61 research outputs found
Measuring Stellar Radial Velocities with a Dispersed Fixed-Delay Interferometer
We demonstrate the ability to measure precise stellar barycentric radial
velocities with the dispersed fixed-delay interferometer technique using the
Exoplanet Tracker (ET), an instrument primarily designed for precision
differential Doppler velocity measurements using this technique. Our
barycentric radial velocities, derived from observations taken at the KPNO 2.1
meter telescope, differ from those of Nidever et al. by 0.047 km/s (rms) when
simultaneous iodine calibration is used, and by 0.120 km/s (rms) without
simultaneous iodine calibration. Our results effectively show that a Michelson
interferometer coupled to a spectrograph allows precise measurements of
barycentric radial velocities even at a modest spectral resolution of R ~ 5100.
A multi-object version of the ET instrument capable of observing ~500 stars per
night is being used at the Sloan 2.5 m telescope at Apache Point Observatory
for the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS),
a wide-field radial velocity survey for extrasolar planets around TYCHO-2 stars
in the magnitude range 7.6<V<12. In addition to precise differential
velocities, this survey will also yield precise barycentric radial velocities
for many thousands of stars using the data analysis techniques reported here.
Such a large kinematic survey at high velocity precision will be useful in
identifying the signature of accretion events in the Milky Way and
understanding local stellar kinematics in addition to discovering exoplanets,
brown dwarfs and spectroscopic binaries.Comment: 9 pages, 4 figures. Accepted for publication in Ap
Geometry of W-algebras from the affine Lie algebra point of view
To classify the classical field theories with W-symmetry one has to classify
the symplectic leaves of the corresponding W-algebra, which are the
intersection of the defining constraint and the coadjoint orbit of the affine
Lie algebra if the W-algebra in question is obtained by reducing a WZNW model.
The fields that survive the reduction will obey non-linear Poisson bracket (or
commutator) relations in general. For example the Toda models are well-known
theories which possess such a non-linear W-symmetry and many features of these
models can only be understood if one investigates the reduction procedure. In
this paper we analyze the SL(n,R) case from which the so-called W_n-algebras
can be obtained. One advantage of the reduction viewpoint is that it gives a
constructive way to classify the symplectic leaves of the W-algebra which we
had done in the n=2 case which will correspond to the coadjoint orbits of the
Virasoro algebra and for n=3 which case gives rise to the Zamolodchikov
algebra. Our method in principle is capable of constructing explicit
representatives on each leaf. Another attractive feature of this approach is
the fact that the global nature of the W-transformations can be explicitly
described. The reduction method also enables one to determine the ``classical
highest weight (h. w.) states'' which are the stable minima of the energy on a
W-leaf. These are important as only to those leaves can a highest weight
representation space of the W-algebra be associated which contains a
``classical h. w. state''.Comment: 17 pages, LaTeX, revised 1. and 7. chapter
Wannier functions for quasi-periodic finite-gap potentials
In this paper we consider Wannier functions of quasi-periodic g-gap () potentials and investigate their main properties. In particular, we discuss
the problem of averaging underlying the definition of Wannier functions for
both periodic and quasi-periodic potentials and express Bloch functions and
quasi-momenta in terms of hyperelliptic functions. Using this approach
we derive a power series expansion of the Wannier function for quasi-periodic
potentials valid at and an asymptotic expansion valid at large
distance. These functions are important for a number of applied problems
Density Correlation Functions in Calogero Sutherland Models
Using arguments from two dimensional Yang-Mills theory and the collective
coordinate formulation of the Calogero-Sutherland model, we conjecture the
dynamical density correlation function for coupling and , where is
an integer. We present overwhelming evidence that the conjecture is indeed
correct.Comment: 12 pages phyzzx, CERN-TH/94.7243 One reference change
The Meson Light-Cone Distribution Amplitudes of Leading Twist Revisited
We give a complete re-analysis of the leading twist quark-antiquark
light-cone distribution amplitudes of longitudinal and transverse
mesons. We derive Wandzura-Wilczek type relations between different
distributions and update the coefficients in their conformal expansion using
QCD sum rules including next-to-leading order radiative corrections. We find
that the distribution amplitudes of quarks inside longitudinally and
transversely polarized mesons have a similar shape, which is in
contradiction to previous analyses.Comment: 21 pages, latex2e, requires a4wide.sty and epsf.sty, 6 PS figures
include
The First Extrasolar Planet Discovered with a New Generation High Throughput Doppler Instrument
We report the detection of the first extrasolar planet, ET-1 (HD 102195b),
using the Exoplanet Tracker (ET), a new generation Doppler instrument. The
planet orbits HD 102195, a young star with solar metallicity that may be part
of the local association. The planet imparts radial velocity variability to the
star with a semiamplitude of m s and a period of 4.11 days.
The planetary minimum mass () is .Comment: 42 pages, 11 figures and 5 tables, Accepted for publication in Ap
ИССЛЕДОВАНИЕ ФАЗОВОГО И ПРИМЕСНОГО СОСТАВА ЛЕНТ КАТОДНЫХ СПЛАВОВ Pd—Ba и Pt—Ba
We have studied the phase and impurity composition of Pd—Ba and Pt—Ba cathode alloys obtained on an A 535.02TO arc melting plant using a technology developed by AO Shokin NPP Istok. The study showed that the concentration of detrimental impurities (C; Zn; Cu; Al) in the specimens is within the allowed range. Pd—Ba tapes are rich in Ba but this does not compromise their quality. We have confirmed the earlier found domination of two−phase composition in Pd—Ba and Pt—Ba alloys where one of the phase is an intermetallic compound (Pd5Ba, Pt5Ba) and the other is a noble metal(the matrix). The intermetallide is distributed in the platinum metal matrix quite inhomogeneously, this tangibly impairing the operation parameters of cathodes produced from these alloys. For the first time we have shown the high efficiency of transmission electron microscopy for studying Pd—Ba and Pt—Ba cathode alloys. We have for the first time found the Pd2О phase in Pd—Ba. It may significantly reduce the secondary electron emission coefficient and the quality of devices based on this alloy. We have determined the Pd and Pd5Ba grain size in the Pd—Ba alloys and the Pt and Pt5Ba grain size in the Pt—Ba alloys. All the Pd and Pt5Ba grains contain high densities of randomly arranged dislocations, and Pt5Ba grains contain internal stresses. Recommendations have been given concerning the improvement of the current Pd—Ba and Pt—Ba cathode alloy tape technology.Изучен примесный и фазовый состав лент катодных сплавов Pd—Ba и Pt— Ba, полученных на установке дуговой плавки А 535.02ТО по технологии, разработанной в АО «НПП «Исток им. Шокина». Установлено, что концентрация вредных примесей (C, Zn, Cu, Al) в исследованных образцах не превышает допустимой нормы. Ленты состава Pd—Ba содержат повышенную концентрацию Ba, однако это не сказывается на их качестве.Подтверждена обнаруженная ранее превалирующая двухфазность сплавов Pd—Ba и Pt—Ba: одна из фаз — интерметаллическое соединение (Pd5Ba, Pt5Ba), вторая — благородный металл (матрица). При этом интерметаллид очень неравномерно распределен в матрице металла платиновой группы, что существенно понижает эксплуатационные характеристики катодов на основе этих сплавов. Впервые показана высокая эффективность просвечивающей электронной микроскопии для исследования катодных сплавов Pd—Ba и Pt—Ba.В сплаве Pd—Ba впервые обнаружена фаза Pd2О. Это может приводить к существенному понижению коэффициента вторичной электронной эмиссии и падению эксплуатационных характеристик приборов на базе этого сплава. Определен размер зерен Pd и Pd5Ba в сплавах Pd—Ba, и зерен Pt и Pt5Ba в сплавах Pt—Ba. Обнаружено, что во всех зернах Pd и Pt5Ba наблюдается высокая плотность хаотически расположенных дислокаций, внутри зерен Pt5Ba имеются напряжения.Приведены рекомендации по совершенствованию существующей технологии получения лент катодных сплавов Pd—Ba и Pt—Ba
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