10,694 research outputs found
Pairing correlations beyond the mean field
We discuss dynamical pairing correlations in the context of configuration
mixing of projected self-consistent mean-field states, and the origin of a
divergence that might appear when such calculations are done using an energy
functional in the spirit of a naive generalized density functional theory.Comment: Proceedings of the XIII Nuclear Physics Workshop ``Maria and Pierre
Curie'' on ``Pairing and beyond - 50 years of the BCS model'', held at
Kazimierz Dolny, Poland, September 27 - October 1, 2006. Int. J. Mod. Phys.
E, in prin
The Isophotal Structure of Early-Type Galaxies in the SDSS: Dependence on AGN Activity and Environment
We study the dependence of the isophotal shape of early-type galaxies on
their absolute B-band magnitude, their dynamical mass, and their nuclear
activity and environment, using an unprecedented large sample of 847 early-type
galaxies identified in the SDSS by Hao et al (2006). We find that the fraction
of disky galaxies smoothly decreases with increasing luminosity. The large
sample allows us to describe these trends accurately with tight linear
relations that are statistically robust against the uncertainty in the
isophotal shape measurements. There is also a host of significant correlations
between the disky fraction and indicators of nuclear activity (both in the
optical and in the radio) and environment (soft X-rays, group mass, group
hierarchy). Our analysis shows however that these correlations can be
accurately matched by assuming that the disky fraction depends only on galaxy
luminosity or mass. We therefore conclude that neither the level of activity,
nor group mass or group hierarchy help in better predicting the isophotal shape
of early-type galaxies.Comment: 31 pages, 10 figures, accepted for publication in Ap
Microlensing events from the 11-year observations of the Wendelstein Calar Alto Pixellensing Project
We present the results of the decade-long M31 observation from the
Wendelstein Calar Alto Pixellensing Project (WeCAPP). WeCAPP has monitored M31
from 1997 till 2008 in both R- and I-filters, thus provides the longest
baseline of all M31 microlensing surveys. The data are analyzed with the
difference imaging analysis, which is most suitable to study variability in
crowded stellar fields. We extracted light curves based on each pixel, and
devised selection criteria that are optimized to identify microlensing events.
This leads to 10 new events, and sums up to a total of 12 microlensing events
from WeCAPP, for which we derive their timescales, flux excesses, and colors
from their light curves. The color of the lensed stars fall between (R-I) =
0.56 to 1.36, with a median of 1.0 mag, in agreement with our expectation that
the sources are most likely bright, red stars at post main-sequence stage. The
event FWHM timescales range from 0.5 to 14 days, with a median of 3 days, in
good agreement with predictions based on the model of Riffeser et al. (2006).Comment: 44 pages, 16 figures, 5 tables. ApJ accepte
The Stellar Kinematic Fields of NGC 3379
We have measured the stellar kinematic profiles of NGC 3379 along four
position angles using the MMT. The data extend 90" from the center, at
essentially seeing-limited resolution out to 17". The mean velocities and
dispersions have total errors better than 10 km/s (frequently better than 5
km/s) out to 55". We find very weak (3 km/s) rotation on the minor axis
interior to 12", and no detectable rotation above 6 km/s from 12" to 50" or
above 16 km/s out to 90" (95% confidence). However, a Fourier reconstruction of
the mean velocity field from all 4 sampled PAs does indicate a 5 degree twist
of the kinematic major axis, opposite to the known isophotal twist. The h_3 and
h_4 parameters are small over the entire observed region. The
azimuthally-averaged dispersion profile joins smoothly at large radii with the
dispersions of planetary nebulae. Unexpectedly, we find sharp bends in the
major-axis rotation curve, also visible (though less pronounced) on the
diagonal position angles. The outermost bend coincides in position with other
sharp kinematic features: an abrupt flattening of the dispersion profile, and
local peaks in h_3 and h_4. All of these features are in a region where the
surface brightness profile departs significantly from a de Vaucouleurs law.
Features such as these are not generally known in ellipticals owing to a lack
of data at comparable resolution; however, very similar behavior is seen the
kinematics of the edge-on S0 NGC 3115. We discuss the suggestion that NGC 3379
could be a misclassified S0; preliminary results from dynamical modeling
indicate that it may be a flattened, weakly triaxial system seen in an
orientation that makes it appear round.Comment: 31 pages incl. 4 tables, Latex, AASTeX v4.0, with 17 eps figures. To
appear in The Astronomical Journal, February 199
The stellar populations of the central region of M31
We continue the analysis of the dataset of our spectroscopic observation
campaign of M31, by deriving simple stellar population properties (age
metallicity and alpha-elements overabundance) from the measurement of Lick/IDS
absorption line indices. We describe their two-dimensional maps taking into
account the dust distribution in M31. 80\% of the values of our age
measurements are larger than 10 Gyr. The central 100 arcsec of M31 are
dominated by the stars of the classical bulge of M31. They are old (11-13 Gyr),
metal-rich (as high as [Z/H]~0.35 dex) at the center with a negative gradient
outwards and enhanced in alpha-elements ([alpha/Fe]~ 0.28+- 0.01 dex). The bar
stands out in the metallicity map, where an almost solar value of [Z/H]
(~0.02+-0.01 dex) with no gradient is observed along the bar position angle
(55.7 deg) out to 600 arcsec from the center. In contrast, no signature of the
bar is seen in the age and [alpha/Fe] maps, that are approximately
axisymmetric, delivering a mean age and overabundance for the bar and the
boxy-peanut bulge of 10-13 Gyr and 0.25-0.27 dex, respectively. The
boxy/peanut-bulge has almost solar metallicity (-0.04+- 0.01 dex). The
mass-to-light ratio of the three components is approximately constant at M/LV ~
4.4-4.7 Msol/Lsol. The disk component at larger distances is made of a mixture
of stars, as young as 3-4 Gyr, with solar metallicity and smaller M/LV (~3+-0.1
Msol/Lsol). We propose a two-phase formation scenario for the inner region of
M31, where most of the stars of the classical bulge come into place together
with a proto-disk, where a bar develops and quickly transforms it into a
boxy-peanut bulge. Star formation continues in the bulge region, producing
stars younger than 10 Gyr, in particular along the bar, enhancing its
metallicity. The disk component appears to build up on longer time-scales.Comment: Language-edited version, Accepted for publication in A&
Vector Casimir effect for a D-dimensional sphere
The Casimir energy or stress due to modes in a D-dimensional volume subject
to TM (mixed) boundary conditions on a bounding spherical surface is
calculated. Both interior and exterior modes are included. Together with
earlier results found for scalar modes (TE modes), this gives the Casimir
effect for fluctuating ``electromagnetic'' (vector) fields inside and outside a
spherical shell. Known results for three dimensions, first found by Boyer, are
reproduced. Qualitatively, the results for TM modes are similar to those for
scalar modes: Poles occur in the stress at positive even dimensions, and cusps
(logarithmic singularities) occur for integer dimensions . Particular
attention is given the interesting case of D=2.Comment: 20 pages, 1 figure, REVTe
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: II. Rotating Versus Non-Rotating Dwarfs
We present spatially-resolved internal kinematics and stellar chemical
abundances for a sample of dwarf elliptical (dE) galaxies in the Virgo Cluster
observed with Keck/ESI. We find that 4 out of 17 dEs have major axis rotation
velocities consistent with rotational flattening, while the remaining dEs have
no detectable major axis rotation. Despite this difference in internal
kinematics, rotating and non-rotating dEs are remarkably similar in terms of
their position in the Fundamental Plane, morphological structure, stellar
populations, and local environment. We present evidence for faint underlying
disks and/or weak substructure in a fraction of both rotating and non-rotating
dEs, but a comparable number of counter-examples exist for both types which
show no evidence of such structure. Absorption-line strengths were determined
based on the Lick/IDS system (Hbeta, Mgb, Fe5270, Fe5335) for the central
region of each galaxy. We find no difference in the line-strength indices, and
hence stellar populations, between rotating and non-rotating dE galaxies. The
best-fitting mean age and metallicity for our 17 dE sample are 5 Gyr and Fe/H =
-0.3 dex, respectively, with rms spreads of 3 Gyr and 0.1 dex. The majority of
dEs are consistent with solar alpha/Fe abundance ratios. By contrast, the
stellar populations of classical elliptical galaxies are, on average, older,
more metal rich, and alpha-enhanced relative to our dE sample. The local
environments of both dEs types appear to be diverse in terms of their proximity
to larger galaxies in real or velocity space within the Virgo Cluster. Thus,
rotating and non-rotating dEs are remarkably similar in terms of their
structure, stellar content, and local environments, presenting a significant
challenge to theoretical models of their formation. (abridged)Comment: 33 pages, 12 figures. To appear in the October 2003 Astronomical
Journal. See http://www.ucolick.org/~mgeha/geha_dE.ps.gz for version with
high resolution figure
Modular space station phase B extension preliminary system design. Volume 2: Operations and crew analyses
All analyses and tradeoffs conducted to establish the MSS operations and crew activities are discussed. The missions and subsystem integrated analyses that were completed to assure compatibility of program elements and consistency with program objectives are presented
Advanced analog television study final report, 4 nov. - 19 dec. 1963
Information bandwidth reduction for analog television signals - Description of multiple interlace syste
Microscopic study of 240Pu, mean-field and beyond
The influence of exact angular-momentum projection and configuration mixing
on properties of a heavy, well-deformed nucleus is discussed for the example of
Pu240. Starting from a self-consistent model using Skyrme interactions, we
analyze the resulting modifications of the deformation energy, the fission
barrier height, the excitation energy of the superdeformed minimum associated
with the fission isomer, the structure of the lowest rotational bands with
normal deformation and superdeformation, and the corresponding quadrupole
moments and transition moments. We present results obtained with the Skyrme
interactions SLy4 and SLy6, which have slightly different surface tensions.Comment: 7 pages REVTEX4, 4 figures. accepted for publication in Phys. Rev.
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