22,694 research outputs found
Near-infrared integral-field spectroscopy of violent starburst environments
Near-infrared (NIR) integral-field spectroscopy (IFS) of violent starburst
environments at high spatial (and spectral) resolution has the potential to
revolutionise our ideas regarding the local interactions between the
newly-formed massive stars and the interstellar medium (ISM) of their host
galaxies. To illustrate this point, I present NIR IFS analysis of the central
starburst region of NGC 1140, obtained with CIRPASS on Gemini-South. While
strong [FeII] emission is found throughout the galaxy, higher-order Brackett
emission is predominantly associated with the northern starburst region. Based
on the spatial distributions of the [FeII] versus Brackett line emission, I
conclude that a galaxy-wide starburst was induced several x 10^7 yr ago, with
more recent starburst activity concentrated around the northern starburst
region. I look forward and discuss the exciting prospects that IFS at higher
spatial (and spectral) resolution will allow us trace (i) the massive outflows
("superwinds") expected to originate in the dense, young massive star clusters
commonly found in intense starburst environments, and (ii) their impact on the
galaxy's ISM.Comment: Submitted to "Adaptive Optics-Assisted Integral-Field Spectroscopy",
Rutten R.G.M., Benn C.R., Mendez J., eds., May 2005, La Palma (Spain), New
Astr. Re
Nitrogen chronology of massive main sequence stars
Rotational mixing in massive main sequence stars is predicted to
monotonically increase their surface nitrogen abundance with time. We use this
effect to design a method for constraining the age and the inclination angle of
massive main sequence stars, given their observed luminosity, effective
temperature, projected rotational velocity and surface nitrogen abundance. This
method relies on stellar evolution models for different metallicities, masses
and rotation rates. We use the population synthesis code STARMAKER to show the
range of applicability of our method. We apply this method to 79 early B-type
main sequence stars near the LMC clusters NGC 2004 and N 11 and the SMC
clusters NGC 330 and NGC 346. From all stars within the sample, 17 were found
to be suitable for an age analysis. For ten of them, which are rapidly rotating
stars without a strong nitrogen enhancement, it has been previously concluded
that they did not evolve as rotationally mixed single stars. This is confirmed
by our analysis, which flags the age of these objects as highly discrepant with
their isochrone ages. For the other seven stars, their nitrogen and isochrone
ages are found to agree within error bars, what validates our method.
Constraints on the inclination angle have been derived for the other 62
stars,with the implication that the nitrogen abundances of the SMC stars, for
which mostly only upper limits are known, fall on average significantly below
those limits. Nitrogen chronology is found to be a new useful tool for testing
stellar evolution and to constrain fundamental properties of massive main
sequence stars. A web version of this tool is provided.Comment: accepted by A&A, 15 pages, 16 figures, 6 table
Bright Ultraviolet Regions and Star Formation Characteristics in Nearby Dwarf Galaxies
We compare star formation in the inner and outer disks of 11 dwarf Irregular
galaxies (dIm) within 3.6 Mpc. The regions are identified on GALEX near-UV
images, and modeled with UV, optical, and near-IR colors to determine masses
and ages. A few galaxies have made 10^5-10^6 Msun complexes in a starburst
phase, while others have not formed clusters in the last 50 Myrs. The maximum
region mass correlates with the number of regions as expected from the
size-of-sample effect. We find no radial gradients in region masses and ages,
even beyond the realm of Halpha emission, although there is an exponential
decrease in the luminosity density and number density of the regions with
radius. Halpha is apparently lacking in the outer parts only because nebular
emission around massive stars is too faint to see. The outermost regions for
the 5 galaxies with HI data formed at average gas surface densities of 1.9-5.9
Msun/pc2. These low average densities imply either that local gas densities are
high or sub-threshold star formation is possible. The distribution of regions
on a log Mass - log age plot is is usually uniform along log age for equal
intervals of log Mass. This uniformity results from either an individual region
mass that varies as 1/age or a region disruption probability that varies as
1/age. A correlation between fading-corrected surface brightness and age
suggests the former.Comment: Astronomical Journal, in press for November 2009. 34 pages, 18
figures, 5 table
Including food systems, biodiversity, nutrition and health in the Post-2020 Global Biodiversity Framework: a submission from the Alliance of Bioversity International and the International Center for Tropical Agriculture.
The Stellar and Gas Kinematics of the LITTLE THINGS Dwarf Irregular Galaxy NGC 1569
In order to understand the formation and evolution of dIm galaxies, one needs
to understand their three-dimensional structure. We present measurements of the
stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy.
The stellar vertical velocity dispersion, , coupled with the
maximum rotational velocity derived from \ion{H}{1} observations, , gives a measure of how kinematically hot the galaxy is, and, therefore,
indicates its structure. We conclude that the stars in NGC 1569 are in a thick
disk with a = 2.4 0.7. In addition to the
structure, we analyze the ionized gas kinematics from \ion{O}{3} observations
along the morphological major axis. These data show evidence for outflow from
the inner starburst region and a potential expanding shell near supermassive
star cluster (SSC) A. When compared to the stellar kinematics, the velocity
dispersion of the stars increase in the region of SSC A supporting the
hypothesis of an expanding shell. The stellar kinematics closely follow the
motion of the gas. Analysis of high resolution \ion{H}{1} data clearly reveals
the presence of an \ion{H}{1} cloud that appears to be impacting the eastern
edge of NGC 1569. Also, an ultra-dense \ion{H}{1} cloud can be seen extending
to the west of the impacting \ion{H}{1} cloud. This dense cloud is likely the
remains of a dense \ion{H}{1} bridge that extended through what is now the
central starburst area. The impacting \ion{H}{1} cloud was the catalyst for the
starburst, thus turning the dense gas into stars over a short timescale,
1 Gyr. We performed a careful study of the spectral energy distribution using
infrared, optical, and ultraviolet photometry producing a state-of-the-art mass
model for the stellar disk. This mass modeling shows that stars dominate the
gravitational potential in the inner 1 kpc.Comment: 49 pages, 25 figures, accepted in A
A kinematic study of the irregular dwarf galaxy NGC 2366 using HI and Halpha observations
Abridged. Context. The metal content of dwarf galaxies and the metal
enrichment of the intergalactic medium both suggest that mass loss from
galaxies is a significant factor for the chemical evolution history of
galaxies, in particular of dwarf galaxies. However, no clear evidence of a
blow-away in local dwarf galaxies has been found so far.
Aims. We therefore performed a detailed kinematic analysis of the neutral and
ionised gas in the nearby star-forming irregular dwarf galaxy NGC 2366 in order
to make predictions about the fate of the gas and to get a more complete
picture of this galaxy.
Methods. A deep Halpha image and Fabry-Perot interferometric data of NGC 2366
were obtained. They were complemented by HI synthesis data from the THINGS
survey. We searched for line-splitting both in Halpha and HI by performing a
Gaussian decomposition. To get an idea whether the expansion velocities are
high enough for a gas blow-away, we used the pseudo-isothermal halo model,
which gives us realistic values for the escape velocities of NGC 2366. The good
data quality also allowed us to discuss some peculiarities of the morphology
and the dynamics in NGC 2366.
Results. A large red-shifted outflow north west of the giant extragalactic
HII region with an expansion velocity of up to 50 km/s is found in Halpha, but
not in HI. Additionally, a blue-shifted component north of the giant
extragalactic HII region was detected both in Halpha and HI with an expansion
velocity of up to 30 km/s. A comparison with the escape velocities of NGC 2366
reveals that the gas does not have enough kinetic energy to leave the
gravitational potential.Comment: 15 pages, 14 figures, accepted for publication by A&
Internet e-ethics in confrontation with an activists' agenda: Yahoo! on trial
A prolonged confrontation between Yahoo! Inc. and French anti-racism activists who ask for the removal of Nazi items from auction sites as well as restricted access to neo-Nazis sites is analyzed. We present the case and its development up to the decision of Yahoo! Inc. to remove the items from yahoo.com following a French court’s verdict against the firm. Using a business ethics approach, we distinguish the legal, technical, philosophical and managerial issues involved in the case and their management by Yahoo! We conclude on the difficulty of governing relations with society from corporate and legal affairs departments at the headquarters level, and on the clash of two visions over the regulation of social freedom.E-business, e-ethics, auctions, legal compliance, internet regulation, freedom of expression, media crisis
Rotational Mixing in Magellanic Clouds B Stars - Theory versus Observation
We have used VLT FLAMES data to constrain the uncertain physics of rotational
mixing in stellar evolution models. We have simulated a population of single
stars and find two groups of observed stars that cannot be explained: (1) a
group of fast rotating stars which do not show evidence for rotational mixing
and (2) a group of slow rotators with strong N enrichment. Binary effects and
fossil magnetic fields may be considered to explain those two groups. We
suggest that the element boron could be used to distinguish between rotational
mixing and the binary scenario. Our single star population simulations quantify
the expected amount of boron in fast and slow rotators and allow a comparison
with measured nitrogen and boron abundances in B-stars.Comment: to appear in Comm. in Astroseismology - Contribution to the
Proceedings of the 38th LIAC, 200
Note From the Editor
Background and AimsTo review published studies on the effectiveness of combining cognitive-behavioural therapy (CBT) and motivational interviewing (MI) to treat comorbid clinical and subclinical alcohol use disorder (AUD) and major depression (MDD) and estimate the effect of this compared with usual care. MethodsWe conducted systematic literature searches in PubMed, PsycINFO and Embase up to June 2013 and identified additional studies through cross-references in included studies and systematic reviews. Twelve studies comprising 1721 patients met our inclusion criteria. The studies had sufficient statistical power to detect small effect sizes. ResultsCBT/MI proved effective for treating subclinical and clinical AUD and MDD compared with controls, with small overall effect sizes at post-treatment [g=0.17, confidence interval (CI)=0.07-0.28, Pless than0.001 for decrease of alcohol consumption and g=0.27, CI: 0.13-0.41, Pless than0.001 for decrease of symptoms of depression, respectively]. Subgroup analyses revealed no significant differences for both AUD and MDD. However, digital interventions showed a higher effect size for depression than face-to-face interventions (g=0.73 and g=0.23, respectively, P=0.030). ConclusionsCombined cognitive-behavioural therapy and motivational interviewing for clinical or subclinical depressive and alcohol use disorders has a small but clinically significant effect in treatment outcomes compared with treatment as usual
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