53,468 research outputs found
Dynamical detection of three triple stellar systems in open clusters
We present a kinematic analysis of three triple stellar systems belonging to
two open clusters: CPD-60{\deg}961 and HD66137 in NGC2516, and HD315031 in
NGC6530. All three systems are hierarchical triples with a close binary bound
to a third body in a wider orbit, whose presence is detected through velocity
variations of the close binary barycentre. Orbital parameters are derived from
radial velocity curves. Absolute parameters for all stars are estimated
assuming cluster membership. Some dynamical and evolutionary aspects of these
systems are discussed, particularly the possible influence of Kozai cycles. The
two systems of NGC2516 have similar orbital configurations with inner periods
of 11.23 d and 8.70 d and outer periods of 9.79 yr and 9.24 yr. We report also
radial velocity measurements of the components of the visual binary
CPD-60{\deg}944 in NGC2516. Including results from previous works, this cluster
would harbor 5 hierarchical triples. The young system HD315031 has an inner
binary with a period of 1.37 d and a very eccentric (e=0.85) outer orbit with a
period of 483 d. Possible dynamical evolutionary scenarios are discussed.
Long-term radial velocity monitoring is highlighted as strategy for the
detection of subsystems with intermediate separations, which are hard to cover
with normal spectroscopic studies or visual techniques.Comment: 9 pages, 5 figures. Accepted by Monthly Notices of the Royal
Astronomical Societ
Photovoltaic array: Power conditioner interface characteristics
The electrical output (power, current, and voltage) of flat plate solar arrays changes constantly, due primarily to changes in cell temperature and irradiance level. As a result, array loads such as dc-to-ac power conditioners must be capable of accommodating widely varying input levels while maintaining operation at or near the maximum power point of the array. The array operating characteristics and extreme output limits necessary for the systematic design of array load interfaces under a wide variety of climatic conditions are studied. A number of interface parameters are examined, including optimum operating voltage, voltage energy, maximum power and current limits, and maximum open circuit voltage. The effect of array degradation and I-V curve fill factor or the array power conditioner interface is also discussed. Results are presented as normalized ratios of power conditioner parameters to array parameters, making the results universally applicable to a wide variety of system sizes, sites, and operating modes
The properties of the stellar populations in ULIRGs I: sample, data and spectral synthesis modelling
We present deep long-slit optical spectra for a sample of 36 Ultraluminous
Infrared Galaxies (ULIRGs), taken with the William Herschel Telescope (WHT) on
La Palma with the aim of investigating the star formation histories and testing
evolutionary scenarios for such objects. Here we present the sample, the
analysis techniques and a general overview of the properties of the stellar
populations. Spectral synthesis modelling has been used in order to estimate
the ages of the stellar populations found in the diffuse light sampled by the
spectra in both the nuclear and extended regions of the target galaxies. We
find that adequate fits can be obtained using combinations of young stellar
populations (YSPs,t_YSP<=2 Gyr), with ages divided into two groups: very young
stellar populations (VYSPs, t_VYSP <=100 Myr) and intermediate-young stellar
populations (IYSPs, 0.1 < t_IYSP <= 2 Gyr). Our results show that YSPs are
present at all locations of the galaxies covered by our slit positions, with
the exception of the northern nuclear region of the ULIRG IRAS 23327+2913.
Furthermore, VYSPs are presents in at least 85% of the 133 extraction apertures
used for this study. Old stellar populations (OSPs, t_{OSP} > 2 Gyr) do not
make a major contribution to the optical light in the majority of the apertures
extracted. In fact they are essential for fitting the spectra in only 5% (7) of
the extracted apertures. The estimated total masses for the YSPs (VYSPs+IYSPs)
are in the range 0.18 x 10^{10} <= M_YSP <= 50 x 10^{10} Msun. We have also
estimated the bolometric luminosities associated with the stellar populations
detected at optical wavelengths, finding that they fall in the range 0.07 x
10^{12} < L_bol < 2.2 x 10^{12} Lsun. In addition, we find that reddening is
significant at all locations in the galaxies.Comment: accepted for publication in MNRA
Minimal anomaly-free chiral fermion sets and gauge coupling unification
We look for minimal chiral sets of fermions beyond the standard model that
are anomaly free and, simultaneously, vectorlike particles with respect to
colour SU(3) and electromagnetic U(1). We then study whether the addition of
such particles to the standard model particle content allows for the
unification of gauge couplings at a high energy scale, above GeV so as to be safely consistent with proton decay bounds. The
possibility to have unification at the string scale is also considered.
Inspired in grand unified theories, we also search for minimal chiral fermion
sets that belong to SU(5) multiplets. Restricting to representations up to
dimension 50, we show that some of these sets can lead to gauge unification at
the GUT and/or string scales.Comment: 13 pages, 5 figures, 8 tables; Comments and references added, final
version to appear in Phys. Rev.
Adaptive statistical pattern classifiers for remotely sensed data
A technique for the adaptive estimation of nonstationary statistics necessary for Bayesian classification is developed. The basic approach to the adaptive estimation procedure consists of two steps: (1) an optimal stochastic approximation of the parameters of interest and (2) a projection of the parameters in time or position. A divergence criterion is developed to monitor algorithm performance. Comparative results of adaptive and nonadaptive classifier tests are presented for simulated four dimensional spectral scan data
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