70,426 research outputs found
Determination of the Higgs boson spin with a linear e+e- collider
The energy dependence of the production cross section of a light Higgs boson
is studied at threshold and compared to the expectations of several spin
assumptions. Cross section measurements at three centre-of-mass energies with
an integrated luminosity of 20 fb-1 allow the confirmation of the scalar nature
of the Higgs Boson.Comment: 4 pages (Latex), 4 figures (Postscript
An HST/COS legacy survey of intervening SiIII absorption in the extended gaseous halos of low-redshift galaxies
Doubly ionized silicon (SiIII) is a powerful tracer of diffuse ionized gas
inside and outside of galaxies. It can be observed in the local Universe in
ultraviolet (UV) absorption against bright extragalactic background sources. We
here present an extensive study of intervening SiIII-selected absorbers and
their relation to the circumgalactic medium (CGM) of galaxies at low redshift
(z<=0.1), based on the analysis of UV absorption spectra along 303
extragalactic lines of sight obtained with the Cosmic Origins Spectrograph
(COS) on board the Hubble Space Telescope (HST). Along a total redshift path of
Dz=24 we identify 69 intervening SiIII systems that all show associated
absorption from other low and high ions. We derive a bias-corrected number
density of dN/dz(SiIII)=2.5 for absorbers with column densities log
N(SiIII)>12.2. We develop a geometrical model for the absorption-cross section
of the CGM around the local galaxy population and find excellent agreement
between the model predictions and the observations. We further compare
redshifts and positions of the absorbers with that of ~64,000 galaxies using
archival galaxy-survey data. For the majority of the absorbers we identify
possible host galaxies within 300 km/s of the absorbers and derive impact
parameters rho<200 kpc, demonstrating that the spatial distributions of SiIII
absorbers and galaxies are highly correlated. Our study indicates that the
majority of SiIII-selected absorbers in our sample trace the CGM of nearby
galaxies within their virial radii at a typical covering fraction of ~70 per
cent. From a detailed ionization model we estimate that diffuse gas in the CGM
around galaxies, as traced by SiIII, contains substantially more baryonic mass
than their neutral interstellar medium.Comment: 32 pages, 17 figures; final version accepted for publication in A&
Carbon burning in intermediate mass primordial stars
The evolution of a zero metallicity 9 M_s star is computed, analyzed and
compared with that of a solar metallicity star of identical ZAMS mass. Our
computations range from the main sequence until the formation of a massive
oxygen-neon white dwarf. Special attention has been payed to carbon burning in
conditions of partial degeneracy as well as to the subsequent thermally pulsing
Super-AGB phase. The latter develops in a fashion very similar to that of a
solar metallicity 9 M_s star, as a consequence of the significant enrichment in
metals of the stellar envelope that ensues due to the so-called third dredge-up
episode. The abundances in mass of the main isotopes in the final ONe core
resulting from the evolution are X(^{16}O) approx 0.59, X(^{20}Ne) approx 0.28
and X(^{24}Mg) approx 0.05. This core is surrounded by a 0.05 M_s buffer mainly
composed of carbon and oxygen, and on top of it a He envelope of mass 10^{-4}
M_sComment: 11 pages, 11 figures, accepted for publication in A&
Spectroscopy of the post-AGB star HD 101584(IRAS 11385-5517)
From an analysis of the spectrum (4000\AA to 8800\AA) of HD~101584 it is
found that most of the neutral and single ionized metallic lines are in
emission. The forbidden emission lines of [OI] 6300\AA and 6363\AA and [CI]
8727\AA are detected, which indicate the presence of a very low excitation
nebula. The H, FeII 6383\AA, NaI D, D lines and the CaII IR
triplet lines show P-Cygni profiles indicating a mass outflow. The H
line shows many velocity components in the profile. The FeII 6383\AA also has
almost the same line profile as the H line indicating that they are
formed in the same region. From the spectrum synthesis analysis we find the
atmospheric parameters to be T=8500K, log g=1.5,
V=13km~s and [Fe/H]=0.0. From an analysis of the absorption
lines the photospheric abundances of some of the elements are derived. Carbon
and nitrogen are found to be overabundant. From the analysis of Fe emission
lines we derived T=6100K200 for the emission line region.Comment: To appear in A&A, 15 pages, 11 figure
Size effect in the ionization energy of PAH clusters
We report the first experimental measurement of the near-threshold
photo-ionization spectra of polycyclic aromatic hydrocarbon clusters made of
pyrene C16H10 and coronene C24H12, obtained using imaging photoelectron
photoion coincidence spectrometry with a VUV synchrotron beamline. The
experimental results of the ionization energy are confronted to calculated ones
obtained from simulations using dedicated electronic structure treatment for
large ionized molecular clusters. Experiment and theory consistently find a
decrease of the ionization energy with cluster size. The inclusion of
temperature effects in the simulations leads to a lowering of this energy and
to a quantitative agreement with the experiment. In the case of pyrene, both
theory and experiment show a discontinuity in the IE trend for the hexamer
Theory of Electromagnetic Wave Transmission through Metallic Gratings of Subwavelength Slits
We present FDTD calculations for transmission of light and other
electromagnetic waves through periodic arrays of slits in a metallic slab. The
results show resonant, frequency dependent, transmittance peaks for
subwavelength widths of the slits which can be up to a factor of ten with
respect to those out of resonance. Although our conclusions agree with previous
work by Lezec and Thio as regards both the magnitude of the enhancement and the
lack of contribution of surface plasmon polaritons of the metal surface to this
effect, we derive an interpretation from a theory that deals with emerging
beam- Rayleigh anomalies of the grating, and with Fabry-Perot resonances of the
perforated slab considered as an effective medium.Comment: 12 pages 3 figure
Bullion production in imperial China and its significance for sulphide ore smelting world-wide
Gold and silver production was of major importance for almost all ancient societies but has been rarely studied archaeologically. Here we present a reconstruction of a previously undocumented technology used to recover gold, silver and lead at the site of Baojia in Jiangxi province, China dated between the 7th and 13th centuries AD. Smelting a mixture of sulphidic and gossan ores in a relatively low temperature furnace under mildly reducing conditions, the process involved the use of metallic iron to reduce lead sulphide to lead metal, which acted as the collector of the precious metals. An experimental reconstruction provides essential information, demonstrating both the significant influence of sulphur on the silicate slag system, and that iron reduction smelting of lead can be carried out at a relatively low temperature. These new findings are relevant for further studies of lead and precious metal smelting slags world-wide. The technological choices of ancient smelters at this site are then discussed in their specific geographical and social-economic settings
A Black Hole of > 6 Solar Masses in the X-ray Nova XTE J1118+480
Observations of the quiescent X-ray nova XTE J1118+480 with the new 6.5-m MMT
have revealed that the velocity amplitude of the dwarf secondary is 698 +/- 14
km/s and the orbital period of the system is 0.17013 +/- 0.00010 d. The implied
value of the mass function, f(M) = 6.00 +/- 0.36 solar masses, provides a hard
lower limit on the mass of the compact primary that greatly exceeds the maximum
allowed mass of a neutron star. Thus we conclude that the compact primary is a
black hole. Among the eleven dynamically established black-hole X-ray novae,
the large mass function of XTE J1118+480 is rivaled only by that of V404 Cyg.
We estimate that the secondary supplies 34% +/- 8% of the total light at 5900A
and that its spectral type is in the range K5V to M1V. A double-humped I-band
light curve is probably due to ellipsoidal modulation, although this
interpretation is not entirely secure because of an unusual 12-minute offset
between the spectroscopic and photometric ephemerides. Assuming that the light
curve is ellipsoidal, we present a provisional analysis which indicates that
the inclination of the system is high and the mass of the black hole is
correspondingly modest. The broad Balmer emission lines (FWHM = 2300-2900 km/s)
also suggest a high inclination. For the range of spectral types given above,
we estimate a distance of 1.8 +/- 0.6 kpc.Comment: 4 pages, 2 figures, to appear in ApJ Letters; Minor changes to Fig 1
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