229 research outputs found
Relations between residential and workplace segregation among newly arrived immigrant men and women
The research leading to these results has received funding from the Estonian Research Council (Institutional Research Grant IUT2-17 on Spatial Population Mobility and Geographical Changes in Urban Regions); the Estonian Science Foundation (grant no. 8774 and 9247); the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 615159 (ERC Consolidator Grant DEPRIVEDHOODS, Socio-spatial inequality, deprived neighbourhoods, and neighbourhood effects); and the Marie Curie Programme under the European Union's Seventh Framework Programme (FP/2007-2013) / Career Integration Grant n. PCIG10-GA-2011-303728 (CIG Grant NBHCHOICE, Neighbourhood choice, neighbourhood sorting, and neighbourhood effects).Contemporary cities are becoming more and more diverse in population as a result of immigration. Research shows that while residential neighborhoods are becoming ethnically more diverse within cities, residential segregation from natives has overall remained persistently high. High levels of segregation are often seen as negative, preventing the integration of immigrants into their host society and having a negative impact on people's lives. Where as most studies of segregation deal with residential neighborhoods, this paper investigates segregation at workplaces for newly arrived immigrant men and women from the Global South to Sweden. By using the domain approach, we focus on the relationship between workplace segregation, residential segregation, and the ethnic composition of households. Using longitudinal register data from Sweden, we find that residential segregation is much weaker related to workplace segregation than revealed by studies using cross-sectional data. Furthermore, the residential context is not an important factor in explaining workplace segregation for immigrant men. The most important factors shaping workplace segregation pertain to economic sector and city size.Publisher PDFPeer reviewe
Investigating star formation in the young open cluster NGC 6383
By studying young open clusters, the mechanisms important for star formation
over several Myr can be examined. For example, accretion rate as a function of
rotational velocity can be investigated. Similarly, sequential star formation
triggered by massive stars with high mass-loss rates can be studied in detail.
We identified and characterized probable members of NGC 6383, as well as
determined cluster parameters. New Stromgren uvby CCD photometry, obtained by
us, is presented. This new data, together with Johnson UBV and 2MASS data in
the NIR, was used to investigate characteristics of pre- as well as zero age
main sequence cluster members. We present Stromgren uvby CCD photometry for 272
stars in the field of NGC 6383 and derive its reddening, E(b-y)=0.21(4)mag, as
well as distance, d=1.7(3)kpc from the Sun. Several stars with NIR excess and
objects in the domain of the classical Herbig Ae/Be and T Tauri stars were
detected. Two previously known variables were identified as rapidly-rotating
PMS stars. The field population is clearly separated from the probable members
in the color-magnitude diagram. NGC 6383 is a young open cluster, with an age
of less than 4 Myr, undergoing continuous star formation. True pre-main
sequence members might be found down to absolute magnitudes of +6mag, with a
variety of rotational velocities and stellar activities.Comment: 7 pages, 6 figures, accepted by A&
Propagation of ionizing radiation in HII regions: the effects of optically thick density fluctuations
The accepted explanation of the observed dichotomy of two orders of magnitude
between in situ measurements of electron density in HII regions, derived from
emission line ratios, and average measurements based on integrated emission
measure, is the inhomogeneity of the ionized medium. This is expressed as a
"filling factor", the volume ratio of dense to tenuous gas, measured with
values of order 10^-3. Implicit in the filling factor model as normally used,
is the assumption that the clumps of dense gas are optically thin to ionizing
radiation. Here we explore implications of assuming the contrary: that the
clumps are optically thick. A first consequence is the presence within HII
regions of a major fraction of neutral hydrogen. We estimate the mean H^o/H^+
ratio for a population of HII regions in the spiral galaxy NGC 1530 to be the
order of 10, and support this inference using dynamical arguments. The
optically thick clumpy models allow a significant fraction of the photons
generated by the ionizing stars to escape from their HII region. We show, by
comparing model predictions with observations, that these models give an
account at least as good as, and probably better than that of conventional
models, of the radial surface brightness distribution and of selected spectral
line diagnostics for physical conditions within HII regions. These models
explain how an HII region can appear, from its line ratios, to be ionization
bounded, yet permit a major fraction of its ionizing photons to escape.Comment: 9 pages, 7 figures (2 of them in colours), accepted for publication
in A&
The high-energy environment in the super-earth system CoRoT-7
High-energy irradiation of exoplanets has been identified to be a key
influence on the stability of these planets' atmospheres. So far,
irradiation-driven mass-loss has been observed only in two Hot Jupiters, and
the observational data remain even more sparse in the super-earth regime. We
present an investigation of the high-energy emission in the CoRoT-7 system,
which hosts the first known transiting super-earth. To characterize the
high-energy XUV radiation field into which the rocky planets CoRoT-7b and
CoRoT-7c are immersed, we analyzed a 25 ks XMM-Newton observation of the host
star. Our analysis yields the first clear (3.5 sigma) X-ray detection of
CoRoT-7. We determine a coronal temperature of ca. 3 MK and an X-ray luminosity
of 3*10^28 erg/s. The level of XUV irradiation on CoRoT-7b amounts to ca. 37000
erg/cm^2/s. Current theories for planetary evaporation can only provide an
order-of-magnitude estimate for the planetary mass loss; assuming that CoRoT-7b
has formed as a rocky planet, we estimate that CoRoT-7b evaporates at a rate of
about 1.3*10^11 g/s and has lost ca. 4-10 earth masses in total.Comment: 5 pages, accepted for publication by Astronomy & Astrophysic
Periodic orbits in the restricted three-body problem and Arnold's -invariant
We apply Arnold's theory of generic smooth plane curves to Stark-Zeeman
systems. This is a class of Hamiltonian dynamical systems that describes the
dynamics of an electron in an external electric and magnetic field, and
includes many systems from celestial mechanics. Based on Arnold's
-invariant, we introduce invariants of periodic orbits in planar
Stark-Zeeman systems and study their behaviour.Comment: 36 Pages, 16 Figure
Properties of the 5- state at 839 keV in 176Lu and the s-process branching at A = 176
The s-process branching at mass number A = 176 depends on the coupling
between the high-K ground state and a low-lying low-K isomer in 176Lu. This
coupling is based on electromagnetic transitions via intermediate states at
higher energies. The properties of the lowest experimentally confirmed
intermediate state at 839 keV are reviewed, and the transition rate between
low-K and high-K states under stellar conditions is calculated on the basis of
new experimental data for the 839 keV state. Properties of further candidates
for intermediate states are briefly analyzed. It is found that the coupling
between the high-K ground state and the low-K isomer in 176Lu is at least one
order of magnitude stronger than previously assumed leading to crucial
consequences for the interpretation of the 176Lu/176Hf pair as an s-process
thermometer.Comment: 11 pages, 4 figures accepted for publication in Phys. Rev.
Photometric signatures of multiple stellar populations in Galactic globular clusters
We have calculated synthetic spectra for typical chemical element mixtures
(i.e., a standard alpha-enhanced distribution, and distributions displaying CN
and ONa anticorrelations) found in the various subpopulations harboured by
Galactic globular clusters. From the spectra we have determined bolometric
corrections to the standard Johnson-Cousins and Stroemgren filters, and finally
predicted colours. These bolometric corrections and colour-transformations,
coupled to our theoretical isochrones with the appropriate chemical
composition, provide a complete and self-consistent set of theoretical
predictions for the effect of abundance variations on the observed cluster CMD.
CNO abundance variations affect mainly wavelengths shorter than 400 nm, due to
the arise of molecular absorption bands in cooler atmospheres. As a
consequence, colour and magnitude changes are largest in the blue filters,
independently of using broad or intermediate bandpasses. Colour-magnitude
diagrams involving uvy and UB filters (and their various possible colour
combinations) are thus the ones best suited to infer photometrically the
presence of multiple stellar generations in individual clusters. They are
particularly sensitive to variations in the N abundance, with the largest
variations affecting the Red Giant Branch (RGB) and lower Main Sequence (MS).
BVI diagrams are expected to display multiple sequences only if the different
populations are characterized by variations of the C+N+O sum and helium
abundance, that lead to changes in luminosity and effective temperature, but
leave the flux distribution above 400 nm practically unaffected. A variation of
just the helium abundance, up to the level we investigate here, affects
exclusively the interior structure of stars, and is largely irrelevant for the
atmospheric structure and the resulting flux distribution in the whole
wavelength range spanned by our analysis.Comment: 15 pages, 15 figures, submitted to A&A, referee comments addresse
The Rest-frame Optical Colors of 99,000 SDSS Galaxies
We synthesize the rest-frame Stroemgren colors using SDSS spectra for 99,088
galaxies selected from Data Release 1. This narrow-band ~200 AA photometric
system (uz, vz, bz, yz), first designed for the determination of effective
temperature, metallicity and gravity of stars, measures the continuum spectral
slope of galaxies in the rest-frame 3200-5800 AA wavelength range. Galaxies
form a remarkably narrow locus (~0.03 mag) in the resulting color-color
diagram. The Bruzual & Charlot population synthesis models suggest that the
position of a galaxy along this locus is controlled by a degenerate combination
of metallicity and age of the dominant stellar population. Galaxy distribution
along the locus is bimodal, with the local minimum corresponding to an ~1 Gyr
old single stellar population. The position perpendicular to the locus is
independent of metallicity and age, and reflects the galaxy's dust content, as
implied by both the models and the statistics of IRAS detections. A comparison
of this locus with the galaxy locus in the H_delta-D_n(4000) diagram, utilized
by Kauffmann et al. (2003) to estimate stellar masses, reveals a tight
correlation, although the two analyzed spectral ranges barely overlap. Overall,
the galaxy spectral energy distribution in the entire UV to near-IR range can
be described as a single-parameter family with an accuracy of 0.1 mag, or
better. This nearly one-dimensional distribution of galaxies in the
multi-dimensional space of measured parameters strongly supports the conclusion
of Yip et al. (2004), based on a principal component analysis, that SDSS galaxy
spectra can be described by a small number of eigenspectra. Apparently, the
contributions of stellar populations that dominate the optical emission from
galaxies are combined in a simple and well-defined way.Comment: Accepted for publication in MNRAS; 19 pages, 28 color figure
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