2,700 research outputs found
Dynamics of the Young Binary LMC Cluster NGC 1850
In this paper we have examined the age and internal dynamics of the young
binary LMC cluster NGC 1850 using BV CCD images and echelle spectra of 52
supergiants. Isochrone fits to a BV color-magnitude diagram revealed that the
primary cluster has an age of Myr while the secondary member
has Myr. BV surface brightness profiles were constructed out
to R 40 pc, and single-component King-Michie (KM) models were applied. The
total cluster luminosity varied from L = 2.60 - 2.65
L\sol\ and L = 1.25 - 1.35 as the anisotropy radius
varied from infinity to three times the scale radius with the isotropic models
providing the best agreement with the data. Of the 52 stars with echelle
spectra, a subset of 36 were used to study the cluster dynamics. The KM radial
velocity distributions were fitted to these velocities yielding total cluster
masses of 5.4 - 5.9 M\sol\ corresponding to M/L =
0.02 M\sol/L\sol\ or M/L = 0.05 M\sol/L\sol.
A rotational signal in the radial velocities has been detected at the 93\%
confidence level implying a rotation axis at a position angle of 100\deg. A
variety of rotating models were fit to the velocity data assuming cluster
ellipticities of . These models provided slightly better
agreement with the radial velocity data than the KM models and had masses that
were systematically lower by a few percent. The preferred value for the slope
of a power-law IMF is a relatively shallow, x = 0.29 \pmm{+0.3}{-0.8}
assuming the B-band M/L or x = 0.71 \pmm{+0.2}{-0.4} for the V-band.Comment: 41 pages (figures available via anonymous FTP as described below
Effective mean-field equations for cigar-shaped and disk-shaped Bose-Einstein condensates
By applying the standard adiabatic approximation and using the accurate
analytical expression for the corresponding local chemical potential obtained
in our previous work [Phys. Rev. A \textbf{75}, 063610 (2007)] we derive an
effective 1D equation that governs the axial dynamics of mean-field
cigar-shaped condensates with repulsive interatomic interactions, accounting
accurately for the contribution from the transverse degrees of freedom. This
equation, which is more simple than previous proposals, is also more accurate.
Moreover, it allows treating condensates containing an axisymmetric vortex with
no additional cost. Our effective equation also has the correct limit in both
the quasi-1D mean-field regime and the Thomas-Fermi regime and permits one to
derive fully analytical expressions for ground-state properties such as the
chemical potential, axial length, axial density profile, and local sound
velocity. These analytical expressions remain valid and accurate in between the
above two extreme regimes. Following the same procedure we also derive an
effective 2D equation that governs the transverse dynamics of mean-field
disk-shaped condensates. This equation, which also has the correct limit in
both the quasi-2D and the Thomas-Fermi regime, is again more simple and
accurate than previous proposals. We have checked the validity of our equations
by numerically solving the full 3D Gross-Pitaevskii equation.Comment: 11 pages, 7 figures; Final version published in Phys. Rev. A;
Manuscript put in the archive and submitted to Phys. Rev. A on 17 July 200
Ground-state properties of trapped Bose-Einstein condensates: Extension of the Thomas-Fermi approximation
We derive general approximate formulas that provide with remarkable accuracy
the ground-state properties of any mean-field scalar Bose-Einstein condensate
with short-range repulsive interatomic interactions, confined in arbitrary
cylindrically symmetric harmonic traps. Our formulation is even applicable for
condensates containing a multiply quantized axisymmetric vortex. We have
checked the validity of our formulas by numerically solving the 3D
Gross-Pitaevskii equation.Comment: 9 pages, 6 figures. Final version published in Phys. Rev. A. New
formulas for the local sound velocity of cigar-shaped and disk-shaped
condensates have been obtained. This paper generalizes our previous work
cond-mat/070169
Gap solitons in elongated geometries: the one-dimensional Gross-Pitaevskii equation and beyond
We report results of a systematic analysis of matter-wave gap solitons (GSs)
in three-dimensional self-repulsive Bose-Einstein condensates (BECs) loaded
into a combination of a cigar-shaped trap and axial optical-lattice (OL)
potential. Basic cases of the strong, intermediate, and weak radial
(transverse) confinement are considered, as well as settings with shallow and
deep OL potentials. Only in the case of the shallow lattice combined with tight
radial confinement, which actually has little relevance to realistic
experimental conditions, does the usual one-dimensional (1D) cubic
Gross-Pitaevskii equation (GPE) furnish a sufficiently accurate description of
GSs. However, the effective 1D equation with the nonpolynomial nonlinearity,
derived in Ref. [Phys. Rev. A \textbf{77}, 013617 (2008)], provides for quite
an accurate approximation for the GSs in all cases, including the situation
with weak transverse confinement, when the soliton's shape includes a
considerable contribution from higher-order transverse modes, in addition to
the usual ground-state wave function of the respective harmonic oscillator.
Both fundamental GSs and their multipeak bound states are considered. The
stability is analyzed by means of systematic simulations. It is concluded that
almost all the fundamental GSs are stable, while their bound states may be
stable if the underlying OL potential is deep enough.Comment: 14 pages, 12 figures; v2: matches published versio
Dynamics of the Globular Cluster NGC 362
In this paper we have examined the internal dynamics of the globular cluster
NGC 362. A V band surface brightness profile (SBP) was constructed from CCD
images, and, after it was determined that the cluster is not post
core-collapse, fit with single- and multi-mass King-Michie (KM) models. The
total cluster luminosity is 1.70 L\sol. A total of
285 stellar spectra were obtained of 215 stars for radial velocity
determinations. Four stars showed strong evidence for radial velocity
variations and are probably members of binary systems. The true cluster binary
fraction was determined from simulations to be 0.15 for circular orbits or 0.27
for orbits with a distribution function ( is eccentricity). This
relatively high binary detection frequency may indicate that NGC 362 is
overabundant in binaries compared to other clusters. The 208 remaining stars
showed no sign of rotation. The best agreement with both the kinematic data and
the SBP were for shallow mass functions and intermediate
amounts of anisotropy in the velocity dispersion tensor. The cluster mass is M
= M\sol\ for a global mass-to-light ratio of M/L =
1.5 - 2.0 M\sol/L\sol. This low value for is in disagreement with the
correlation between and the height above the Galactic disk seen for a
sample of other clusters. The results are also different from the sharp turn-up
in the low mass end of mass functions derived from some deep luminosity
functions of three other globular clusters.Comment: 31 pages plus five figure
Composition Mixing during Blue Straggler Formation and Evolution
We use smoothed-particle hydrodynamics to examine differences between direct
collisions of single stars and binary star mergers in their roles as possible
blue straggler star formation mechanisms. We find in all cases that core helium
in the progenitor stars is largely retained in the core of the remnant, almost
independent of the type of interaction or the central concentration of the
progenitor stars.
We have also modelled the subsequent evolution of the hydrostatic remnants,
including mass loss and energy input from the hydrodynamical interaction. The
combination of the hydrodynamical and hydrostatic models enables us to predict
that little mixing will occur during the merger of two globular cluster stars
of equal mass. In contrast to the results of Proctor Sills, Bailyn, & Demarque
(1995), we find that neither completely mixed nor unmixed models can match the
absolute colors of observed blue stragglers in NGC 6397 at all luminosity
levels. We also find that the color distribution is probably the crucial test
for explanations of BSS formation - if stellar collisions or mergers are the
correct mechanisms, a large fraction of the lifetime of the straggler must be
spent away from the main sequence. This constraint appears to rule out the
possibility of completely mixed models. For NGC 6397, unmixed models predict
blue straggler lifetimes ranging from about 0.1 to 4 Gyr, while completely
mixed models predict a range from about 0.6 to 4 Gyr.Comment: AASTeX, 28 pg., accepted for ApJ, also available at
http://ucowww.ucsc.edu/~erics/bspaper.htm
Error induced by the estimation of the corneal power and the effective lens position with a rotationally asymmetric refractive multifocal intraocular lens
AIM: To evaluate the prediction error in intraocular lens (IOL) power calculation for a rotationally asymmetric refractive multifocal IOL and the impact on this error of the optimization of the keratometric estimation of the corneal power and the prediction of the effective lens position (ELP). METHODS: Retrospective study including a total of 25 eyes of 13 patients (age, 50 to 83y) with previous cataract surgery with implantation of the Lentis Mplus LS-312 IOL (Oculentis GmbH, Germany). In all cases, an adjusted IOL power (PIOLadj) was calculated based on Gaussian optics using a variable keratometric index value (nkadj) for the estimation of the corneal power (Pkadj) and on a new value for ELP (ELPadj) obtained by multiple regression analysis. This PIOLadj was compared with the IOL power implanted (PIOLReal) and the value proposed by three conventional formulas (Haigis, Hoffer Q and Holladay). RESULTS: PIOLReal was not significantly different than PIOLadj and Holladay IOL power (P>0.05). In the Bland and Altman analysis, PIOLadj showed lower mean difference (-0.07 D) and limits of agreement (of 1.47 and -1.61 D) when compared to PIOLReal than the IOL power value obtained with the Holladay formula. Furthermore, ELPadj was significantly lower than ELP calculated with other conventional formulas (P<0.01) and was found to be dependent on axial length, anterior chamber depth and Pkadj. CONCLUSION: Refractive outcomes after cataract surgery with implantation of the multifocal IOL Lentis Mplus LS-312 can be optimized by minimizing the keratometric error and by estimating ELP using a mathematical expression dependent on anatomical factors
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