2,693 research outputs found
General non-rotating perfect-fluid solution with an abelian spacelike C_3 including only one isometry
The general solution for non-rotating perfect-fluid spacetimes admitting one
Killing vector and two conformal (non-isometric) Killing vectors spanning an
abelian three-dimensional conformal algebra (C_3) acting on spacelike
hypersurfaces is presented. It is of Petrov type D; some properties of the
family such as matter contents are given. This family turns out to be an
extension of a solution recently given in \cite{SeS} using completely different
methods. The family contains Friedman-Lema\^{\i}tre-Robertson-Walker particular
cases and could be useful as a test for the different FLRW perturbation
schemes. There are two very interesting limiting cases, one with a non-abelian
G_2 and another with an abelian G_2 acting non-orthogonally transitively on
spacelike surfaces and with the fluid velocity non-orthogonal to the group
orbits. No examples are known to the authors in these classes.Comment: Submitted to GRG, Latex fil
Competition Between Lolium Perenne L. and Anthoxanthum Odoratum L. at Two Levels of Phosphate and Potash
The spatial and age distribution of stellar populations in DDO 190
The spatial distribution of stellar populations, the star formation history,
and other properties of the dIrr galaxy DDO 190 have been analyzed using
color--magnitude diagrams (CMDs) of about 3900 resolved stars and the Ha fluxes
of HII regions. From the mean color index of the red giant branch, a mean
metallicity [Fe/H]=-2.0 is obtained. The I magnitude of the TRGB has been used
to estimate the distance. DDO 190 is 2.9+/-0.2 Mpc from the Milky Way, 2.1 Mpc
from the M 94 group (CnV-I), 2.4 Mpc from the M 81 group and 2.9 Mpc from the
barycenter of the Local Group, all indicating that it is an isolated, field
galaxy. The surface-brightness distribution of the galaxy is well fitted by
ellipses of ellipticity e=1-a/b=0.1 and P.A.=82deg. The radial star density
distribution follows an exponential law of scale length a=43."4, corresponding
to 611 pc. The Holmberg semi-major axis to mu_B=26.5 is estimated to be
r^B_(26.5)=3.'0. Stellar populations of different ages in DDO 190 show strong
spatial decoupling, the oldest population appearing much more extended than the
youngest. Stars younger than 0.1 Gyr occupy only the central 40'' (0.55 kpc);
stars younger than a few (~4) Gyr extend out to ~80'' (125 kpc), and for larger
galactocentric distances only older stars seem to be present. This behavior is
found in all the dIrr galaxies for which spatially extended studies have been
performed and could be related with the kinematical history of the galaxy.Comment: To be published in the AJ. 29 pages, 13 figure
A G1-like globular cluster in NGC 1023
The structure of a very bright (MV = -10.9) globular cluster in NGC 1023 is
analyzed on two sets of images taken with the Hubble Space Telescope. From
careful modeling of King profile fits to the cluster image, a core radius of
0.55+/-0.1 pc, effective radius 3.7+/-0.3 pc and a central V-band surface
brightness of 12.9+/-0.5 mag / square arcsec are derived. This makes the
cluster much more compact than Omega Cen, but very similar to the brightest
globular cluster in M31, G1 = Mayall II. The cluster in NGC 1023 appears to be
very highly flattened with an ellipticity of about 0.37, even higher than for
Omega Cen and G1, and similar to the most flattened clusters in the Large
Magellanic Cloud.Comment: 14 pages, 3 figures, 1 table. Accepted for AJ, Oct 200
M31 Transverse Velocity and Local Group Mass from Satellite Kinematics
We present several different statistical methods to determine the transverse
velocity vector of M31. The underlying assumptions are that the M31 satellites
on average follow the motion of M31 through space, and that the galaxies in the
outer parts of the Local Group on average follow the motion of the Local Group
barycenter through space. We apply the methods to the line-of-sight velocities
of 17 M31 satellites, to the proper motions of the 2 satellites M33 and IC 10,
and to the line-of-sight velocities of 5 galaxies near the Local Group turn
around radius, respectively. This yields 4 independent but mutually consistent
determinations of the heliocentric M31 transverse velocities in the West and
North directions, with weighted averages = -78+/-41 km/s and =
-38+/-34 km/s. The Galactocentric tangential velocity of M31 is 42 km/s, with
1-sigma confidence interval V_tan <= 56 km/s. The implied M31-Milky Way orbit
is bound if the total Local Group mass M exceeds 1.72^{+0.26}_{-0.25}x10^{12}
solar masses. If indeed bound, then the timing argument combined with the known
age of the Universe implies that M = 5.58^{+0.85}_{-0.72}x10^{12} solar masses.
This is on the high end of the allowed mass range suggested by cosmologically
motivated models for the individual structure and dynamics of M31 and the Milky
Way, respectively. It is therefore possible that the timing mass is an
overestimate of the true mass, especially if one takes into account recent
results from the Millennium Simulation that show that there is also a
theoretical uncertainty of 41 percent (Gaussian dispersion) in timing mass
estimates. The M31 transverse velocity implies that M33 is in a tightly bound
orbit around M31. This may have led to some tidal deformation of M33. It will
be worthwhile to search for observational evidence of this.Comment: ApJ in press, 14 pages, including 3 figures (has minor revisions with
respect to previously posted version to address referee comments
Fracture risk reduction with use of dipeptidyl peptidase-4 inhibitors:is there immortal time bias?
Compliance with international guidelines for chronic inflammatory neuropathies
ERare diseasesâ management guidelines are produced with the primary aim of improving practice and standards of care for patients and may represent a useful framework for clinical practice. The EFNS/PNS (European Federation of Neurological Societies/Peripheral Nerve Society) guidelines for CIDP (chronic inflammatory demyelinating polyneuropathy) and MMN (multifocal motor neuropathy) were last published in 2010 (1, 2). Enthusiasm of the audience for whom they are produced, arguably primarily nonâsubâspecialists, is however largely unexplored. Compliance to these guidelines by neuromuscular and/or peripheral nerve specialists has not been investigated
Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies: I. M33
Near-infrared images obtained with the Canada-France-Hawaii Telescope (CFHT)
Adaptive Optics Bonnette (AOB) are used to investigate the stellar content
within 18 arcsec of the center of the Local Group spiral galaxy M33. AGB stars
with near-infrared spectral-energy distributions similar to those of giants in
the solar neighborhood and Baade's Window are detected over most of the field.
The bolometric luminosity function (LF) of these stars has a discontinuity near
M_{bol} = -5.25, and comparisons with evolutionary tracks suggest that most of
the AGB stars formed in a burst of star formation 1 - 3 Gyr in the past. The
images are also used to investigate the integrated near-infrared photometric
properties of the nucleus and the central light concentration. The nucleus is
bluer than the central light concentration, in agreement with previous studies
at visible wavelengths. The CO index of the central light concentration 0.5
arcsec from the galaxy center is 0.05, which corresponds to [Fe/H] = -1.2 for
simple stellar systems. Hence, the central light concentration could not have
formed from the chemically-enriched material that dominates the present-day
inner disk of M33.Comment: 23 pages of text + 11 figures; to appear in A
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