236 research outputs found
A Slope Instability Case History Involving Swelling Clay in Southern Brazil
This paper describes a slope instability case history involving swelling clay. A 9-m high slope was cut in 3 sedimentary layers during the construction of a single-carriage road. A complex slope failure mechanism was identified during site investigation, consisting of: (a) a progressive surficial degradation, particularly of the lower swelling clay layer. (b) a deep-seated slope failure, and (c) the toppling failure of the upper stronger layers. Site investigation included SPT testing, undisturbed sampling and in situ suction measurement. Laboratory testing consisted of: (a) soil characterization by X-ray diffraction analysis, particle-size analysis and Atterberg limits tests; (b) evaluation of effective shear strength parameters using direct shear tests and ring shear tests: and (c) determination of soil-water characteristic curves. Slope stability analyses were carried out followed by comparison with observed field performance
Discovery of new Milky Way star cluster candidates in the 2MASS point source catalog III. Follow-up observations of cluster candidates in the Galactic Center region
This paper is part of a project to search the inner Milky Way for hidden
massive clusters and to address the question of whether our Galaxy still forms
clusters similar to the progenitors of the present-day globular clusters.
We report high angular resolution deep near-infrared imaging of 21 cluster
candidates selected from the catalogues of Bica et al. (2003) and Dutra et
al.(2003) in a region around the Galactic Center. These catalogues were created
from visual inspection of the 2MASS images. Seven objects appear to be genuine
clusters, and for these objects we present estimates of extinction, distance
and in some cases age and mass.
Our estimated masses range from 1200 to 5500 solar masses. These clusters are
thus significantly smaller than any Galactic globular cluster, and indicate
that the formation of massive young clusters such as Arches and Quintuplet is
not common in the present-day Milky Way.
The remaining 14 objects are either not clusters or cannot be classified
based on our data.Comment: 8 pages, 19 figures, accepted for publication in A&
High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP~1
The globular cluster HP~1 is projected at only 3.33 degrees from the Galactic
center. Together with its distance, this makes it one of the most central
globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a
metallicity of [Fe/H]~-1.0. This means that it probably is one of the oldest
objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern
of the first stars as well as the early chemical enrichment and early formation
of stellar populations. High-resolution spectra obtained for six stars were
analyzed to derive the abundances of the light elements C, N, O, Na, and Al,
the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y , Zr, Ba,
La, and Eu.} High-resolution spectra of six red giants that are confirmed
members of the bulge globular cluster HP~1 were obtained with the 8m VLT
UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration.
The spectroscopic parameter derivation was based on the excitation and
ionization equilibrium of FeI and FeII. We confirm a mean metallicity of [Fe/H]
= -1.06~0.10, by adding the two stars that were previously analyzed in HP~1.
The alpha-elements O and Mg are enhanced by about +0.3<[O,Mg/Fe]<+0.5 dex, Si
is moderately enhanced with +0.15<[Si/Fe]<+0.35dex, while Ca and Ti show lower
values of -0.04<[Ca,Ti/Fe]<+0.28dex. The r-element Eu is also enhanced with
[Eu/Fe]~+0.4, which together with O and Mg is indicative of early enrichment by
type II supernovae. Na and Al are low, but it is unclear if Na-O are
anticorrelated. The heavy elements are moderately enhanced, with
-0.20<[La/Fe]<+0.43dex and 0.0<[Ba/Fe]<+0.75~dex, which is compatible with
r-process formation. The spread in Y, Zr, Ba, and La abundances, on the other
hand, appears to be compatible with the spinstar scenario or other additional
mechanisms such as the weak r-process.Comment: 15 pages, 8 figures In press in Astronomy & Astrophysics (2016
High-resolution abundance analysis of red giants in the globular cluster NGC 6522
The [Sr/Ba] and [Y/Ba] scatter observed in some galactic halo stars that are
very metal-poor stars and in a few individual stars of the oldest known Milky
Way globular cluster NGC 6522,have been interpreted as evidence of early
enrichment by massive fast-rotating stars (spinstars). Because NGC 6522 is a
bulge globular cluster, the suggestion was that not only the very-metal poor
halo stars, but also bulge stars at [Fe/H]~-1 could be used as probes of the
stellar nucleosynthesis signatures from the earlier generations of massive
stars, but at much higher metallicity. For the bulge the suggestions were based
on early spectra available for stars in NGC 6522, with a medium resolution of
R~22,000 and a moderate signal-to-noise ratio. The main purpose of this study
is to re-analyse the NGC 6522 stars previously reported using new
high-resolution (R~45,000) and high signal-to-noise spectra (S/N>100). We aim
at re-deriving their stellar parameters and elemental ratios, in particular the
abundances of the neutron-capture s-process-dominated elements such as Sr, Y,
Zr, La, and Ba, and of the r-element Eu. High-resolution spectra of four giants
belonging to the bulge globular cluster NGC 6522 were obtained at the 8m VLT
UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVESconfiguration.
The spectroscopic parameters were derived based on the excitation and
ionization equilibrium of \ion{Fe}{I} and \ion{Fe}{II}. Our analysis confirms a
metallicity [Fe/H] = -0.95+-0.15 for NGC 6522, and the overabundance of the
studied stars in Eu (with +~0.2 < [Eu/Fe] < +~0.4) and alpha-elements O and Mg.
The neutron-capture s-element-dominated Sr, Y, Zr, Ba, La now show less
pronounced variations from star to star. Enhancements are in the range 0.0 <
[Sr/Fe] < +0.4, +0.23 < [Y/Fe] < +0.43, 0.0 < [Zr/Fe] < +0.4, 0.0 < [La/Fe] <
+0.35,and 0.05 < [Ba/Fe] < +0.55.Comment: date of acceptation: 31/07/2014, in press, 24 pages, 19
figures,Astronomy & Astrophysics, 201
Ultraviolet-Optical observations of the Seyfert 2 Galaxies NGC 7130, NGC 5135 and IC 3639: Implications for the Starburst-AGN Connection
We present and discuss HST (WFPC2 and FOC) images and UV GHRS spectra plus
ground-based near UV through to near IR spectra of three Seyfert 2 nuclei (NGC
7130, NGC 5135 and IC 3639). These galaxies, together to Mrk 477, were selected
from a bigger sample that comprises the 20 brightest Seyfert 2 nuclei, with the
goal to study the origin of the UV-optical-near IR featureless continuum in
Seyfert 2 nuclei. These four galaxies have bolometric luminosities, as computed
with the four IRAS bands, of 10^11 Lsol. They are close enough to be resolved
with HST the nuclear zone. This makes these Seyfert 2 galaxies benchmarks to
study the Starburst-AGN connection in more distant galaxies.
The data provide direct evidence of the existence of a central nuclear
starburst that dominates the UV light, and that seem to be responsible for the
origin of the so called featureless continuum. These starbursts are dusty and
compact. They have sizes (from less than 100 pc to a few hundred pc) much
smaller and closer to the nucleus than that seen in the prototype Seyfert 2
galaxy NGC 1068. The bolometric luminosity of these starbursts is similar to
the estimated bolometric luminosities of their obscured Seyfert 1 nuclei, and
thus they contribute in the same amount to the overall energetics of these
galaxies.Comment: to be published in ApJ 505, September issue. The figures are in a tar
files at: http://www.iaa.es/~rosa/Seyfert
Earth pressure on cantilever walls at design retained heights
There are many methods for the analysis and design of embedded cantilever retaining walls. They involve various different simplifications of the pressure distribution to allow calculation of the limiting equilibrium retained height and the bending moment when the retained height is less than the limiting equilibrium value, i.e. the serviceability case. Recently, a new method for determining the serviceability earth pressure and bending moment has been proposed. This method makes an assumption defining the point of zero net pressure. This assumption implies that the passive pressure is not fully mobilised immediately below the excavation level. The finite element analyses presented in this paper examine the net pressure distribution on walls in which the retained height is less, than the limiting equilibrium value. The study shows that for all practical walls, the earth pressure distributions on the front and back of the wall are at their limit values, Kp and K-a respectively, when the lumped factor of safety F-r is less than or equal to2.0. A rectilinear net pressure distribution is proposed that is intuitively logical. It produces good predictions of the complete bending moment diagram for walls in the service configuration and the proposed method gives results that have excellent agreement with centrifuge model tests. The study shows that the method for determining the serviceability bending moment suggested by Padfield and Mair(1) in the CIRIA Report 104 gives excellent predictions of the maximum bending moment in practical cantilever walls. It provides the missing data that have been needed to verify and justify the CIRIA 104 method
New galactic star clusters discovered in the VVV survey : Candidates projected on the inner disk and bulge
Context. VISTA Variables in the VĂa Láctea (VVV) is one of six ESO Public Surveys using the 4 meter Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey covers the Milky Way bulge and an adjacent section of the disk, and one of the principal objectives is to search for new star clusters within previously unreachable obscured parts of the Galaxy. Aims. The primary motivation behind this work is to discover and analyze obscured star clusters in the direction of the inner Galactic disk and bulge. Methods. Regions of the inner disk and bulge covered by the VVV survey were visually inspected using composite JHKS color images to select new cluster candidates on the basis of apparent overdensities. DR1, DR2, CASU, and point spread function photometry of 10 Ă— 10 arcmin fields centered on each candidate cluster were used to construct color-magnitude and color-color diagrams. Follow-up spectroscopy of the brightest members of several cluster candidates was obtained in order to clarify their nature. Results. We report the discovery of 58 new infrared cluster candidates. Fundamental parameters such as age, distance, and metallicity were determined for 20 of the most populous clusters.Peer reviewedFinal Accepted Versio
Ages and Metallicities of Extragalactic Globular Clusters from Spectral and Photometric Fits of Stellar Population Synthesis Models
Spectra of galaxies contain an enormous amount of information about the
relative mixture of ages and metallicities of constituent stars. We present a
comprehensive study designed to extract the maximum information from spectra of
data quality typical in large galaxy surveys. We test fitting techniques using
the Bruzual-Charlot 2003 high resolution simple stellar population synthesis
models to simultaneously estimate the ages and metallicities of 101 globular
clusters in M31 and the Magellanic Clouds. The clusters cover a wide range of
ages and metallicities, 4 Myr to 20 Gyr and -1.6 < [Fe/H] < +0.3, estimated by
other methods in the literature. We compare results from model fits to both the
spectra and photometry and find that fits to continuum-normalized (CN) spectra
over the entire range available, typically 350-1000 nm for this sample,
provides the best results. For clusters older than 1 Gyr we agree with
literature ages to 0.16 dex (35%) and [Fe/H] to 0.12 dex. For younger clusters
we agree with literature ages to 0.3 dex (63%), but cannot constrain the
metallicity. It is particularly important to use the entire CN spectrum to
avoid problems with model continua for young objects and to break
age-metallicity degeneracies of broadband photometry. Our required S/N = 15-30
for 20% age uncertainties and 30-55 for 10% uncertainties over spectral
resolutions of 5-25 Angstroms. This technique should work well for the
age-metallicity parameter space expected for early-type galaxies at z~1,
although individual galaxy spectral S/N may require the coaddition of a few
like objects.Comment: 70 pages, 18 figures, ApJ, in pres
The Metal Content of the Bulge Globular Cluster NGC 6528
High resolution spectra of five stars in the bulge globular cluster NGC 6528
were obtained at the 8m VLT UT2-Kueyen telescope with the UVES spectrograph.
Out of the five stars, two of them showed evidence of binarity. The target
stars belong to the horizontal and red giant branch stages, at 4000<T_eff<4800
K. Multiband V,I,J,H,Ks photometry was used to derive initial effective
temperatures and gravities. The main purpose of this study is the determination
of metallicity and elemental ratios for this template bulge cluster, as a basis
for the fundamental calibration of metal-rich populations. The present analysis
provides a metallicity [Fe/H] = -0.1\pm0.2 and the alpha-elements O, Mg and Si,
show [alpha/Fe] ~ +0.1, whereas Ca and Ti are around the solar value or below,
resulting in an overall metallicity Z ~ Zsun.Comment: 13 pages, 13 figures, A&A in pres
Global survey of star clusters in the Milky Way I. The pipeline and fundamental parameters in the second quadrant
Aims: On the basis of the PPMXL star catalogue we performed a survey of star
clusters in the second quadrant of the Milky Way. Methods: From the PPMXL
catalogue of positions and proper motions we took the subset of stars with
near-infrared photometry from 2MASS and added the remaining 2MASS stars without
proper motions (called 2MAst, i.e. 2MASS with astrometry). We developed a
data-processing pipeline including interactive human control of a standardised
set of multi-dimensional diagrams to determine kinematic and photometric
membership probabilities for stars in a cluster region. The pipeline
simultaneously produced the astrophysical parameters of a cluster. From
literature we compiled a target list of presently known open and globular
clusters, cluster candidates, associations, and moving groups. From established
member stars we derived spatial parameters (coordinates of centres and radii of
the main morphological parts of clusters) and cluster kinematics (average
proper motions and sometimes radial velocities). For distance, reddening, and
age determination we used specific sets of theoretical isochrones. Tidal
parameters were obtained by a fit of three-parameter King profiles to the
observed density distributions of members. Results: We investigated all 871
objects in the 2nd Galactic quadrant, of which we successfully treated 642 open
clusters, 2 globular clusters, and 8 stellar associations. The remaining 219
objects (24%) were recognised by us to be nonexistent clusters, duplicate
entries, or clusters too faint for 2MAst. We found that our sample is complete
in the 2nd quadrant up to a distance of 2 kpc, where the average surface
density is 94 clusters per kpc. Compared with literature values we found
good agreement in spatial and kinematic data, as well as for optical distances
and reddening. Small, but systematic offsets were detected in the age
determination.Comment: published in Astronomy and Astrophysics, 10 pages, 7 figures (plus 3
pages of appendices incl. 2 more figures), catalogues will be available at
the CDS, all the machine-readable online data described in appendices A, B,
and C are also available at:
http://www.aip.de/People/rdscholz/kharchenko_etal_2012
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