7,092 research outputs found
Cosmic Neutron Star Merger Rate and Gravitational Waves constrained by the R Process Nucleosynthesis
The cosmic evolution of the neutron star merger (NSM) rate can be deduced
from the observed cosmic star formation rate. This allows to estimate the rate
expected in the horizon of the gravitational wave detectors advanced Virgo and
ad LIGO and to compare those rates with independent predictions. In this
context, the rapid neutron capture process, or r process, can be used as a
constraint assuming NSM is the main astrophysical site for this nucleosynthetic
process. We compute the early cosmic evolution of a typical r process element,
Europium. Eu yields from NSM are taken from recent nucleosynthesis
calculations. The same approach allows to compute the cosmic rate of Core
Collapse SuperNovae (CCSN) and the associated evolution of Eu. We find that the
bulk of Eu observations at high iron abundance can be rather well fitted by
either CCSN or NSM scenarios. However, at lower metallicity, the early Eu
cosmic evolution favors NSM as the main astrophysical site for the r process. A
comparison between our calculations and spectroscopic observations at very low
metallicities allows to constrain the coalescence timescale in the NSM scenario
to about 0.1 to 0.2 Gyr. These values are in agreement with the coalescence
timescales of some observed binary pulsars. Finally, the cosmic evolution of Eu
is used to put constraints on the NSM rate, the merger rate in the horizon of
the gravitational wave detectors advanced Virgo/ad LIGO, as well as the
expected rate of electromagnetic counterparts to mergers (kilonovae) in large
near-infrared surveys.Comment: accepted in MNRAS, 19 page
Grid of theoretical NLTE equivalent widths of four Ba II lines and barium abundance in cool stars
We present a grid of computed non-local thermodynamic equilibrium (NLTE)
equivalent widths (EW) and NLTE abundance corrections for four Ba II lines:
4554, 5853, 6141, and 6496 A. The grid can be useful in deriving the NLTE
barium abundance in stars having parameters in the following ranges: effective
temperature from 4000 K to 6500 K, surface gravity log g from 0 to 5,
microturbulent velocity 0 km s^-1 to 3 km s^-1, metallicity [Fe/H] from -2 to
+0.5, and [Ba/Fe] from -0.4 to +0.6. The NLTE abundance can be either derived
by EW interpolation (using the observed Ba II line EW) or by using the NLTE
correction applied to a previously determined LTE abundance. Ba II line
equivalent widths and the NLTE corrections were calculated using the updated
MULTI code and the Ba II atomic model that was previously applied to determine
the NLTE barium abundance in different types of stars. The grid is available
on-line through the web, and we find that the grid Ba NLTE corrections are
almost as accurate as direct NLTE profile fitting (to within 0.05-0.08 dex).
For the weakest Ba II line (5853 A) the LTE abundances almost agree with the
NLTE abundances, whereas the other three Ba II lines, 4554, 6141, and 6496 A,
need NLTE corrections even at the highest metallicities tested here. The 4554 A
line is extremely strong and should not be used for abundance analysis above
[Fe/H]= -1. Furthermore, we tested the impact of different model atmospheres
and spectrum synthesis codes and found average differences of 0.06 dex and 0.09
dex, respectively, for all four lines. At these metallicities we find an
average Delta NLTE of +/-0.1 dex for the three useful Ba lines for subsolar
cool dwarfs.Comment: 9 pages 8 figures submitted to A&
Becker on Ewald on Foucault on Becker : American Neoliberalism and Michel Foucault\u27s 1979 \u3ci\u3eBirth of Biopolitics\u3c/i\u3e Lectures
In a series of lectures delivered in 1979 at the Collège de France under the title The Birth of Biopolitics, Michel Foucault conducted a close reading of Gary Becker’s writings on human capital and on crime and punishment, within the context of an elaboration and critique of American neoliberalism. Foucault was assisted at the time, at the Collège de France, by François Ewald. Since then, there has been ongoing debate over Foucault’s views about neoliberalism. In this historic meeting at the University of Chicago between Professors Becker and Ewald, Professor Ewald presents a framework to understand Foucault’s writings on Becker; Professor Bernard Harcourt offers a different reading of Foucault’s views on neoliberalism; and Professor Becker responds to Foucault’s lectures and to possible critical readings of his work on human capital. Apology or critique – that is the motivating question in this rich encounter between contemporary French philosophy and American economic theory
Becker and Foucault on Crime and Punishment – A Conversation with Gary Becker, François Ewald, and Bernard Harcourt: The Second Session
In his 1979 lectures at the Collège de France, The Birth of Biopolitics, Michel Foucault discussed and analyzed Gary Becker’s economic theory of crime and punishment, originally published in The Journal of Political Economy in 1968 under the title “Crime and Punishment: An Economic Approach.” In this historic, second encounter at the University of Chicago, Gary Becker responds to Foucault’s lectures and possible critical readings of his writings on crime and punishment, in conversation with Professors François Ewald (who was, at the time in 1979, Foucault’s assistant at the Collège and one of Foucault’s closest interlocutors) and Bernard Harcourt (a punishment theorist and an editor of Foucault’s lectures). The rich encounter explores potential overlaps, complementarities, and conflicts between Foucault’s theoretical work on punishment (both in Birth of Biopolitics and Discipline and Punish) and Becker’s economic theory of crime, builds on the previous confrontation over American neoliberalism, and provides a bridge between contemporary French philosophy and American economic theory
Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. II. NGC 3256 Clusters
We present Gemini optical spectroscopy of 23 young star clusters in NGC3256.
We find that the cluster ages range are from few Myr to ~150 Myr. All these
clusters are relatively massive (2--40)x 10^{5} \msun$ and appear to be of
roughly 1.5 \zo metallicity. The majority of the clusters in our sample follow
the same rotation curve as the gas and hence were presumably formed in the
molecular-gas disk. However, a western subsample of five clusters has
velocities that deviate significantly from the gas rotation curve. These
clusters may either belong to the second spiral galaxy of the merger or may
have formed in tidal-tail gas falling back into the system. We discuss our
observations in light of other known cluster populations in merging galaxies,
and suggest that NGC 3256 is similar to Arp 220, and hence may become an
Ultra-luminous Infrared Galaxy as the merger progresses and the star-formation
rate increases.
Some of the clusters which appeared as isolated in our ground-based images
are clearly resolved into multiple sub-components in the HST-ACS images. The
same effect has been observed in the Antennae galaxies, showing that clusters
are often not formed in isolation, but instead tend to form in larger groups or
cluster complexes.Comment: 20 pages, 10 figures, 3 tables; Accepted Ap
X-Shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars
The extremely metal-poor stars are the direct descendants of the first
generation stars. They carry the chemical signature of the pristine Universe at
the time they formed, shortly after the Big Bang. We aim to derive information
about extremely metal-poor stars from their observed spectra. Four extremely
metal-poor stars were selected from the Sloan Digital Sky Survey (SDSS) and
observed during the guaranteed observing time of X-Shooter. The X-Shooter
spectra were analysed using an automatic code, MyGIsFOS, which is based on a
traditional analysis method. It makes use of a synthetic grid computed from
one-dimensional, plane-parallel, hydrostatic model atmospheres. The low
metallicity derived from the SDSS spectra is confirmed here. Two kinds of stars
are found. Two stars are confirmed to be extremely metal-poor, with no evidence
of any enhancement in carbon. The two other stars are strongly enhanced in
carbon. We could not derive iron abundance for one of them, while [Ca/H] is
below -4.5. Two of the stars are members of the rare population of extremely
metal-poor stars low in alpha elements.Comment: A&A in pres
TOPoS: I. Survey design and analysis of the first sample
The metal-weak tail of the metallicity distribution function (MDF) of the
Galactic Halo stars contains crucial information on the formation mode of the
first generation of stars. To determine this observationally, it is necessary
to observe large numbers of extremely metal-poor stars. We present here the
Turn-Off Primordial Stars survey (TOPoS) that is conducted as an ESO Large
Programme at the VLT. This project has {four} main goals: (i) to understand the
formation of low-mass stars in a low-metallicity gas: determine the metal-weak
tail of the halo MDF below [M/H]=-3.5. In particular, we aim at determining the
critical metallicity, that is the lowest metallicity sufficient for the
formation of low-mass stars; (ii) to determine the relative abundance of the
elements in extremely metal-poor stars, which are the signature of the massive
first stars; (iii) to determine the trend of the lithium abundance at the time
when the Galaxy formed; and (iv) to derive the fraction of C-enhanced extremely
metal-poor stars with respect to normal extremely metal-poor stars. The large
number of stars observed in the SDSS provides a good sample of candidates of
stars at extremely low metallicity. Candidates with turn-off colours down to
magnitude g=20 were selected from the low-resolution spectra of SDSS by means
of an automated procedure. X-Shooter has the potential of performing the
necessary follow-up spectroscopy, providing accurate metallicities and
abundance ratios for several key elements for these stars. We here present the
stellar parameters of the first set of stars. The nineteen stars range in iron
abundance between -4.1 and -2.9 dex relative to the Sun. Two stars have a high
radial velocity and, according to our estimate of their kinematics, appear to
be marginally bound to the Galaxy and are possibly accreted from another
galaxy.Comment: A&A accepted for publicatio
French Innovative Processes in the Field of Thermal TreatmentFor Decommissioning and Legacy Waste
International audienceIn order to optimize decommissioning waste management and better anticipate related issues, French nuclear waste producers CEA and AREVA, and the French Agency in charge of radioactive waste disposal (ANDRA) have decided to collectively develop technologies mastering costs, schedules and dose uptake as well as optimizing waste volumes and repository safety. In this context, several innovative projects have emerged over the past few years to develop specific thermal treatment processes. This paper focus on four new processes, presenting their goals, technical descriptions and first experimental results
Neutron-Capture Elements in the Early Galaxy: Insights from a Large Sample of Metal-Poor Giants
New abundances for neutron-capture (n-capture) elements in a large sample of
metal-poor giants from the Bond survey are presented. The spectra were acquired
with the KPNO 4-m echelle and coude feed spectrographs, and have been analyzed
using LTE fine-analysis techniques with both line analysis and spectral
synthesis. Abundances of eight n-capture elements (Sr, Y, Zr, Ba, La, Nd, Eu,
Dy) in 43 stars have been derived from blue (lambda = 4070--4710, R~20,000, S/N
ratio~100-200) echelle spectra and red (lambda = 6100--6180, R~22,000, S/N
ratio~100-200) coude spectra, and the abundance of Ba only has been derived
from the red spectra for an additional 27 stars. Overall, the abundances show
clear evidence for a large star-to-star dispersion in the heavy element-to-iron
ratios. The new data also confirm that at metallicities [Fe/H] <~ --2.4, the
abundance pattern of the heavy (Z >= 56) n-capture elements in most giants is
well-matched to a scaled Solar System r-process nucleosynthesis pattern. The
onset of the main r-process can be seen at [Fe/H] ~ --2.9. Contributions from
the s-process can first be seen in some stars with metallicities as low as
[Fe/H] ~ --2.75, and are present in most stars with metallicities [Fe/H] >
--2.3. The lighter n-capture elements (Sr-Y-Zr) are enhanced relative to the
heavier r-process element abundances. Their production cannot be attributed
solely to any combination of the Solar System r- and main s-processes, but
requires a mixture of material from the r-process and from an additional
n-capture process which can operate at early Galactic time.Comment: Text + 5 Tables and 11 Figures: Submitted to the Astrophysical
Journa
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