4,508 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
A revised comparison of distant and nearby solar twins
Properties of solar twins reported by Lehmann et al. (2023) at kiloparsec
distances from the local standard of rest (LSR) are compared to solar twins
within 100 pc of the Sun. These have velocity distributions closely similar to
those of the nearby twins in addition to closely matching ,
and . The new twins are at slightly higher galactic
latitudes, and are somewhat closer to the Galactic center. Additionally, they
may be significantly older than nearby solar twins.Comment: Revised and updated version of 2023 RNAAS 7, 8
The interaction between transpolar arcs and cusp spots
Transpolar arcs and cusp spots are both auroral phenomena which occur when
the interplanetary magnetic field is northward. Transpolar arcs are associated
with magnetic reconnection in the magnetotail, which closes magnetic flux and
results in a "wedge" of closed flux which remains trapped, embedded in the
magnetotail lobe. The cusp spot is an indicator of lobe reconnection at the
high-latitude magnetopause; in its simplest case, lobe reconnection
redistributes open flux without resulting in any net change in the open flux
content of the magnetosphere. We present observations of the two phenomena
interacting--i.e., a transpolar arc intersecting a cusp spot during part of its
lifetime. The significance of this observation is that lobe reconnection can
have the effect of opening closed magnetotail flux. We argue that such events
should not be rare
The Masses Of The B-Stars In The High Galactic Latitude Eclipsing Binary IT Lib
A number of blue stars which appear to be similar to Population I B-stars in
the star forming regions of the galactic disk are found more than 1 kpc from
the galactic plane. Uncertainties about the true distances and masses of these
high latitude B-stars has fueled a debate as to their origin and evolutionary
status. The eclipsing binary IT Lib is composed of two B-stars, is
approximately one kiloparsec above the galactic plane, and is moving back
toward the plane. Observations of the light and velocity curves presented here
lead to the conclusion that the B-stars in this system are massive young
main-sequence stars. While there are several possible explanations, it appears
most plausible that the IT Lib system formed in the disk about 30 million years
ago and was ejected on a trajectory taking it to its present position.Comment: 26 pages, 3 figures, accepted for publication in the PASP (January
2003
Two-dimensional solitons on the surface of magnetic fluids
We report an observation of a stable soliton-like structure on the surface of
a ferrofluid, generated by a local perturbation in the hysteretic regime of the
Rosensweig instability. Unlike other pattern-forming systems with localized 2D
structures, magnetic fluids are characterized by energy conservation; hence
their mechanism of soliton stabilization is different from the previously
discussed gain/loss balance mechanism. The radioscopic measurements of the
soliton's surface profile suggest that locking on the underlying periodic
structure is instrumental in its stabilization.Comment: accepted for publication by Physical Review Letter
Static Response Function for Longitudinal and Transverse Excitations in Superfluid Helium
The sum rule formalism is used to evaluate rigorous bounds for the density
and current static response functions in superfluid helium at zero temperature.
Both lower and upper bounds are considered. The bounds are expressed in terms
of ground state properties (density and current correlation funtions) and of
the interatomic potential. The results for the density static response
significantly improve the Feynman approximation and turn out to be close to the
experimental (neutron scattering) data. A quantitative prediction for the
transverse current response is given. The role of one-phonon and multi-particle
excitations in the longitudinal and transverse channels is discussed.
(Phys.Rev.B, in press)Comment: 19 pages (plain TeX) and 3 Figures (postscript), UTF-26
Relevance of pseudospin symmetry in proton-nucleus scattering
The manifestation of pseudospin-symmetry in proton-nucleus scattering is
discussed. Constraints on the pseudospin-symmetry violating scattering
amplitude are given which require as input cross section and polarization data,
but no measurements of the spin rotation function. Application of these
constraints to p-58Ni and p-208Pb scattering data in the laboratory energy
range of 200 MeV to 800 MeV, reveals a significant violation of the symmetry at
lower energies and a weak one at higher energies. Using a schematic model
within the Dirac phenomenology, the role of the Coulomb potential in
proton-nucleus scattering with regard to pseudospin symmetry is studied. Our
results indicate that the existence of pseudospin-symmetry in proton-nucleus
scattering is questionable in the whole energy region considered and that the
violation of this symmetry stems from the long range nature of the Coulomb
interaction.Comment: 22 pages including 9 figures, correction of 1 reference, revision of
abstract and major modification of chapter 4, Fig. 6, and Fig. 7; addition of
Fig. 8 and Fig.
Recommended from our members
Flux transfer events at the magnetopause and in the ionosphere
On December 1, 1986 the ISEE 1 and 2 spacecraft pair passed through the dayside magnetopause at a location which mapped approximately to ionospheric field-line foot-points near the fields of view of the EISCAT radar and photometers and an all-sky camera on Svalbard. The magnetosheath magnetic field was southward and duskward at the time, and flux transfer events (FTEs) were observed at the ISEE location. At the same time, the EISCAT radar observed ionospheric flow bursts of up to 1 km s−1. The peak of each burst followed an FTE observation at ISEE by a few minutes. The bursts, each lasting ten or fifteen minutes, were comprised of first a westward then a poleward flow. An all-sky camera at Ny Ålesund observed dayside auroral breakup forms during or shortly after the flow bursts, moving westward then poleward. While these flow bursts and associated dayside auroral forms have been previously reported in association with southward IMF orientations, this is the first observation of a direct link to FTEs at the magnetopause. On this occasion, the lower limit on the inferred potential associated with the FTEs is roughly 10 kV. Their inferred east-west extent in the ionosphere ranges between 700 and 1000 km, corresponding to a 3 – 5 RE local time extent at the average magnetopause
Epitaxial Growth of Thin Films -- a Statistical Mechanical Model
A theoretical framework is developed to describe experiments on the structure
of epitaxial thin films, particularly niobium on sapphire. We extend the
hypothesis of dynamical scaling to apply to the structure of thin films from
its conventional application to simple surfaces. We then present a
phenomenological continuum theory that provides a good description of the
observed scattering and the measured exponents. Finally the results of
experiment and theory are compared.Comment: 10 pages, 3 figures, minor revisions. accepted for publication in J
Phys Condense Matte
Optical Conductivity in a Two-Band Superconductor: Pb
We demonstrate the effect of bandstructure on the superconducting properties
of Pb by calculating the strong-coupling features in the optical conductivity,
, due to the electron-phonon interaction. The importance of
momentum dependence in the calculation of the properties of superconductors has
previously been raised for MgB. Pb resembles MgB in that it is a two
band superconductor in which the bands' contributions to the Fermi surface have
very different topologies. We calculate by calculating a
memory function which has been recently used to analyze of
BiSrCaCuO. In our calculations the two components of
the Fermi surface are described by parameterizations of de Haas--van Alphen
data. We use a phonon spectrum which is a fit to neutron scattering data. By
including the momentum dependence of the Fermi surface good agreement is found
with the experimentally determined strong-coupling features which can be
described by a broad peak at around 4.5 meV and a narrower higher peak around 8
meV of equal height. The calculated features are found to be dominated by
scattering between states within the third band. By contrast scattering between
states in the second band leads to strong-coupling features in which the height
of the high energy peak is reduced by compared to that of the low
energy peak. This result is similar to that in the conventional isotropic
(momentum independent) treatment of superconductivity. Our results show that it
is important to use realistic models of the bandstructure and phonons, and to
avoid using momentum averaged quantities, in calculations in order to get
quantitatively accurate results
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