615 research outputs found
Graduate Program in Astrophysics in Split
Beginning in autumn 2008 the first generation of astronomy master students
will start a 2 year course in Astrophysics offered by the Physics department of
the University of Split, Croatia
(http://fizika.pmfst.hr/astro/english/index.html). This unique master course in
South-Eastern Europe, following the Bologna convention and given by astronomers
from international institutions, offers a series of comprehensive lectures
designed to greatly enhance students' knowledge and skills in astrophysics, and
prepare them for a scientific career. An equally important aim of the course is
to recognise the areas in which astronomy and astrophysics can serve as a
national asset and to use them to prepare young people for real life
challenges, enabling graduates to enter the modern society as a skilled and
attractive work-force. In this contribution, I present an example of a
successful organisation of international astrophysics studies in a developing
country, which aims to become a leading graduate program in astrophysics in the
broader region. I will focus on the benefits of the project showing why and in
what way astronomy can be interesting for third world countries, what are the
benefits for the individual students, nation and region, but also research,
science and the astronomical community in general.Comment: proceedings of IAU SpS5, Astronomy for the Developing world, eds. J.
Hearnshaw & P. Martine
Kinemetry: a generalisation of photometry to the higher moments of the line-of-sight velocity distribution
We present a generalisation of surface photometry to the higher-order moments
of the line-of-sight velocity distribution of galaxies observed with
integral-field spectrographs. The generalisation follows the approach of
surface photometry by determining the best fitting ellipses along which the
profiles of the moments can be extracted and analysed by means of harmonic
expansion. The assumption for the odd moments (e.g. mean velocity) is that the
profile along an ellipse satisfies a simple cosine law. The assumption for the
even moments (e.g velocity dispersion) is that the profile is constant, as it
is used in surface photometry. We find that velocity profiles extracted along
ellipses of early-type galaxies are well represented by the simple cosine law
(with 2% accuracy), while possible deviations are carried in the fifth harmonic
term which is sensitive to the existence of multiple kinematic components, and
has some analogy to the shape parameter of photometry. We compare the
properties of the kinematic and photometric ellipses and find that they are
often very similar. Finally, we offer a characterisation of the main velocity
structures based only on the kinemetric parameters which can be used to
quantify the features in velocity maps (abridged).Comment: 17 pages, 11 figures. MNRAS in press. High resolution version of the
paper is available at
http://www.strw.leidenuniv.nl/sauron/papers/krajnovic2005_kinemetry.pdf and
software implementation of the method is freely available at
http://www-astro.physics.ox.ac.uk/~dxk/idl
Large Eddy Simulation Exploration of Passive Flow Control Around an Ahmed Body
Large eddy simulations (LES) are used to study passive flow control for drag reduction in a simplified ground vehicle. Add-on devices in the form of short cylinders are used for the formation of streaks in the streamwise direction that lead to the separation delay. The results of the present numerical simulations are compared with the experimental data and show good agreement. The two-stage flow control mechanism is analyzed from the LES results. It was found to be in agreement with the previous experimental observations that the counter-rotating vortices behind the impinging devices influence the separation only indirectly through the longitudinal vortices further downstream
Measuring the low mass end of the Mbh - sigma relation
We show that high quality laser guide star (LGS) adaptive optics (AO)
observations of nearby early-type galaxies are possible when the tip-tilt
correction is done by guiding on nuclei while the focus compensation due to the
changing distance to the sodium layer is made 'open loop'. We achieve
corrections such that 40% of flux comes from R<0.2 arcsec. To measure a black
hole mass (Mbh) one needs integral field observations of both high spatial
resolution and large field of view. With these data it is possible to determine
the lower limit to Mbh even if the spatial resolution of the observations are
up to a few times larger than the sphere of influence of the black hole.Comment: 4 pages, 2 figures, LaTeX. To appear in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista and C.C. Popescu, AIP Conf. Ser., in pres
The flow around a simplified tractor-trailer model studied by large eddy simulation
Large-eddy simulation (LES) is used to study the flow around a simplified tractor-trailer model. The model consists of two boxes placed in tandem. The front box represents the cab of a tractor-trailer road vehicle and the rear box represents the trailer. The LES was made at the Reynolds number of 0.51Ă—106 based on the height of the rear box and the inlet air velocity. Two variants of the model were studied, one where the leading edges on the front box are sharp and one where the edges are rounded. One small and one large gap width between the two boxes were studied for both variants. Two computational grids were used in the LES simulations and a comparison was made with available experimental force measurements. The results of the LES simulations were used to analyze the flow field around the cab and in the gap between the two boxes of the tractor-trailer model. Large vortical structures around the front box and in the gap were identified. The flow field analysis showed how these large vortical structures are responsible for the difference in the drag force for the model that arises when the leading edges on the front box are rounded and the gap width is varied
Simulations of flow around a simplified train model with a drag reducing device
Partially Averaged Navier Stokes is used to
simulate the flow around a simple train model.
The train model has previously been studied in
wind tunnel experiments and has a length to
height/width ratio of 7:1. The Reynolds number
based on the height of the train model is 0.37 x 10^6.
For this Reynolds number, the flow separates from
the curved leading edges on the front then attaches
again on the roof and sides forming a boundary
layer there before separating in the wake. The first
case is of the natural flow around the train model
where direct comparison to experimental data of drag
coefficient and pressure coefficient are made. In the
second case an open cavity is placed on the base
of the train model with the aim of reducing the
overall drag on the model. The results show that the
drag for model with the cavity is reduced by some
10% compared to the drag of the natural case. The
agreement to experimental data for the natural case
is not perfect but the general features in the flow field
are simulated correctly
A way to deal with the fringe-like pattern in VIMOS-IFU data
The use of integral field units is now commonplace at all major observatories
offering efficient means of obtaining spectral as well as imaging information
at the same time. IFU instrument designs are complex and spectral images have
typically highly condensed formats, therefore presenting challenges for the IFU
data reduction pipelines. In the case of the VLT VIMOS-IFU, a fringe-like
pattern affecting the spectra well into the optical and blue wavelength regime
as well as artificial intensity variations, require additional reduction steps
beyond standard pipeline processing. In this research note we propose an
empirical method for the removal of the fringe-like pattern in the spectral
domain and the intensity variations in the imaging domain. We also demonstrate
the potential consequences for data analysis if the effects are not corrected.
Here we use the example of deriving stellar velocity, velocity dispersion and
absorption line-strength maps for early-type galaxies. We derive for each
spectrum, reduced by the ESO standard VIMOS pipeline, a correction-spectrum by
using the median of the eight surrounding spectra as a proxy for the
unaffected, underlying spectrum. This method relies on the fact that our
science targets (nearby ETGs) cover the complete FoV of the VIMOS-IFU with
slowly varying spectral properties and that the exact shape of the fringe-like
pattern is nearly independent and highly variable between neighboring spatial
positions. We find that the proposed correction methods for the removal of the
fringe-like pattern and the intensity variations in VIMOS-IFU data-cubes are
suitable to allow for meaningful data analysis in our sample of nearby
early-type galaxies. Since the method relies on the scientific target
properties it is not suitable for general implementation in the pipeline
software for VIMOS.Comment: 7 pages, 10 figures, accepted for publication in A&A, new version
after comments from language edito
- …