2,096 research outputs found
A new measurement of the baryonic fraction using the sparse NGC 3258 group of galaxies
New X-ray observations of the sparse NGC 3258 group of galaxies made by the
ASCA satellite with good spectral and spatial resolution has revealed that this
group has a gravitational potential deep enough to prohibit significant mass
removal from the system. The baryonic fraction within 240 kpc is found to be
0.065 +0.051/-0.020 for h_{50}=1, where h_{50}=H_0/50 km/s/Mpc, in good
agreement with the universal value of 0.05 +/-0.01 predicted by standard Big
Bang nucleosynthesis for a Universe with Omega_0=1 and h_{50}=1. Since the deep
potential of the NGC 3258 group ensures that all pristine intragroup gas has
been retained, the baryonic fraction of the NGC 3258 group is indicative of the
universal value. Consequently it seems premature to rule out a critical
Universe.Comment: 19 pages Latex, using aasms4.sty, paper also available at
http://www.dsri.dk/~kristian To appear in Astrophysical Journal Letter
The Interpretation of Near-Infrared Star Counts at the South Galactic Pole
We present new deep counts of stars at the South Galactic Pole (SGP)
taken with the NAOJ PICNIC camera to . Star-galaxy separation to
was accomplished effectively using image profiles because the pixel
size we used is 0.509 arcsec. We interpret these counts using the SKY (Cohen
1994) model of the Galactic point source sky and determine the relative
normalization of halo-to-disk populations, and the location of the Sun relative
to the Galactic plane, within the context of this model. The observed star
counts constrain these parameters to be: halo/disk 1/900 and
z=16.52.5 pc. These values have been used to correct our SGP
galaxy counts for contamination by the point source Galactic foreground.Comment: accepted for publication in AJ, 15 pages with 2 figure
Variation of Inner Radius of Dust Torus in NGC4151
The long-term optical and near infrared monitoring observations for a type 1
act ive galactic nucleus NGC 4151 were carried out for six years from 2001 to
2006 b y using the MAGNUM telescope, and delayed response of flux variations in
the band to those in the band was clearly
detected. Based on cross correlation analysis, we precisely measured a lag time
for eight separate periods, and we found that is not
constant changing be tween 30 and 70 days during the monitoring period. Since
is the ligh t travel time from the central energy source out to the
surrounding dust torus, this is the first convincing evidence that the inner
radius of dust torus did ch ange in an individual AGN. In order to relate such
a change of with a change of AGN luminosity , we presented a
method of taking an average of th e observed -band fluxes that corresponds
to the measured value of , and we found that the time-changing track
of NGC 4151 in the versus diagram during the monitoring period
deviates from the relation of expected from dust
reverberation. This result, combined with t he elapsed time from period to
period for which was measured, indicat es that the timescale of dust
formation is about one year, which should be taken into account as a new
constraint in future studies of dust evolution in AGNs.Comment: 5 pages, 3 figures, To appear in the ApJ Lette
Spin-Glass-like Transition and Hall Resistivity of Y2-xBixIr2O7
Various physical properties of the pyrochlore oxide Y2-xBixIr2O7 have been
studied. The magnetizations M measured under the conditions of the
zero-field-cooling(ZFC) and the field-cooling(FC) have different values below
the temperature T=TG. The anomalous T-dependence of the electrical
resistivities r and the thermoelectric powers S observed at around TG indicates
that the behavior of the magnetization is due to the transition to the state
with the spin freezing. In this spin-frozen state, the Hall resistivities rH
measured with the ZFC and FC conditions are found to have different values,
too, in the low temperature phase (T<TG). Possible mechanisms which induce such
the hysteretic behavior are discussed.Comment: 9 pages, 7 figures, J. Phys. Soc. Jpn. 72 (2003) No.
Kinematics of Metal-Poor Stars in the Galaxy. II. Proper Motions for a Large Non-Kinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected without
kinematic bias, and with available radial velocities, distance estimates, and
metal abundances in the range 0.0 <= [Fe/H] <= -4.0. This update of the Beers
and Sommer-Larsen (1995) catalog includes newly-derived homogeneous photometric
distance estimates, revised radial velocities for a number of stars with
recently obtained high-resolution spectra, and refined metallicities for stars
originally identified in the HK objective-prism survey (which account for
nearly half of the catalog) based on a recent re-calibration. A subset of 1258
stars in this catalog have available proper motions, based on measurements
obtained with the Hipparcos astrometry satellite, or taken from the updated
Astrographic Catalogue (AC 2000; second epoch positions from either the Hubble
Space Telescope Guide Star Catalog or the Tycho Catalogue), the Yale/San Juan
Southern Proper Motion (SPM) Catalog 2.0, and the Lick Northern Proper Motion
(NPM1) Catalog. Our present catalog includes 388 RR Lyrae variables (182 of
which are newly added), 38 variables of other types, and 1680 non-variables,
with distances in the range 0.1 to 40 kpc.Comment: 31 pages, including 8 figures, to appear in AJ (June 2000), full
paper with all figures embedded available at
http://pluto.mtk.nao.ac.jp/people/chiba/preprint/halo4
Equilibrium Properties of Mouse-Torpedo Acetylcholine Receptor Hybrids Expressed in Xenopus Oocytes
This study used messenger RNA encoding each subunit (α, β, γ
and δ) of the nicotinic acetylcholine (ACh) receptor from mouse BC3H-1 cells and from Torpedo electric organ. The mRNA was synthesized in vitro by transcription with SP6 polymerase from cDNA clones. All 16 possible combinations that include one mRNA for each of α, β, γ and δ were injected into oocytes. After allowing 2-8 d for translation and assembly, we assayed each oocyte for (a) receptor assembly, measured by the binding of [^125]α-bungarotoxin to the oocyte surface, and (b) ACh-induced conductance, measured under voltage clamp at various membrane potentials. All combinations yielded detectable
assembly (30-fold range among different combinations) and ACh-induced
conductances (>1,000-fold range at 1 µM). On double-logarithmic coordinates, the dose-response relations all had a slope near 2 for low concentrations of ACh. Data were corrected for variations in efficiency of translation among identically injected oocytes by expressing ACh-induced conductance per femtomole
of α-bungarotoxin-binding sites. Five combinations were tested for d-tubocurarine
inhibition by the dose-ratio method; the apparent dissociation
constant ranged from 0.08 to 0.27 µM. Matched responses and geometric
means are used for describing the effects of changing a particular subunit
(mouse vs. Torpedo) while maintaining the identity of the other subunits. A
dramatic subunit-specific effect is that of the β subunit on voltage sensitivity of
the response: g_ACh(-90 mV)/g_Ach(+30 mV) is always at least 1, but this ratio
increases by an average of 3.5-fold if β_M replaces β_T. Also, combinations
including γ_T or δ_M usually produce greater receptor assembly than combinations
including the homologous subunit from the other species. Finally, E_ACh is
defined as the concentration of ACh inducing 1 µS/fmol at -60 mV; E_ACh is
consistently lower for α_m. We conclude that receptor assembly, voltage sensitivity,
and E_ACh are governed by different properties
Evolution of the Luminosity Density in the Universe: Implications for the Nonzero Cosmological Constant
We show that evolution of the luminosity density of galaxies in the universe
provides a powerful test for the geometry of the universe. Using reasonable
galaxy evolution models of population synthesis which reproduce the colors of
local galaxies of various morphological types, we have calculated the
luminosity density of galaxies as a function of redshift . Comparison of the
result with recent measurements by the Canada-France Redshift Survey in three
wavebands of 2800{\AA}, 4400{\AA}, and 1 micron at z<1 indicates that the
\Lambda-dominated flat universe with \lambda_0 \sim 0.8 is favored, and the
lower limit on \lambda_0 yields 0.37 (99% C.L.) or 0.53 (95% C.L.) if
\Omega_0+\lambda_0=1. The Einstein-de Sitter universe with (\Omega_0,
\lambda_0)=(1, 0) and the low-density open universe with (0.2, 0) are however
ruled out with 99.86% C.L. and 98.6% C.L., respectively. The confidence levels
quoted apply unless the standard assumptions on galaxy evolution are
drastically violated. We have also calculated a global star formation rate in
the universe to be compared with the observed rate beyond z \sim 2. We find
from this comparison that spiral galaxies are formed from material accretion
over an extended period of a few Gyrs, while elliptical galaxies are formed
from initial star burst at z >~ 5 supplying enough amount of metals and
ionizing photons in the intergalactic medium.Comment: 11 pages including 3 figures, LaTeX, uses AASTeX. To Appear in ApJ
Letter
Electrical transport properties of bulk MgB2 materials synthesized by the electrolysis on fused mixtures of MgCl2, NaCl, KCl and MgB2O4
Electrolysis was carried out on fused mixtures of MgCl2, NaCl, KCl and MgB2O4
under an Ar flow at 600C. Electrical resistivity measurements for the grown
deposits show an onset of superconducting transition at 37 K in the absence of
applied magnetic field. The resistivity decreases down to zero below 32 K. From
an applied-field dependence of resistivity, an upper critical field and a
coherence length were calculated to be 9.7 T and 5.9 nm at 0 K, respectively
Determining from cluster correlation function
It is shown how data on the cluster correlation function can be used in order
to reconstruct the density of the pregalactic density field on the cluster mass
scale. The method is applied to the data on the cluster correlation amplitude
-- richness dependence. The spectrum of the recovered density field has the
same shape as the density field derived from data on the galaxy correlation
function which is measured as function of linear scales. Matching the two
amplitudes relates the mass to the comoving scale it contains and thereby leads
to a direct determination of . The resultant density parameter turns
out to be =0.25.Comment: to appear in Physics Reports, "Dark Matter 98", vol.30
- …