376,697 research outputs found
Space-Time Transfinite Interpolation of Volumetric Material Properties
The paper presents a novel technique based on extension of a general mathematical method of transfinite interpolation to solve an actual problem in the context of a heterogeneous volume modelling area. It deals with time-dependent changes to the volumetric material properties (material density, colour and others) as a transformation of the volumetric material distributions in space-time accompanying geometric shape transformations such as metamorphosis. The main idea is to represent the geometry of both objects by scalar fields with distance properties, to establish in a higher-dimensional space a time gap during which the geometric transformation takes place, and to use these scalar fields to apply the new space-time transfinite interpolation to volumetric material attributes within this time gap. The proposed solution is analytical in its nature, does not require heavy numerical computations and can be used in real-time applications. Applications of this technique also include texturing and displacement mapping of time-variant surfaces, and parametric design of volumetric microstructures
Exploring the formation of spheroidal galaxies out to z ∼ 1.5 in GOODS
The formation of massive spheroidal galaxies is studied on a visually classified sample extracted from the Advanced Camera for Surveys/Hubble Space Telescope (ACS/HST) images of the Great Observatories Origins Deep Survey north and south fields, covering a total area of 360 arcmin . The sample size (910 galaxies brighter than i = 24) allows us to explore in detail the evolution over a wide range of redshifts (0.4 10 M galaxies by a factor of 2 between z = 1 and 0, in contrast with a factor of ∼50 for lower mass galaxies (10 <M / M <10 ). One-quarter of the whole sample of early types are photometrically classified as blue galaxies. On a volume-limited sample out to z <0.7, the average stellar mass of the blue ellipticals is 5 × 10 M compared to 4 × 10 M for red ellipticals. On a volume-limited subsample out to z = 1.4 probing the brightest galaxies (M <-21), we find the median redshift of blue and red early types: 1.10 and 0.85, respectively. Blue early types only amount to 4 per cent of this sample (compared to 26 per cent in the full sample). The intrinsic colour distribution correlates overall bluer colours with blue cores (positive radial gradients of colour), suggesting an inside-out process of formation. The redshift evolution of the observed colour gradients is incompatible with a significant variation in stellar age within each galaxy. The slope of the Kormendy relation in the subsample of massive galaxies does not change over 0.4 <z <1.4 and is compatible with z = 0 values. The 'zero-point' of the Kormendy relation (i.e. the surface brightness at a fixed half-light radius) is 1 mag fainter (in the B band) for the subsample of low-mass (M <3.5 × 10 M ) early types.Peer reviewe
Probing the dusty stellar populations of the Local Volume Galaxies with JWST/MIRI
The Mid-Infrared Instrument (MIRI) for the {\em James Webb Space Telescope}
(JWST) will revolutionize our understanding of infrared stellar populations in
the Local Volume. Using the rich {\em Spitzer}-IRS spectroscopic data-set and
spectral classifications from the Surveying the Agents of Galaxy Evolution
(SAGE)-Spectroscopic survey of over a thousand objects in the Magellanic
Clouds, the Grid of Red supergiant and Asymptotic giant branch star ModelS
({\sc grams}), and the grid of YSO models by Robitaille et al. (2006), we
calculate the expected flux-densities and colors in the MIRI broadband filters
for prominent infrared stellar populations. We use these fluxes to explore the
{\em JWST}/MIRI colours and magnitudes for composite stellar population studies
of Local Volume galaxies. MIRI colour classification schemes are presented;
these diagrams provide a powerful means of identifying young stellar objects,
evolved stars and extragalactic background galaxies in Local Volume galaxies
with a high degree of confidence. Finally, we examine which filter combinations
are best for selecting populations of sources based on their JWST colours.Comment: 16 pages, 7 figures, 2 online tables; accepted for publication in Ap
Kepler Fourier concepts: The performance of the Kepler data pipeline
Given the extreme precision attainable with the Kepler Space Telescope, the
mitigation of instrumental artefacts is very important. In an earlier paper
(Murphy 2012), the characteristics of Kepler data were discussed in light of
their effect on asteroseismology. We continue this discussion now that data
processed with the new PDC-MAP pipeline are publicly available; users should
use the latest data reductions available at the Mikulski Archive for Space
Telescopes (MAST), not just for PDC, but also for improvements in the attached
meta-data. We discuss the injection of noise in the frequency range 0-24 c/d
(up to ~277 {\mu}Hz) by the PDC-LS pipeline into ~15 per cent of light-curves.Comment: 4 pages, 7 figures of which 4 are colour. On material presented at
the conference "The Modern Era of Helio- and Asteroseismology" held at
Obergurgl, Austria, May 2012. Published in AN (Volume 333, Issue 10, Pages
1057-1060
The globular clusters-stellar haloes connection in early type galaxies
This paper explores if, and to what an extent, the stellar populations of
early type galaxies can be traced through the colour distribution of their
globular cluster systems. The analysis, based on a galaxy sample from the Virgo
ACS data, is an extension of a previous approach that has been successful in
the cases of the giant ellipticals NGC 1399 and NGC 4486, and assumes that the
two dominant GC populations form along diffuse stellar populations sharing the
cluster chemical abundances and spatial distributions. The results show that a)
Integrated galaxy colours can be matched to within the photometric
uncertainties and are consistent with a narrow range of ages; b) The inferred
mass to luminosity ratios and stellar masses are within the range of values
available in the literature; c) Most globular cluster systems occupy a thick
plane in the volume space defined by the cluster formation efficiency, total
stellar mass and projected surface mass density. The formation efficiency
parameter of the red clusters shows a dependency with projected stellar mass
density that is absent for the blue globulars. In turn, the brightest galaxies
appear clearly detached from that plane as a possible consequence of major past
mergers; d) The stellar mass-metallicity relation is relatively shallow but
shows a slope change at . Galaxies with smaller
stellar masses show predominantly unimodal globular cluster colour
distributions. This result may indicate that less massive galaxies are not able
to retain chemically enriched intestellar matter.Comment: 19 pages, 10 figure
Global survey of star clusters in the Milky Way: III. 139 new open clusters at high Galactic latitudes
Context. An earlier analysis of the Milky Way Star Cluster (MWSC) catalogue revealed an apparent lack of old (t � 1 Gyr) open clusters in the solar neighbourhood (d � 1 kpc). Aims. To fill this gap we undertook a search for hitherto unknown star clusters, assuming that the missing old clusters reside at high Galactic latitudes | b | > 20°. Methods. We were looking for stellar density enhancements using a star count algorithm on the 2MASS point source catalogue. To increase the contrast between potential clusters and the field, we applied filters in colour-magnitude space according to typical colour-magnitude diagrams of nearby old open clusters. The subsequent comparison with lists of known objects allowed us to select thus far unknown cluster candidates. For verification they were processed with the standard pipeline used within the MWSC survey for computing cluster membership probabilities and for determining structural, kinematic, and astrophysical parameters. Results. In total we discovered 782 density enhancements, 524 of which were classified as real objects. Among them 139 are new open clusters with ages 8.3 < log (t [yr]) < 9.7, distances d< 3 kpc, and distances from the Galactic plane 0.3 <Z< 1 kpc. This new sample has increased the total number of known high latitude open clusters by about 150%. Nevertheless, we still observe a lack of older nearby clusters up to 1 kpc from the Sun. This volume is expected to still contain about 60 unknown clusters that probably escaped our detection algorithm, which fails to detect sparse overdensities with large angular size
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