991 research outputs found
Sustaining Public Engagement: Embedded Deliberation in Local Communities
Describes nine communities using organized deliberation to consider public issues over several years and their accomplishments and analyzes how public deliberation addresses deficits in local democratic governance. Includes benchmarks and strategies
Spectro-photometric Evolution of Elliptical Galaxies. II. Models with infall
In this paper we present new chemo-spectro-photometric models of elliptical
galaxies in which infall of primordial gas is allowed to occur. They aim to
simulate the collapse of a galaxy made of two components, i.e. luminous
material and dark matter. The mass of the dark component is assumed to be
constant in time, whereas that of the luminous material is supposed to accrete
at a suitable rate. They also include the effect of galactic winds powered by
supernova explosions and stellar winds from massive, early-type stars. The
models are constrained to match a number of properties of elliptical galaxies,
i.e. the slope and mean colours of the colour-magnitude relation (CMR), V
versus (V--K), the UV excess as measured by the colour (1550--V) together with
the overall shape of the integrated spectral energy distribution (ISED) in the
ultraviolet, the relation between the Mg2 index and (1550--V), the mass to blue
luminosity ratio M/Lb as a function of the B luminosity, and finally the
broad-band colours (U--B), (B--V), (V--I), (V--K), etc.Comment: pages 22, 20 postscript figures, 2 external table (tab2_infall using
supertabular.sty and tab5_infall using supertabular1.sty
Pre-Main sequence Turn-On as a chronometer for young clusters: NGC346 as a benchmark
We present a novel approach to derive the age of very young star clusters, by
using the Turn-On (TOn). The TOn is the point in the color-magnitude diagram
(CMD) where the pre-main sequence (PMS) joins the main sequence (MS). In the MS
luminosity function (LF) of the cluster, the TOn is identified as a peak
followed by a dip. We propose that by combining the CMD analysis with the
monitoring of the spatial distribution of MS stars it is possible to reliably
identify the TOn in extragalactic star forming regions. Compared to alternative
methods, this technique is complementary to the turn-off dating and avoids the
systematic biases affecting the PMS phase. We describe the method and its
uncertainties, and apply it to the star forming region NGC346, which has been
extensively imaged with the Hubble Space Telescope (HST). This study extends
the LF approach in crowded extragalactic regions and opens the way for future
studies with HST/WFC3, JWST and from the ground with adaptive optics.Comment: 6 pages, 4 figures. Accepted for publication in ApJ Letter
The Star Formation History of NGC 1705: a Post-Starburst Galaxy on the Verge of Activity
We infer the star formation history in different regions of the blue compact
dwarf NGC 1705 by comparing synthetic color-magnitude diagrams with HST optical
and near-infrared photometry. We find that NGC 1705 is not a young galaxy
because its star formation commenced at least 5 Gyr ago. On the other hand, we
confirm the existence of a recent burst of star formation between 15 and 10 Myr
ago. We also find evidence for new strong activity, which started 3 Myr ago and
is still continuing. The old population is spread across the entire galaxy,
while the young and intermediate stars are more concentrated in the central
regions. We derive an almost continuous star formation with variable rate, and
exclude the presence of long quiescent phases between the episodes during the
last ~1 Gyr. The central regions experienced an episode of star formation of
\~0.07 Msun/yr (for a Salpeter initial mass function [IMF]) 15 to 10 Myr ago.
This coincides with the strong activity in the central super star cluster. We
find a rate of ~0.3 Msun/yr for the youngest ongoing burst which started ~3 Myr
ago. This is higher than in other dwarfs and comparable to the rate of NGC
1569. The star formation rate of earlier episodes is not especially high and
falls in the range 10^{-3}-10^{-1} Msun/yr. The IMF is close to the Salpeter
value or slightly steeper.Comment: 34 pages, including 6 tables and 14 .ps figures (9 in colour), AJ in
pres
Reflection on the CEMS-MIM business project about renovas internationalisation and new sales channels expansion with a brief analysis on echange rate risk management and hedging strategies
CEMSThe present work project examines Renova’s intent to enter four new markets, namely Hong
Kong, Dubai, Macau and Las Vegas, and to expand into new sales channels, specifically the
luxury Horeca segment. The study deals also with the analysis of the risk of exchange rate
changes, which Renova might face during its internationalisation plan and how it can manage
its exposure.
Findings show that Renova should enter Hong Kong and Macau in a segmented way by
targeting few specific hotels and restaurants and by exporting its premium coloured paper
products. Furthermore, the company should hedge its exchange rate risk exposure
A new inverse method for stellar population synthesis and error analysis
The stellar population synthesis in unresolved composite objects is a very
tricky problem. Indeed, it is a degenerate problem since many parameters affect
the observables. The stellar population synthesis issue thus deserves a deep
and rigourous analysis. In this paper we present a method of inversion which
uses as observables the intensities at each pixel of a galactic spectrum and
provides the stellar contribution to luminosity of all stars considered in a
database. The main contribution of this paper to the synthesis problem is that
it provides an analytical computation of the uncertainties accompanying a
solution. This constitutes an important improvement relative to previous
methods which do not provide such infomation except in the method described by
Pelat (1997) and Moultaka & Pelat (2000). The latter uses the equivalent widths
and intensities of stellar spectra in order to reproduce the equivalent widths
of a galactic spectrum. The novelty of this work relative to the previous one
is that the dust emission present in the IR spectra can be modeled as well as
the velocity dispersion of stars that broadens the lines of a galactic
spectrum. Tests are also performed in order to estimate the reliability of the
method and the influence on the results of an additive continuum present in a
studied spectrum, for example in the case of AGNs.Comment: 12 pages, 4 figures, 7 tables. In press in A&
The Resolved Stellar Populations in NGC 1705
We present HST photometry of the resolved stellar population in the dwarf
irregular galaxy NGC 1705. The galaxy has been observed with both WFPC2 and
NICMOS, and successful images have been obtained in the F555W, F814W, F110W and
F160W bands. The optical fields cover most of the galaxy, while the infrared
field (NIC2) maps only its central regions. The optical photometry provides
\~20000 objects down to m_F555W ~ 29 in the PC field of view and ~ 20000 in the
three WFCs. In the infrared we have been able to resolve ~ 2400 stars down to
m_{F110W}, m_{F160W} ~ 26. A subsample of 1834 stars have been unambiguously
measured in all the four bands. The corresponding color-magnitude diagrams
(CMDs) confirm the existence of an age gradient, showing that NGC 1705 hosts
both young (a few Myr old) and very old (up to 15 Gyr old) stars, with the
former strongly concentrated toward the galactic center and the latter present
everywhere, but much more easily visible in the external regions. The tip of
the red giant branch (TRGB) is clearly visible both in the optical and in the
infrared CMDs and allows us to derive the galaxy distance. Taking into account
the uncertainties related to both the photometry and the TRGB magnitude --
distance relation, we find that the distance modulus of NGC 1705 is
(m-M)_0=28.54 +- 0.26, corresponding to a distance D=5.1 +- 0.6 Mpc.Comment: aastex, 37 pages, 13 (reduced resolution) .ps figures. Accepted by
AJ. Full resolution figures are available upon request to the first autho
The evolution of H{\sc ii} galaxies: Testing the bursting scenario through the use of self-consistent models
We have computed a series of realistic and self-consistent models of the
emitted spectra of H{\sc ii} galaxies. Our models combine different codes of
chemical evolution, evolutionary population synthesis and photoionization. The
emitted spectrum of H{\sc ii} galaxies is reproduced by means of the
photoionization code CLOUDY, using as ionizing spectrum the spectral energy
distribution of the modelled H{\sc ii} galaxy, which in turn is calculated
according to a Star Formation History (SFH) and a metallicity evolution given
by a chemical evolution model that follows the abundances of 15 different
elements. The contribution of emission lines to the broad-band colours is
explicitly taken into account.
The results of our code are compared with photometric and spectroscopic data
of H{\sc ii} galaxies. Our technique reproduces observed diagnostic diagrams,
abundances, equivalent width-colour and equivalent width-metallicity relations
for local H{\sc ii} galaxies.Comment: 13 figures and 2 tables, accepted for publication in MNRAS Main
Journa
New Near-Infrared Surface Brightness Fluctuation Models
We present new theoretical models for surface brightness fluctuations in the
near-infrared. We show the time evolution of near-infrared brightness
fluctuation properties over large age and metallicity ranges, i.e., from 12 Myr
to 16 Gyr, and from Z/Zsun=1/50 to Z/Zsun=2.5, for single age, single
metallicity stellar populations. All the stellar models are followed from the
zero age main sequence to the central carbon ignition for massive stars, or to
the end of the thermally pulsing regime of the asymptotic giant branch phase
for low and intermediate mass stars. The new models are compared with observed
near-infrared fluctuation absolute magnitudes and colours for a sample of
Magellanic Cloud star clusters and Fornax Cluster galaxies. For star clusters
younger than ~3 Gyr, the predicted near-infrared fluctuation properties are in
a satisfactory agreement with observed ones over a wide range of stellar
population metallicities. However, for older star clusters, the agreement
between the observed and predicted near-IR brightness fluctuations depends on
how the surface brightness absolute magnitudes are estimated. The computed set
of models are not able to match the observed near-IR fluctuation absolute
magnitudes and colours simultaneously. We argue that the observed discrepancies
between the predicted and observed properties of old MC superclusters are more
likely due to observational reasons.Comment: MNRAS, 2005, 362, 1208 (12 pages, 7 figures
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