1,023 research outputs found
La balance des paiements en 2005.
Le solde des transactions courantes sâest fortement dĂ©gradĂ© pour atteindre â 1,6 % du PIB. Les investissements directs ont enregistrĂ© un rebond significatif.Balance des paiements, transactions courantes, solde commercial, investissements directs, investissements de portefeuille, fusions et acquisitions.
The Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations
We analyze single-stellar-population (SSP) equivalent parameters for 50 local
elliptical galaxies as a function of their structural parameters. These
galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H],
log t, log , and [E/Fe]. SSP age and velocity dispersion can be taken
as the two independent parameters that specify a galaxy's location in this
``hyperplane.'' The hyperplane can be decomposed into two sub-relations: (1) a
``Z-plane,'' in which [Z/H] is a linear function of log and log t; and
(2) a relation between [E/Fe] and in which [E/Fe] is larger in
high- galaxies. Cluster and field ellipticals follow the same
hyperplane, but their (,t) distributions within it differ. Nearly all
cluster galaxies are old; the field ellipticals span a large range in SSP age.
The tight Mg-- relations of these ellipticals can be understood as
two-dimensional projections of the metallicity hyperplane showing it edge-on;
the tightness of these relations does not necessarily imply a narrow range of
ages at fixed . The relation between [E/Fe] and is consistent
with a higher effective yield of Type II SNe elements at higher . The
Z-plane is harder to explain and may be a powerful clue to star formation in
elliptical galaxies if it proves to be general. Present data favor a
``frosting'' model in which low apparent SSP ages are produced by adding a
small frosting of younger stars to an older base population. If the frosting
abundances are close to or slightly greater than the base population, simple
two-component models run along lines of constant in the Z-plane, as
required. This favors star formation from well-mixed pre-enriched gas rather
than unmixed low-metallicity gas from an accreted object. (Abridged)Comment: To be published in the June 2000 issue of the Astronomical Journal.
28 pages, 13 figures, uses emulateap
How Dry Are Red Mergers?
The focus of current research in galaxy evolution has increasingly turned to
understanding the effect that mergers have on the evolution of systems on the
red sequence. For those interactions purported to occur dissipationlessly (so
called "dry mergers"), it would appear that the role of gas is minimal.
However, if these mergers are not completely dry, then even low levels of gas
may be detectable. The purpose of our study is to test whether early type
galaxies with HI in or around them, or "wet" ellipticals, would have been
selected as dry mergers by the criteria in van Dokkum (2005, AJ, 130, 2647). To
that end, we examine a sample of 20 early types from the HI Rogues Gallery with
neutral hydrogen in their immediate environs. Of these, the 15 brightest and
reddest galaxies match the optical dry merger criteria, but in each case, the
presence of HI means that they are not truly dry.Comment: 8 pages plus 1 table and 5 figures; accepted for publication in A
The Surface Brightness Fluctuations and Globular Cluster Populations of M87 and its Companions
Using the surface brightness fluctuations in HST WFPC-2 images, we determine
that M87, NGC 4486B, and NGC 4478 are all at a distance of ~16 Mpc, while NGC
4476 lies in the background at ~21 Mpc. We also examine the globular clusters
of M87 using archived HST fields. We detect the bimodal color distribution, and
find that the amplitude of the red peak relative to the blue peak is greatest
near the center. This feature is in good agreement with the merger model of
elliptical galaxy formation, where some of the clusters originated in
progenitor galaxies while other formed during mergers.Comment: 5 pages, 2 figure
Morphological classification and structural parameters for early-type galaxies in the Coma cluster
We present the results of an isophotal shape analysis of three samples of
galaxies in the Coma cluster. Quantitative morphology, together with structural
and photometric parameters, is given for each galaxy. Special emphasis has been
placed on the detailed classification of early-type galaxies.
The three samples are: i) a sample of 97 early-type galaxies brighter than
m = 17.00 falling within one degree from the center of the Coma cluster;
these galaxies were observed with CCD cameras, mostly in good to excellent
resolution conditions; ii) a magnitude complete sample of 107 galaxies of all
morphological types down to m = 17.00 falling in a circular region of 50
arcmin diameter, slightly offcentered to the North-West of the cluster center;
the images for this and the next sample come from digitized photographic
plates; iii) a complete comparison sample of 26 galaxies of all morphological
types down to m = 16.05 (or m 17.5), also in a region of 50
arcmin diameter, but centered 2.6 degrees West of the cluster center.
The reliability of our morphological classifications and structural
parameters of galaxies, down to the adopted magnitude limits, is assessed by
comparing the results on those galaxies for which we had images taken with
different instrumentation and/or seeing conditions, and by comparing our
results with similar data from other observers.Comment: 22 pages, including 4 figures and 4 tables, uuencoded, gzipped
postscrip
The Age Difference between the Globular Cluster Sub-populations in NGC 4472
The age difference between the two main globular cluster sub-populations in
the Virgo giant elliptical galaxy, NGC 4472 (M 49), has been determined using
HST WFPC2 images in the F555W and F814W filters. Accurate photometry has been
obtained for several hundred globular clusters in each of the two main
sub-populations, down to more than one magnitude below the turn-over of their
luminosity functions. This allows precise determinations of both the mean
colors and the turn-over magnitudes of the two main sub-populations. By
comparing the data with various population synthesis models, the
age-metallicity pairs that fit both the observed colors and magnitudes have
been identified. The metal-poor and the metal-rich globular clusters are found
to be coeval within the errors ( Gyr). If one accepts the validity of
our assumptions, these errors are dominated by model uncertainties. A
systematic error of up to 4 Gyr could affect this result if the blue and the
red clusters have significantly different mass distributions. However, that one
sub-population is half as old as the other is excluded at the 99% confidence
level. The different globular cluster populations are assumed to trace the
galaxy's major star-formation episodes. Consequently, the vast majority of
globular clusters, and by implication the majority of stars, in NGC 4472 formed
at high redshifts but by two distinct mechanisms or in two episodes.Comment: 32 pages, including 12 postscript figures, accepted for publication
in the Astronomical Journal, December 1999 issu
PBxplore: a tool to analyze local protein structure and deformability with Protein Blocks
This paper describes the development and application of a suite of tools, called PBxplore, to analyze the dynamics and deformability of protein structures using Protein Blocks (PBs). Proteins are highly dynamic macromolecules, and a classical way to analyze their inherent flexibility is to perform molecular dynamics simulations. The advantage of using small structural prototypes such as PBs is to give a good approximation of the local structure of the protein backbone. More importantly, by reducing the conformational complexity of protein structures, PBs allow analysis of local protein deformability which cannot be done with other methods and had been used efficiently in different applications. PBxplore is able to process large amounts of data such as those produced by molecular dynamics simulations. It produces frequencies, entropy and information logo outputs as text and graphics. PBxplore is available at https://github.com/pierrepo/PBxplore and is released under the open-source MIT license
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