313 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&
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
Microstructural characterization and simulation of damage for geared sheet components
The evolution of damage in geared components manufactured from steel sheets was investigated, to analyse the influence of damage caused by the sheet-bulk-metal forming. Due to the inhomogeneous and multi-axial deformation in the investigated parts, different aspects such as the location-dependent shape and size of voids are analysed by means of various microscopic methods. In particular, a method to characterize the state of damage evolution, i. e. void nucleation, growth and coalescence using scanning electron microscopy (SEM) is applied. The investigations reveal a strong dependence of the void area fraction, shape of voids and thus damage evolution on the loading mode. The microstructural analysis is complemented with FEM simulations using material models which consider the characteristics of the void evolution. © Published under licence by IOP Publishing Ltd
Molecular Outflows and a Mid-Infrared Census of the Massive Star Formation Region Associated with IRAS 18507+0121
We have observed the central region of the infrared-dark cloud filament associated with IRAS 18507+0121 at millimeter wavelengths in CO(J = 1-0), ^(13)CO(J = 1-0), and C^(18)O(J = 1-0) line emission and with Spitzer at mid-infrared wavelengths. Five massive outflows from two cloud cores were discovered. Three outflows are centered on or near an ultracompact (UC) H II region (G34.4+0.23), while the remaining two outflows originate from the millimeter core G34.4+0.23 MM. Modeling of the spectral energy distributions of the mid-infrared sources identified 31 young stellar objects in the filament with a combined stellar mass of ~127 ± 27 M_☉. An additional 22 sources were identified as probable cluster members based on the presence of strong 24 μm emission. The total star formation efficiency in the G34.4 cloud filament is estimated to be ~7%, while the massive and intermediate-mass star formation efficiency in the entire cloud filament is estimated to be roughly 2%. A comparison of the gravitational binding energy with the outflow kinetic energy suggests that the compact core containing G34.4+0.23 MM is being destroyed by its molecular outflows, whereas the outflows associated with the more massive core surrounding the G34.4 UC H II region are not likely to totally disrupt the cloud. In addition, a qualitative evaluation of the region appears to suggest that stars in this region may have formed in two stages: first lower mass stars formed and then, a few Myr later, the more massive stars began to form
Near-infrared follow-up to the May 2008 activation of SGR 1627-41
On 28 May 2008, the Swift satellite detected the first reactivation of SGR
1627-41 since its discovery in 1998.
Following this event we began an observing campaign in near infrared
wavelengths to search for a possible counterpart inside the error circle of
this SGR, which is expected to show flaring activity simultaneous to the high
energy flares or at least some variability as compared to the quiescent state.
For the follow-up we used the 0.6m REM robotic telescope at La Silla
Observatory, which allowed a fast response within 24 hours and, through
director discretionary time, the 8.2m Very Large Telescope at Paranal
Observatory. There, we observed with NACO to produce high angular resolution
imaging with the aid of adaptive optics.
These observations represent the fastest near infrared observations after an
activation of this SGR and the deepest and highest spatial resolution
observations of the Chandra error circle.
5 sources are detected in the immediate vicinity of the most precise X-ray
localisation of this source. For 4 of them we do not detect variability,
although the X-ray counterpart experimented a significant decay during our
observation period. The 5th source is only detected in one epoch, where we have
the best image quality, so no variability constrains can be imposed and remains
as the only plausible counterpart. We can impose a limit of Ks > 21.6
magnitudes to any other counterpart candidate one week after the onset of the
activity. Our adaptive optics imaging, with a resolution of 0.2" provides a
reference frame for subsequent studies of future periods of activity.Comment: Accepted for publication in A&
The photometric evolution of dissolving star clusters I: First predictions
We calculated the broad-band photometric evolution of unresolved star
clusters, including the preferential loss of low-mass stars due to mass
segregation. The stellar mass function of a cluster evolves due to three
effects: (a) the evolution of massive stars; (b) early tidal effects reduce the
mass function independently of the stellar mass; (c) after mass segregation has
completed, tidal effects preferentially remove the lowest-mass stars from the
cluster. Results: (1) During the first ~40% of the lifetime of a cluster the
cluster simply gets fainter due to the loss of stars by tidal effects. (2)
Between ~40 and ~80% of its lifetime the cluster gets bluer due to the loss of
low-mass stars. This will result in an underestimate of the age of clusters if
standard cluster evolution models are used (0.15 -- 0.5 dex). (3) After ~80% of
the total lifetime of a cluster it will rapidly get redder. This is because
stars at the low-mass end of the main sequence, which are preferentially lost,
are bluer than the AGB stars that dominate the light at long wavelengths,
resulting in an age overestimate. (4) Clusters with mass segregation and the
preferential loss of low-mass stars evolve along almost the same tracks in
colour-colour diagrams as clusters without mass segregation. Therefore it will
be difficult to distinguish this effect from that due to the cluster age for
unresolved clusters, unless the total lifetime of the clusters can be
estimated. (5) The changes in the colour evolution of unresolved clusters due
to the preferential loss of low-mass stars will affect the determination of the
SFHs. (6) The preferential loss of low-mass stars might explain the presence of
old (~13 Gyr) clusters in NGC 4365 which are photometrically disguised as
intermediate-age clusters (2 - 5 Gyr). [Abridged]Comment: accepted for publication in A&
Star Formation in the Starburst Cluster in NGC 3603
We have used new, deep, visible and near infrared observations of the compact
starburst cluster in the giant HII region NGC 3603 and its surroundings with
the WFC3 on HST and HAWK-I on the VLT to study in detail the physical
properties of its intermediate mass (~ 1 - 3 M_sun) stellar population. We show
that after correction for differential extinction and actively accreting stars,
and the study of field star contamination, strong evidence remains for a
continuous spread in the ages of pre-main sequence stars in the range ~ 2 to ~
30 Myr within the temporal resolution available. Existing differences among
presently available theoretical models account for the largest possible
variation in shape of the measured age histograms within these limits. We also
find that this isochronal age spread in the near infrared and visible
Colour-Magnitude Diagrams cannot be reproduced by any other presently known
source of astrophysical or instrumental scatter that could mimic the luminosity
spread seen in our observations except, possibly, episodic accretion. The
measured age spread and the stellar spatial distribution in the cluster are
consistent with the hypothesis that star formation started at least 20-30 Myrs
ago progressing slowly but continuously up to at least a few million years ago.
All the stars in the considered mass range are distributed in a flattened
oblate spheroidal pattern with the major axis oriented in an approximate
South-East - North-West direction, and with the length of the equatorial axis
decreasing with increasing age. This asymmetry is most likely due to the fact
that star formation occurred along a filament of gas and dust in the natal
molecular cloud oriented locally in this direction.Comment: 21 pages, 19 figures, accepted for publication in Astrophysics &
Space Scienc
Coherent strong-field control of multiple states by a single chirped femtosecond laser pulse
We present a joint experimental and theoretical study on strong-field
photo-ionization of sodium atoms using chirped femtosecond laser pulses. By
tuning the chirp parameter, selectivity among the population in the highly
excited states 5p, 6p, 7p and 5f, 6f is achieved. Different excitation pathways
enabling control are identified by simultaneous ionization and measurement of
photoelectron angular distributions employing the velocity map imaging
technique. Free electron wave packets at an energy of around 1 eV are observed.
These photoelectrons originate from two channels. The predominant 2+1+1
Resonance Enhanced Multi-Photon Ionization (REMPI) proceeds via the strongly
driven two-photon transition , and subsequent
ionization from the states 5p, 6p and 7p whereas the second pathway involves
3+1 REMPI via the states 5f and 6f. In addition, electron wave packets from
two-photon ionization of the non-resonant transiently populated state 3p are
observed close to the ionization threshold. A mainly qualitative five-state
model for the predominant excitation channel is studied theoretically to
provide insights into the physical mechanisms at play. Our analysis shows that
by tuning the chirp parameter the dynamics is effectively controlled by dynamic
Stark-shifts and level crossings. In particular, we show that under the
experimental conditions the passage through an uncommon three-state "bow-tie"
level crossing allows the preparation of coherent superposition states
A frozen super-Earth orbiting a star at the bottom of the Main Sequence
We observed the microlensing event MOA-2007-BLG-192 at high angular
resolution in JHKs with the NACO adaptive optics system on the VLT while the
object was still amplified by a factor 1.23 and then at baseline 18 months
later. We analyzed and calibrated the NACO photometry in the standard 2MASS
system in order to accurately constrain the source and the lens star fluxes. We
detect light from the host star of MOA-2007-BLG-192Lb, which significantly
reduces the uncertainties in its char- acteristics as compared to earlier
analyses. We find that MOA-2007-BLG-192L is most likely a very low mass late
type M-dwarf (0.084 [+0.015] [-0.012] M\odot) at a distance of 660 [+100] [-70]
pc orbited by a 3.2 [+5.2] [-1.8] M\oplus super-Earth at 0.66 [+0.51] [-0.22]
AU. We then discuss the properties of this cold planetary system.Comment: published version A&A 540, A78 (2012) A&A, 10 pages, 7 Figure
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