719 research outputs found
Re-growth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W
Previous studies have reported the existence of two counter-rotating stellar
disks in the early-type spiral galaxy NGC7217. We have obtained high-resolution
optical spectroscopic data (R ~ 9000) with the new fiber-based Integral Field
Unit instrument VIRUS-W at the 2.7m telescope of the McDonald Observatory in
Texas. Our analysis confirms the existence of two components. However, we find
them to be co-rotating. The first component is the more luminous (~ 77% of the
total light), has the higher velocity dispersion (~ 170 km/s) and rotates
relatively slowly (projected = 50 km/s). The lower luminosity second
component, (~ 23% of the total light), has a low velocity dispersion (~ 20
km/s) and rotates quickly (projected = 150 km/s). The difference in
the kinematics of the two stellar components allows us to perform a kinematic
decomposition and to measure the strengths of their Mg and Fe Lick indices
separately. The rotational velocities and dispersions of the less luminous and
faster component are very similar to those of the interstellar gas as measured
from the [OIII] emission. Morphological evidence of active star formation in
this component further suggests that NGC7217 may be in the process of
(re)growing a disk inside a more massive and higher dispersion stellar halo.
The kinematically cold and regular structure of the gas disk in combination
with the central almost dust-free morphology allows us to compare the dynamical
mass inside of the central 500pc with predictions from a stellar population
analysis. We find agreement between the two if a Kroupa stellar initial mass
function is assumed.Comment: accepted for publication by MNRA
J/\Psi production in two-photon collisions at next-to-leading order
In this paper, we report on the calculation of the cross section of J/\Psi
plus jet inclusive production in direct two-photon collisions at
next-to-leading order within the factorization formalism of nonrelativistic
quantum chromodynamics (NRQCD). Theoretical predictions for the future e^+e^-
linear collider TESLA are also presented.Comment: 5 pages, 2 figures, talk given at the 7th DESY Workshop on Elementary
Particle Theory: Loops and Legs in Quantum Field Theory, Zinnowitz, Germany,
25-30 April, 2004: added references for section
The O2, pH and Ca2+ Microenvironment of Benthic Foraminifera in a High CO2 World
Ocean acidification (OA) can have adverse effects on marine calcifiers. Yet, phototrophic marine calcifiers elevate their external oxygen and pH microenvironment in daylight, through the uptake of dissolved inorganic carbon (DIC) by photosynthesis. We studied to which extent pH elevation within their microenvironments in daylight can counteract ambient seawater pH reductions, i.e. OA conditions. We measured the O2 and pH microenvironment of four photosymbiotic and two symbiont-free benthic tropical foraminiferal species at three different OA treatments (∼432, 1141 and 2151 µatm pCO2). The O2 concentration difference between the seawater and the test surface (ΔO2) was taken as a measure for the photosynthetic rate. Our results showed that O2 and pH levels were significantly higher on photosymbiotic foraminiferal surfaces in light than in dark conditions, and than on surfaces of symbiont-free foraminifera. Rates of photosynthesis at saturated light conditions did not change significantly between OA treatments (except in individuals that exhibited symbiont loss, i.e. bleaching, at elevated pCO2). The pH at the cell surface decreased during incubations at elevated pCO2, also during light incubations. Photosynthesis increased the surface pH but this increase was insufficient to compensate for ambient seawater pH decreases. We thus conclude that photosynthesis does only partly protect symbiont bearing foraminifera against OA
Universality and the approach to the continuum limit in lattice gauge theory
The universality of the continuum limit and the applicability of renormalized
perturbation theory are tested in the SU(2) lattice gauge theory by computing
two different non-perturbatively defined running couplings over a large range
of energies. The lattice data (which were generated on the powerful APE
computers at Rome II and DESY) are extrapolated to the continuum limit by
simulating sequences of lattices with decreasing spacings. Our results confirm
the expected universality at all energies to a precision of a few percent. We
find, however, that perturbation theory must be used with care when matching
different renormalized couplings at high energies.Comment: 33 pages, 172 kB uu-tar-compressed ps-fil
A Precise Determination of the Running Coupling in the SU(3) Yang-Mills Theory
A non-perturbative finite-size scaling technique is used to study the
evolution of the running coupling (in a certain adapted scheme) in the SU(3)
Yang-Mills theory. At low energies contact is made with the fundamental
dynamical scales, such as the string tension K, while at larger energies the
coupling is shown to evolve according to perturbation theory. In that regime
the coupling in the MS-bar scheme of dimensional regularization is obtained
with an estimated total error of a few percent.Comment: pages 0-27, ps-file 255491 bytes, preprint DESY 93-114 (CERN-TH
6996/93
Non-perturbative O(a) improvement of lattice QCD
The coefficients multiplying the counterterms required for O() improvement
of the action and the isovector axial current in lattice QCD are computed
non-perturbatively, in the quenched approximation and for bare gauge couplings
in the range . A finite-size method based on the
Schr\"odinger functional is employed, which enables us to perform all
calculations at zero or nearly zero quark mass. As a by-product the critical
hopping parameter is obtained at all couplings considered.Comment: typo in eq. (7.3) corrected; 26 pages, postscript fil
The Zeta Herculis binary system revisited. Calibration and seismology
We have revisited the calibration of the visual binary system Zeta Herculis
with the goal to give the seismological properties of the G0 IV sub-giant Zeta
Her A. We have used the most recent physical and observational data. For the
age we have obtained 3387 Myr, for the masses respectively 1.45 and 0.98 solar
mass, for the initial helium mass fraction 0.243, for the initial mass ratio of
heavy elements to hydrogen 0.0269 and for the mixing-length parameters
respectively 0.92 and 0.90 using the Canuto & Mazitelli (1991, 1992) convection
theory. Our results do not exclude that Zeta Her A is itself a binary
sub-system; the mass of the hypothetical unseen companion would be smaller than
0.05 solar mass. The adiabatic oscillation spectrum of Zeta Her A is found to
be a complicated superposition of acoustic and gravity modes; some of them have
a dual character. This greatly complicates the classification of the non-radial
modes. The echelle diagram used by the observers to extract the frequencies
will work for ell=0, 2, 3. The large difference is found to be of the order of
42 mu Hz, in agreement with the Martic et al. (2001) seismic observations.Comment: 12 pages, A&A in pres
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