70 research outputs found
Morphological Properties of PPNs: Mid-IR and HST Imaging Surveys
We will review our mid-infrared and HST imaging surveys of the circumstellar
dust shells of proto-planetary nebulae. While optical imaging indirectly probes
the dust distribution via dust-scattered starlight, mid-IR imaging directly
maps the distribution of warm dust grains. Both imaging surveys revealed
preferencially axisymmetric nature of PPN dust shells, suggesting that
axisymmetry in planetary nebulae sets in by the end of the asymptotic giant
branch phase, most likely by axisymmetric superwind mass loss. Moreover, both
surveys yielded two morphological classes which have one-to-one correspondence
between the two surveys, indicating that the optical depth of circumstellar
dust shells plays an equally important role as the inclination angle in
determining the morphology of the PPN shells.Comment: 6 pages + 8 figures, to appear in the proceedings of the conference,
"Post-AGB Objects (proto-planetary nebulae) as a Phase of Stellar Evolution",
Torun, Poland, July 5-7, 2000, eds. R. Szczerba, R. Tylenda, and S.K. Gorny.
Figures have been degraded to minimize the total file siz
Formation of PAHs and Carbonaceous Solids in Gas-Phase Condensation Experiments
Carbonaceous grains represent a major component of cosmic dust. In order to
understand their formation pathways, they have been prepared in the laboratory
by gas-phase condensation reactions such as laser pyrolysis and laser ablation.
Our studies demonstrate that the temperature in the condensation zone
determines the formation pathway of carbonaceous particles. At temperatures
lower than 1700 K, the condensation by-products are mainly polycyclic aromatic
hydrocarbons (PAHs), that are also the precursors or building blocks for the
condensing soot grains. The low-temperature condensates contain PAH mixtures
that are mainly composed of volatile 3-5 ring systems. At condensation
temperatures higher than 3500 K, fullerene-like carbon grains and fullerene
compounds are formed. Fullerene fragments or complete fullerenes equip the
nucleating particles. Fullerenes can be identified as soluble components.
Consequently, condensation products in cool and hot astrophysical environments
such as cool and hot AGB stars or Wolf Rayet stars should be different and
should have distinct spectral properties.Comment: 7 pages, 5 figure
Peculiarities and variations in the optical spectrum of the post-AGB star V448Lac=IRAS22223+4327
Repeated observations with high spectral resolution acquired in 1998-2008 are
used to study the temporal behavior of the spectral line profiles and velocity
field in the atmosphere and circumstellar envelope of the post-AGB star
V448Lac. Asymmetry of the profiles of the strongest absorption lines with
low-level excitation potentials less 1eV and time variations of these profiles
have been detected, most prominently the profiles of the resonance lines of
BaII, YII, LaII, SiII. The peculiarity of these profiles can be explained using
a superposition of stellar absorption line and shell emission lines. Emission
in the (0;1) 5635A Swan band of the C2 molecule has been detected in the
spectrum of V448Lac for the first time. The core of the Halpha line displays
radial velocity variations with an amplitude ~8 km/s. Radial velocity
variations displayed by weakest metallic lines with lower amplitudes, 1-2 km/s,
may be due to atmospheric pulsations. Differential line shifts, 0 -- 8 km/s,
have been detected on various dates. The position of the molecular spectrum is
stationary in time, indicating a constant expansion velocity of the
circumstellar shell, Vexp=15.2 km/s, as derived from the C2 and NaI lines.Comment: 19 pages, 8 figures, 1 tabl
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
The atmospheric parameters and spectral interpolator for the stars of MILES
Context. Empirical libraries of stellar spectra are used for stellar
classification and synthesis of stellar populations. MILES is a medium
spectral-resolution library in the optical domain covering a wide range of
temperatures, surface gravities and metallicities. Aims. We re-determine the
atmospheric parameters of these stars in order to improve the homogeneity and
accuracy. We build an interpolating function that returns a spectrum as a
function of the three atmospheric parameters, and finally, we characterize the
precision of the wavelength calibration and stability of the spectral
resolution. Methods. We use the ULySS program with the ELODIE library as a
reference and compare the results with literature compilations. Results. We
obtain precisions of 60 K, 0.13 and 0.05 dex respectively for Teff, log g and
[Fe/H] for the FGK stars. For the M stars, the mean errors are 38 K, 0.26 and
0.12 dex, and for the OBA 3.5%, 0.17 and 0.13 dex. We construct an interpolator
that we test against the MILES stars themselves. We test it also by measuring
the atmospheric parameters of the CFLIB stars with MILES as reference and find
it to be more reliable than the ELODIE interpolator for the evolved hot stars,
like in particular those of the blue horizontal branch.Comment: A&A accepted, 29 pages, 6 figure
Three dimensional C-, S- and E-transforms
Three dimensional continuous and discrete Fourier-like transforms, based on
the three simple and four semisimple compact Lie groups of rank 3, are
presented. For each simple Lie group, there are three families of special
functions (-, -, and -functions) on which the transforms are built.
Pertinent properties of the functions are described in detail, such as their
orthogonality within each family, when integrated over a finite region of
the 3-dimensional Euclidean space (continuous orthogonality), as well as when
summed up over a lattice grid (discrete orthogonality). The
positive integer sets up the density of the lattice containing . The
expansion of functions given either on or on is the paper's main
focus.Comment: 24 pages, 13 figure
Envelhecimento por Deformação em Juntas Soldadas de Tubos de Aço API5L X65Q sem Costura
Post-AGB stars in the SMC as tracers of stellar evolution: the extreme s-process enrichment of the 21 micrometer star J004441.04-732136.4
By virtue of their spectral types, favourable bolometric corrections as well
as their constrained distances, post-AGB stars in external galaxies offer
unprecedented tests to AGB nucleosynthesis and dredge-up predictions. We focus
here on one object J004441.04-732136.4, which is the only known 21 micrometer
source of the SMC. Spectral abundance results reveal J004441.04-732136.4 to be
one of the most s-process enriched objects found up to date, while the
photospheric C/O ratio of 1.9 +- 0.7, shows the star is only modestly C-rich.
J004441.04-732136.4 also displays a low [Fe/H] = -1.34 +- 0.32, which is
significantly lower than the mean metallicity of the SMC. From the SED, a
luminosity of 7600 +- 200 solar luminosities is found, together with E(B-V) =
0.64 +- 0.02. According to evolutionary post-AGB tracks, the initial mass
should be approximately 1.3 solar masses. The photometric variability shows a
clear period of 97.6 +- 0.3 days. The detected C/O as well as the high
s-process overabundances (e.g. [Y/Fe] = 2.15, [La/Fe] = 2.84) are hard to
reconcile with the predictions. The chemical models also predict a high Pb
abundance, which is not compatible with the detected spectrum, and a very high
12C/13C, which is not yet constrained by observations. The predictions are only
marginally dependent on the evolution codes used. We show that our theoretical
predictions match the s-process distribution, but fail in reproducing the
detected high overabundances and predict a high Pb abundance which is not
detected. Additionally, there remain serious problems in explaining the
observed pulsational properties of this source.Comment: 15 pages, 18 figures, accepted for publication in A&A Main Journa
First results on ProtoDUNE-SP liquid argon time projection chamber performance from a beam test at the CERN Neutrino Platform
The ProtoDUNE-SP detector is a single-phase liquid argon time projection chamber with an active volume of 7.2× 6.1× 7.0 m3. It is installed at the CERN Neutrino Platform in a specially-constructed beam that delivers charged pions, kaons, protons, muons and electrons with momenta in the range 0.3 GeV/c to 7 GeV/c. Beam line instrumentation provides accurate momentum measurements and particle identification. The ProtoDUNE-SP detector is a prototype for the first far detector module of the Deep Underground Neutrino Experiment, and it incorporates full-size components as designed for that module. This paper describes the beam line, the time projection chamber, the photon detectors, the cosmic-ray tagger, the signal processing and particle reconstruction. It presents the first results on ProtoDUNE-SP\u27s performance, including noise and gain measurements, dE/dx calibration for muons, protons, pions and electrons, drift electron lifetime measurements, and photon detector noise, signal sensitivity and time resolution measurements. The measured values meet or exceed the specifications for the DUNE far detector, in several cases by large margins. ProtoDUNE-SP\u27s successful operation starting in 2018 and its production of large samples of high-quality data demonstrate the effectiveness of the single-phase far detector design
Formation of Microphases and Constituents from Remaining Austenite Decomposition in API X80 Steel Under Different Processing Conditions
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