19,020 research outputs found
Planetary Nebula Candidates in Extragalactic Young Star Clusters
During an analysis of optical spectra of 80 young star clusters in several
nearby spiral galaxies, [O III] and [N II] emission lines were noted in some
cases. Three of these emission line sources are identified as likely planetary
nebula (PN) candidates and may represent a rare opportunity to study PNe whose
progenitor stars are known to be of intermediate masses. This paper presents
and discusses basic properties of the PN candidates and their host clusters.
Based on the observed emission line fluxes, the excitation parameters and
luminosities of the nebulae are derived. This allows a crude placement of the
central stars in two of the objects on the H-R diagram, and their temperatures
and luminosities are found to be consistent with post-AGB model tracks for a
central star mass of about 0.60 Msun. Host cluster ages and masses are
estimated from broad-band colours and by comparison with model SSP spectra. One
of the host clusters has an age of 32-65 Myrs, corresponding to a main sequence
turn-off mass of M(TO) = 6.6-9.0 Msun. For the other cluster the age is 282-407
Myrs, corresponding to M(TO) = 3.2-3.6 Msun. By estimating the number of stars
evolving off the main sequence per year, a total of 6 PNe are expected in our
full sample of 80 clusters for aPN lifetime of 10000 years. The factor of two
disagreement with the actual observed number may be due, among other things, to
uncertainties in PN lifetimes. It is interesting to note that all three PN
candidates are associated with clusters which are more diffuse than average.
While PNe have previously been found in some old globular clusters, the
candidates identified here are among the first identified in young star
clusters.Comment: 10 pages, 9 figures. Accepted for publication in A&
Observations of mesoscale vertical velocities around frontal zones
Vertical velocity and reflectivity data obtained with a VHF Doppler radar over a 15-day period in October and November of 1981 are analyzed. Standard radiosonde data and surface observations were used to locate two occluded fronts, two warm fronts, and a cold front that passed the radar site. These fronts are also evident in the radar reflectivity data. Most studies of the vertical circulation patterns associated with mososcale systems have used precipitation and cloud formations as tracers. Unlike other observational techniques, the VHF radar permits the continuous measurement of the three-dimensional air velocity vector in time and height from a fixed location. With the beam in a vertically pointing position, signals are scattered from turbulent variations in the refractive index with half the scale of the radar wavelength and by regions with sudden changes in the refractive index associated with horizontally stratified layers. Generally, the strongest echoes occur at the maximum in the vertical gradient of refractivity, usually at the base of a temperature inversion, such as the tropopause. VHF radars can also be used to locate atmospheric fronts, which are characterized by static stability, large horizontal temperature gradients, large vorticities, and vertical wind shears. These radars can provide the velocity field data needed to study wave motions associated with fronts and compare the actual vertical circulation to theoretical predictions
Comparison of vertical velocities analyzed by a numerical model and measured by a VHF wind profiler
The use of wind profilers for measuring vertical velocities in the troposphere and lower stratosphere is potentially of great interest for verification of forecasts, diagnosis of mesoscale circulations, and studies of wave motions. The studies of profiler vertical velocities to date have shown that the observed patterns of ascent and subsidence are reasonable when compared to the synoptic conditions. However, difficulties arise when a direct verification of the profiler vertical winds is sought. Since no other technique can measure the vertical velocities over the same height range and with the same claimed accuracy as the profilers, direct comparisons are impossible. The only alternative is to compare the measurements to analyzed vertical velocity fields. Here, researchers compare vertical measurements made with the SOUSY VHF radar over a period of 11 days at the beginning of November 1981 to the analyzed vertical velocities produced by the European Center for Medium-range Weather Forecasting (ECMWF) model for grid points near the radar site
Influence of Conjugated Linoliec Acid (CLA) on Belly and Bacon Quality From Pigs Fed Various Diets
A study was initiated to investigate the feeding of conjugated linoleic acid (CLA) to market barrows to achieve improvements of bacon quality characteristics. CLA was fed at 55 kg of body weight to 113 kg of body weight. CLA improved belly firmness (P\u3c0.05) for all diets according to the belly bar firmness test but CLA did not improve bacon sliceability. Bacon slabs from CLA-supplemented pigs were firmer according to the compression test. Dietary CLA increased the percentage of saturated fatty acids and CLA isomers in bacon
Co-universal algebras associated to product systems, and gauge-invariant uniqueness theorems
Let X be a product system over a quasi-lattice ordered group. Under mild
hypotheses, we associate to X a C*-algebra which is co-universal for injective
Nica covariant Toeplitz representations of X which preserve the gauge coaction.
Under appropriate amenability criteria, this co-universal C*-algebra coincides
with the Cuntz-Nica-Pimsner algebra introduced by Sims and Yeend. We prove two
key uniqueness theorems, and indicate how to use our theorems to realise a
number of reduced crossed products as instances of our co-universal algebras.
In each case, it is an easy corollary that the Cuntz-Nica-Pimsner algebra is
isomorphic to the corresponding full crossed product.Comment: 40 pages, 2 figures; v2: minor changes to the introduction,
references added and update
A dynamical and kinematical model of the Galactic stellar halo and possible implications for galaxy formation scenarios
We re-analyse the kinematics of the system of blue horizontal branch field
(BHBF) stars in the Galactic halo (in particular the outer halo), fitting the
kinematics with the model of radial and tangential velocity dispersions in the
halo as a function of galactocentric distance r proposed by Sommer-Larsen,
Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF
stars. The basic result is that the character of the stellar halo velocity
ellipsoid changes markedly from radial anisotropy at the sun to tangential
anisotropy in the outer parts of the Galactic halo (r greater than approx 20
kpc). Specifically, the radial component of the stellar halo's velocity
ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/-
10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The
rapid decrease in the radial velocity dispersion is matched by an increase in
the tangential velocity dispersion, with increasing r.
Our results may indicate that the Galaxy formed hierarchically (partly or
fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation
scenario, which for quite a while has been favoured by most theorists and
recently also has been given some observational credibility by HST observations
of a potential group of small galaxies, at high redshift, possibly in the
process of merging to a larger galaxy (Pascarelle et al 1996).Comment: Latex, 16 pages. 2 postscript figures. Submitted to the Astrophysical
Journal. also available at http://astro.utu.fi/~cflynn/outerhalo.htm
A Semiconductor Nanowire-Based Superconducting Qubit
We introduce a hybrid qubit based on a semiconductor nanowire with an
epitaxially grown superconductor layer. Josephson energy of the transmon-like
device ("gatemon") is controlled by an electrostatic gate that depletes
carriers in a semiconducting weak link region. Strong coupling to an on-chip
microwave cavity and coherent qubit control via gate voltage pulses is
demonstrated, yielding reasonably long relaxation times (0.8 {\mu}s) and
dephasing times (1 {\mu}s), exceeding gate operation times by two orders of
magnitude, in these first-generation devices. Because qubit control relies on
voltages rather than fluxes, dissipation in resistive control lines is reduced,
screening reduces crosstalk, and the absence of flux control allows operation
in a magnetic field, relevant for topological quantum information
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