613 research outputs found
Constrained reconstruction of 3D curves and surfaces using integral spline operators
In the context of direct/reverse engineering processes one of the main problem is the reconstruction of curves and surfaces starting from a cloud of points. Most of the times the (re)constructed curves and surfaces have to satisfy some particular geometric constraints and functional properties related to the desired shapes. In this paper, referring to 3D curves and surfaces, we propose an algorithm based on an interpolatory variation diminishing integral spline operator characterized by the presence of shape parameters. In order to choose the best value for the shape parameters different functionals can be adopted. Some test cases are presented in order to show the effectiveness of the proposed algorithm: both academic and real world test cases are considered
REPRESENTATION OF DAM-BREACH GEOMETRY ON AREGULAR 2-D MESH USING QUADTREE LOCAL MESHREFINEMENT
River hydrodynamicsUnsteady open channel flow and dam brea
Breaking the core-envelope symmetry in p-mode pulsating stars
It has been shown that there is a potential ambiguity in the asteroseismic
determination of the location of internal structures in a pulsating star. We
show how, in the case of high-order non-radial acoustic modes, it is possible
to remove this ambiguity by considering modes of different degree. To support
our conclusions we have investigated the seismic signatures of sharp density
variations in the structure of quasi-homogeneous models.Comment: 3 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Representation of dam-breach geometry on a regular 2-D mesh using quadtree local mesh refinement
River hydrodynamicsUnsteady open channel flow and dam brea
CLES, Code Liegeois d'Evolution Stellaire
Cles is an evolution code recently developed to produce stellar models
meeting the specific requirements of studies in asteroseismology. It offers the
users a lot of choices in the input physics they want in their models and its
versatility allows them to tailor the code to their needs and implement easily
new features. We describe the features implemented in the current version of
the code and the techniques used to solve the equations of stellar structure
and evolution. A brief account is given of the use of the program and of a
solar calibration realized with it.Comment: Comments: 8 pages, Astrophys. Space Sci. CoRoT-ESTA Volume, in the
pres
Testing abundance-age relations beyond solar analogues with Kepler LEGACY stars
The prospects of using abundance ratios as stellar age indicators appear promising for solar analogues, but the usefulness of this technique for stars spanning a much wider parameter space remains to be established. We present abundances of 21 elements in a sample of 13 bright FG dwarfs drawn from the Kepler LEGACY sample to examine the applicability of the abundance-age relations to stars with properties strongly departing from solar. These stars have precise asteroseismic ages that can be compared to the abundance-based estimates. We analyse the well-known binary 16 Cyg AB for validation purposes and confirm the existence of a slight metal enhancement ( 3c0.02 dex) in the primary, which might arise from planetary formation and/or ingestion. We draw attention to systematic errors in some widely used catalogues of non-seismic parameters that may significantly bias asteroseismic inferences. In particular, we find evidence that the ASPCAP Teff scale used for the APOKASC catalogue is too cool for dwarfs and that the [Fe/H] values are underestimated by 3c0.1 dex. In addition, a new seismic analysis of the early F-type star KIC 9965715 relying on our spectroscopic constraints shows that the star is more massive and younger than previously thought. We compare seismic ages to those inferred from empirical abundance-age relations based on ages from PARSEC isochrones and abundances obtained in the framework of the HARPS-GTO programme. These calibrations depend on the stellar effective temperature, metallicity, and/or mass. We find that the seismic and abundance-based ages differ on average by 1.5-2 Gyr, while taking into account a dependency on one or two stellar parameters in the calibrations leads to a global improvement of up to 3c0.5 Gyr. However, even in that case we find that seismic ages are systematically larger by 3c0.7 Gyr. We argue that it may be ascribed to a variety of causes including the presence of small zero-point offsets between our abundances and those used to construct the calibrations or to the choice of the set of theoretical isochrones. The conclusions above are supported by the analysis of literature data for a larger number of Kepler targets. For this extended sample, we find that incorporating a Teff dependency largely corrects for the fact that the abundance-based ages are lower/larger with respect to the seismic estimates for the cooler/hotter stars. Although investigating age dating methods relying on abundance data is worth pursuing, we conclude that further work is needed to improve both their precision and accuracy for stars that are not solar analogues
HD 174884: a strongly eccentric, short-period early-type binary system discovered by CoRoT
Accurate photometric CoRoT space observations of a secondary seismological
target, HD 174884, led to the discovery that this star is an astrophysically
important double-lined eclipsing spectroscopic binary in an eccentric orbit (e
of about 0.3), unusual for its short (3.65705d) orbital period. The high
eccentricity, coupled with the orientation of the binary orbit in space,
explains the very unusual observed light curve with strongly unequal primary
and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT 'seismo'
passband. Without the high accuracy of the CoRoT photometry, the secondary
eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up
program provided 45 high dispersion spectra. The analysis of the CoRoT light
curve was performed with an adapted version of PHOEBE that supports CoRoT
passbands. The final solution was obtained by simultaneous fitting of the light
and the radial velocity curves. Individual star spectra were derived by
spectrum disentangling. The uncertainties of the fit were derived by bootstrap
resampling and the solution uniqueness was tested by heuristic scanning. The
results provide a consistent picture of the system composed of two late B
stars. The Fourier analysis of the light curve fit residuals yields two
components, with orbital frequency multiples and an amplitude of about 0.1
mmag, which are tentatively interpreted as tidally induced pulsations. An
extensive comparison with theoretical models is carried out by means of the
Levenberg-Marquardt minimization technique and the discrepancy between models
and the derived parameters is discussed. The best fitting models yield a young
system age of 125 million years which is consistent with the eccentric orbit
and synchronous component rotation at periastron.Comment: 15 pages, 12 figures. Accepted for publication by A&
Seismic detection of acoustic sharp features in the CoRoT target HD49933
The technique of determining the acoustic location of layers of sharp changes
in the sound speed inside a star from the oscillatory signal in its frequencies
is applied on a solar-type star, the CoRoT target, HD49933. We are able to
determine the acoustic depth of the second helium ionisation zone of HD49933 to
be 794 +55/-68 seconds. The acoustic depth of the base of the convective zone
is found to be 1855 +173/-412 seconds where the large error bars reflect the
ambiguity in the result, which is difficult to determine with present precision
on the frequencies because of the intrinsically weak nature of the signal. The
positions of both these layers are consistent with those in a representative
stellar model of HD49933.Comment: Accepted for publication in Astronomy & Astrophysic
Probable nonradial g-mode pulsation in early A-type stars
A survey for line profile variability in early A-type stars has been
performed in order to detect nonradial pulsation signatures. The star HR 6139,
with spectral type A2V and estimated T_eff=8800 K, shows evident line profile
variations that can be explained by oscillations in prograde g-modes. This
feature and the known photometric variability are similar to those observed in
the Slowly Pulsating B-type stars. However HR 6139 is much cooler than the cool
border of the instability strip of such variables, and it is hotter than the
blue edge of the delta Scuti instability strip. There are indications of a tiny
variability also in other four objects, whose nature is not yet clear.Comment: 4 pages, 5 figures; accepted for publication in A&A (letter
Wastewater treatment using artificial wetlands
In the study described in this paper, pilot scale vertical
flow wetlands were evaluated as a potential wastewater
treatment system for agricultural wastewater exiting from
swine farm. The criteria used for evaluation were based on
water quality requirements for irrigation
- …