3,363 research outputs found
Counter-Rotation in Disk Galaxies
Counter-rotating galaxies host two components rotating in opposite directions
with respect to each other. The kinematic and morphological properties of
lenticulars and spirals hosting counter-rotating components are reviewed.
Statistics of the counter-rotating galaxies and analysis of their stellar
populations provide constraints on the formation scenarios which include both
environmental and internal processes.Comment: 10 pages, 2 figures. To appear in ASP Conf. Ser., Multi-Spin
Galaxies, E. Iodice and E. M. Corsini (eds.
Bulge properties and dark matter content of early-type barred galaxies
The dynamics of a barred galaxy depends on the pattern speed of its bar. The
only direct method for measuring the pattern speed of a bar is the
Tremaine-Weinberg technique. This method is best suited to the analysis of the
distribution and dynamics of the stellar component. Therefore it has been
mostly used for early-type barred galaxies. Most of them host a classical
bulge. On the other hand, a variety of indirect methods, which are based on the
analysis of the distribution and dynamics of the gaseous component, has been
used to measure the bar pattern speed in late-type barred galaxies. Nearly all
the measured bars are as rapidly rotating as they can be. By comparing this
result with high-resolution numerical simulations of bars in dark matter halos,
it is possible to conclude that these bars reside in maximal disks.Comment: 4 pages. To appear in the proceedings of IAU Symposium 245 "Formation
and Evolution of Galaxy Bulges", M. Bureau, E. Athanassoula, and B. Barbuy,
ed
Direct measurements of bar pattern speeds
The dynamics of a barred galaxy depends on the angular velocity or pattern
speed of its bar. Indeed, it is related to the location of corotation where
gravitational and centrifugal forces cancel out in the rest frame of the bar.
The only direct method for measuring the bar pattern speed is the
Tremaine-Weinberg technique. This method is best suited to the analysis of the
distribution and kinematics of the stellar component in absence of significant
star formation and patchy dust obscuration. Therefore, it has been mostly used
for early-type barred galaxies. The main sources of uncertainties on the
directly-measured bar pattern speeds are discussed. There are attempts to
overcome the selection bias of the current sample of direct measurements by
extending the application of the Tremaine-Weinberg method to the gaseous
component. Furthermore, there is a variety of indirect methods which are based
on the analysis of the gas distribution and kinematics. They have been largely
used to measure the bar pattern speed in late-type barred galaxies. Nearly all
the bars measured with direct and indirect methods end close to their
corotation radius, i.e., they are as rapidly rotating as they can be.Comment: 8 pages, 1 figure. To appear in "Tumbling, twisting, and winding
galaxies: Pattern speeds along the Hubble sequence", E. M. Corsini and V. P.
Debattista (eds.), Memorie della Societa` Astronomica Italian
The dark matter content of early-type barred galaxies
The dynamics of a barred galaxy depends on the pattern speed of its bar. The
only direct method for measuring the pattern speed of a bar is the
Tremaine-Weinberg technique. This method relies on the analysis of the
distribution and dynamics of the stellar component. It is best suited to
gas-poor galaxies and therefore it has been restricted to early-type barred
galaxies. On the other hand, a variety of indirect methods, which are based on
the analysis of the distribution and dynamics of the gaseous component, has
been used to measure the bar pattern speed in late-type barred galaxies. The
complete sample of galaxies for which the bar pattern speed has been directly
measured with the Tremaine-Weinberg method is given. Nearly all the measured
bars are as rapidly rotating as they can be. By comparing this result with
recent high-resolution N-body simulations of bars in cosmologically-motivated
dark matter halos, it is possible to conclude that these bars are not located
inside centrally-concentrated halos.Comment: 5 pages. Proceedings of "Baryons in Dark Matter Halos". Novigrad,
Croatia, 5-9 Oct 2004. Editors: R. Dettmar, U. Klein, P. Salucci. Published
by SISS
Numerical study on active and passive trailing edge morphing applied to a multi-MW wind turbine section
A progressive increasing in turbine dimension has characterized the technological development in offshore wind energy utilization. This aspect reflects on the growing in blade length and weight. For very large turbines, the standard control systems may not be optimal to give the best performance and the best vibratory load damping, keeping the condition of maximum energy production. For this reason, some new solutions have been proposed in research. One of these is the possibility of morphs the blade surface in an active way (increasing the performance in low wind region) or passive (load reduction) way.
In this work, we present a numerical study on the active and passive trailing edge morphing, applied to large wind turbines. In particular, the study focuses on the aerodynamic response of a midspan blade section, in terms of fluid structure interaction (FSI) and driven surface deformation.
We test the active system in a simple start-up procedure and the passive system in a power production with turbulent wind conditions, that is, two situations in which we expect these systems could improve the performance.
All the computations are carried out with a FSI code, which couples a 2D-CFD solver, a moving mesh solver (both implemented in OpenFOAM library) and a FEM solver.
We evaluate all the boundary conditions to apply in the section problem by simulating the 5MW NREL wind turbine with the NREL CAE-tools developed for wind turbine simulation
Properties of bars in the local universe
We studied the fraction and properties of bars in a sample of about 3000
galaxies extracted from SDSS-DR5. This represents a volume limited sample with
galaxies located between redshift 0.01-20, and
inclination i < 60. Interacting galaxies were excluded from the sample. The
fraction of barred galaxies in our sample is 45%. We found that 32% of S0s, 55%
of early-type spirals, and 52% of late-type spirals are barred galaxies. The
bars in S0s galaxies are weaker than those in later-type galaxies. The bar
length and galaxy size are correlated, being larger bars located in larger
galaxies. Neither the bar strength nor bar length correlate with the local
galaxy density. On the contrary, the bar properties correlate with the
properties of their host galaxies. Galaxies with higher central light
concentration host less and weaker bars.Comment: 2 pages, 1 figure to appear in the proceedings of "Formation and
Evolution of Galaxy Disks", Rome, October 2007, Eds. J. Funes and E. M.
Corsin
The V_c-sigma_c relation in high and low surface brightness galaxies
We investigate the relation between the asymptotic circular velocity, V_c,
and the central stellar velocity dispersion, sigma_c, in galaxies. We consider
a new sample of high surface brightness spiral galaxies (HSB), low surface
brightness spiral galaxies (LSB), and elliptical galaxies with HI-based V_c
measurements. We find that: 1) elliptical galaxies with HI measurements fit
well within the relation; 2) a linear law can reproduce the data as well as a
power law (used in previous works) even for galaxies with sigma_c < 70 km/s; 3)
LSB galaxies, considered for the first time with this respect, seem to behave
differently, showing either larger V_c values or smaller sigma_c values.Comment: 2 pages, 2 figures, to appear in Proc. IAU Symp. 222, "The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei" eds. Th. Storchi
Bergmann, L.C. Ho & H.R. Schmitt (Cambridge University Press
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