36 research outputs found
The IntraCluster Medium: An Invariant Stellar IMF
Evidence supporting the hypothesis of an invariant stellar Initial Mass
Function is strong and varied. The intra-cluster medium in rich clusters of
galaxies is one of the few contrary locations where recent interpretations of
the chemical abundances have favoured an IMF that is biased towards massive
stars, compared to the `normal' IMF. This interpretation hinges upon the
neglect of Type Ia supernovae to the ICM enrichment, and a particular choice of
the nucleosynthesis yields of Type II supernovae. We demonstrate here that when
one adopts yields determined empirically from observations of Galactic stars,
rather than the uncertain model yields, a self-consistent picture may be
obtained with an invariant stellar IMF, and about half of the iron in the ICM
being produced by Type Ia supernovae.Comment: 9 pages, LateX (aaspp4 macro), including one postscript figure.
Accepted, ApJ Letter
Comparison of carbohydrate utilization in man using indirect calorimetry and mass spectrometry after an oral load of 100 g naturally-labelled [13C]glucose
1. Carbohydrate (CHO) oxidation was measured simultaneously in a group of five normal subjects after an oral load of 100 g naturally-labelled [13C]glucose, using indirect calorimetry and mass spectrometry. 2. CHO utilization, calculated from the results of indirect calorimetry, increased 30 min after the glucose load to reach a peak at 90 min. It then decreased to reach basal values at 380 min. Cumulative total CHO oxidation at 480 min was 83±8g, and CHO oxidized above basal levels, 37±3 g. 3. Enrichment of expired carbon dioxide with 13C began at 60 min and maximum values were observed at 270 min. At 480 min, cumulative CHO oxidation measured by use of [13C]glucose was 29 g. The difference from calorimetric values can be attributed in part to the slow isotopic dilution in the glucose and bicarbonate pools. 4. Thus, approximately 30% of the glucose load was oxidized during the 8 h after its ingestion and this accounts for a significant part of the increased CHO oxidation (37 g), as measured by indirect calorimetr
Chemical Evolution of Galaxies
Chemical evolution of galaxies brings together ideas on stellar evolution and
nucleosynthesis with theories of galaxy formation, star formation and galaxy
evolution, with all their associated uncertainties. In a new perspective
brought about by the Hubble Deep Field and follow-up investigations of global
star formation rates, diffuse background etc., it has become necessary to
consider the chemical composition of dark baryonic matter as well as that of
visible matter in galaxies.Comment: 6 pages, AAS LaTeX macros v5.0, Millennium Essay to appear in PASP,
Feb 200
Galactic Cosmic Rays from Supernova Remnants (I) - a Cosmic Ray Composition controlled by Volatility and Mass-to-Charge Ratio
This is the first of a series of papers analysing the Galactic Cosmic Ray
composition and origin. We show that the Galactic Cosmic Ray source (GCRS)
composition is best described in terms of (i) a general enhancement of the
refractory elements relative to the volatile ones, and (ii) among the volatile
elements, an enhancement of the heavier elements relative to the lighter ones;
this mass dependence most likely reflects a mass-to-charge (A/Q) dependence of
the acceleration efficiency; among the refractory elements, there is NO such
enhancement of heavier species, or only a much weaker one. We regard as
coincidental the similarity between the GCRS composition and that of the solar
corona, which is biased according to first ionization potential. In a companion
paper, this GCRS composition is interpreted in terms of an acceleration by
supernova shock waves of interstellar and/or circumstellar (eg Ne22 rich
Wolf-Rayet wind) gas-phase and especially dust material.Comment: 23 pages plain TeX and 6 postscript figures, to appear in ApJ, also
available from ftp://wonka.physics.ncsu.edu/pub/elliso
Chandra ACIS Survey of M33 (ChASeM33): The enigmatic X-ray emission from IC131
We present the first X-ray analysis of the diffuse hot ionized gas and the
point sources in IC131, after NGC604 the second most X-ray luminous giant HII
region in M33. The X-ray emission is detected only in the south eastern part of
IC131 (named IC131-se) and is limited to an elliptical region of ~200pc in
extent. This region appears to be confined towards the west by a hemispherical
shell of warm ionized gas and only fills about half that volume. Although the
corresponding X-ray spectrum has 1215 counts, it cannot conclusively be told
whether the extended X-ray emission is thermal, non-thermal, or a combination
of both. A thermal plasma model of kT_e=4.3keV or a single power law of
Gamma=2.1 fit the spectrum equally well. If the spectrum is purely thermal
(non-thermal), the total unabsorbed X-ray luminosity in the 0.35-8keV energy
band amounts to L_X = 6.8(8.7)x10^35erg/s. Among other known HII regions
IC131-se seems to be extreme regarding the combination of its large extent of
the X-ray plasma, the lack of massive O stars, its unusually high electron
temperature (if thermal), and the large fraction of L_X emitted above 2keV
(~40-53%). A thermal plasma of ~4keV poses serious challenges to theoretical
models, as it is not clear how high electron temperatures can be produced in
HII regions in view of mass-proportional and collisionless heating. If the gas
is non-thermal or has non-thermal contributions, synchrotron emission would
clearly dominate over inverse Compton emission. It is not clear if the same
mechanisms which create non-thermal X-rays or accelerate CRs in SNRs can be
applied to much larger scales of 200pc. In both cases the existing theoretical
models for giant HII regions and superbubbles do not explain the hardness and
extent of the X-ray emission in IC131-se.Comment: 28 pages, 7 figures and 2 tables. Accepted for publication in ApJ.
For a high resolution version of the paper see
http://hea-www.harvard.edu/vlp_m33_public/publications.htm
NGC 1624-2: A slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field
This paper presents a first observational investigation of the faint Of?cp
star NGC 1624-2, yielding important new constraints on its spectral and
physical characteristics, rotation, magnetic field strength, X-ray emission and
magnetospheric properties. Modeling the spectrum and spectral energy
distribution, we conclude that NGC 1624-2 is a main sequence star of mass M
{\simeq} 30 M{\odot}, and infer an effective temperature of 35 {\pm} 2 kK and
log g = 4.0 {\pm} 0.2. Based on an extensive time series of optical spectral
observations we report significant variability of a large number of spectral
lines, and infer a unique period of 157.99 {\pm} 0.94 d which we interpret as
the rotational period of the star. We report the detection of a very strong -
5.35 {\pm} 0.5 kG - longitudinal magnetic field , coupled with probable
Zeeman splitting of Stokes I profiles of metal lines confirming a surface field
modulus of 14 {\pm} 1 kG, consistent with a surface dipole of polar
strength >~ 20 kG. This is the largest magnetic field ever detected in an
O-type star, and the first report of Zeeman splitting of Stokes I profiles in
such an object. We also report the detection of reversed Stokes V profiles
associated with weak, high-excitation emission lines of O iii, which we propose
may form in the close magnetosphere of the star. We analyze archival Chandra
ACIS-I X-ray data, inferring a very hard spectrum with an X-ray efficiency log
Lx/Lbol = -6.4, a factor of 4 larger than the canonical value for O-type stars
and comparable to that of the young magnetic O-type star {\theta}1 Ori C and
other Of?p stars. Finally, we examine the probable magnetospheric properties of
the star, reporting in particular very strong magnetic confinement of the
stellar wind, with {\eta}* {\simeq} 1.5 {\times} 10^4, and a very large Alfven
radius, RAlf = 11.4 R*.Comment: 17 pages, MNRAS accepted and in pres
The X-ray Transient 2XMMi J003833.3+402133: A Candidate Magnetar at High Galactic Latitude
We present detailed analysis of the transient X-ray source 2XMMi
J003833.3+402133 detected by XMM-Newton in January 2008 during a survey of M
31. The X-ray spectrum is well fitted by either a steep power law plus a
blackbody model or a double blackbody model. Prior observations with
XMM-Newton, Chandra, Swift and ROSAT spanning 1991 to 2007, as well as an
additional Swift observation in 2011, all failed to detect this source. No
counterpart was detected in deep optical imaging with the Canada France Hawaii
Telescope down to a 3sigma lower limit of g = 26.5 mag. This source has
previously been identified as a black hole X-ray binary in M 31. While this
remains a possibility, the transient behaviour, X-ray spectrum, and lack of an
optical counterpart are equally consistent with a magnetar interpretation for
2XMMi J003833.3+402133. The derived luminosity and blackbody emitting radius at
the distance of M 31 argue against an extragalactic location, implying that if
it is indeed a magnetar it is located within the Milky Way but 22deg out of the
plane. The high Galactic latitude could be explained if 2XMMi J003833.3+402133
were an old magnetar, or if its progenitor was a runaway star that traveled
away from the plane prior to going supernova.Comment: 16 pages, 5 figures, 4 tables, accepted for publication in ApJ
following moderate revisio
Stellar populations of early-type galaxies in different environments I. Line-strength indices
Aims: This paper commences a series devoted to the study of the stellar
content of early-type galaxies. The goal of the series is to set constraints on
the evolutionary status of these objects.
Methods: In this paper we describe the details of the galaxy sample, the
observations, and the data reduction. Line-strength indices and velocity
dispersions sigma are measured in 98 early-type galaxies drawn from different
environments, and the relation of the indices with the velocity dispersion
analysed in detail.
Results: The present sample indicates that some of the index-sigma relations
depend on galaxy environment. In particular, the slope of the relation between
Balmer lines and sigma is steeper for galaxies in the Virgo cluster, small
groups, and in the field than for galaxies in the Coma cluster. In several
indices there is also a significant offset in the zero point between the
relations defined by the different subsamples. The slopes of the index-sigma
relation for the Virgo and low-density environment galaxies are explained by a
variation of both age and metallicity with velocity dispersion, as previously
noted in other studies. For the galaxies in the Coma cluster, however, the
relation of the indices with sigma only requires a variation of the abundance
along the sigma sequence. In agreement with other studies we find that the
models that better reproduce the slopes are those in which the alpha elements
vary more than the Fe-peak elements along the sigma sequence, while, at a given
sigma, older galaxies show an higher alpha/Fe ratio.
Conclusions: The results can be explained assuming that galaxies in the Coma
cluster have experienced a truncated star formation and chemical enrichment
history compared to a more continuous time-extended history for their
counterparts in lower density environments.Comment: accepted for publication in A&
Observations of metals in the intra-cluster medium
Because of their deep gravitational potential wells, clusters of galaxies
retain all the metals produced by the stellar populations of the member
galaxies. Most of these metals reside in the hot plasma which dominates the
baryon content of clusters. This makes them excellent laboratories for the
study of the nucleosynthesis and chemical enrichment history of the Universe.
Here we review the history, current possibilities and limitations of the
abundance studies, and the present observational status of X-ray measurements
of the chemical composition of the intra-cluster medium. We summarise the
latest progress in using the abundance patterns in clusters to put constraints
on theoretical models of supernovae and we show how cluster abundances provide
new insights into the star-formation history of the Universe.Comment: 28 pages, 12 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 16; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Increasing Glencore's sustainable management performance: recommendation and risks, statements based on literature and best practices
The main purpose of this report is to provide Glencore with applicable recommendations so that it can improve its sustainable reputation. The second purpose of the work is to present all risks incurred by Glencore’s non-application of sustainable recommendations. Recommendations and risks have been developed based on literature, interviews and companies’ good practices. Sustainability reports of mining companies publicly quoted have been intensively used to grasp the different sustainability criterions known and applied in the sector. Recommendations and risks analysis have been presented in a consistent manner throughout the report as per the following: 1st good practice based on literature is presented, 2nd Glencore’s practice is highlighted, 3rd recommendations are formulated and 4th risks if Glencore does not implement these recommendations are also developed. The work starts with a brief presentation of Glencore including its flotation as well as its merger with Xstrata. The work then considers the global economic growth and its impact on the health of extractive companies as well as on the environment and the population. Secondly, as the goal of this work is not to criticize the commodity sector but rather to improve it, the importance and knowledge of trading and mining activities, to balance supply and demand, is also demonstrated. Thirdly, the environment of the sector going toward more transparency with many supporting initiatives and the reputational risk mining and trading will face if they do not reckon on this trend is mentioned. Finally, in order to familiarize the reader with Glencore’s top controversies, various examples on Glencore’s past negative experiences are given and explained. These examples include tax, corporate, transparency, secrecy, pollution and human rights issues. This introduction phase is followed by the core of the analysis that features the following results: The results of this report demonstrate that despite Glencore’s relatively recent active engagement in sustainability development, the company is still classified as a relatively poor performer compared to competitors. Moreover, a little less than thirty recommendations related mainly to transparency, communication and management have been formulated and eighteen risks have been established. The report concludes with the responsibility companies have in developing countries. The role of a company active in the mining sector in countries where governance is very weak is not necessarily to improve governance, human rights and legal loopholes all by itself, but it is essential that it does not aggravate the situation. The job of a mining company is to win a so called “license to operate” through trust-building established over several years of upright practices and understands that many benefits will follow