6,228 research outputs found
L'arbre fontaine
Dans certaines rÊgions montagneuses rÊgulièrement ventÊes, soumises à un climat ocÊanique comme au Chili, en Afrique du Sud ou au Cap-Vert, une mer de brouillard règne en quasi permanence. Ces conditions mÊtÊorologiques très singulières permettent à la vÊgÊtation de prospÊrer malgrÊ de faibles pluies. Arbres et arbustes captent l'eau des brouillards et des bruines, donnant naissance à de vÊritables forêts dites nÊbuleuses. Ces fontaines vÊgÊtales sont exploitÊes par l'homme depuis la nuit des temps pour rÊcupÊrer de l'eau potable et dÊvelopper une vie agricole. VÊritable don des dieux, l'arbre fontaine a parfois ÊtÊ ÊlevÊ au rang d'arbre sacrÊ comme dans l'Île de Hierro aux Canaries, point de dÊpart de la recherche des auteurs de cet article. (RÊsumÊ d'auteur
Infrared Study of Fullerene Planetary Nebulae
We present a study of 16 PNe where fullerenes have been detected in their
Spitzer spectra. This large sample of objects offers an unique opportunity to
test conditions of fullerene formation and survival under different metallicity
environments as we are analyzing five sources in our own Galaxy, four in the
LMC, and seven in the SMC. Among the 16 PNe under study, we present the first
detection of C60 (possibly also C70) fullerenes in the PN M 1-60 as well as of
the unusual 6.6, 9.8, and 20 um features (possible planar C24) in the PN K
3-54. Although selection effects in the original samples of PNe observed with
Spitzer may play a potentially significant role in the statistics, we find that
the detection rate of fullerenes in C-rich PNe increases with decreasing
metallicity (5% in the Galaxy, 20% in the LMC, and 44% in the SMC). CLOUDY
photoionization modeling matches the observed IR fluxes with central stars that
display a rather narrow range in effective temperature (30,000-45,000 K),
suggesting a common evolutionary status of the objects and similar fullerene
formation conditions. The observed C60 intensity ratios in the Galactic sources
confirm our previous finding in the MCs that the fullerene emission is not
excited by the UV radiation from the central star. CLOUDY models also show that
line- and wind-blanketed model atmospheres can explain many of the observed
[NeIII]/[NeII] ratios by photoionization suggesting that possibly the UV
radiation from the central star, and not shocks, are triggering the
decomposition of the circumstellar dust grains. With the data at hand, we
suggest that the most likely explanation for the formation of fullerenes and
graphene precursors in PNe is that these molecular species are built from the
photo-chemical processing of a carbonaceous compound with a mixture of aromatic
and aliphatic structures similar to that of HAC dust.Comment: Accepted for publication in ApJ (43 pages, 11 figures, and 4 tables).
Small changes to fit the proof-corrected article to be published in Ap
The formation of fullerenes: clues from new C60, C70, and (possible) planar C24 detections in Magellanic Cloud Planetary Nebulae
We present ten new Spitzer detections of fullerenes in Magellanic Cloud
Planetary Nebulae, including the first extragalactic detections of the C70
molecule. These new fullerene detections together with the most recent
laboratory data permit us to report an accurate determination of the C60 and
C70 abundances in space. Also, we report evidence for the possible detection of
planar C24 in some of our fullerene sources, as indicated by the detection of
very unusual emission features coincident with the strongest transitions of
this molecule at ~6.6, 9.8, and 20 um. The infrared spectra display a complex
mix of aliphatic and aromatic species such as hydrogenated amorphous carbon
grains (HACs), PAH clusters, fullerenes, and small dehydrogenated carbon
clusters (possible planar C24). The coexistence of such a variety of molecular
species supports the idea that fullerenes are formed from the decomposition of
HACs. We propose that fullerenes are formed from the destruction of HACs,
possibly as a consequence of shocks driven by the fast stellar winds, which can
sometimes be very strong in transition sources and young PNe. This is supported
by the fact that many of our fullerene-detected PNe show altered [NeIII]/[NeII]
ratios suggestive of shocks as well as P-Cygni profiles in their UV lines
indicative of recently enhanced mass loss.Comment: Accepted for publication in The Astrophysical Journal Letters (16
pages, 2 Tables and 3 figures
Revealing the mid-infrared emission structure of IRAS 16594-4656 and IRAS 07027-7934
TIMMI2 diffraction-limited mid-infrared images of a multipolar
proto-planetary nebula IRAS 16594-4656 and a young [WC] elliptical planetary
nebula IRAS 07027-7934 are presented. Their dust shells are for the first time
resolved (only marginally in the case of IRAS 07027-7934) by applying the
Lucy-Richardson deconvolution algorithm to the data, taken under exceptionally
good seeing conditions (<0.5"). IRAS 16594-4656 exhibits a two-peaked
morphology at 8.6, 11.5 and 11.7 microns which is mainly attributed to emission
from PAHs. Our observations suggest that the central star is surrounded by a
toroidal structure observed edge-on with a radius of 0.4" (~640 AU at an
assumed distance of 1.6 kpc) with its polar axis at P.A.~80 degrees, coincident
with the orientation defined by only one of the bipolar outflows identified in
the HST optical images. We suggest that the material expelled from the central
source is currently being collimated in this direction and that the multiple
outflow formation has not been coeval. IRAS 07027-7934 shows a bright,
marginally extended emission (FWHM=0.3") in the mid-infrared with a slightly
elongated shape along the N-S direction, consistent with the morphology
detected by HST in the near-infrared. The mid-infrared emission is interpreted
as the result of the combined contribution of small, highly ionized PAHs and
relatively hot dust continuum. We propose that IRAS 07027-7934 may have
recently experienced a thermal pulse (likely at the end of the AGB) which has
produced a radical change in the chemistry of its central star.Comment: 35 pages, 8 figures (figures 1, 2, 4 and 6 are in low resolution)
accepted for publication in Ap
Potential of the Julia programming language for high energy physics computing
Research in high energy physics (HEP) requires huge amounts of computing and
storage, putting strong constraints on the code speed and resource usage. To
meet these requirements, a compiled high-performance language is typically
used; while for physicists, who focus on the application when developing the
code, better research productivity pleads for a high-level programming
language. A popular approach consists of combining Python, used for the
high-level interface, and C++, used for the computing intensive part of the
code. A more convenient and efficient approach would be to use a language that
provides both high-level programming and high-performance. The Julia
programming language, developed at MIT especially to allow the use of a single
language in research activities, has followed this path. In this paper the
applicability of using the Julia language for HEP research is explored,
covering the different aspects that are important for HEP code development:
runtime performance, handling of large projects, interface with legacy code,
distributed computing, training, and ease of programming. The study shows that
the HEP community would benefit from a large scale adoption of this programming
language. The HEP-specific foundation libraries that would need to be
consolidated are identifiedComment: 32 pages, 5 figures, 4 table
Bow shocks, nova shells, disc winds and tilted discs: the nova-like V341 Ara has it all
V341 Ara was recently recognized as one of the closest (d â 150 pc) and brightest (V â 10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow shock, where the systemâs accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multiwavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10â16 d and typical amplitude of â1 mag. High-cadence photometry from theTransiting Exoplanet Survey Satellite (TESS) reveals for the first time both the orbital period and a ânegative superhumpâ period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect antiphased absorption and emission-line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white-dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [OâIII] emission produced in the bow shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a âguest starâ mentioned in Chinese historical records in AD 1240. If this marks the date of the systemâs nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory
New Young Star Candidates in the Taurus-Auriga Region as Selected From WISE
The Taurus Molecular Cloud subtends a large solid angle on the sky, in excess
of 250 square degrees. The search for legitimate Taurus members to date has
been limited by sky coverage as well as the challenge of distinguishing members
from field interlopers. The Wide-field Infrared Survey Explorer (WISE) has
recently observed the entire sky, and we take advantage of the opportunity to
search for young stellar object (YSO) candidate Taurus members from a ~260
square degree region designed to encompass previously-identified Taurus
members. We use near- and mid-infrared colors to select objects with apparent
infrared excesses and incorporate other catalogs of ancillary data to present:
a list of rediscovered Taurus YSOs with infrared excesses (taken to be due to
circumstellar disks), a list of rejected YSO candidates (largely galaxies), and
a list of 94 surviving candidate new YSO-like Taurus members. There is likely
to be contamination lingering in this candidate list, and follow-up spectra are
warranted.Comment: Accepted to ApJ
Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV
A search for new physics is presented based on an event signature of at least
three jets accompanied by large missing transverse momentum, using a data
sample corresponding to an integrated luminosity of 36 inverse picobarns
collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector
at the LHC. No excess of events is observed above the expected standard model
backgrounds, which are all estimated from the data. Exclusion limits are
presented for the constrained minimal supersymmetric extension of the standard
model. Cross section limits are also presented using simplified models with new
particles decaying to an undetected particle and one or two jets
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
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