415 research outputs found
26Al yields from rotating Wolf--Rayet star models
We present new Al stellar yields from rotating Wolf--Rayet stellar
models which, at solar metallicity, well reproduce the observed properties of
the Wolf-Rayet populations. These new yields are enhanced with respect to
non--rotating models, even with respect to non--rotating models computed with
enhanced mass loss rates. We briefly discuss some implications of the use of
these new yields for estimating the global contribution of Wolf-Rayet stars to
the quantity of Al now present in the Milky Way.Comment: 6 pages, 2 figures, to appear in New Astronomy Review
Grids of stellar models. VIII. From 0.4 to 1.0 Msun at Z=0.020 and Z=0.001, with the MHD equation of state
We present stellar evolutionary models covering the mass range from 0.4 to 1
Msun calculated for metallicities Z=0.020 and 0.001 with the MHD equation of
state (Hummer & Mihalas, 1988; Mihalas et al. 1988; D\"appen et al. 1988). A
parallel calculation using the OPAL (Rogers et al. 1996) equation of state has
been made to demonstrate the adequacy of the MHD equation of state in the range
of 1.0 to 0.8 Msun (the lower end of the OPAL tables). Below, down to 0.4 Msun,
we have justified the use of the MHD equation of state by theoretical arguments
and the findings of Chabrier & Baraffe (1997).
We use the radiative opacities by Iglesias & Rogers (1996), completed with
the atomic and molecular opacities by Alexander & Fergusson (1994). We follow
the evolution from the Hayashi fully convective configuration up to the red
giant tip for the most massive stars, and up to an age of 20 Gyr for the less
massive ones. We compare our solar-metallicity models with recent models
computed by other groups and with observations.
The present stellar models complete the set of grids computed with the same
up-to-date input physics by the Geneva group [Z=0.020 and 0.001, Schaller et
al. (1992), Bernasconi (1996), and Charbonnel et al. (1996); Z=0.008, Schaerer
et al. (1992); Z=0.004, Charbonnel et al. (1993); Z=0.040, Schaerer et al.
(1993); Z=0.10, Mowlavi et al. (1998); enhanced mass loss rate evolutionary
tracks, Meynet et al. (1994)].Comment: Accepted for publication in A&A Supplement Serie
FUSE Measurements of Interstellar Fluorine
The source of fluorine is not well understood, although core-collapse
supernovae, Wolf-Rayet stars, and asymptotic giant branch stars have been
suggested. A search for evidence of the nu process during Type II supernovae is
presented. Absorption from interstellar F I is seen in spectra of HD 208440 and
HD 209339A acquired with the Far Ultraviolet Spectroscopic Explorer. In order
to extract the column density for F I from the line at 954 A, absorption from
H2 has to be modeled and then removed. Our analysis indicates that for H2
column densities less than about 3 x 10^20 cm^-2, the amount of F I can be
determined from lambda 954. For these two sight lines, there is no clear
indication for enhanced F abundances resulting from the nu process in a region
shaped by past supernovae.Comment: 17 pages, 4 figures, accepted for publication in Ap
High-Energy sources before INTEGRAL -- INTEGRAL reference catalog --
We describe the INTEGRAL reference catalog which classifies previously known
bright X-ray and gamma-ray sources before the launch of INTEGRAL. These sources
are, or have been at least once, brighter than ~1 mCrab above 3 keV, and are
expected to be detected by INTEGRAL. This catalog is being used in the INTEGRAL
Quick Look Analysis to discover new sources or significantly variable sources.
We compiled several published X-ray and gamma-ray catalogs, and surveyed recent
publications for new sources. Consequently, there are 1122 sources in our
INTEGRAL reference catalog. In addition to the source positions, we show an
approximate spectral model and expected flux for each source, based on which we
derive expected INTEGRAL counting rates. Assuming the default instrument
performances and at least ~10^5 sec exposure time for any part of the sky, we
expect that INTEGRAL will detect at least ~700 sources below 10 keV and ~400
sources above 20 keV over the mission life.Comment: Accepted to A&A Letter INTEGRAL special issu
The production of short-lived radionuclides by new non-rotating and rotating Wolf-Rayet model stars
It has been speculated that WR winds may have contaminated the forming solar
system, in particular with short-lived radionuclides (half-lives in the
approximate 10^5 - 10^8 y range) that are responsible for a class of isotopic
anomalies found in some meteoritic materials. We revisit the capability of the
WR winds to eject these radionuclides using new models of single non-exploding
WR stars with metallicity Z = 0.02. The earlier predictions for non-rotating WR
stars are updated, and models for rotating such stars are used for the first
time in this context. We find that (1) rotation has no significant influence on
the short-lived radionuclide production by neutron capture during the core
He-burning phase, and (2) 26Al, 36Cl, 41Ca, and 107Pd can be wind-ejected by a
variety of WR stars at relative levels that are compatible with the meteoritic
analyses for a period of free decay of around 10^5 y between production and
incorporation into the forming solar system solid bodies. We confirm the
previously published conclusions that the winds of WR stars have a radionuclide
composition that can meet the necessary condition for them to be a possible
contaminating agent of the forming solar system. Still, it remains to be
demonstrated from detailed models that this is a sufficient condition for these
winds to have provided a level of pollution that is compatible with the
observations.Comment: 8 pages, 8 figure
Gaia eclipsing binary and multiple systems. Two-Gaussian models applied to OGLE-III eclipsing binary light curves in the Large Magellanic Cloud
The advent of large scale multi-epoch surveys raises the need for automated
light curve (LC) processing. This is particularly true for eclipsing binaries
(EBs), which form one of the most populated types of variable objects. The Gaia
mission, launched at the end of 2013, is expected to detect of the order of few
million EBs over a 5-year mission.
We present an automated procedure to characterize EBs based on the geometric
morphology of their LCs with two aims: first to study an ensemble of EBs on a
statistical ground without the need to model the binary system, and second to
enable the automated identification of EBs that display atypical LCs. We model
the folded LC geometry of EBs using up to two Gaussian functions for the
eclipses and a cosine function for any ellipsoidal-like variability that may be
present between the eclipses. The procedure is applied to the OGLE-III data set
of EBs in the Large Magellanic Cloud (LMC) as a proof of concept. The bayesian
information criterion is used to select the best model among models containing
various combinations of those components, as well as to estimate the
significance of the components.
Based on the two-Gaussian models, EBs with atypical LC geometries are
successfully identified in two diagrams, using the Abbe values of the original
and residual folded LCs, and the reduced . Cleaning the data set from
the atypical cases and further filtering out LCs that contain non-significant
eclipse candidates, the ensemble of EBs can be studied on a statistical ground
using the two-Gaussian model parameters. For illustration purposes, we present
the distribution of projected eccentricities as a function of orbital period
for the OGLE-III set of EBs in the LMC, as well as the distribution of their
primary versus secondary eclipse widths.Comment: 20 pages, 29 figures. Submitted to A&
Probable hepatic capillariosis and hydatidosis in an adolescent from the late Roman period buried in Amiens (France)
Two calcified objects recovered from a 3rd to 4th-century grave of an adolescent in Amiens (Northern France) were identified as probable hydatid cysts. By using thin-section petrographic techniques, probable Calodium hepaticum (syn. Capillaria hepatica) eggs were identified in the wall of the cysts. Human hepatic capillariosis has not been reported from archaeological material so far, but could be expected given the poor level of environmental hygiene prevalent in this period. Identification of tissue-dwelling parasites such as C. hepaticum in archaeological remains is particularly dependent on preservation conditions and taphonomic changes and should be interpreted with caution due to morphological similarities with Trichuris sp. eggs
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