we
suggest that the large M 17 accretion disc is forming an intermediate to
high-mass protostar. Part of the accreted material is expelled through a
symmetric bipolar jet/outflow.Comment: 6 pages, 3 figures, accepted by MNRAS (16 May 2008
Giant crystals inside mitochondria of equine chondrocytes
The present study reports for the first time the presence of giant crystals in mitochondria of equine chondrocytes. These structures show dark contrast in TEM images as well as a granular substructure of regularly aligned 12 nm small units. Different zone axes of the crystalline structure were analysed by means of Fourier transformation of lattice-resolution TEM images proving the crystalline nature of the structure. Elemental analysis reveals a high content of nitrogen referring to protein. The outer shape of the crystals is geometrical with an up to hexagonal profile in cross sections. It is elongated, spanning a length of several micrometres through the whole cell. In some chondrocytes, several crystals were found, sometimes combined in a single mitochondrion. Crystals were preferentially aligned along the long axis of the cells, thus appearing in the same orientation as the chondrocytes in the tissue. Although no similar structures have been found in the cartilage of any other species investigated, they have been found in cartilage repair tissue formed within a mechanically stimulated equine chondrocyte construct. Crystals were mainly located in superficial regions of cartilage, especially in joint regions of well-developed superficial layers, more often in yearlings than in adult horses. These results indicate that intramitochondrial crystals are related to the high mechanical stress in the horse joint and potentially also to the increased metabolic activity of immature individuals.(VLID)353386
The cool atmospheres of the binary brown dwarf eps Indi B
We have imaged Indi B, the closest brown dwarf binary known, with
VISIR at the VLT in three narrow-band mid-infrared bandpasses located around
8.6m, 10.5m and 11.3m. We are able to spatially resolve both
components, and determine accurate mid-infrared photometry for both components
independently. In particular, our VISIR observations probe the NH feature
in the atmospheres of the cooler and warmer brown dwarfs. For the first time,
we can disentangle the contributions of the two components, and find that % our
photometry of IndiBb is in good agreement with recent ``cloud-free''
atmosphere models having an effective temperature of K.
With an assumed age of 1 Gyr for the Indi system, component Ba
agrees more with K rather than with
K, as suggested by SPITZER spectroscopic observations of
the combined Indi B system (Roellig et al., 2004). Even higher
effective temperatures appear inconsistent with our absolute photometry, as
they would imply an unphysical small size of the brown dwarf IndiBa.Comment: 4 pages, 2 figure
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