1,155 research outputs found
AL 3 (BH 261): a new globular cluster in the Galaxy
AL~3 (BH 261), previously classified as a faint open cluster candidate, is
shown to be a new globular cluster in the Milky Way, by means of B, V and I
Color-Magnitude Diagrams. The main feature of AL~3 is a prominent blue extended
Horizontal Branch. Its Color-Magnitude Diagrams match those of the intermediate
metallicity cluster M~5. The cluster is projected in a rich bulge field, also
contaminated by the disk main sequence. The globular cluster is located in the
Galactic bulge at a distance from the Sun d = 6.00.5 kpc. The
reddening is E(B-V)=0.360.03 and the metallicity is estimated to be [Fe/H]
-1.30.25. AL~3 is probably one of the least massive globular
clusters of the Galaxy.Comment: 6 figures. Astrophysical Journal Letters, in pres
Magnetic properties of commensurate Bose-Bose mixtures in one-dimensional optical lattices
We investigate magnetic properties of strongly interacting bosonic mixtures
confined in one dimensional geometries, focusing on recently realized Rb-K
gases with tunable interspecies interactions. By combining analytical
perturbation theory results with density-matrix-renormalization group
calculations, we provide quantitative estimates of the ground state phase
diagram as a function of the relevant microscopic quantities, identifying the
more favorable experimental regimes in order to access the various magnetic
phases. Finally, we qualitatively discuss the observability of such phases in
realistic setups when finite temperature effects have to be considered.Comment: 9 pages, 7 figures, to be published in EPJ ST special issue on "Novel
Quantum Phases and Mesoscopic Physics in Quantum Gases
An Accurate, Easy to Use Abundace Scale for Globular Clusters Based on 2.2um Spectra of Giant Stars
We present a new method for the determination of [Fe/H] for globular
clusters. This new method is based on moderate resolution (R~1500) near-IR
spectroscopy in the K-band of 6 to 10 of the brightest giants in a cluster. Our
calibration is derived from spectra of 105 stars in 15 globular clusters. From
measurements of the equivalent widths of three features in these spectra, Na,
Ca, and CO, we are able to reproduce the Zinn & West (1984) abundance scale as
updated by Harris (1996) to better than 0.10 dex for clusters with near solar
[Fe/H] down to an [Fe/H] of -1.8. Three advantages of this method are that it
can be used for metal rich, heavily reddened globulars in crowded fields, it
does not require any knowledge of any other cluster or stellar parameters such
as reddening, distance, or luminosity, and it requires only minimal telescope
time. If stellar (J-K)0 and MK values are available as well, the accuracy of
the [Fe/H] estimate is further improved. Observations of as few as three stars
per cluster still gives an [Fe/H] estimate wich is nearly as reliable as that
based on two to three times as many stars.
The accuracy of an [Fe/H] value based on observations of CO absorption alone
is significantly less than that which results from the three spectroscopic
indices. However, we predict that space-based observations of this feature in
the integrated light of stellar systems will prove to be of great value for
abundance determinations at distances as far as the Coma cluster of galaxies.Comment: 53 pages, 16 Postscript figures. Submitted to the A
A Near-Infrared Photometric Study of the Low Latitude Globular Clusters Liller 1, Djorgovski 1, HP 1, and NGC 6528
Images recorded through J, H, Ks, 2.2 micron continuum, and 2.3 micron CO
filters are used to investigate the stellar contents of the low Galactic
latitude globular clusters NGC 6528, Liller 1, Djorgovski 1, and HP 1, as well
as surrounding bulge fields. Metallicities are estimated for the latter three
clusters by comparing the colors and CO indices of giant branch stars with
those in other clusters and the bulge, while reddenings are estimated from the
colors of bright bulge stars in the surrounding fields. In some cases the
metallicities and reddenings are significantly different from previous
estimates.Comment: 32 pages, and 28 figure
Scaling of excitations in dimerized and frustrated spin-1/2 chains
We study the finite-size behavior of the low-lying excitations of spin-1/2
Heisenberg chains with dimerization and next-to-nearest neighbors interaction,
J_2. The numerical analysis, performed using density-matrix renormalization
group, confirms previous exact diagonalization results, and shows that, for
different values of the dimerization parameter \delta, the elementary triplet
and singlet excitations present a clear scaling behavior in a wide range of
\ell=L/\xi (where L is the length of the chain and \xi is the correlation
length). At J_2=J_2c, where no logarithmic corrections are present, we compare
the numerical results with finite-size predictions for the sine-Gordon model
obtained using Luscher's theory. For small \delta we find a very good agreement
for \ell > 4 or 7 depending on the excitation considered.Comment: 4 pages, 4 eps figures, RevTeX 4 class, same version as in PR
Kinematics of the Galactic Globular Cluster System: New Radial Velocities for Clusters in the Direction of the Inner Galaxy
HIRES on the Keck I telescope has been used to measure the first radial
velocities for stars belonging to eleven, heavily-reddened globular clusters in
the direction of the inner Galaxy. The question of kinematic substructuring
among the Galactic globular cluster system is investigated using an updated
catalog of globular cluster distances, metallicities and velocities. It is
found that the population of metal-rich globular clusters shows significant
rotation at all Galactocentric radii. For the metal-rich clusters within 4 kpc
of the Galactic center, the measured rotation velocity and line-of-sight
velocity dispersion are similar to those of bulge field stars. We investigate
claims that the metal-rich clusters are associated with the central Galactic
bar by comparing the kinematics of the innermost clusters to that of the atomic
hydrogen in the inner Galaxy. The longitude-velocity diagram of both metal-rich
and metal-poor clusters bears a remarkable similarity to that of the gas,
including the same non-circular motions which have traditionally been
interpreted as evidence for a Galactic bar, or, alternatively, a
non-axisymmetric bulge. However, uncertainties in the existing
three-dimensional Galactocentric positions for most of the clusters do not yet
allow an unambiguous discrimination between the competing scenarios of
membership in a rigidly rotating bar, or in a bulge which is an oblate
isotropic rotator. We conclude that the majority of metal-rich clusters within
the central 4 kpc of the Galaxy are probably associated with the bulge/bar, and
not the thick disk. (ABRIDGED)Comment: 18 pages, including 7 of 13 postscript figures. Figures 1-6 available
at http://astro.caltech.edu/~pc. Accepted for publication in the Astronomical
Journa
Far-infrared absorption and the metal-to-insulator transition in hole-doped cuprates
By studying the optical conductivity of BSLCO and YCBCO, we show that the
metal-to-insulator transition (MIT) in these hole-doped cuprates is driven by
the opening of a small gap at low T in the far infrared. Its width is
consistent with the observations of Angle-Resolved Photoemission Spectroscopy
in other cuprates, along the nodal line of the k-space. The gap forms as the
Drude term turns into a far-infrared absorption, whose peak frequency can be
approximately predicted on the basis of a Mott-like transition. Another band in
the mid infrared softens with doping but is less sensitive to the MIT.Comment: To be published on Physical Review Letter
Heavy elements Ba, La, Ce, Nd, and Eu in 56 Galactic bulge red giants
Aims. The aim of this work is the study of abundances of the heavy elements
Ba, La, Ce, Nd, and Eu in 56 bulge giants (red giant branch and red clump) with
metallicities ranging from -1.3 dex to 0.5 dex. Methods. We obtained
high-resolution spectra of our giant stars using the FLAMES-UVES spectrograph
on the Very Large Telescope. We inspected four bulge fields along the minor
axis. Results. We measure the chemical evolution of heavy elements, as a
function of metallicity, in the Galactic bulge. Conclusions. The [Ba, La, Ce,
Nd/Fe] vs. [Fe/H] ratios decrease with increasing metallicity, in which aspect
they differ from disc stars. In our metal-poor bulge stars, La and Ba are
enhanced relative to their thick disc counterpart, while in our metal-rich
bulge stars La and Ba are underabundant relative to their disc counterpart.
Therefore, this contrast between bulge and discs trends indicates that bulge
and (solar neighbourhood) thick disc stars could behave differently. An
increase in [La, Nd/Eu] with increasing metallicity, for metal-rich stars with
[Fe/H] > 0 dex, may indicate that the s-process from AGB stars starts to
operate at a metallicity around solar. Finally, [Eu/Fe] follows the
[{\alpha}/Fe] behaviour, as expected, since these elements are produced by SNe
type II.Comment: 12 pages, 10 figures, accepted for publication in A&
Low loss Ge-on-Si waveguides operating in the 8â14 ”m atmospheric transmission window
Germanium-on-silicon waveguides were modeled, fabricated and characterized at wavelengths ranging from 7.5 to 11 ”m. Measured waveguide losses are below 5 dB/cm for both TE and TM polarization and reach values of ⌠1 dB/cm for ℠10 ”m wavelengths for the TE polarization. This work demonstrates experimentally for the first time that Ge-on-Si is a viable waveguide platform for sensing in the molecular fingerprint spectral region. Detailed modeling and analysis is presented to identify the various loss contributions, showing that with practical techniques losses below 1 dB/cm could be achieved across the full measurement range
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