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Author name code: cayrel
ADS astronomy entries on 2022-09-14
author:"Cayrel, Roger"
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Title: The <SUP>6</SUP>Li/<SUP>7</SUP>Li isotopic ratio in the
metal-poor binary CS22876-032
Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.;
Ludwig, H. -G.; Steffen, M.; Monaco, L.; Cayrel, R.
2019A&A...628A.111G Altcode: 2019arXiv190705109G
<BR /> Aims: We present high-resolution and high-quality UVES
spectroscopic data of the metal-poor double-lined spectroscopic binary
CS 22876-032 ([Fe/H] approximately -3.7 dex). Our goal is to derive
the <SUP>6</SUP>Li/<SUP>7</SUP>Li isotopic ratio by analysing the
Li I λ 670.8 nm doublet. <BR /> Methods: We co-added all 28 useful
spectra normalised and corrected for radial velocity to the rest frame
of the primary star. We fitted the Li profile with a grid of the 3D
non-local thermodynamic equilibrium (NLTE) synthetic spectra to take
into account the line profile asymmetries induced by stellar convection,
and performed Monte Carlo simulations to evaluate the uncertainty of
the fit of the Li line profile. <BR /> Results: We checked that the
veiling factor does not affect the derived isotopic ratio, <SUP>6</SUP>
Li/<SUP>7</SUP>Li, and only modifies the Li abundance, A(Li), by
about 0.15 dex. The best fit of the Li profile of the primary star
provides A(Li) = 2.17 ± 0.01 dex and <SUP>6</SUP> Li/<SUP>7</SUP>Li =
8<SUB>-5</SUB><SUP>+2</SUP>% at 68% confidence level. In addition, we
improved the Li abundance of the secondary star at A(Li) = 1.55 ± 0.04
dex, which is about 0.6 dex lower than that of the primary star. <BR
/> Conclusions: The analysis of the Li profile of the primary star is
consistent with no detection of <SUP>6</SUP> Li and provides an upper
limit to the isotopic ratio of <SUP>6</SUP> Li/<SUP>7</SUP>Li <
10% at this very low metallicity, about 0.5 dex lower in metallicity
than previous attempts for detection of <SUP>6</SUP> Li in extremely
metal poor stars. These results do not solve or worsen the cosmological
<SUP>7</SUP> Li problem, nor do they support the need for non-standard
<SUP>6</SUP>Li production in the early Universe. <P />The two averaged
spectra are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A111">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A111</A>Based
on observations made with the Very Large Telescope (VLT) at ESO Paranal
Observatory, Chile, Programme 080.D-0333.
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Title: VizieR Online Data Catalog: Li in BPS CS22876-032 spectrum
(Gonzalez Hernandez+, 2019)
Authors: Gonzalez Hernandez, J. I.; Bonifacio, P.; Caffau, E.; Ludwig,
H. -G.; Steffen, M.; Monaco, L.; Cayrel, R.
2019yCat..36280111G Altcode:
Average co-added, rebinned spectra in the region around the LiI 670.8nm
resonance line of the two stellar components of the metal-poor binary
CS 22876-032 A and CS 22876-032 B. For each star, wavelength, normalised
flux and flux error are given. <P />(2 data files).
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Title: TOPoS. V. Abundance ratios in a sample of very metal-poor
turn-off stars
Authors: François, P.; Caffau, E.; Bonifacio, P.; Spite, M.; Spite,
F.; Cayrel, R.; Christlieb, N.; Gallagher, A. J.; Klessen, R.; Koch,
A.; Ludwig, H. -G.; Monaco, L.; Plez, B.; Steffen, M.; Zaggia, S.
2018A&A...620A.187F Altcode: 2018arXiv181100035F
Context. Extremely metal-poor stars are keys to understand the early
evolution of our Galaxy. The ESO large programme TOPoS has been tailored
to analyse a new set of metal-poor turn-off stars, whereas most of
the previously known extremely metal-poor stars are giant stars. <BR
/> Aims: Sixty five turn-off stars (preselected from SDSS spectra)
have been observed with the X-shooter spectrograph at the ESO VLT Unit
Telescope 2, to derive accurate and detailed abundances of magnesium,
silicon, calcium, iron, strontium and barium. <BR /> Methods: We
analysed medium-resolution spectra (R ≃ 10 000) obtained with the
ESO X-shooter spectrograph and computed the abundances of several
α and neutron-capture elements using standard one-dimensional local
thermodynamic equilibrium (1D LTE) model atmospheres. <BR /> Results:
Our results confirms the super-solar [Mg/Fe] and [Ca/Fe] ratios in
metal-poor turn-off stars as observed in metal-poor giant stars. We
found a significant spread of the [α/Fe] ratios with several stars
showing subsolar [Ca/Fe] ratios. We could measure the abundance of
strontium in 12 stars of the sample, leading to abundance ratios
[Sr/Fe] around the Solar value. We detected barium in two stars
of the sample. One of the stars (SDSS J114424-004658) shows both
very high [Ba/Fe] and [Sr/Fe] abundance ratios (>1 dex). <P
/>Based on observations collected at the European Organisation for
Astronomical Research in the Southern Hemisphere under ESO programme ID
189.D-0165. <P />Equivalent widths of the Fe lines are only, and Tables
A.1 and A.2 are also available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A187">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A187</A>
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Title: VizieR Online Data Catalog: Very metal-poor turn-off stars
abundances (Francois+, 2018)
Authors: Francois, P.; Caffau, E.; Bonifacio, P.; Spite, M.; Spite,
F.; Cayrel, R.; Christlieb, N.; Gallagher, A.; Klessen, R.; Koch,
A.; Ludwig, H. -G.; Monaco, L.; Plez, B.; Steffen, M.; Zaggia, S.
2018yCat..36200187F Altcode:
Sixty five turn-off stars (preselected from SDSS spectra) have been
observed with the X-Shooter spectrograph at the ESO VLT Unit Telescope
2, to derive accurate and detailed abundances of magnesium, silicon,
calcium, iron, strontium and barium. We analysed medium-resolution
spectra (R~10000) obtained with the ESO X-Shooter spectrograph and
computed the abundances of several alpha and neutron-capture elements
using standard one-dimensional local thermodynamic equilibrium (1D LTE)
model atmospheres. <P />(3 data files).
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Title: TOPoS. IV. Chemical abundances from high-resolution
observations of seven extremely metal-poor stars
Authors: Bonifacio, P.; Caffau, E.; Spite, M.; Spite, F.; Sbordone,
L.; Monaco, L.; François, P.; Plez, B.; Molaro, P.; Gallagher, A. J.;
Cayrel, R.; Christlieb, N.; Klessen, R. S.; Koch, A.; Ludwig, H. -G.;
Steffen, M.; Zaggia, S.; Abate, C.
2018A&A...612A..65B Altcode: 2018arXiv180103935B
Context. Extremely metal-poor (EMP) stars provide us with indirect
information on the first generations of massive stars. The TOPoS
survey has been designed to increase the census of these stars and to
provide a chemical inventory that is as detailed as possible. <BR />
Aims: Seven of the most iron-poor stars have been observed with the
UVES spectrograph at the ESO VLT Kueyen 8.2 m telescope to refine
their chemical composition. <BR /> Methods: We analysed the spectra
based on 1D LTE model atmospheres, but also used 3D hydrodynamical
simulations of stellar atmospheres. <BR /> Results: We measured carbon
in six of the seven stars: all are carbon-enhanced and belong to the
low-carbon band, defined in the TOPoS II paper. We measured lithium
(A(Li) = 1.9) in the most iron-poor star (SDSS J1035+0641, [Fe/H]
<-5.2). We were also able to measure Li in three stars at [Fe/H]
-4.0, two of which lie on the Spite plateau. We confirm that SDSS
J1349+1407 is extremely rich in Mg, but not in Ca. It is also very
rich in Na. Several of our stars are characterised by low α-to-iron
ratios. <BR /> Conclusions: The lack of high-carbon band stars at low
metallicity can be understood in terms of evolutionary timescales
of binary systems. The detection of Li in SDSS J1035+0641 places a
strong constraint on theories that aim at solving the cosmological
lithium problem. The Li abundance of the two warmer stars at [Fe/H]
-4.0 places them on the Spite plateau, while the third, cooler star,
lies below. We argue that this suggests that the temperature at which
Li depletion begins increases with decreasing [Fe/H]. SDSS J1349+1407
may belong to a class of Mg-rich EMP stars. We cannot assess if there
is a scatter in α-to-iron ratios among the EMP stars or if there are
several discrete populations. However, the existence of stars with
low α-to-iron ratios is supported by our observations. <P />Based
on observations obtained at ESO Paranal Observatory, Programmes
189.D-0165,090.D-0306, 093.D-0136, and 096.D-0468.
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Title: Using the CIFIST grid of CO<SUP>5</SUP>BOLD 3D model
atmospheres to study the effects of stellar granulation on photometric
colours. I. Grids of 3D corrections in the UBVRI, 2MASS, HIPPARCOS,
Gaia, and SDSS systems
Authors: Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.;
Castelli, F.; Gallagher, A. J.; Kučinskas, A.; Prakapavičius, D.;
Cayrel, R.; Freytag, B.; Plez, B.; Homeier, D.
2018A&A...611A..68B Altcode: 2017arXiv171200024B
Context. The atmospheres of cool stars are temporally and spatially
inhomogeneous due to the effects of convection. The influence of
this inhomogeneity, referred to as granulation, on colours has never
been investigated over a large range of effective temperatures and
gravities. Aim. We aim to study, in a quantitative way, the impact of
granulation on colours. <BR /> Methods: We use the CIFIST (Cosmological
Impact of the FIrst Stars) grid of CO5BOLD (COnservative COde for the
COmputation of COmpressible COnvection in a BOx of L Dimensions, L = 2,
3) hydrodynamical models to compute emerging fluxes. These in turn are
used to compute theoretical colours in the UBV RI, 2MASS, HIPPARCOS,
Gaia and SDSS systems. Every CO5BOLD model has a corresponding one
dimensional (1D) plane-parallel LHD (Lagrangian HydroDynamics) model
computed for the same atmospheric parameters, which we used to define
a "3D correction" that can be applied to colours computed from fluxes
computed from any 1D model atmosphere code. As an example, we illustrate
these corrections applied to colours computed from ATLAS models. <BR />
Results: The 3D corrections on colours are generally small, of the order
of a few hundredths of a magnitude, yet they are far from negligible. We
find that ignoring granulation effects can lead to underestimation of
Teff by up to 200 K and overestimation of gravity by up to 0.5 dex, when
using colours as diagnostics. We have identified a major shortcoming in
how scattering is treated in the current version of the CIFIST grid,
which could lead to offsets of the order 0.01 mag, especially for
colours involving blue and UV bands. We have investigated the Gaia and
HIPPARCOS photometric systems and found that the (G - H<SUB>p</SUB>),
(BP - RP) diagram is immune to the effects of granulation. In addition,
we point to the potential of the RVS photometry as a metallicity
diagnostic. <BR /> Conclusions: Our investigation shows that the
effects of granulation should not be neglected if one wants to use
colours as diagnostics of the stellar parameters of F, G, K stars. A
limitation is that scattering is treated as true absorption in our
current computations, thus our 3D corrections are likely an upper
limit to the true effect. We are already computing the next generation
of the CIFIST grid, using an approximate treatment of scattering. <P
/>The appendix tables are only available at the CDS via anonymous ftp
to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(<A href="http://cdsarc.u-strasbg.fr">http://130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A68">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A68</A>
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Title: VizieR Online Data Catalog: 3D correction in 5 photometric
systems (Bonifacio+, 2018)
Authors: Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.;
Castelli, F.; Gallagher, A. J.; Kucinskas, A.; Prakapavicius, D.;
Cayrel, R.; Freytag, B.; Plez, B.; Homeier, D.
2018yCat..36110068B Altcode:
We have used the CIFIST grid of CO5BOLD models to investigate the
effects of granulation on fluxes and colours of stars of spectral
type F, G, and K. <P />We publish tables with 3D corrections that
can be applied to colours computed from any 1D model atmosphere. For
Teff>=5000K, the corrections are smooth enough, as a function
of atmospheric parameters, that it is possible to interpolate the
corrections between grid points; thus the coarseness of the CIFIST
grid should not be a major limitation. However at the cool end there
are still far too few models to allow a reliable interpolation. <P
/>(20 data files).
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Title: Using CO5BOLD models to predict the effects of granulation
on colours .
Authors: Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.;
Castelli, F.; Gallagher, A. J.; Prakapavičius, D.; Kučinskas, A.;
Cayrel, R.; Freytag, B.; Plez, B.; Homeier, D.
2017MmSAI..88...90B Altcode:
In order to investigate the effects of granulation on fluxes and
colours, we computed the emerging fluxes from the models in the
CO5BOLD grid with metallicities [M/H]=0.0,-1.0,-2.0 and -3.0. These
fluxes have been used to compute colours in different photometric
systems. We explain here how our computations have been performed and
provide some results.
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Title: TOPoS. III. An ultra iron-poor multiple CEMP system
Authors: Caffau, E.; Bonifacio, P.; Spite, M.; Spite, F.; Monaco, L.;
Sbordone, L.; François, P.; Gallagher, A. J.; Plez, B.; Zaggia, S.;
Ludwig, H. -G.; Cayrel, R.; Koch, A.; Steffen, M.; Salvadori, S.;
Klessen, R.; Glover, S.; Christlieb, N.
2016A&A...595L...6C Altcode: 2016arXiv161004106C
<BR /> Aims: One of the primary objectives of the TOPoS survey
is to search for the most metal-poor stars. Our search has led
to the discovery of one of the most iron-poor objects known, SDSS
J092912.32+023817.0. This object is a multiple system, in which two
components are clearly detected in the spectrum. <BR /> Methods:
We have analysed 16 high-resolution spectra obtained using the UVES
spectrograph at the ESO 8.2 m VLT telescope to measure radial velocities
and determine the chemical composition of the system. <BR /> Results:
Cross correlation of the spectra with a synthetic template yields a
double-peaked cross-correlation function (CCF) for eight spectra, and
in one case there is evidence for the presence of a third peak. Chemical
analysis of the spectrum obtained by averaging all the spectra for which
the CCF showed a single peak found that the iron abundance is [Fe/H] =
-4.97. The system is also carbon enhanced with [C/Fe] = +3.91 (A(C) =
7.44). From the permitted oxygen triplet we determined an upper limit
for oxygen of [O/Fe] < +3.52 such that C/O > 1.3. We are also
able to provide more stringent upper limits on the Sr and Ba abundances
([Sr/Fe] < +0.70, and [Ba/Fe] < +1.46, respectively). <P />Based
on observations made with ESO Telescopes at the La Silla Paranal
Observatory under programme ID 094.D-0488 and 096.D-0616.
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Title: HST/STIS abundances in the uranium rich metal poor star CS
31082-001: Constraints on the r-Process
Authors: Siqueira-Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau,
E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen,
J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François,
P.; Molaro, P.
2016JPhCS.665a2056S Altcode:
As a brief revision, the origin of heavy elements and the role of
abundances in extremely metal-poor (EMP) stars are presented. Heavy
element abundances in the EMP uranium-rich star CS 31082-001
based mainly on near-UV spectra from STIS/HST are presented. These
results should be useful for a better characterisation of the neutron
exposure(s) that produced the r-process elements in this star, as well
as a guide for improving nuclear data and astrophysical site modelling,
given that the new element abundances not available in previous works
(Ge, Mo, Lu, Ta, W, Re, Pt, Au, and Bi) make CS 31082-001 the most
completely well studied r-II object, with a total of 37 detections of
n-capture elements.
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Title: The photospheric solar oxygen project. IV. 3D-NLTE
investigation of the 777 nm triplet lines
Authors: Steffen, M.; Prakapavičius, D.; Caffau, E.; Ludwig, H. -G.;
Bonifacio, P.; Cayrel, R.; Kučinskas, A.; Livingston, W. C.
2015A&A...583A..57S Altcode: 2015arXiv150803487S
Context. The solar photospheric oxygen abundance is still widely
debated. Adopting the solar chemical composition based on the "low"
oxygen abundance, as determined with the use of three-dimensional (3D)
hydrodynamical model atmospheres, results in a well-known mismatch
between theoretical solar models and helioseismic measurements
that is so far unresolved. <BR /> Aims: We carry out an independent
redetermination of the solar oxygen abundance by investigating the
center-to-limb variation of the O i IR triplet lines at 777 nm in
different sets of spectra. <BR /> Methods: The high-resolution and high
signal-to-noise solar center-to-limb spectra are analyzed with the
help of detailed synthetic line profiles based on 3D hydrodynamical
CO5BOLD model atmospheres and 3D non-LTE line formation calculations
with NLTE3D. The idea is to exploit the information contained in the
observations at different limb angles to simultaneously derive the
oxygen abundance, A(O), and the scaling factor S<SUB>H</SUB> that
describes the cross-sections for inelastic collisions with neutral
hydrogen relative to the classical Drawin formula. Using the same
codes and methods, we compare our 3D results with those obtained from
the semi-empirical Holweger-Müller model atmosphere as well as from
different one-dimensional (1D) reference models. <BR /> Results: With
the CO5BOLD 3D solar model, the best fit of the center-to-limb variation
of the triplet lines is obtained when the collisions by neutral hydrogen
atoms are assumed to be efficient, i.e., when the scaling factor
S<SUB>H</SUB> is between 1.2 and 1.8, depending on the choice of the
observed spectrum and the triplet component used in the analysis. The
line profile fits achieved with standard 1D model atmospheres (with
fixed microturbulence, independent of disk position μ) are clearly
of inferior quality compared to the 3D case, and give the best match
to the observations when ignoring collisions with neutral hydrogen
(S<SUB>H</SUB> = 0). The results derived with the Holweger-Müller model
are intermediate between 3D and standard 1D. <BR /> Conclusions: The
analysis of various observations of the triplet lines with different
methods yields oxygen abundance values (on a logarithmic scale where
A(H) = 12) that fall in the range 8.74 <A(O) < 8.78, and our
best estimate of the 3D non-LTE solar oxygen abundance is A(O) = 8.76
± 0.02. All 1D non-LTE models give much lower oxygen abundances,
by up to -0.15 dex. This is mainly a consequence of the assumption
of a μ-independent microturbulence. An independent determination of
the relevant collisional cross-sections is essential to substantially
improve the accuracy of the oxygen abundance derived from the O i IR
triplet. <P />Appendices E and F are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526406/olm">http://www.aanda.org</A>
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Title: TOPoS . II. On the bimodality of carbon abundance in CEMP
stars Implications on the early chemical evolution of galaxies
Authors: Bonifacio, P.; Caffau, E.; Spite, M.; Limongi, M.; Chieffi,
A.; Klessen, R. S.; François, P.; Molaro, P.; Ludwig, H. -G.; Zaggia,
S.; Spite, F.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark, P. C.;
Glover, S. C. O.; Hammer, F.; Koch, A.; Monaco, L.; Sbordone, L.;
Steffen, M.
2015A&A...579A..28B Altcode: 2015arXiv150405963B
Context. In the course of the Turn Off Primordial Stars (TOPoS) survey,
aimed at discovering the lowest metallicity stars, we have found several
carbon-enhanced metal-poor (CEMP) stars. These stars are very common
among the stars of extremely low metallicity and provide important
clues to the star formation processes. We here present our analysis
of six CEMP stars. <BR /> Aims: We want to provide the most complete
chemical inventory for these six stars in order to constrain the
nucleosynthesis processes responsible for the abundance patterns. <BR
/> Methods: We analyse both X-Shooter and UVES spectra acquired at the
VLT. We used a traditional abundance analysis based on OSMARCS 1D local
thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum
line formation code. <BR /> Results: Calcium and carbon are the only
elements that can be measured in all six stars. The range is -5.0 ≤
[Ca/H] <-2.1 and 7.12 ≤ A(C) ≤ 8.65. For star SDSS J1742+2531
we were able to detect three Fe i lines from which we deduced [Fe/H]
= -4.80, from four Ca ii lines we derived [Ca/H] = -4.56, and from
synthesis of the G-band we derived A(C) = 7.26. For SDSS J1035+0641 we
were not able to detect any iron lines, yet we could place a robust
(3σ) upper limit of [Fe/H] < -5.0 and measure the Ca abundance,
with [Ca/H] = -5.0, and carbon, A(C) = 6.90, suggesting that this star
could be even more metal-poor than SDSS J1742+2531. This makes these
two stars the seventh and eighth stars known so far with [Fe/H] <
-4.5, usually termed ultra-iron-poor (UIP) stars. No lithium is detected
in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a
robust upper limit of A(Li) < 1.8 for both stars. <BR /> Conclusions:
Our measured carbon abundances confirm the bimodal distribution of
carbon in CEMP stars, identifying a high-carbon band and a low-carbon
band. We propose an interpretation of this bimodality according to which
the stars on the high-carbon band are the result of mass transfer from
an AGB companion, while the stars on the low-carbon band are genuine
fossil records of a gas cloud that has also been enriched by a faint
supernova (SN) providing carbon and the lighter elements. The abundance
pattern of the UIP stars shows a large star-to-star scatter in the
[X/Ca] ratios for all elements up to aluminium (up to 1 dex), but
this scatter drops for heavier elements and is at most of the order
of a factor of two. We propose that this can be explained if these
stars are formed from gas that has been chemically enriched by several
SNe, that produce the roughly constant [X/Ca] ratios for the heavier
elements, and in some cases the gas has also been polluted by the
ejecta of a faint SN that contributes the lighter elements in variable
amounts. The absence of lithium in four of the five known unevolved
UIP stars can be explained by a dominant role of fragmentation in the
formation of these stars. This would result either in a destruction
of lithium in the pre-main-sequence phase, through rotational mixing
or to a lack of late accretion from a reservoir of fresh gas. The
phenomenon should have varying degrees of efficiency. <P />Based on
observations obtained at ESO Paranal Observatory, programme 091.D-0288,
091.D-0305, 189.D-0165.Appendix A is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201425266/olm">http://www.aanda.org</A>Tables
4 is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A28">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A28</A>
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Title: VizieR Online Data Catalog: Abundances of 3 CEMP stars
(Bonifacio+, 2015)
Authors: Bonifacio, P.; Caffau, E.; Spite, M.; Limongi, M.; Chieffi,
A.; Klessen, R. S.; Francois, P.; Molaro, P.; Ludwig, H. -G.; Zaggia,
S.; Spite, F.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark, P. C.;
Glover, S. C. O.; Hammer, F.; Koch, A.; Monaco, L.; Sbordone, L.;
Steffen, M.
2015yCat..35790028B Altcode:
We analyse both X-Shooter and UVES spectra acquired at the VLT. We used
a traditional abundance analysis based on OSMARCS 1D Local Thermodynamic
Equilibrium (LTE) model atmospheres and the TURBOSPECTRUM line formation
code. <P />(2 data files).
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Title: High-resolution abundance analysis of very metal-poor r-I stars
Authors: Siqueira Mello, C.; Hill, V.; Barbuy, B.; Spite, M.; Spite,
F.; Beers, T. C.; Caffau, E.; Bonifacio, P.; Cayrel, R.; François,
P.; Schatz, H.; Wanajo, S.
2014A&A...565A..93S Altcode: 2014arXiv1404.0234S
Context. Moderately r-process-enriched stars (r-I; +0.3 ≤ [Eu/Fe]
≤ +1.0) are at least four times as common as those that are greatly
enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the
abundances in their atmospheres are important tools for obtaining a
better understanding of the nucleosynthesis processes responsible
for the origin of the elements beyond the iron peak. <BR /> Aims:
The main aim of this work is to derive abundances for a sample of
seven metal-poor stars with -3.4 ≤ [Fe/H] ≤ -2.4 classified as
r-I stars, to understand the role of these stars for constraining
the astrophysical nucleosynthesis event(s) that is (are) responsible
for the production of the r-process, and to investigate whether they
differ, in any significant way, from the r-II stars. <BR /> Methods:
We carried out a detailed abundance analysis based on high-resolution
spectra obtained with the VLT/UVES spectrograph, using spectra in the
wavelength ranges 3400-4500 Å, 6800-8200 Å, and 8700-10 000 Å, with
resolving power R ~ 40 000 (blue arm) and R ~ 55 000 (red arm). The
OSMARCS LTE 1D model atmosphere grid was employed, along with the
spectrum synthesis code Turbospectrum. <BR /> Results: We have derived
abundances of the light elements Li, C, and N, the α-elements Mg,
Si, S, Ca, and Ti, the odd-Z elements Al, K, and Sc, the iron-peak
elements V, Cr, Mn, Fe, Co, and Ni, and the trans-iron elements from
the first peak (Sr, Y, Zr, Mo, Ru, and Pd), the second peak (Ba, La,
Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os
and Ir, as upper limits), and the actinides (Th) regions. The results
are compared with values for these elements for r-II and "normal"
very and extremely metal-poor stars reported in the literature, ages
based on radioactive chronometry are explored using different models,
and a number of conclusions about the r-process and the r-I stars
are presented. Hydrodynamical models were used for some elements,
and general behaviors for the 3D corrections were presented. Although
the abundance ratios of the second r-process peak elements (usually
associated with the main r-process) are nearly identical for r-I
and r-II stars, the first r-process peak abundance ratios (probably
associated with the weak r-process) are more enhanced in r-I stars than
in r-II stars, suggesting that differing nucleosynthesis pathways were
followed by stars belonging to these two different classifications. <P
/>Observations obtained with the VLT, at the European Southern
Observatory, Paranal, Chile, under proposal 080.D-0194(A)
(PI:V. Hill).Appendix A is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201423826/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: r-Process abundances in metal-poor Galactic halo stars
Authors: Siqueira-Mello, C.; Barbuy, B.; Spite, M.; Spite, F.; Caffau,
E.; Hill, V.; Wanajo, S.; François, P.; Bonifacio, P.; Cayrel, R.
2014MmSAI..85..232S Altcode:
The site of the r-process is not completely defined, and several
models try to explain the origin of the trans-Fe elements. Observed
abundances are the best clues to bring some light to this multiplicity
of possible mechanisms, and the extremely metal-poor (EMP) Galactic
halo stars have a special role in this problem. In this contribution
we present the solution of a long-standing problem about the origin
of the heavy elements in the metal-poor halo subgiant star HD 140283,
and its correlation with the Truran's theory. Next, we describe the
results obtained with the EMP r-II star CS 31082-001 in the frame of
the ESO Large Program “First Stars”. Using STIS/HST observations we
provide abundances for elements never presented before in this stars,
making CS 31082-001 the most complete r-II object studied, with a total
of 37 detections of neutron-capture elements. Finally, we present the
results obtained from a sample of seven r-I stars, showing how those
objects can help us solving the heavy elements problem. Conclusions
are also described.
---------------------------------------------------------
Title: Barbier, Daniel
Authors: Cayrel, Roger
2014bea..book..160C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chalonge, Daniel
Authors: Cayrel, Roger
2014bea..book..398C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The first generations of stars
Authors: Caffau, E.; Gallagher, A.; Bonifacio, P.; Cayrel, R.;
Christlieb, N.; Clark, P. C.; Francois, P.; Glover, S.; Klessen,
R. S.; Koch, A.; Ludwig, H. G.; Monaco, L.; Plez, B.; Sbordone, L.;
Spite, M.; Spite, F.; Steffen, M.; Zaggia, S.
2014nic..confE..53C Altcode: 2014PoS...204E..53C
No abstract at ADS
---------------------------------------------------------
Title: TOPoS: chemical study of extremely metal-poor stars.
Authors: Caffau, E.; Sbordone, L.; Bonifacio, P.; Cayrel, R.;
Christlieb, N.; Clark, P.; François, P.; Glover, S.; Klessen, R.;
Koch, A.; Ludwig, H. -G.; Monaco, L.; Plez, B.; Spite, F.; Spite,
M.; Steffen, M.; Zaggia, S.
2014MmSAI..85..222C Altcode:
The extremely metal-poor (EMP) stars hold in their atmospheres
the fossil record of the chemical composition of the early phases
of the Galactic evolution. The chemical analysis of such objects
provides important constraints on these early phases. EMP stars
are very rare objects; to dig them out, large amounts of data have
to be processed. With an automatic procedure, we analysed objects
with colours of Turn-Off stars from the Sloan Digital Sky Survey to
select a sample of good candidate EMP stars. In the latest years,
we observed a sample of these candidates with X-Shooter and UVES,
and we have an ongoing ESO large programme to use these spectrographs
to observe EMP stars. I will report here the results on metallicity
and Strontium abundance. <P />Based on observations obtained at ESO
Paranal Observatory, programme 189.D-0165(A)
---------------------------------------------------------
Title: 6Li/7Li isotopic ratio in the most metal-poor binary
CS22876-032
Authors: Gonzalez-Hernandez, J.; Caffau, E.; Ludwig, H. G.; Bonifacio,
P.; Steffen, M.; Monaco, L.; Cayrel, R.
2014nic..confE..23G Altcode: 2014PoS...204E..23G
No abstract at ADS
---------------------------------------------------------
Title: High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars
Authors: Siqueira Mello, C.; Hill, V.; Barbuy, B.; Spite, M.; Spite,
F.; Beers, T.; Caffau, E.; Bonifacio, P.; Cayrel, R.; Francois, P.;
Schatz, H.; Wanajo, S.
2014nic..confE.157S Altcode: 2014PoS...204E.157S
No abstract at ADS
---------------------------------------------------------
Title: X-shooter GTO: evidence for a population of extremely
metal-poor, alpha-poor stars
Authors: Caffau, E.; Bonifacio, P.; François, P.; Sbordone, L.;
Spite, M.; Monaco, L.; Plez, B.; Spite, F.; Zaggia, S.; Ludwig,
H. -G.; Cayrel, R.; Molaro, P.; Randich, S.; Hammer, F.; Hill, V.
2013A&A...560A..15C Altcode: 2013arXiv1309.4913C
Context. 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. <BR /> Aims: We aim to derive information about extremely
metal-poor stars from their observed spectra. <BR /> Methods: 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. <BR /> Results: 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. <P
/>Based on observations obtained at ESO Paranal Observatory, GTO
programme 089.D-0039.
---------------------------------------------------------
Title: TOPoS. I. Survey design and analysis of the first sample
Authors: Caffau, E.; Bonifacio, P.; Sbordone, L.; François, P.;
Monaco, L.; Spite, M.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark,
P.; Glover, S.; Klessen, R.; Koch, A.; Ludwig, H. -G.; Spite, F.;
Steffen, M.; Zaggia, S.
2013A&A...560A..71C Altcode: 2013arXiv1310.6963C
Context. 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. <BR /> Aims: 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 in
extremely metal-poor stars the relative abundances of the elements that
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 candidate stars
at extremely low metallicity. <BR /> Methods: 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. <BR /> Results: We present here 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. <P />Based on observations obtained at ESO Paranal
Observatory, GTO programme 189.D-0165(A).
---------------------------------------------------------
Title: First stars. XVI. HST/STIS abundances of heavy elements in
the uranium-rich metal-poor star CS 31082-001
Authors: Siqueira Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau,
E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen,
J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François,
P.; Molaro, P.
2013A&A...550A.122S Altcode: 2012arXiv1212.0211S
Context. The origin and site(s) of the r-process nucleosynthesis is(are)
still not known with certainty, but complete, detailed r-element
abundances offer our best clues. The few extremely metal-poor (EMP)
stars with large r-element excesses allow us to study the r-process
signatures in great detail, with minimal interference from later stages
of Galactic evolution. CS 31082-001 is an outstanding example of the
information that can be gathered from these exceptional stars. <BR />
Aims: Here we aim to complement our previous abundance determinations
for third-peak r-process elements with new and improved results for
elements of the first and second r-process peaks from near-UV HST/STIS
and optical UVES spectra. These results should provide new insight
into the nucleosynthesis of the elements beyond iron. <BR /> Methods:
The spectra were analyzed by a consistent approach based on an OSMARCS
LTE model atmosphere and the Turbospectrum spectrum synthesis code
to derive abundances of heavy elements in CS 31082-001, and using
updated oscillator strengths from the recent literature. Synthetic
spectra were computed for all lines of the elements of interest
to check for proper line intensities and possible blends in these
crowded spectra. Our new abundances were combined with the best
previous results to provide reliable mean abundances for the first
and second-peak r-process elements. <BR /> Results: We present new
abundances for 23 neutron-capture elements, 6 of which - Ge, Mo,
Lu, Ta, W, and Re - have not been reported before. This makes CS
31082-001 the most completely studied r-II star, with abundances for
a total of 37 neutron-capture elements. We also present the first
NLTE+3D abundance of lead in this star, further constraining the
nature of the r-process. <P />Based on observations made with the
NASA/ESA Hubble Space Telescope (HST) through the Space Telescope
Science Institute, operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS5-26555; and
with the ESO Very Large Telescope at Paranal Observatory, Chile;
Progr. ID 165.N-0276.Appendix A is available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Oxygen spectral line synthesis: 3D non-LTE with
CO<SUP>5</SUP>BOLD hydrodynamical model atmospheres.
Authors: Prakapavičius, D.; Steffen, M.; Kučinskas, A.; Ludwig,
H. -G.; Freytag, B.; Caffau, E.; Cayrel, R.
2013MSAIS..24..111P Altcode: 2013arXiv1303.2016P
In this work we present first results of our current project aimed at
combining the 3D hydrodynamical stellar atmosphere approach with non-LTE
(NLTE) spectral line synthesis for a number of key chemical species. We
carried out a full 3D-NLTE spectrum synthesis of the oxygen IR 777 nm
triplet, using a modified and improved version of our NLTE3D package to
calculate departure coefficients for the atomic levels of oxygen in a
CO<SUP>5</SUP>BOLD 3D hydrodynamical solar model atmosphere. Spectral
line synthesis was subsequently performed with the Linfor3D code. In
agreement with previous studies, we find that the lines of the
oxygen triplet produce deeper cores under NLTE conditions, due to
the diminished line source function in the line forming region. This
means that the solar oxygen IR 777 nm lines should be stronger in NLTE,
leading to negative 3D NLTE-LTE abundance corrections. Qualitatively
this result would support previous claims for a relatively low solar
oxygen abundance. Finally, we outline several further steps that need
to be taken in order to improve the physical realism and numerical
accuracy of our current 3D-NLTE calculations.
---------------------------------------------------------
Title: r-process abundances in the EMP star CS 31082-001 using
STIS/HST
Authors: Siqueira-Mello, C., Jr.; Spite, M.; Barbuy, B.; Spite, F.;
Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.;
Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio,
P.; François, P.; Molaro, P.
2012sf2a.conf..129S Altcode:
We present a brief revision of the origin of heavy elements and the role
of abundances in extremely metal-poor (EMP) stars, in providing improved
constraints on the nature of the early nucleosynthesis mechanisms. Heavy
element abundances in the EMP uranium-rich star CS 31082-001 based
mainly on near-UV spectra from STIS/HST are presented. With new
abundances for 9 n-elements not available in previous works (Ge, Mo,
Lu, Ta, W, Re, Pt, Au, and Bi) this work makes CS 31082-001 the most
completely well studied r-II object, with a total of 37 detections
of n-capture elements. These results should be useful for a better
characterisation of the neutron exposure(s) that produced the r-process
elements in this star, as well as a guide for improving nuclear data
and astrophysical site modelling.
---------------------------------------------------------
Title: A primordial star in the heart of the Lion
Authors: Caffau, E.; Bonifacio, P.; François, P.; Spite, M.; Spite,
F.; Zaggia, S.; Ludwig, H. -G.; Steffen, M.; Mashonkina, L.; Monaco,
L.; Sbordone, L.; Molaro, P.; Cayrel, R.; Plez, B.; Hill, V.; Hammer,
F.; Randich, S.
2012A&A...542A..51C Altcode: 2012arXiv1203.2607C
Context. The discovery and chemical analysis of extremely metal-poor
stars permit a better understanding of the star formation of the first
generation of stars and of the Universe emerging from the Big Bang. <BR
/> Aims: We report the study of a primordial star situated in the centre
of the constellation Leo (SDSS J102915+172927). <BR /> Methods: The
star, selected from the low-resolution spectrum of the Sloan Digital
Sky Survey, was observed at intermediate (with X-Shooter at VLT) and
at high spectral resolution (with UVES at VLT). The stellar parameters
were derived from the photometry. The standard spectroscopic analysis
based on 1D ATLAS models was completed by applying 3D and non-LTE
corrections. <BR /> Results: An iron abundance of [Fe/H ] = -4.89 makes
SDSS J102915+172927 one of the lowest [Fe/H] stars known. However,
the absence of measurable C and N enhancements indicates that it has
the lowest metallicity, Z ≤ 7.40 × 10<SUP>-7</SUP> (metal-mass
fraction), ever detected. No oxygen measurement was possible. <BR />
Conclusions: The discovery of SDSS J102915+172927 highlights that
low-mass star formation occurred at metallicities lower than previously
assumed. Even lower metallicity stars may yet be discovered, with a
chemical composition closer to the composition of the primordial gas
and of the first supernovae. <P />Based on observations obtained at ESO
Paranal Observatory, GTO programme 086.D-0094 and programme 286.D-5045.
---------------------------------------------------------
Title: NLTE determination of the calcium abundance and 3D corrections
in extremely metal-poor stars
Authors: Spite, M.; Andrievsky, S. M.; Spite, F.; Caffau, E.; Korotin,
S. A.; Bonifacio, P.; Ludwig, H. -G.; François, P.; Cayrel, R.
2012A&A...541A.143S Altcode: 2012arXiv1204.1139S
Context. Calcium is a key element for constraining the models of
chemical enrichment of the Galaxy. <BR /> Aims: Extremely metal-poor
stars contain the fossil records of the chemical composition of the
early Galaxy and it is important to compare Ca abundance with abundances
of other light elements, that are supposed to be synthesized in the
same stellar evolution phases. <BR /> Methods: The NLTE profiles of the
calcium lines were computed in a sample of 53 extremely metal-poor stars
with a modified version of the program MULTI, which allows a very good
description of the radiation field. <BR /> Results: With our new model
atom we are able to reconcile the abundance of Ca deduced from the Ca
I and Ca II lines in Procyon. This abundance is found to be solar. We
find that [Ca/Fe] = 0.50±0.09 in the early Galaxy, a value slightly
higher than the previous LTE estimations. The scatter of the ratios
[X/Ca] is generally smaller than the scatter of the ratio [X/Mg] where
X is a "light metal" (O, Na, Mg, Al, S, and K) with the exception of
Al. These scatters cannot be explained by error of measurements, except
for oxygen. Surprisingly, the scatter of [X/Fe] is always equal to, or
even smaller than, the scatter around the mean value of [X/Ca]. We note
that at low metallicity, the wavelength of the Ca I resonance line is
shifted relative to the (weaker) subordinate lines, a signature of the
effect of convection. The Ca abundance deduced from the Ca I resonance
line (422.7 nm) is found to be systematically smaller at very low
metallicity than the abundance deduced from the subordinate lines. Our
computations of the effects of convection (3D effects) are not able to
explain this difference. A fully consistent 3D NLTE model atmosphere
and line formation scheme would be necessary to fully capture the
physics of the stellar atmosphere. <P />Based on observations obtained
with the ESO Very Large Telescope at Paranal Observatory, Chile (Large
Programme "First Stars", ID 165.N-0276(A); P.I.: R. Cayrel).The NLTE
corrections of the Ca lines are available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/541/A143">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/541/A143</A>
---------------------------------------------------------
Title: VizieR Online Data Catalog: NLTE Corrections of the Ca lines
(Spite+, 2012)
Authors: Spite, M.; Andrievsky, S. M.; Spite, F.; Caffau, E.; Korotin,
S. A.; Bonifacio, P.; Ludwig, H. -G.; Francois, P.; Cayrel, R.
2012yCat..35410143S Altcode: 2012yCat..35419143S
The NLTE corrections were computed for 51 CaI lines and 16 CaII lines
for a grid of models with different metallicities from [Fe/H]=0.0
to [Fe/H]=-3. These corrections must be added to the LTE value of
[Ca/H], they were computed only if the equivalent width of the Ca line
was stronger than 3mÅ. In the tables the model is given in the form
(Teff, logg, [Fe/H], [Ca/Fe]) where Teff is the effective temperature,
and logg the logarithm of the surface gravity) <P />(5 data files).
---------------------------------------------------------
Title: <SUP>6</SUP>Li detection in metal-poor stars: can 3D model
atmospheres solve the second lithium problem?
Authors: Steffen, M.; Cayrel, R.; Caffau, E.; Bonifacio, P.; Ludwig,
H. -G.; Spite, M.
2012MSAIS..22..152S Altcode: 2012arXiv1206.2239S
The presence of <SUP>6</SUP>Li in the atmospheres of metal-poor
halo stars is usually inferred from the detection of a subtle extra
depression in the red wing of the <SUP>7</SUP>Li doublet line at
670.8 nm. However, as pointed out recently by \cite{Cayrel2007},
the intrinsic line asymmetry caused by convective flows in the
photospheres of cool stars is almost indistinguishable from the
asymmetry produced by a weak <SUP>6</SUP>Li blend on a (presumed)
symmetric <SUP>7</SUP>Li profile. Previous determinations of the
<SUP>6</SUP>Li/ <SUP>7</SUP>Li isotopic ratio based on 1D model
atmospheres, ignoring the convection-induced line asymmetry, must
therefore be considered as upper limits. By comparing synthetic
1D LTE and 3D non-LTE line profiles of the <SUP>i</SUP>Li 670.8 nm
feature, we quantify the differential effect of the convective line
asymmetry on the derived <SUP>6</SUP>Li abundance as a function of
effective temperature, gravity, and metallicity. As expected, we
find that the asymmetry effect systematically reduces the resulting
<SUP>6</SUP>Li/<SUP>7</SUP>Li ratios. Depending on the stellar
parameters, the 3D-1D offset in <SUP>6</SUP>Li/<SUP>7</SUP>Li ranges
between -0.005 and -0.020. When this purely theoretical correction is
taken into account for the \cite{A2006} sample of stars, the number of
significant <SUP>6</SUP>Li detections decreases from 9 to 5 (2sigma
criterion), or from 5 to 2 (3sigma criterion). <P />We also present
preliminary results of a re-analysis of high-resolution, high S/N
spectra of individual metal-poor turn-off stars, to see whether the
second Lithium problem actually disappears when accounting properly for
convection and non-LTE line formation in 3D stellar atmospheres. Out
of 8 stars, HD 84937 seems to be the only significant (2sigma )
detection of <SUP>6</SUP>Li. In view of our results, the existence of
a <SUP>6</SUP>Li plateau appears questionable.
---------------------------------------------------------
Title: Preliminary determination of the Non-LTE Calcium abundance
in a sample of extremely metal-poor stars*
Authors: Spite, M.; Spite, F.; Bonifacio, P.; Caffau, E.; Andrievsky,
S.; Korotin, S.; Cayrel, R.; François, P.
2011sf2a.conf..353S Altcode:
The abundance ratios of the elements found in the extremely metal-poor
stars (EMP) are a test of the yields predicted by the models of
supernovae. For precise comparisons, it is of course preferable to
avoid the approximation of LTE. The difference of LTE and NLTE profiles
is displayed for three strong lines. The NLTE abundances of Ca are
derived from the profiles of about 15 Ca I lines in the EMP giants and
about 10 lines in the turnoff stars. The improved abundance trends
are consistent with a [Ca/Fe] ratio constant vs. [Fe/H], and with a
[Ca/Mg] ratio slightly declining when [Mg/H] increases. Also [Ca/Mg]
presents a scatter larger than [Ca/Fe]. As far as the comparison
with sulfur (another alpha elment) is concerned we find that [S/Ca]
presents a scatter smaller than [S/Mg].
---------------------------------------------------------
Title: The Hα Balmer line as an effective temperature criterion
Authors: Cayrel, R.; van't Veer-Menneret, C.; Allard, N. F.;
Stehlé, C.
2011sf2a.conf..267C Altcode:
For eleven stars with an accurate effective temperature derived from
their apparent angular diameter we determine the effective temperature
of the Kurucz Atlas9 model that provides the best fit of the computed
theoretical Hα profile (using the recent theoretical advances) with the
corresponding observed profile, extracted from the S4N spectroscopic
database. The two sets of effective temperatures have a significant
offset, but are tightly correlated, with a correlation coefficient
of 0.9976. The regression straight line of T_{eff}(direct) versus
T_{eff}(Hα) enables us to reach the true effective temperature from
the spectroscopic observation of the Hα profile, with an rms error
of only 30 K. This provides a way of obtaining the true effective
temperature of a reddened star.
---------------------------------------------------------
Title: X-shooter Finds an Extremely Primitive Star
Authors: Caffau, E.; Bonifacio, P.; François, P.; Sbordone, L.;
Monaco, L.; Spite, M.; Spite, F.; Ludwig, H. -G.; Cayrel, R.; Zaggia,
S.; Hammer, F.; Randich, S.; Molaro, P.; Hill, V.
2011Msngr.146...28C Altcode:
Low-mass extremely metal-poor (EMP) stars hold the fossil record of
the chemical composition of the early phases of the Universe in their
atmospheres. Chemical analysis of such objects provides important
constraints on these early phases. EMP stars are rather rare objects:
to dig them out, large amounts of data have to be considered. We have
analysed stars from the Sloan Digital Sky Survey using an automatic
procedure and selected a sample of good candidate EMP stars, which we
observed with the spectrographs X-shooter and UVES. We could confirm
the low metallicity of our sample of stars, and we succeeded in finding
a record metal-poor star.
---------------------------------------------------------
Title: X-Shooter GTO: chemical analysis of a sample of EMP candidates
Authors: Caffau, E.; Bonifacio, P.; François, P.; Spite, M.; Spite,
F.; Zaggia, S.; Ludwig, H. -G.; Monaco, L.; Sbordone, L.; Cayrel,
R.; Hammer, F.; Randich, S.; Hill, V.; Molaro, P.
2011A&A...534A...4C Altcode: 2011arXiv1109.0992C
Context. Extremely metal-poor stars (EMP) are very rare objects that
hold in their atmospheres the fossil record of the chemical composition
of the early phases of Galactic evolution. Finding these objects and
determining their chemical composition provides important constraints
on these early phases. <BR /> Aims: Using a carefully designed selection
method, we chose a sample of candidate EMP stars from the low resolution
spectra of the Sloan Digital Sky Survey and observed them with X-Shooter
at the VLT to confirm their metallicities and determine abundances
for as many elements as possible. <BR /> Methods: The X-Shooter
spectra are analysed by means of one-dimensional, plane-parallel,
hydrostatic model atmospheres. Corrections for the granulation effects
are computed using CO5BOLD hydrodynamical simulations. <BR /> Results:
All the candidates are confirmed to be EMP stars, proving the efficiency
of our selection method within about 0.5 dex. The chemical composition
of this sample is compatible with those of brighter samples, suggesting
that the stars in the Galactic halo are well mixed. <BR /> Conclusions:
These observations show that it is feasible to observe, in a limited
amount of time, a large sample of about one hundred stars among EMP
candidates selected from the SDSS. Such a size of sample will allow us,
in particular, to confirm or refute the existence of a vertical drop
in the Galactic halo metallicity distribution function around [Fe/H] ~
-3.5. <P />Based on observations obtained at ESO Paranal Observatory,
GTO programme 086.D-0094.
---------------------------------------------------------
Title: First stars. XV. Third-peak r-process element and actinide
abundances in the uranium-rich star CS31082-001
Authors: Barbuy, B.; Spite, M.; Hill, V.; Primas, F.; Plez, B.;
Cayrel, R.; Spite, F.; Wanajo, S.; Siqueira Mello, C.; Andersen, J.;
Nordström, B.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P.
2011A&A...534A..60B Altcode:
Context. A small fraction of extremely metal-poor (EMP) stars exhibit
moderate to extreme excesses of heavy neutron-capture elements
produced in the r-process. The production site(s) of these elements
in the early Galaxy remain(s) unclear, as is the reason for their
occasional enhancement in the otherwise regular pattern of abundances
of elements up to the iron peak. The detailed abundance pattern of the
heaviest elements in EMP stars provides insight into their origin and
role in the chemical enrichment of the early Galaxy and in radioactive
nucleochronology. <BR /> Aims: The EMP giant star CS 31082-001 ([Fe/H]
~ -2.9) exhibits an extreme enhancement of neutron-capture elements
([r/Fe] ~ +1.7) with U and Th enhanced by a further ~+0.7 dex,
and a minimum of blending by molecular lines such as CH or CN. A
rich inventory of r-process element abundances was established
previously from optical spectra. Here we aim to supplement these
data with abundances from near-UV spectroscopy of the third-peak
neutron-capture elements, which are crucial for understanding the
synthesis of the heaviest elements. <BR /> Methods: Near-UV spectra
from HST/STIS were analysed with LTE model atmospheres and spectrum
synthesis calculations to derive new abundances of Os, Ir, Pt, Au, Bi
and Pb in CS 31082-001. <BR /> Results: Together with earlier data,
the resulting abundance pattern for the r-process elements provides
improved constraints on the nature of the r-process. The observed U
and Th abundances and the initial production ratio place CS 31082-001
as one of the oldest stars in the Galaxy, consistent with its extreme
metal deficiency. Comparison with the heaviest stable reference elements
and with the daughter nuclides Pb and Bi provides a consistency check
on this age determination. Finally, the existence of such r-element
rich stars indicate that the early chemical evolution of the Galaxy
was localised and inhomogeneous. <P />Based on observations made with
the NASA/ESA Hubble Space Telescope (HST) through the Space Telescope
Science Institute, operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS5-26555; and
with the ESO Very Large Telescope at Paranal Observatory, Chile;
Progr. ID 165.N-0276.
---------------------------------------------------------
Title: An extremely primitive star in the Galactic halo
Authors: Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick;
Sbordone, Luca; Monaco, Lorenzo; Spite, Monique; Spite, François;
Ludwig, Hans-G.; Cayrel, Roger; Zaggia, Simone; Hammer, François;
Randich, Sofia; Molaro, Paolo; Hill, Vanessa
2011Natur.477...67C Altcode: 2012arXiv1203.2612C
The early Universe had a chemical composition consisting of
hydrogen, helium and traces of lithium; almost all other elements
were subsequently created in stars and supernovae. The mass fraction
of elements more massive than helium, Z, is known as `metallicity'. A
number of very metal-poor stars has been found, some of which have a
low iron abundance but are rich in carbon, nitrogen and oxygen. For
theoretical reasons and because of an observed absence of stars
with Z<1.5×10<SUP>-5</SUP>, it has been suggested that low-mass
stars cannot form from the primitive interstellar medium until it
has been enriched above a critical value of Z, estimated to lie in
the range 1.5×10<SUP>-8</SUP> to 1.5×10<SUP>-6</SUP> (ref. 8),
although competing theories claiming the contrary do exist. (We
use `low-mass' here to mean a stellar mass of less than 0.8 solar
masses, the stars that survive to the present day.) Here we report the
chemical composition of a star in the Galactic halo with a very low Z
(<=6.9×10<SUP>-7</SUP>, which is 4.5×10<SUP>-5</SUP> times that
of the Sun) and a chemical pattern typical of classical extremely
metal-poor stars--that is, without enrichment of carbon, nitrogen
and oxygen. This shows that low-mass stars can be formed at very low
metallicity, that is, below the critical value of Z. Lithium is not
detected, suggesting a low-metallicity extension of the previously
observed trend in lithium depletion. Such lithium depletion implies
that the stellar material must have experienced temperatures above
two million kelvin in its history, given that this is necessary to
destroy lithium.
---------------------------------------------------------
Title: The Hα Balmer line as an effective temperature
criterion. I. Calibration using 1D model stellar atmospheres
Authors: Cayrel, R.; van't Veer-Menneret, C.; Allard, N. F.;
Stehlé, C.
2011A&A...531A..83C Altcode:
<BR /> Aims: We attempt to derive the true effective temperature
of a star from the spectroscopic observation of its Hα Balmer line
profile. <BR /> Methods: The method is possible thanks to advances
in two respects. First there have been progresses in the theoretical
treatment of the broadening mechanisms of Hα. Second, there has been
a rapid increase in the number of stars with an apparent diameter
measured with an accuracy of the order of 1 percent, enabling us to
obtain an accurate effective temperature T<SUB>eff</SUB> for a dozen
of stars using the direct method by means of combining the apparent
diameter and the bolometric flux. <BR /> Results: For the eleven
stars with an accurate effective temperature derived from their
apparent angular diameter we determined the effective temperature
of the Kurucz Atlas9 model that provides the best fit of the computed
theoretical Hα profile (using the recent theoretical advances) with the
corresponding observed profile, extracted from the S4N spectroscopic
database. The two sets of effective temperatures have a significant
offset, but are tightly correlated, with a correlation coefficient of
0.9976. The regression straight line of T<SUB>eff</SUB>(direct) versus
T<SUB>eff</SUB>(Hα) enables us to reach the true effective temperature
from the spectroscopic observation of the Hα profile, with an rms
error of only 30 K. This provides a way of obtaining the true effective
temperature of a reddened star. <BR /> Conclusions: We succeeded in
obtaining empirically the true stellar effective temperature from
Hα profile using Kurucz's Atlas9 grid of 1D model atmospheres. Full
understanding of the difference between T<SUB>eff</SUB>(direct)
and T<SUB>eff</SUB>(Hα) would require a 3D approach, with radiative
hydrodynamical models, which will be the subject of a future paper.
---------------------------------------------------------
Title: NLTE strontium abundance in a sample of extremely metal poor
stars and the Sr/Ba ratio in the early Galaxy
Authors: Andrievsky, S. M.; Spite, F.; Korotin, S. A.; François,
P.; Spite, M.; Bonifacio, P.; Cayrel, R.; Hill, V.
2011A&A...530A.105A Altcode: 2011arXiv1104.0476A
Context. Heavy element abundances in extremely metal-poor stars
provide strong constraints on the processes of forming these
elements in the first stars. <BR /> Aims: We attempt to determine
precise abundances of strontium in a homogeneous sample of extremely
metal-poor stars. <BR /> Methods: The abundance of strontium in 54
very or extremely metal-poor stars, was redetermined by abandoning
the local thermodynamic equilibrium (LTE) hypothesis, and fitting
non-LTE (NLTE) profiles to the observed spectral lines. The corrected
Sr abundances and previously obtained NLTE Ba abundances are compared
to the predictions of several hypothetical formation processes for the
lighter neutron-capture elements. <BR /> Results: Our NLTE abundances
confirm the previously determined huge scatter of the strontium
abundance in low metallicity stars. This scatter is also found (and
is even larger) at very low metallicities (i.e. early in the chemical
evolution). The Sr abundance in the extremely metal-poor (EMP) stars
is compatible with the main r-process involved in other processes
(or by variations of the r-process), as we briefly discuss.
---------------------------------------------------------
Title: Lines of heavy elements and Feiiin the UV of CS 31082-001
Authors: Barbuy, B.; Siqueira Mello, C., Jr.; Spite, M.; Spite, F.;
Bonifacio, P.; Hill, V.; Primas, F.; Plez, B.; Cayrel, R.; François,
P.; Sneden, C.; Beers, T. C.; Andersen, J.; Nordström, B.; Molaro, P.
2011CaJPh..89..357B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: First stars. XIV. Sulfur abundances in extremely metal-poor
stars
Authors: Spite, M.; Caffau, E.; Andrievsky, S. M.; Korotin, S. A.;
Depagne, E.; Spite, F.; Bonifacio, P.; Ludwig, H. -G.; Cayrel, R.;
François, P.; Hill, V.; Plez, B.; Andersen, J.; Barbuy, B.; Beers,
T. C.; Molaro, P.; Nordström, B.; Primas, F.
2011A&A...528A...9S Altcode: 2010arXiv1012.4358S
Context. Precise S abundances are important in the study of the
early chemical evolution of the Galaxy. In particular the site of the
formation remains uncertain because, at low metallicity, the trend
of this α-element versus [Fe/H] remains unclear. Moreover, although
sulfur is not bound significantly in dust grains in the ISM, it seems
to behave differently in DLAs and old metal-poor stars. <BR /> Aims:
We attempt a precise measurement of the S abundance in a sample of
extremely metal-poor stars observed with the ESO VLT equipped with
UVES, taking into account NLTE and 3D effects. <BR /> Methods: The
NLTE profiles of the lines of multiplet 1 of S I were computed with a
version of the program MULTI, including opacity sources from ATLAS9
and based on a new model atom for S. These profiles were fitted to
the observed spectra. <BR /> Results: We find that sulfur in EMP stars
behaves like the other α-elements, with [S/Fe] remaining approximately
constant below [Fe/H] = -3. However, [S/Mg] seems to decrease slightly
with increasing [Mg/H]. The overall abundance patterns of O, Na, Mg,
Al, S, and K are most closely matched by the SN model yields by Heger
& Woosley. The [S/Zn] ratio in EMP stars is solar, as also found
in DLAs. We derive an upper limit to the sulfur abundance [S/Fe] <
+0.5 for the ultra metal-poor star CS 22949-037. This, along with a
previously reported measurement of zinc, argues against the conjecture
that the light-element abundance pattern of this star (and by analogy,
the hyper iron-poor stars HE 0107-5240 and HE 1327-2326) would be
due to dust depletion. <P />Based on observations obtained with the
ESO Very Large Telescope at Paranal (Large Programme "First Stars",
ID 165, N-0276, P.I.: Cayrel.
---------------------------------------------------------
Title: Extremely metal-poor stars in SDSS fields
Authors: Bonifacio, P.; Caffau, E.; François, P.; Sbordone, L.;
Ludwig, H. -G.; Spite, M.; Molaro, P.; Spite, F.; Cayrel, R.; Hammer,
F.; Hill, V.; Nonino, M.; Randich, S.; Stelzer, B.; Zaggia, S.
2011AN....332..251B Altcode: 2011arXiv1101.3139B
Some insight on the first generation of stars can be obtained from
the chemical composition of their direct descendants, extremely
metal-poor stars (EMP), with metallicity less than or equal to 1/1000
of the solar metallicity. Such stars are exceedingly rare, the most
successful surveys, for this purpose, have so far provided only about
100 stars with 1/1 000 the solar metallicity and 4 stars with about
1/10 000 of the solar metallicity. The Sloan Digital Sky Survey has
the potential to provide a large number of candidates of extremely
low metallicity. X-shooter has the unique capability of performing the
necessary follow-up spectroscopy providing accurate metallicities and
abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr, ...) for
EMP candidates. We here report on the results for the first two stars
observed in the course of our Franco-Italian X-shooter GTO. The two
stars were targeted to be of metallicity around -3.0, the analysis of
the X-shooter spectra showed them to be of metallicity around -2.0,
but with a low α to iron ratio, which explains the underestimate of
the metallicity from the SDSS spectra. The efficiency of X-shooter
allows an in situ study of the outer halo, for the two stars studied
here we estimate distances of 3.9 and 9.1 kpc, these are likely the
most distant dwarf stars studied in detail to date. <P />Based on
spectra obtained with X-shooter at the 8.2-m Kueyen ESO telescope,
GTO programmes 085.D-0194 and 086.D.0094.
---------------------------------------------------------
Title: First stars. XIII. Two extremely metal-poor RR Lyrae stars
Authors: Hansen, C. J.; Nordström, B.; Bonifacio, P.; Spite, M.;
Andersen, J.; Beers, T. C.; Cayrel, R.; Spite, F.; Molaro, P.; Barbuy,
B.; Depagne, E.; François, P.; Hill, V.; Plez, B.; Sivarani, T.
2011A&A...527A..65H Altcode: 2011arXiv1101.2207H
Context. The chemical composition of extremely metal-poor stars (EMP
stars; [Fe/H] < ~ -3) is a unique tracer of early nucleosynthesis
in the Galaxy. As such stars are rare, we wish to find classes of
luminous stars which can be studied at high spectral resolution. <BR />
Aims: We aim to determine the detailed chemical composition of the two
EMP stars CS 30317-056 and CS 22881-039, originally thought to be red
horizontal-branch (RHB) stars, and compare it to earlier results for EMP
stars as well as to nucleosynthesis yields from various supernova (SN)
models. In the analysis, we discovered that our targets are in fact the
two most metal-poor RR Lyrae stars known. <BR /> Methods: Our detailed
abundance analysis, taking into account the variability of the stars,
is based on VLT/UVES spectra (R ≃ 43 000) and 1D LTE OSMARCS model
atmospheres and synthetic spectra. For comparison with SN models we also
estimate NLTE corrections for a number of elements. <BR /> Results: We
derive LTE abundances for the 16 elements O, Na, Mg, Al, Si, S, Ca, Sc,
Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba, in good agreement with earlier values
for EMP dwarf, giant and RHB stars. Li and C are not detected in either
star. NLTE abundance corrections are newly calculated for O and Mg and
taken from the literature for other elements. The resulting abundance
pattern is best matched by model yields for supernova explosions with
high energy and/or significant asphericity effects. <BR /> Conclusions:
Our results indicate that, except for Li and C, the surface composition
of EMP RR Lyr stars is not significantly affected by mass loss, mixing
or diffusion processes; hence, EMP RR Lyr stars should also be useful
tracers of the chemical evolution of the early Galactic halo. The
observed abundance ratios indicate that these stars were born from an
ISM polluted by energetic, massive (25-40 M<SUB>⊙</SUB>) and /or
aspherical supernovae, but the NLTE corrections for Sc and certain
other elements do play a role in the choice of model. <P />Based
on observations made with the ESO Very Large Telescope at Paranal
Observatory, Chile (Large Programme "First Stars", ID 165.N-0276(A);
P.I. R. Cayrel).Table 5 and Appendix A are only available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Probing the Galactic thick disc vertical properties and
interfaces
Authors: Katz, D.; Soubiran, C.; Cayrel, R.; Barbuy, B.; Friel, E.;
Bienaymé, O.; Perrin, M. -N.
2011A&A...525A..90K Altcode:
<BR /> Aims: This work investigates the properties (metallicity and
kinematics) and interfaces of the Galactic thick disc as a function of
height above the Galactic plane. The main aim is to study the thick
disc in a place where it is the main component of the sample. <BR />
Methods: We take advantage of former astrometric work in two fields
of several square degrees in which accurate proper motions were
measured down to V-magnitudes of 18.5 in two directions, one near
the north galactic pole and the other at a galactic latitude of 46°
and galactic longitude near 0°. Spectroscopic observations have been
acquired in these two fields for a total of about 400 stars down to
magnitude 18.0, at spectral resolutions of 3.5 to 6.25 Å. The spectra
have been analysed with the code ETOILE, comparing the target stellar
spectra with a grid of 1400 reference stellar spectra. This comparison
allowed us to derive the parameters effective temperature, gravity,
[Fe/H] and absolute magnitude for each target star. <BR /> Results:
The Metallicity Distribution Function (MDF) of the thin-thick-disc-halo
system is derived for several height intervals between 0 and 5 kpc above
the Galactic plane. The MDFs show a decrease of the ratio of the thin
to thick disc stars between the first and second kilo-parsec. This
is consistent with the classical modelling of the vertical density
profile of the disc with 2 populations with different scale heights. A
vertical metallicity gradient, ∂[Fe/H]/∂z = -0.068 ± 0.009 dex
kpc<SUP>-1</SUP>, is observed in the thick disc. It is discussed
in terms of scenarios of formation of the thick disc. <P />Based on
observations obtained at the Canada-France-Hawaii Telescope (CFHT)
which is operated by the National Research Council of Canada, the
Institut National des Sciences de l'Univers of the Centre National de
la Recherche Scientifique of France, and the University of Hawaii and
at the T193cm telescope, Observatoire de Haute-Provence, France.Full
Tables A.1-A.3, B.1-B.3 are only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A90">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A90</A>
---------------------------------------------------------
Title: The metal-poor end of the Spite plateau. I. Stellar parameters,
metallicities, and lithium abundances
Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.;
Behara, N. T.; González Hernández, J. I.; Steffen, M.; Cayrel, R.;
Freytag, B.; van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite,
M.; Spite, F.; Beers, T. C.; Christlieb, N.; François, P.; Hill, V.
2010A&A...522A..26S Altcode: 2010arXiv1003.4510S
Context. The primordial nature of the Spite plateau is at odds with
the WMAP satellite measurements, implying a primordial Li production
at least three times higher than observed. It has also been suggested
that A(Li) might exhibit a positive correlation with metallicity below
[Fe/H] ~ -2.5. Previous samples studied comprised few stars below
[Fe/H] = -3. <BR /> Aims: We present VLT-UVES Li abundances of 28
halo dwarf stars between [Fe/H] = -2.5 and -3.5, ten of which have
[Fe/H] <-3. <BR /> Methods: We determined stellar parameters and
abundances using four different T<SUB>eff</SUB> scales. The direct
infrared flux method was applied to infrared photometry. Hα wings were
fitted with two synthetic grids computed by means of 1D LTE atmosphere
models, assuming two different self-broadening theories. A grid of Hα
profiles was finally computed by means of 3D hydrodynamical atmosphere
models. The Li i doublet at 670.8 nm has been used to measure A(Li)
by means of 3D hydrodynamical NLTE spectral syntheses. An analytical
fit of A(Li)<SUB>3D, NLTE</SUB> as a function of equivalent width,
T<SUB>eff</SUB>, log g, and [Fe/H] has been derived and is made
available. <BR /> Results: We confirm previous claims that A(Li)
does not exhibit a plateau below [Fe/H] = -3. We detect a strong
positive correlation with [Fe/H] that is insensitive to the choice of
T<SUB>eff</SUB> estimator. From a linear fit, we infer a steep slope
of about 0.30 dex in A(Li) per dex in [Fe/H], which has a significance
of 2-3σ. The slopes derived using the four T<SUB>eff</SUB> estimators
are consistent to within 1σ. A significant slope is also detected
in the A(Li)-T<SUB>eff</SUB> plane, driven mainly by the coolest
stars in the sample (T<SUB>eff</SUB> < 6250), which appear to be
Li-poor. However, when we remove these stars the slope detected in
the A(Li)-[Fe/H] plane is not altered significantly. When the full
sample is considered, the scatter in A(Li) increases by a factor
of 2 towards lower metallicities, while the plateau appears very
thin above [Fe/H] = -2.8. At this metallicity, the plateau lies at
<A(Li)<SUB>3D, NLTE</SUB>> = 2.199±0.086. <BR /> Conclusions:
The meltdown of the Spite plateau below [Fe/H] ~ -3 is established,
but its cause is unclear. If the primordial A(Li) were that derived
from standard BBN, it appears difficult to envision a single depletion
phenomenon producing a thin, metallicity independent plateau above
[Fe/H] = -2.8, and a highly scattered, metallicity dependent
distribution below. That no star below [Fe/H] = -3 lies above the
plateau suggests that they formed at plateau level and experienced
subsequent depletion. <P />Based on observations made with the ESO Very
Large Telescope at Paranal Observatory, Chile (Programmes 076.A-0463
and 077.D-0299).Full Table 3 is available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/522/A26">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/522/A26</A>IDL
code (appendix) is only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: VizieR Online Data Catalog: Thick disc vertical properties
(Katz+, 2011)
Authors: Katz, D.; Soubiran, C.; Cayrel, R.; Barbuy, B.; Friel, E.;
Bienayme, O.; Perrin, M. -N.
2010yCat..35250090K Altcode: 2010yCat..35259090K
Tables A1, A2 and A3: coordinates and parameters of the 346 CARELEC and
CFHT program stars analysed in this study. <P />Table B1: parameters
of the 1398 ELODIE reference spectra used to derive the stellar
characteristics of the program stars. <P />Tables B2 and B3: parameters
of the 45 CARELEC validation stars and 46 CFHT validation stars used to
assess the accuracy and precision of the stellar atmospheric parameters
derivation method. It should be noted that 2 stars "of" M71 (KC-124,
KC-223) and 3 stars "of" M5 (I-52, III-44 and IV-61) discussed in
the article but considered as not belonging to these clusters are not
listed in table B3. <P />(6 data files).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Fe Abundances in metal-poor stars
(Sbordone+ 2010)
Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.;
Behara, N. T.; Gonzalez Hernandez, J. I.; Steffen, M.; Cayrel, R.;
Freytag, B.; van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite,
M.; Spite, F.; Beers, T. C.; Christlieb, N.; Francois, P.; Hill, V.
2010yCat..35220026S Altcode: 2010yCat..35229026S
Line-by-line abundances for FeI and FeII lines used to estimate
metallicity and gravity for the program stars. The first column lists
the star name, then the ion (FeI or FeII) The the wavelength in nm,
the loggf, the measured EW (pm) and the derived abundance assuming the
four stellar parameter sets used in the article, respectively 3D, BA,
ALI and IRFM. <P />(3 data files).
---------------------------------------------------------
Title: Convection and <SUP>6</SUP>Li in the atmospheres of metal-poor
halo stars
Authors: Steffen, Matthias; Cayrel, R.; Bonifacio, P.; Ludwig, H. -G.;
Caffau, E.
2010IAUS..268..215S Altcode: 2010arXiv1001.3274S
Based on 3D hydrodynamical model atmospheres computed with the
CO<SUP>5</SUP>BOLD code and 3D non-LTE (NLTE) line formation
calculations, we study the effect of the convection-induced line
asymmetry on the derived <SUP>6</SUP>Li abundance for a range in
effective temperature, gravity, and metallicity covering the stars
of the Asplund et al. (2006) sample. When the asymmetry effect
is taken into account for this sample of stars, the resulting
<SUP>6</SUP>Li/<SUP>7</SUP>Li ratios are reduced by about 1.5% on
average with respect to the isotopic ratios determined by Asplund et
al. (2006). This purely theoretical correction diminishes the number
of significant <SUP>6</SUP>Li detections from 9 to 4 (2σ criterion),
or from 5 to 2 (3σ criterion). In view of this result the existence
of a <SUP>6</SUP>Li plateau appears questionable. A careful reanalysis
of individual objects by fitting the observed lithium 6707 Å doublet
both with 3D NLTE and 1D LTE synthetic line profiles confirms that the
inferred <SUP>6</SUP>Li abundance is systematically lower when using
3D NLTE instead of 1D LTE line fitting. Nevertheless, halo stars with
unquestionable <SUP>6</SUP>Li detection do exist even if analyzed in
3D-NLTE, the most prominent example being HD 84937.
---------------------------------------------------------
Title: The metal-poor end of the Spite plateau: gravity sensitivity
of the Hα wings fitting.
Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.;
Behara, N.; Gonzalez-Hernandez, J. I.; Steffen, M.; Cayrel, R.;
Freytag, B.; Van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite,
M.; Spite, F.; Beers, T. C.; Christlieb, N.; François, P.; Hill, V.
2010IAUS..268..355S Altcode:
We recently presented (Sbordone et al., 2009a) the largest sample to
date of lithium abundances in extremely metal-poor (EMP) Halo dwarf and
Turn-Off (TO) stars. One of the most crucial aspects in estimating Li
abundances is the T<SUB>eff</SUB> determination, since the Li I 670.8
nm doublet is highly temperature sensitive. In this short contribution
we concentrate on the T<SUB>eff</SUB> determination based on Hα wings
fitting, and on its sensitivity to the chosen stellar gravity.
---------------------------------------------------------
Title: Main-sequence and sub-giant stars in the globular cluster
NGC 6397: The complex evolution of the lithium abundance
Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.;
Steffen, M.; Ludwig, H. -G.; Behara, N.; Sbordone, L.; Cayrel, R.;
Zaggia, S.
2010IAUS..268..257G Altcode: 2009arXiv0912.4105G
Thanks to the high multiplex and efficiency of Giraffe at the VLT
we have been able for the first time to observe the Li I doublet in
the Main Sequence stars of a globular cluster. At the same time we
observed Li in a sample of Sub-Giant stars of the same B-V colour. <P
/>Our final sample is composed of 84 SG stars and 79 MS stars. In
spite of the fact that SG and MS span the same temperature range we
find that the equivalent widths of the Li I doublet in SG stars are
systematically larger than those in MS stars, suggesting a higher Li
content among SG stars. This is confirmed by our quantitative analysis
carried out making use of 1D hydrostatic plane-parallel models and
3D hydrodynamical simulations of the stellar atmospheres. <P />We
derived the effective temperatures of stars in our the sample from Hα
fitting. Theoretical profiles were computed using 3D hydrodynamical
simulations and 1D ATLAS models. Therefore, we are able to determined
1D and 3D-based effective temperatures. We then infer Li abundances
taking into account non-local thermodynamical equilibrium effects when
using both 1D and 3D models. <P />We find that SG stars have a mean
Li abundance higher by 0.1 dex than MS stars. This result is obtained
using both 1D and 3D models. We also detect a positive slope of Li
abundance with effective temperature, the higher the temperature the
higher the Li abundance, both for SG and MS stars, although the slope
is slightly steeper for MS stars. These results provide an unambiguous
evidence that the Li abundance changes with evolutionary status. <P
/>The physical mechanisms responsible for this behaviour are not yet
clear, and none of the existing models seems to describe accurately
these observations. Based on these conclusions, we believe that the
cosmological lithium problem still remains an open question.
---------------------------------------------------------
Title: <SUP>6</SUP>Li in metal-poor halo stars: real or spurious?
Authors: Steffen, M.; Cayrel, R.; Bonifacio, P.; Ludwig, H. -G.;
Caffau, E.
2010IAUS..265...23S Altcode: 2009arXiv0910.5917S
The presence of convective motions in the atmospheres of metal-poor
halo stars leads to systematic asymmetries of the emergent spectral
line profiles. Since such line asymmetries are very small, they can be
safely ignored for standard spectroscopic abundance analysis. However,
when it comes to the determination of the <SUP>6</SUP>Li/<SUP>7</SUP>Li
isotopic ratio, q(Li)=n(<SUP>6</SUP>Li)/n(<SUP>7</SUP>Li), the
intrinsic asymmetry of the <SUP>7</SUP>Li line must be taken into
account, because its signature is essentially indistinguishable from
the presence of a weak <SUP>6</SUP>Li blend in the red wing of the
<SUP>7</SUP>Li line. In this contribution we quantity the error of the
inferred <SUP>6</SUP>Li/<SUP>7</SUP>Li isotopic ratio that arises if
the convective line asymmetry is ignored in the fitting of the λ6707
Å lithium blend. Our conclusion is that <SUP>6</SUP>Li/<SUP>7</SUP>Li
ratios derived by Asplund et al. (2006), using symmetric line profiles,
must be reduced by typically Δq(Li) ≈ 0.015. This diminishes the
number of certain <SUP>6</SUP>Li detections from 9 to 4 stars or less,
casting some doubt on the existence of a <SUP>6</SUP>Li plateau.
---------------------------------------------------------
Title: Evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the
Galaxy, from a NLTE analysis
Authors: Spite, M.; Spite, F.; Bonifacio, P.; Hill, V.; Andrievsky,
S.; Cayrel, R.; François, P.; Korotin, S.
2010IAUS..265..380S Altcode:
In the framework of he ESO Large Program “First Stars”, high
resolution (R=45000) high S/N ratio spectra have been obtained for
a sample of Extremely Metal Poor Stars (EMP stars), 35 giants and 18
turnoff stars. Among them 37 have a very low metallicity: [Fe/H]<
-2.9.
---------------------------------------------------------
Title: HST-STIS abundances in the uranium-rich very metal-poor star
CS 31082-001
Authors: Barbuy, B.; Spite, M.; Hill, V.; Primas, F.; Plez, B.; Cayrel,
R.; Sneden, C.; Spite, F.; Beers, T. C.; Andersen, J.; Nordström,
B.; Bonifacio, P.; François, P.; Molaro, P.; Siqueira-Mello, C.
2010IAUS..265..120B Altcode:
The abundance derivation of heavy r-elements may provide a better
understanding of the r-process, and the determination of several
reference r-elements should allow a better determination of the
star's age. The spatial ultraviolet (UV) region presents a large
number of lines of heavy elements, and in some cases such as Bi,
Pt, Au, detectable lines are only available in the UV. The extreme
“r-process star” CS 31082-001 ([Fe/H] = -2.9) was observed in the
spatial UV in order to determine abundances of the heavy elements,
using STIS on board HST.
---------------------------------------------------------
Title: Solar abundances and 3D model atmospheres
Authors: Ludwig, Hans-Günter; Caffau, Elisabetta; Steffen, Matthias;
Bonifacio, Piercarlo; Freytag, Bernd; Cayrel, Roger
2010IAUS..265..201L Altcode: 2009arXiv0911.4248L
We present solar photospheric abundances for 12 elements from optical
and near-infrared spectroscopy. The abundance analysis was conducted
employing 3D hydrodynamical (CO<SUP>5</SUP>BOLD) as well as standard
1D hydrostatic model atmospheres. We compare our results to others
with emphasis on discrepancies and still lingering problems, in
particular exemplified by the pivotal abundance of oxygen. We argue
that the thermal structure of the lower solar photosphere is very
well represented by our 3D model. We obtain an excellent match of
the observed center-to-limb variation of the line-blanketed continuum
intensity, also at wavelengths shortward of the Balmer jump.
---------------------------------------------------------
Title: The metal-poor end of the Spite plateau
Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.;
Behara, N.; Gonzalez-Hernandez, J. I.; Steffen, M.; Cayrel, R.;
Freytag, B.; Van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite,
M.; Spite, F.; Beers, T. C.; Christlieb, N.; François, P.; Hill, V.
2010IAUS..265...75S Altcode:
We present the largest sample available to date of lithium abundances in
extremely metal poor (EMP) Halo dwarfs. Four T<SUB>eff</SUB> estimators
are used, including IRFM and Hα wings fitting against 3D hydrodynamical
synthetic profiles. Lithium abundances are computed by means of 1D and
3D-hydrodynamical NLTE computations. Below [Fe/H]~-3, a strong positive
correlation of A(Li) with [Fe/H] appears, not influenced by the choice
of the Teff estimator. A linear fit finds a slope of about 0.30 dex in
A(Li) per dex in [Fe/H], significant to 2-3 σ, and consistent within
1 σ among all the T<SUB>eff</SUB> estimators. The scatter in A(Li)
increases significantly below [Fe/H]~-3. Above, the plateau lies at
<A(Li)<SUB>3D, NLTE</SUB>> = 2.199 ± 0.086. If the primordial
A(Li) is the one derived from standard Big Bang Nucleosynthesis
(BBN), it appears difficult to envision a single depletion phenomenon
producing a thin, metallicity independent plateau above [Fe/H] = -2.8,
and a highly scattered, metallicity dependent distribution below.
---------------------------------------------------------
Title: NLTE strontium abundances in extremely metal poor halo stars
Authors: Andrievsky, S.; Spite, M.; Korotin, S.; Spite, F.; Bonifacio,
P.; Cayrel, R.; Francois, P.; Hill, V.
2010nuco.confE..94A Altcode: 2010PoS...100E..94A
No abstract at ADS
---------------------------------------------------------
Title: Non-LTE abundances of Mg and K in extremely metal-poor stars
and the evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the
Milky Way
Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.;
Bonifacio, P.; Cayrel, R.; François, P.; Hill, V.
2010A&A...509A..88A Altcode: 2010arXiv1001.1207A
<BR /> Aims: LTE abundances of light elements in extremely metal-poor
(EMP) stars have been previously derived from high quality spectra. New
derivations, free from the NLTE effects, will better constrain the
models of the Galactic chemical evolution and the yields of the very
first supernovae. <BR /> Methods: The NLTE profiles of the magnesium
and potassium lines have been computed in a sample of 53 extremely
metal-poor stars with a modified version of the program MULTI and
adjusted to the observed lines in order to derive the abundances of
these elements. <BR /> Results: The NLTE corrections for magnesium
and potassium are in good agreement with the works found in the
literature. The abundances are slightly changed, reaching a better
precision: the scatter around the mean of the abundance ratios
has decreased. Magnesium may be used with confidence as reference
element. Together with previously determined NLTE abundances of sodium
and aluminum, the new ratios are displayed, for comparison, along the
theoretical trends proposed by some models of the chemical evolution
of the Galaxy, using different models of supernovae. <P />Based on
observations obtained with the ESO Very Large Telescope at Paranal
Observatory (Large Programme “First Stars”, ID 165.N-0276; P.I.:
R. Cayrel.
---------------------------------------------------------
Title: Lithium abundances of main-sequence and subgiant stars in
the globular cluster NGC 6397
Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.;
Steffen, M.; Ludwig, H. -G.; Behara, N.; Sbordone, L.; Cayrel, R.;
Zaggia, S.
2010IAUS..266..407G Altcode: 2009arXiv0910.2305G
We present FLAMES/GIRAFFE spectroscopy obtained with the Very Large
Telescope (VLT). Using these observations, we have been able (for the
first time) to observe the Lii doublet in the main-sequence (MS) stars
of a globular cluster. We also observed Li in a sample of subgiant (SG)
stars of the same B - V colour. Our final sample is composed of 84 SG
and 79 MS stars. In spite of the fact that SG and MS stars span the same
temperature range, we find that the equivalent widths of the Lii doublet
in SG stars are systematically greater than in MS stars, suggesting a
higher Li content among SG stars. This is confirmed by our quantitative
analysis, which makes use of both 1D and 3D model atmospheres. We find
that SG stars show, on average, a higher Li abundance, by 0.1 dex, than
MS stars. We also detect a positive slope of Li abundance with effective
temperature: the higher the temperature the higher the Li abundance,
both for SG and MS stars, although the slope is slightly steeper for MS
stars. These results provide unambiguous evidence that the Li abundance
changes with evolutionary state. The physical mechanisms that contribute
to this are not yet clear, since none of the proposed models seem to
describe accurately the observations. Whether such a mechanism can
explain the cosmological lithium problem is still an open question.
---------------------------------------------------------
Title: HST-STIS abundances in the uranium-rich metal-poor star
CS31082-001
Authors: Barbuy, B.; Spite, M.; Hill, V.; Primas, F.; Plez, B.;
Cayrel, R.; Sneden, C.; Beers, T.; Andersen, J. R.; Nordström, B.;
Bonifacio, P.; Francois, P.; Molaro, P.
2010nuco.confE..77B Altcode: 2010PoS...100E..77B
No abstract at ADS
---------------------------------------------------------
Title: Lithium in the globular cluster NGC 6397. Evidence for
dependence on evolutionary status
Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.;
Steffen, M.; Ludwig, H. -G.; Behara, N. T.; Sbordone, L.; Cayrel,
R.; Zaggia, S.
2009A&A...505L..13G Altcode: 2009arXiv0909.0983G
Context: Most globular clusters are believed to host a single
stellar population. They can thus be considered a good place to
study the Spite plateau and to search for possible evolutionary
modifications of the Li content. <BR />Aims: We want to determine the
Li content of subgiant (SG) and main sequence (MS) stars of the old,
metal-poor globular cluster NGC 6397. This work was aimed not only
at studying possible Li abundance variations but also to investigate
the cosmological Li discrepancy. <BR />Methods: Here, we present
FLAMES/GIRAFFE observations of a sample of 84 SG and 79 MS stars in
NGC 6397 selected in a narrow range of B-V colour and, therefore,
effective temperatures. We determine both effective temperatures and
Li abundances using three-dimensional hydrodynamical model atmospheres
for all the MS and SG stars of the sample. <BR />Results: We find
a significant difference in the Li abundance between SG stars and
MS stars, the SG stars having an abundance higher by almost 0.1
dex on average. We also find a decrease in the lithium abundance
with decreasing effective temperature, both in MS and SG stars,
albeit with a significantly different slope for the two classes of
stars. This suggests that the lithium abundance in these stars is,
indeed, altered by some process, which is temperature-dependent. <BR
/>Conclusions: The lithium abundance pattern observed in NGC 6397 is
different from what is found among field stars, casting some doubt on
the use of globular cluster stars as representative of Population II
with respect to the lithium abundance. None of the available theories
of Li depletion appears to satisfactorily describe our observations. <P
/>Based on observations obtained with FLAMES/GIRAFFE at VLT Kueyen
8.2 m telescope in programme 079.D-0399(A). Table and Figs. 3-10 are
only available in electronic form at http://www.aanda.org Table 2
is available in electronic form at http://www.aanda.org and at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/505/L13
---------------------------------------------------------
Title: VizieR Online Data Catalog: Lithium in NGC 6397 (Gonzalez
Hernandez+, 2009)
Authors: Gonzalez Hernandez, J. I.; Bonifacio, P.; Caffau, E.; Steffen,
M.; Ludwig, H. -G.; Behara, N. T.; Sbordone, L.; Cayrel, R.; Zaggia, S.
2009yCat..35059013G Altcode:
Photometric data of the dwarf and subgiant stars of the globular
cluster NGC 6397. We also provide the signal-to-noise of the spectra,
the 3D and 1D Halpha-based effective temperatures, 3D Li abundances,
and the equivalent widths and errors: dEWa: Error of the equivalent
width measurements estimated from a fitting routine that uses as
free parameters the velocity shift, the continuum location, and the
equivalent width of the Li line. dEWb: Error of the equivalent width
associated to the signal-to-noise ratio and the wavelength dispersion
of the spectra, derived using Cayrel's formula (Cayrel, 1988, IAU
Symp. 132: The Impact of Very High S/N Spectroscopy on Stellar Physics,
132, 345). <P />(1 data file).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Extremely metal-poor turnoff
stars abundances (Bonifacio+, 2009)
Authors: Bonifacio, P.; Spite, M.; Cayrel, R.; Hill, V.; Spite,
F.; Francois, P.; Plez, B.; Ludwig, H. -G.; Caffau, E.; Molaro, P.;
Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T. C.; Nordstroem, B.;
Primas, F.
2009yCat..35010519B Altcode:
The detailed chemical abundances of extremely metal-poor (EMP) stars
are key guides to understanding the early chemical evolution of the
Galaxy. Most existing data, however, treat giant stars that may have
experienced internal mixing later. We aim to compare the results for
giants with new, accurate abundances for all observable elements in
18 EMP turnoff stars. VLT/UVES spectra at ~45000 and S/N ~130 per
pixel (330-1000nm) are analysed with OSMARCS model atmospheres and
the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc,
Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. For Ca, Ni, Sr, and Ba, we find
excellent consistency with our earlier sample of EMP giants, at all
metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co
are ~0.2dex larger than in giants of similar metallicity. Mg and Si
abundances are ~0.2dex lower (the giant [Mg/Fe] values are slightly
revised), while Zn is again ~0.4dex higher than in giants of similar
[Fe/H] (6 stars only). For C, the dwarf/giant discrepancy could
possibly have an astrophysical cause, but for the other elements it
must arise from shortcomings in the analysis. Approximate computations
of granulation (3D) effects yield smaller corrections for giants than
for dwarfs, but suggest that this is an unlikely explanation, except
perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide
consistent abundances between dwarfs and giants, unlike the LTE results,
and would be highly desirable for the other discrepant elements as
well. Meanwhile, we recommend using the giant abundances as reference
data for Galactic chemical evolution models. <P />(3 data files).
---------------------------------------------------------
Title: First stars XII. Abundances in extremely metal-poor turnoff
stars, and comparison with the giants
Authors: Bonifacio, P.; Spite, M.; Cayrel, R.; Hill, V.; Spite, F.;
François, P.; Plez, B.; Ludwig, H. -G.; Caffau, E.; Molaro, P.;
Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T. C.; Nordström, B.;
Primas, F.
2009A&A...501..519B Altcode: 2009arXiv0903.4174B
Context: The detailed chemical abundances of extremely metal-poor (EMP)
stars are key guides to understanding the early chemical evolution
of the Galaxy. Most existing data, however, treat giant stars that
may have experienced internal mixing later. <BR />Aims: We aim to
compare the results for giants with new, accurate abundances for all
observable elements in 18 EMP turnoff stars. <BR />Methods: VLT/UVES
spectra at R ~ 45 000 and S/N ~ 130 per pixel (λλ 330-1000 nm)
are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM
code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co,
Ni, Zn, Sr, and Ba. <BR />Results: For Ca, Ni, Sr, and Ba, we find
excellent consistency with our earlier sample of EMP giants, at all
metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and
Co are ~0.2 dex larger than in giants of similar metallicity. Mg
and Si abundances are ~0.2 dex lower (the giant [Mg/Fe] values are
slightly revised), while Zn is again ~0.4 dex higher than in giants
of similar [Fe/H] (6 stars only). <BR />Conclusions: For C, the
dwarf/giant discrepancy could possibly have an astrophysical cause,
but for the other elements it must arise from shortcomings in the
analysis. Approximate computations of granulation (3D) effects yield
smaller corrections for giants than for dwarfs, but suggest that this
is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE
computations for Na and Al provide consistent abundances between dwarfs
and giants, unlike the LTE results, and would be highly desirable for
the other discrepant elements as well. Meanwhile, we recommend using
the giant abundances as reference data for Galactic chemical evolution
models. <P />Based on observations obtained with the ESO Very Large
Telescope at Paranal Observatory, Chile (Large Programme “First
Stars”, ID 165.N-0276; P.I.: R. Cayrel, and Programme 078.B-0238;
P.I.: M. Spite). Appendices A-C are only available in electronic form
at http://www.aanda.org Table 7 is only available in electronic form
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/519
---------------------------------------------------------
Title: Chemical composition and kinematics of Galactic disk
stars. Commentary on: Edvardsson B., Andersen J., Gustafsson B.,
et al., 1993, A&A, 275, 101
Authors: Barbuy, B.; Cayrel, R.
2009A&A...500..443B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Tracing SN yields in metal-poor HB stars
Authors: Hansen, C. J.; Nordström, B.; Cayrel, R.; Spite, M.; Spite,
F.; Hill, V.; Plez, B.; Andersen, J.; Beers, T. C.; Sivarani, T.;
Depagne, E.; François, P.; Primas, F.; Barbuy, B.
2009IAUS..254P..31H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Halo chemistry and first stars. The chemical composition of
the matter in the early Galaxy, from C to Mg†
Authors: Spite, M.; Bonifacio, P.; Cayrel, R.; Spite, F.; Francois,
P.; Ludwig, H. G.; Caffau, E.; Andrievsky, S.; Barbuy, B.; Plez, B.;
Molaro, P.; Andersen, J.; Beers, T.; Depagne, E.; Nordström, B.;
Primas, F.
2009IAUS..254..349S Altcode:
From NLTE computations of the magnesium abundance in a sample
of extremely metal-poor giants we derive [Mg/Fe]=+0.7, leading to
[Al/Mg]=-0.80 and [Na/Mg]=-0.85 in the early Galaxy. The ratio [O/Mg]
should be near to the solar value. Measurements of nitrogen abundances
derived from the analysis of the NH band in eight more stars confirm
the large scatter of the ratios [N/Fe] and [N/O] in the early Galaxy.
---------------------------------------------------------
Title: Evolution of the barium abundance in the early Galaxy from
a NLTE analysis of the Ba lines in a homogeneous sample of EMP stars
Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.;
François, P.; Bonifacio, P.; Cayrel, R.; Hill, V.
2009A&A...494.1083A Altcode: 2009arXiv0902.0450A
Context: Barium is a key element in constraining the evolution of
the (not well understood) r-process in the first galactic stars and
currently the Ba abundances in these very metal-poor stars were mostly
measured under the Local Thermodynamical Equilibrium (LTE) assumption,
which may lead in general to an underestimation of Ba. <BR />Aims:
We present here determinations of the barium abundance taking into
account the non-LTE (NLTE) effects in a sample of extremely metal-poor
stars (EMP stars): 6 turnoff stars and 35 giants. <BR />Methods:
The NLTE profiles of the three unblended Ba II lines (4554 Å, 5853
Å, 6496 Å) have been computed. The computations were made with a
modified version of the MULTI code, applied to an atomic model of the
Ba atom with 31 levels of Ba I, 101 levels of Ba II, and compared to
the observations. <BR />Results: The ratios of the NLTE abundances of
barium relative to Fe are slightly shifted towards the solar ratio. In
the plot of [Ba/Fe] versus [Fe/H], the slope of the regression line is
slightly reduced as is the scatter. In the interval -3.3 <[Fe/H] <
-2.6, [Ba/Fe] decreases with a slope of about 1.4 and a scatter close
to 0.44. For [Fe/H] <-3.3 the number of stars is not sufficient to
decide whether [Ba/Fe] keeps decreasing (and then CD-38:245 should be
considered as a peculiar “barium-rich star”) or if a plateau is
reached as soon as [Ba/Fe] ≈ -1. In both cases the scatter remains
quite large, larger than what can be accounted for by the measurement
and determination errors, suggesting the influence of a complex process
of Ba production, and/or inefficient mixing in the early Galaxy. <P
/>Based on observations obtained with the ESO Very Large Telescope at
Paranal Observatory (Large Programme “First Stars”, ID 165.N-0276;
P.I.: R. Cayrel.
---------------------------------------------------------
Title: The ESO Large Programme “First Stars”
Authors: Bonifacio, P.; Andersen, J.; Andrievsky, S. M.; Barbuy, B.;
Beers, T. C.; Caffau, E.; Cayrel, R.; Depagne, E.; François, P.;
González Hernández, J. I.; Hansen, C. J.; Herwig, F.; Hill, V.;
Korotin, S. A.; Ludwig, H. -G.; Molaro, P.; Nordström, B.; Plez,
B.; Primas, F.; Sivarani, T.; Spite, F.; Spite, M.
2009ASSP....9...31B Altcode: 2008arXiv0801.1293B; 2009svlt.conf...31B
In ESO period 65 (April-September 2000) the large programme 165.N-0276,
led by Roger Cayrel, began making use of UVES at the Kueyen VLT
telescope. Known within the Team and outside as "First Stars", it was
aimed at obtaining high resolution, high signal-to-noise ratio spectra
in the range 320 nm-1000 nm for a large sample of extremely metal-poor
(EMP) stars identified from the HK objective prism survey [T.C. Beers,
G.W. Preston, S.A. Shectman in Astron. J. 90, 2089 (1985); T.C. Beers,
G.W. Preston, S.A. Shectman in Astron. J. 103, 1987 (1992)]. The goal
was to use these spectra to determine accurate atmospheric parameters
and chemical composition of these stars which are among the oldest
objects amenable to our detailed study. Although these stars are not
the first generation of stars they must be very close descendants of
the first generation. One may hope to gain insight on the nature of
the progenitors from detailed information on the descendants.
---------------------------------------------------------
Title: The photospheric solar oxygen project. I. Abundance analysis
of atomic lines and influence of atmospheric models
Authors: Caffau, E.; Ludwig, H. -G.; Steffen, M.; Ayres, T. R.;
Bonifacio, P.; Cayrel, R.; Freytag, B.; Plez, B.
2008A&A...488.1031C Altcode: 2008arXiv0805.4398C
Context: The solar oxygen abundance has undergone a major downward
revision in the past decade, the most noticeable one being the
update including 3D hydrodynamical simulations to model the solar
photosphere. Up to now, such an analysis has only been carried out
by one group using one radiation-hydrodynamics code. <BR />Aims:
We investigate the photospheric oxygen abundance considering lines
from atomic transitions. We also consider the relationship between
the solar model used and the resulting solar oxygen abundance, to
understand whether the downward abundance revision is specifically
related to 3D hydrodynamical effects. <BR />Methods: We performed
a new determination of the solar photospheric oxygen abundance by
analysing different high-resolution high signal-to-noise ratio atlases
of the solar flux and disc-centre intensity, making use of the latest
generation of CO5BOLD 3D solar model atmospheres. <BR />Results: We
find 8.73 ≤ log (N_O/N_H) +12 ≤ 8.79. The lower and upper values
represent extreme assumptions on the role of collisional excitation
and ionisation by neutral hydrogen for the NLTE level populations
of neutral oxygen. The error of our analysis is ± (0.04± 0.03)
dex, the last being related to NLTE corrections, the first error
to any other effect. The 3D “granulation effects” do not play a
decisive role in lowering the oxygen abundance. <BR />Conclusions:
Our recommended value is log (N_O/N_H) = 8.76 ± 0.07, considering our
present ignorance of the role of collisions with hydrogen atoms on the
NLTE level populations of oxygen. The reasons for lower O abundances in
the past are identified as (1) the lower equivalent widths adopted and
(2) the choice of neglecting collisions with hydrogen atoms in the
statistical equilibrium calculations for oxygen. <P />This paper is
dedicated to the memory of Hartmut Holweger.
---------------------------------------------------------
Title: NLTE determination of the aluminium abundance in a homogeneous
sample of extremely metal-poor stars
Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.;
Bonifacio, P.; Cayrel, R.; Hill, V.; François, P.
2008A&A...481..481A Altcode: 2008arXiv0802.1519A
Aims: Aluminium is a key element to constrain the models of the chemical
enrichment and the yields of the first supernovae. But obtaining precise
Al abundances in extremely metal-poor (EMP) stars requires that the
non-LTE effects be carefully taken into account. <BR />Methods: The NLTE
profiles of the blue resonance aluminium lines have been computed in a
sample of 53 extremely metal-poor stars with a modified version of the
program MULTI applied to an atomic model of the Al atom with 78 levels
of Al I and 13 levels of Al II, and compared to the observations. <BR
/>Results: With these new determinations, all the stars of the sample
show a ratio Al/Fe close to the solar value: [Al/Fe] = -0.06±0.10
with a very small scatter. These results are compared to the models
of the chemical evolution of the halo using different models of SN II
and are compatible with recent computations. The sodium-rich giants
are not found to be also aluminium-rich and thus, as expected, the
convection in these giants only brings to the surface the products
of the Ne-Na cycle. <P />Based on observations obtained with the ESO
Very Large Telescope at Paranal Observatory, Chile (Large Programme
“First Stars”, ID 165.N-0276(A); P.I.: R. Cayrel).
---------------------------------------------------------
Title: First stars XI. Chemical composition of the extremely
metal-poor dwarfs in the binary CS 22876-032
Authors: González Hernández, J. I.; Bonifacio, P.; Ludwig, H. -G.;
Caffau, E.; Spite, M.; Spite, F.; Cayrel, R.; Molaro, P.; Hill, V.;
François, P.; Plez, B.; Beers, T. C.; Sivarani, T.; Andersen, J.;
Barbuy, B.; Depagne, E.; Nordström, B.; Primas, F.
2008A&A...480..233G Altcode: 2007arXiv0712.2949G
Context: Unevolved metal-poor stars constitute a fossil record of the
early Galaxy, and can provide invaluable information on the properties
of the first generations of stars. Binary systems also provide direct
information on the stellar masses of their member stars. <BR />Aims:
The purpose of this investigation is a detailed abundance study of the
double-lined spectroscopic binary CS 22876-032, which comprises the two
most metal-poor dwarfs known. <BR />Methods: We used high-resolution,
high-S/N ratio spectra from the UVES spectrograph at the ESO VLT
telescope. Long-term radial-velocity measurements and broad-band
photometry allowed us to determine improved orbital elements and
stellar parameters for both components. We used OSMARCS 1D models and
the turbospectrum spectral synthesis code to determine the abundances
of Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also
used the CO^5BOLD model atmosphere code to compute the 3D abundance
corrections, notably for Li and O. <BR />Results: We find a metallicity
of [Fe/H] ~ -3.6 for both stars, using 1D models with 3D corrections of
~-0.1 dex from averaged 3D models. We determine the oxygen abundance
from the near-UV OH bands; the 3D corrections are large, -1 and -1.5
dex for the secondary and primary respectively, and yield [O/Fe] ~
0.8, close to the high-quality results obtained from the [OI] 630
nm line in metal-poor giants. Other [ α/Fe] ratios are consistent
with those measured in other dwarfs and giants with similar [Fe/H],
although Ca and Si are somewhat low ([X/Fe] ⪉ 0). Other element
ratios follow those of other halo stars. The Li abundance of the
primary star is consistent with the Spite plateau, but the secondary
shows a lower abundance; 3D corrections are small. <BR />Conclusions:
The Li abundance in the primary star supports the extension of the Spite
Plateau value at the lowest metallicities, without any decrease. The
low abundance in the secondary star could be explained by endogenic
Li depletion, due to its cooler temperature. If this is not the case,
another, yet unknown mechanism may be causing increased scatter in A(Li)
at the lowest metallicities.
---------------------------------------------------------
Title: Self-broadening of the hydrogen Balmer α line
Authors: Allard, N. F.; Kielkopf, J. F.; Cayrel, R.; van't
Veer-Menneret, C.
2008A&A...480..581A Altcode:
Context: Profiles of hydrogen lines in stellar spectra are determined
by the properties of the hydrogen atom and the structure of the star's
atmosphere. Hydrogen line profiles are therefore a very important
diagnostic tool in stellar modeling. In particular they are widely
used as effective temperature criterion for stellar atmospheres in
the range T_eff 5500-7000 K. <BR />Aims: In cool stars such as the Sun
hydrogen is largely neutral and the electron density is low. The line
center width at half maximum and the spectral energy distribution in
the wings are determined primarily by collisions with hydrogen atoms
due to their high relative density. This work aims to provide benchmark
calculations of Balmer α based on recent H2 potentials. <BR />Methods:
For the first time an accurate determination of the broadening of
Balmer α by atomic hydrogen is made in a unified theory of collisional
line profiles using ab initio calculations of molecular hydrogen
potential energies and transition matrix elements among singlet and
triplet electronic states. <BR />Results: We computed the shape,
width and shift of the Balmer α line perturbed by neutral hydrogen
and studied their dependence on temperature. We present results
over the full range of temperatures from 3000 to 12 000 K needed for
stellar spectra models. <BR />Conclusions: Our calculations lead to
larger values than those obtained with the commonly used Ali &
Griem (1966, Phys. Rev. A, 144, 366) theory and are closer to the
recent calculations of Barklem et al. (2000a, A&A, 355, L5; 2000b,
A&A, 363, 1091). We conclude that the line parameters are dependent
on the sum of many contributing molecular transitions, each with a
different temperature dependence, and we provide tables for Balmer
α. The unified line shape theory with complete molecular potentials
also predicts additional opacity in the far non-Lorentzian wing.
---------------------------------------------------------
Title: CS 22876-032: The Most Metal-Poor Dwarfs. Abundances and
3D Effects
Authors: González Hernández, J. I.; Bonifacio, P.; Ludwig, H. -G.;
Caffau, E.; Spite, M.; Spite, F.; Cayrel, R.; Molaro, P.; Hill, V.;
François, P.; Plez, B.; Beers, T. C.; Sivarani, T.; Andersen, J.;
Barbuy, B.; Depagne, E.; Nordström, B.; Primas, F.
2008AIPC..990..175G Altcode: 2008AIPC..990..175H
Unevolved extremely metal-poor stars offer us a unique tool to infer
knowledge of the first generation of stars. We have analysed UVES
high-resolution spectra of the double-lined spectroscopic binary CS
22876-032 which comprises the two most metal-poor dwarfs currently
known. In particular, we determine the oxygen (from OH lines in the
near-UV) and lithium abundances taking into account 3D effects. <P
/>The long-time baseline radial velocity measurements and photometric
data available allowed us to determine the orbital elements as well as
stellar parameters of both components. We use OSMARCS 1D models and the
TURBOSPECTRUM spectral synthesis code to determine the abundances of Li,
O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also use the
CO<SUP>5</SUP> BOLD 3D model atmosphere code to predict the 3D abundance
corrections, mainly for Li, O and Fe. <P />We find a metallicity
of [Fe/H]~-3.6 for both stars using 1D models with 3D corrections
of ~-0.1 dex from horizontal and temporal averaged 3D models. The
[α/Fe] ratios are consistent with those found for metal-poor giants
with similar [Fe/H], although Ca and Si are rather low, [X/Fe]~=0. The
1D O abundance, [O/Fe]~2 for both stars, is very large, but 3D models
predict abundance corrections of roughly -1.0 dex and -1.5 dex for the
secondary and primary stars, respectively. These 3D corrections bring
the O abundances derived from near-UV OH bands in these two dwarfs
closer to other high-quality measurements from the forbidden [OI]
630 nm line in metal-poor giants. The Li abundance is consistent with
the Spite plateau, although the secondary star shows a lower abundance.
---------------------------------------------------------
Title: The Metal-Poor End of the Lithium Plateau
Authors: Sbordone, L.; Bonifacio, P.; González Hernández, J. I.;
Cayrel, R.; Behara, N.; Molaro, P.; Plez, B.; Francois, P.; Christlieb,
N.; Ludwig, H. -G.; Sivarani, T.; Beers, T. C.; van't Veer, C.
2008AIPC..990..339S Altcode:
We present our current sample of Lithium abundances in 28 low
metallicity dwarf and Turn Off (TO) stars ([Fe/H] between -2.5
and -3.5), based on high resolution, high signal to noise echelle
spectra. Nine new stars have been added to the Bonifacio et al. [1]
sample, and the full sample has been reanalyzed in order to take into
account the effect of two different possible temperature scales. In
fact, the Li abundance measurement based on the 670.8 nm line is
highly sensitive to temperature, and Teff scales are still poorly
calibrated at low metallicities. First, the effective temperature has
been derived from Hα profile fitting, and second, directly from the
star's infrared flux. The two methods offer similar precision but are
affected by different uncertainties and systematics. The infrared flux
method (IRFM) leads to a larger Teff dispersion than the Hα profile
fitting, while also producing an offset of about 150 K towards hotter
temperatures. This leads to a contraction of the metallicity scale
of the sample, which encompasses [Fe/H] = -3.7 to -2.5 when using
Hα calibrated temperatures, and [Fe/H] = -3.4 to -2.5 when using
IRFM. The higher average IRFM temperature increases somewhat the mean
Li abundance, changing from A(Li)Hα = 2.10 to A(Li)IRFM = 2.18
---------------------------------------------------------
Title: Overview of the Li problem in metal-poor stars and new results
on 6Li
Authors: Cayrel, R.; Steffen, M.; Bonifacio, P.; Ludwig, H. -G.;
Caffau, E.
2008nuco.confE...2C Altcode: 2008arXiv0810.4290C; 2008PoS....53E...2C
Two problems are discussed here. The first one is the 0.4 dex
discrepancy between the 7Li abundance derived from the spectra
of metal-poor halo stars on the one hand, and from Big Bang
nucleosynthesis, based on the cosmological parameters constrained
by the WMAP measurements, on the other hand. Lithium, indeed,
can be depleted in the convection zone of unevolved stars. The
understanding of the hydrodynamics of the crucial zone near the
bottom of the convective envelope in dwarfs or turn-off stars of solar
metallicity has recently made enormous progress with the inclusion of
internal gravity waves. However, similar work for metal-poor stars is
still lacking. Therefore it is not yet clear whether the depletion
occurring in the metal-poor stars themselves is adequate to produce
a 7Li plateau. The second problem pertains to the large amount of
6Li recently found in metal-poor halo stars. The convection-related
asymmetry of the 7Li line could mimic the signal attributed so far
to the weak blend of 6Li in the red wing of the 7Li line. Theoretical
computations show that the signal generated by the asymmetry of 7Li is
2.0, 2.1, and 3.7 per cent for [Fe/H]= -3.0, -2.0, -1.0, respectively
(Teff =6250 K and log g=4.0 [cgs]). In addition we re-investigate
the statistical properties of the 6Li plateau and show that previous
analyses were biased. Our conclusion is that the 6Li plateau can be
reinterpreted in terms of intrinsic line asymmetry, without the need
to invoke a contribution of 6Li. (abridged)
---------------------------------------------------------
Title: First stars. VIII. Enrichment of the neutron-capture elements
in the early Galaxy
Authors: François, P.; Depagne, E.; Hill, V.; Spite, M.; Spite, F.;
Plez, B.; Beers, T. C.; Andersen, J.; James, G.; Barbuy, B.; Cayrel,
R.; Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F.
2007A&A...476..935F Altcode: 2007arXiv0709.3454F
Context: Extremely metal-poor (EMP) stars in the halo of the Galaxy
are sensitive probes of the production of the first heavy elements
and the efficiency of mixing in the early interstellar medium. The
heaviest measurable elements in such stars are our main guides
to understanding the nature and astrophysical site(s) of early
neutron-capture nucleosynthesis. <BR />Aims: Our aim is to measure
accurate, homogeneous neutron-capture element abundances for the sample
of 32 EMP giant stars studied earlier in this series, including 22
stars with [Fe/H]< -3.0. <BR />Methods: Based on high-resolution,
high S/N spectra from the ESO VLT/UVES, 1D, LTE model atmospheres,
and synthetic spectrum fits, we determine abundances or upper limits
for the 16 elements Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy,
Ho, Er, Tm, and Yb in all stars. <BR />Results: As found earlier,
[Sr/Fe], [Y/Fe], [Zr/Fe] and [Ba/Fe] are below Solar in the EMP stars,
with very large scatter. However, we find a tight anti-correlation of
[Sr/Ba], [Y/Ba], and [Zr/Ba] with [Ba/H] for -4.5 <[Ba/H] <
-2.5, also when subtracting the contribution of the main r-process
as measured by [Ba/H]. Spectra of even higher S/N ratio are needed
to confirm and extend these results below [Fe/H] ≃ -3.5. The huge,
well-characterised scatter of the [n-capture/Fe] ratios in our EMP
stars is in stark contrast to the negligible dispersion in the [
α/Fe] and [Fe-peak/Fe] ratios for the same stars found in Paper V. <BR
/>Conclusions: These results demonstrate that a second (“weak” or
LEPP) r-process dominates the production of the lighter neutron-capture
elements for [Ba/H] < -2.5. The combination of very consistent [
α/Fe] and erratic [n-capture/Fe] ratios indicates that inhomogeneous
models for the early evolution of the halo are needed. Our accurate data
provide strong constraints on future models of the production and mixing
of the heavy elements in the early Galaxy. <P />Based on observations
made with the ESO Very Large Telescope at Paranal Observatory, Chile
(program ID 165.N-0276(A); P.I: R. Cayrel).
---------------------------------------------------------
Title: Line shift, line asymmetry, and the ^6Li/^7Li isotopic ratio
determination
Authors: Cayrel, R.; Steffen, M.; Chand, H.; Bonifacio, P.; Spite,
M.; Spite, F.; Petitjean, P.; Ludwig, H. -G.; Caffau, E.
2007A&A...473L..37C Altcode: 2007arXiv0708.3819C
Context: Line asymmetries are generated by convective Doppler shifts in
stellar atmospheres, especially in metal-poor stars, where convective
motions penetrate to higher atmospheric levels. Such asymmetries are
usually neglected in abundance analyses. The determination of the
^6Li/^7Li isotopic ratio is prone to suffering from such asymmetries,
as the contribution of ^6Li is a slight blending reinforcement of the
red wing of each component of the corresponding ^7Li line, with respect
to its blue wing. <BR />Aims: The present paper studies the halo star
HD 74000 and estimates the impact of convection-related asymmetries
on the Li isotopic ratio determination. <BR />Methods: Two methods
are used to meet this aim. The first, which is purely empirical,
consists in deriving a template profile from another element that can
be assumed to originate in the same stellar atmospheric layers as Li
I, producing absorption lines of approximately the same equivalent
width as individual components of the ^7Li I resonance line. The
second method consists in conducting the abundance analysis based on
NLTE line formation in a 3D hydrodynamical model atmosphere, taking
into account the effects of photospheric convection. <BR />Results:
The results of the first method show that the convective asymmetry
generates an excess absorption in the red wing of the ^7Li absorption
feature that mimics the presence of ^6Li at a level comparable to
the hitherto published values. This opens the possibility that only
an upper limit on ^6Li/^7Li has thus far been derived. The second
method confirms these findings. <BR />Conclusions: From this work,
it appears that a systematic reappraisal of former determinations of
^6Li abundances in halo stars is warranted. <P />Based on observations
carried out at the European Southern Observatory (ESO), under prog. ID
75.D-0600. Tables 1-3, and additional references are only available
in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Abundances in extremely metal-poor stars: comparison of the
trends of abundance ratios in giants and turnoff stars
Authors: Spite, Monique; Bonifacio, Piercarlo; Cayrel, Roger; Spite,
François; Hill, Vanessa; Andersen, Johannes; Barbuy, Beatriz; Beers,
Timothy; Depagne, Eric; François, Patrick; Molaro, Paolo; Nordström,
Birgitta; Plez, Bertrand; Primas, Francesca
2007IAUS..239..280S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: NLTE determination of the sodium abundance in a homogeneous
sample of extremely metal-poor stars
Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.;
Bonifacio, P.; Cayrel, R.; Hill, V.; François, P.
2007A&A...464.1081A Altcode: 2007astro.ph..1199A
Context: Abundance ratios in extremely metal-poor (EMP) stars are a good
indication of the chemical composition of the gas in the earliest phases
of the Galaxy evolution. It had been found from an LTE analysis that
at low metallicity, and in contrast with most of the other elements,
the scatter of [Na/Fe] versus [Fe/H] was surprisingly large and that,
in giants, [Na/Fe] decreased with metallicity. <BR />Aims: Since it
is well-known that the formation of sodium lines is very sensitive
to non-LTE effects, to firmly establish the behaviour of the sodium
abundance in the early Galaxy, we have used high quality observations
of a sample of EMP stars obtained with UVES at the VLT, and we
have taken into account the non-LTE line formation of sodium. <BR
/>Methods: The profiles of the two resonant sodium D lines (only
these sodium lines are detectable in the spectra of EMP stars) have
been computed in a sample of 54 EMP giants and turn-off stars (33 of
them with [Fe/H]<-3.0) with a modified version of the code MULTI,
and compared to the observed spectra. <BR />Results: With these new
determinations in the range {-4 <[Fe/H]< -2.5}, both [Na/Fe] and
[Na/Mg] are almost constant with a low scatter. In the turn-off stars
and "unmixed" giants (located in the low RGB): [Na/Fe] = -0.21 ± 0.13
or [Na/Mg] = -0.45 ± 0.16. These values are in good agreement with
the recent determinations of [Na/Fe] and [Na/Mg] in nearby metal-poor
stars. Moreover we confirm that all the sodium-rich stars are "mixed"
stars (i.e., giants located after the bump, which have undergone
an extra mixing). None of the turn-off stars is sodium-rich. As a
consequence it is probable that the sodium enhancement observed in
some mixed giants is the result of a deep mixing.
---------------------------------------------------------
Title: First stars VII - Lithium in extremely metal poor dwarfs
Authors: Bonifacio, P.; Molaro, P.; Sivarani, T.; Cayrel, R.; Spite,
M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.;
Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F.
2007A&A...462..851B Altcode: 2006astro.ph.10245B
Context: The primordial lithium abundance is a key prediction of
models of big bang nucleosynthesis, and its abundance in metal-poor
dwarfs (the Spite plateau) is an important, independent observational
constraint on such models. <BR />Aims: This study aims to determine the
level and constancy of the Spite plateau as definitively as possible
from homogeneous high-quality VLT-UVES spectra of 19 of the most
metal-poor dwarf stars known. <BR />Methods: Our high-resolution
(R∼ 43 000), high S/N spectra are analysed with OSMARCS 1D LTE
model atmospheres and turbospectrum synthetic spectra to determine
effective temperatures, surface gravities, and metallicities, as well
as Li abundances for our stars. <BR />Results: Eliminating a cool
subgiant and a spectroscopic binary, we find 8 stars to have -3.5 <
[Fe/H] < -3.0 and 9 stars with -3.0 < [Fe/H] < -2.5. Our best
value for the mean level of the plateau is A(Li) =2.10± 0.09. The
scatter around the mean is entirely explained by our estimate of the
observational error and does not allow for any intrinsic scatter in
the Li abundances. In addition, we conclude that a systematic error of
the order of 200 K in any of the current temperature scales remains
possible. The iron excitation equilibria in our stars support our
adopted temperature scale, which is based on a fit to wings of the
Hα line, and disfavour hotter scales, which would lead to a higher
Li abundance, but fail to achieve excitation equilibrium for iron. <BR
/>Conclusions: We confirm the previously noted discrepancy between the
Li abundance measured in extremely metal-poor turnoff stars and the
primordial Li abundance predicted by standard Big-Bang nucleosynthesis
models adopting the baryonic density inferred from WMAP. We discuss
recent work explaining the discrepancy in terms of diffusion and
find that uncertain temperature scales remain a major question. <P
/>Based on observations made with the ESO Very Large Telescope at
Paranal Observatory, Chile (Large Programme “First Stars”, ID
165.N-0276(A); P.I. R. Cayrel). Tables 4-8 and Appendix A are only
available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: First stars X. The nature of three unevolved carbon-enhanced
metal-poor stars
Authors: Sivarani, T.; Beers, T. C.; Bonifacio, P.; Molaro, P.; Cayrel,
R.; Herwig, F.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy,
B.; Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F.
2006A&A...459..125S Altcode: 2006astro.ph..8112S
Context: .On the order of 20% of the very metal-poor stars in the
Galaxy exhibit large carbon enhancements. It is important to establish
which astrophysical sites and processes are responsible for the
elemental abundance patterns of this early Galactic population.<BR />
Aims: .We seek to understand the nature of the progenitors of three
main-sequence turnoff Carbon-Enhanced Metal-Poor (CEMP) stars, CS
31080-095, CS 22958-042, and CS 29528-041, based on a detailed abundance
analysis. <BR /> Methods: .From high-resolution VLT/UVES spectra (R∼
43 000), we determine abundances or upper limits for Li, C, N, O, and
other important elements, as well as <SUP>12</SUP>C/<SUP>13</SUP>C
isotopic ratios. <BR /> Results: .All three stars have -3.30 ≤
[Fe/H] ≤ -2.85 and moderate to high CNO abundances. CS 22958-042
is one of the most carbon-rich CEMP stars known ([ C/Fe] = +3.2),
while CS 29528-041 (one of the few N-enhanced metal-poor stars known)
is one of the most nitrogen rich ([ N/Fe] = +3.0). Oxygen is very
high in CS 31080-095 ([ O/Fe] = +2.35) and in CS 22958-042 ([ O/Fe]
= +1.35). All three stars exhibit [ Sr/Fe] < 0; Ba is not detected
in CS 22958-042 ([ Ba/Fe] < -0.53), but it is moderately enhanced
([ Ba/Fe] ∼ 1) in the other two stars. CS 22958-042 displays one of
the largest sodium overabundances yet found in CEMP stars ([ Na/Fe] =
+2.8). CS 22958-042 has <SUP>12</SUP>C/<SUP>13</SUP>C = 9, similar to
most other CEMP stars without enhanced neutron-capture elements, while
<SUP>12</SUP>C/<SUP>13</SUP>C ≥ 40 in CS 31080-095. CS 31080-095 and
CS 29528-041 have A(Li) ∼ 1.7, below the Spite Plateau, while Li is
not detected in CS 22958-042. <BR /> Conclusions: .CS 22958-042 is a
CEMP-no star, but the other two stars are in no known class of CEMP
star and thus either constitute a new class or are a link between the
CEMP-no and CEMP-s classes, adding complexity to the abundance patterns
for CEMP stars. We interpret the abundance patterns in our stars to
imply that current models for the presumed AGB binary progenitors
lack an extra-mixing process, similar to those apparently operating
in RGB stars.
---------------------------------------------------------
Title: The oldest stars in the Milky Way
Authors: Cayrel, R.
2006RPPh...69.2823C Altcode:
In the framework of modern cosmology, the first stars formed in the
cores of dark matter overdensities of a few million solar masses
(M<SUB>odot</SUB>), when small density fluctuations present in the
early universe first attained large amplitudes. Then, the Jeans
gravitational instability triggered a run-away collapse, enabling
these cores to reach stellar densities, provided that the baryonic
matter was able to efficiently radiate away the heat gained from
gravitational potential energy during the collapse. Thanks to recent
enormous progress in knowledge of the microwave cosmological background
(in particular observations by the NASA Wilkinson Microwave Anisotropy
Probe), the chemical composition of matter produced during primordial
nucleosynthesis in the first 15 min after the Big Bang is completely
constrained, and one can confidently identify the chemical composition
of the matter from which the first stars were born. Stars with such
a composition are called, for historical reasons, Population III
stars. <P />The nature of the first stars has aroused the curiosity of
theoreticians and observers alike. Important progress has been made
on both sides in the last ten years. A brief account of these recent
advances is presented here. When and where the first stars formed is
now fairly well understood. One major uncertainty that remains however
concerns the distribution of masses of the first stars. It is almost
certain that these masses were above the mass required to have such
stars still radiating today, i.e. above 0.9 times the mass of the Sun,
according to stellar evolution computations. This is unfortunate
for observers, who have endeavoured for many decades to find even
a single example of a Population III star. However, in the course
of their searches, they have at least observed stars with chemical
compositions that are very close to the primordial composition. A few
stars have been identified, polluted by only 3 × 10<SUP>-6</SUP> in
mass by elements not produced by the primordial nucleosynthesis, but by
supernova nucleosynthesis. The study of the chemical composition of this
tiny fraction of matter is a wonderfully rich source of information on
true Population III objects, which synthesized the elements composing
it, and then ejected these elements into the surrounding primordial
medium, producing the matter from which were born the still observable
low-mass stars scrutinized by observers.
---------------------------------------------------------
Title: First stars IX - Mixing in extremely metal-poor
giants. Variation of the <SUP>12</SUP>C/<SUP>13</SUP>C, [Na/Mg] and
[Al/Mg] ratios
Authors: Spite, M.; Cayrel, R.; Hill, V.; Spite, F.; François,
P.; Plez, B.; Bonifacio, P.; Molaro, P.; Depagne, E.; Andersen, J.;
Barbuy, B.; Beers, T. C.; Nordström, B.; Primas, F.
2006A&A...455..291S Altcode: 2006astro.ph..5056S
Context: .Extremely metal-poor (EMP) stars preserve a fossil record
of the composition of the ISM when the Galaxy formed. It is crucial,
however, to verify whether internal mixing has modified their
surface composition, especially in the giants where most elements
can be studied. <BR /> Aims: .We aim to understand the CNO abundance
variations found in some, but not all EMP field giants analysed
earlier. Mixing beyond the first dredge-up of standard models is
required, and its origin needs clarification. <BR /> Methods:
.The <SUP>12C/^{13</SUP>C} ratio is the most robust diagnostic
of deep mixing, because it is insensitive to the adopted stellar
parameters and should be uniformly high in near-primordial gas. We
have measured <SUP>12C and ^{13</SUP>C} abundances in 35 EMP giants
(including 22 with {[Fe/H] < -3.0}) from high-quality VLT/UVES
spectra analysed with LTE model atmospheres. Correlations with other
abundance data are used to study the depth of mixing. <BR /> Results:
.The <SUP>12C/^{13</SUP>C} ratio is found to correlate with [C/Fe]
(and Li/H), and clearly anti-correlate with [N/Fe], as expected if the
surface abundances are modified by CNO processed material from the
interior. Evidence for such deep mixing is observed in giants above
{log L/L<SUB>⊙</SUB> = 2.6}, brighter than in less metal-poor stars,
but matching the bump in the luminosity function in both cases. Three
of the mixed stars are also Na- and Al-rich, another signature of deep
mixing, but signatures of the ON cycle are not clearly seen in these
stars. <BR /> Conclusions: .Extra mixing processes clearly occur in
luminous RGB stars. They cannot be explained by standard convection,
nor in a simple way by rotating models. The Na- and Al-rich giants
could be AGB stars themselves, but an inhomogeneous early ISM or
pollution from a binary companion remain possible alternatives.
---------------------------------------------------------
Title: Abundance of heavy elements in extremely metal-poor stars
Authors: François, P.; Depagne, E.; Hill, V.; Spite, M.; Spite,
F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.;
Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F.
2006AIPC..847..205F Altcode:
This paper reports on the abundance determination of neutron-capture
elements in 32 extremely metal-poor stars. The study is based on
the analysis of high quality spectra obtained with UVES+Kueyen. The
results are compared with the most recent analyses of spectra mostly
taken with other 10m class telescopes.
---------------------------------------------------------
Title: The chemical evolution of barium and europium in the Milky Way
Authors: Cescutti, G.; François, P.; Matteucci, F.; Cayrel, R.;
Spite, M.
2006A&A...448..557C Altcode: 2005astro.ph.10496C
Aims.We compute the evolution of the abundances of barium and europium
in the Milky Way and we compare our results to the observed abundances
from the recent UVES Large Program "First Stars".Methods.We use a
chemical evolution model that reproduces the majority of observational
constraints.Results.We confirm that barium is a neutron capture element
mainly produced in the low mass AGB stars during the thermal-pulsing
phase by the <SUP>13</SUP>C neutron source, in a slow neutron capture
process. However, in order to reproduce the [Ba/Fe] vs. [Fe/H]
as well as the Ba solar abundance, we suggest that Ba is also
produced as an r-process element by massive stars in the range 10-30
M<SUB>⊙</SUB>. On the other hand, europium should be only an r-process
element produced in the same range of masses (10-30 M<SUB>⊙</SUB>),
at variance with previous suggestions indicating a smaller mass range
for the Eu producers. As it is well known, there is a large spread in
the [Ba/Fe] and [Eu/Fe] ratios at low metallicities, although smaller
in the newest data. With our model we estimate for both elements (Ba
and Eu) the ranges for the r-process yields from massive stars that
better reproduce the trend of the data. We find that with the same
yields able to explain the observed trends, the large spread in the
[Ba/Fe] and [Eu/Fe] ratios cannot be explained even in the context of
an inhomogeneous models for the chemical evolution of our Galaxy. We
therefore derive the amount by which the yields should be modified
to fully account for the observed spread. We then discuss several
possibilities to explain the size of the spread. We suggest that the
production ratio of [Ba/Eu] could be almost constant in massive stars.
---------------------------------------------------------
Title: Sulphur in the Early Ages of the Galaxy
Authors: Depagne, E.; Hill, V.; Spite, M.; François, P.; Spite,
F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.;
Bonifacio, P.; Nordström, B.; Primas, F.
2006cams.book..128D Altcode:
We present here the results of the measurement of the sulphur abundance
in very metal-poor stars. Our sample covers the [-4;-2] range of
metallicity, and thus allows us to constraint the chemical evolution
models and also to put some key constraints on the supernovae models.
---------------------------------------------------------
Title: Evidence of Mixing in Extremely Metal-Poor Giants
Authors: Spite, M.; Cayrel, R.; Spite, F.; Hill, V.; François, P.;
Depagne, E.; Barbuy, B.; Bonifacio, P.; Molaro, P.; Primas, F.; Beers,
T.; Plez, B.; Nordström, B.; Andersen, J.
2006cams.book..200S Altcode:
Thirty five extremely metal-poor (EMP) giants (22 of them with a
metallicity [Fe/H] ≤ -3.0) have been observed with UVES at the
VLT. In these stars the abundance of lithium carbon and nitrogen and
also the <SUP>12</SUP>C/<SUP>13</SUP>C ratio have been measured. It
is shown that, in about half of them, the carbon abundance and the
lithium abundance are very low, on the contrary the nitrogen abundance
is high. Moreover the value of the <SUP>12</SUP>C/<SUP>13</SUP>C ratio
is close to the equilibrium value of the CN cycle. All these phenomena
imply a mixing between the surface of the star and the H burning
layers. We also study the influence of the mixing on the oxygen,
sodium and aluminum abundance.
---------------------------------------------------------
Title: Constraints on the yields of the first supernovae in the
Universe
Authors: Cayrel, Roger
2006isna.confE.207C Altcode: 2006PoS....28E.207C
The study of the chemical composition of the most primitive stars
of the galactic halo has been made possible with the help of large
surveys aimed at finding such stars, and by powerful new instruments,
as the Keck telescopes, the Subaru telescope, and the ESO Very Large
Telescope. The atmospheres of these primitive stars possess, per
hydrogen atom, from 1/1000th to 1/10000th less supernovae-made elements
than the Sun, and reflect the yields of the first supernovae. It was
once expected that these yields would show a larger scatter than those
in the more metal-rich Population II stars, which have been enriched
by many more supernovae explosions than the earlier generations. If
we leave aside one class of objects, the Carbon-Enhanced Metal-Poor
(CEMP) stars, which is the topic of another talk at this conference, a
rather well-defined set of abundance ratios emerge for C to Zn amongst
the most primitive population, with a scatter that is surprisingly
small. The quality of the high-resolution spectroscopic data is
such that the observed level of scatter in the measured elemental
abundances for these species is no longer limited by accuracy of
the observations, nor by other errors inherent to the analysis of
the data. By way of contrast, amongst the neutron-capture elements
produced by the r-process, at a given metallicity a spread reaching a
factor of over 1000 exists for elements such as Ba. The stable portion
of the r-process pattern observed in such stars is the second peak
(Z = 56 to 72), in which the relative abundances of these elements in
very metal-poor stars are almost indistinguishable from their inferred
proportions in solar-system material. Recent observations have permitted
the determination of the abundances of uranium, tho- rium, and lead
produced by the r-process in extremely metal-poor stars, and indicate
that lead is mainly produced by radioactive decay of the actinides (as
opposed to other direct channels). In addition, the observed U/Th ratio
has been shown to be the best available radioactive cosmic chronometer,
on timescales of interest to cosmology.
---------------------------------------------------------
Title: First Stars: Abundance Patterns from O to Zn and Derived SNe
Yields in the Early Galaxy
Authors: Cayrel, R.; Spite, M.
2006cams.book..114C Altcode:
Most of the work reported here has been conducted within the ESO
Large Programme 165.N-0276 "Galaxy Formation, Early Nucleosynthesis,
and the First Stars", which has covered 4 periods 65-68, from April
2000 to November 2001, with a total of 38 nights in visitor mode. The
team had R. Cayrel as PI, and 13 CoIs:
---------------------------------------------------------
Title: Abundance of Heavy Elements in Extremely Metal-Poor Stars
Authors: François1, P.; Cayrel, R.; Depagne, E.; Spite, M.; Hill,
V.; Spite, F.; Plez, B.; Beers, T.; Primas, F.; Andersen, J.; Barbuy,
B.; Bonifacio, P.; Molaro, P.; Nordström, B.
2006cams.book..122F Altcode:
In the framework of the VLT Large program "First Stars" (165.N-0276(A)),
we have measured the abundance of 13 heavy elements using high quality
UVES spectra. In this paper, we report on the abundance of Sr and Ba
in this sample of stars. In 1995, McWilliam et al. [4] showed that the
[Sr/Fe] and [Ba/Fe] ratios exhibited a large dispersion in metal-poor
stars. If these 2 elements are produced by the same nucleosynthetic
process, then the variation of [Sr/Ba] as a function of metallicity
should be constant . However, it is known (see Arlandini et al. 1999
[1] for example) that a significant part of Sr is built by s-process in
massive stars. As this process is a secondary process, it is unlikely
that this process is fully in operation at the early stages of the
chemical evolution. On figure 1a, the [Sr/Ba] vs [Fe/H] are plotted
together with some data found in the literature.
---------------------------------------------------------
Title: Les premieres etoiles ne sont plus la...
Authors: Cayrel, R.
2006LAstr.120..216C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: “First Stars, First Nucleosynthesis", New results and a
few Perspectives
Authors: Spite, M.; Cayrel, R.; Hill, V.; Plez, B.; François, P.;
Spite, F.; Depagne, E.
2005sf2a.conf...65S Altcode:
We present here briefly some results of the project “First Stars" and
in particular the comparison between extremely metal-poor turn off stars
and giants of the low Red Giant Branch which were supposed to be free
from any substantial mixing with the H burning layer. The observations
suggest more mixing in the low RGB stars than predicted by the models.
---------------------------------------------------------
Title: Very metal poor stars in the Milky Way: constraints on stellar
nucleosynthesis
Authors: Chiappini, C.; Matteucci, F.; François, P.; Cayrel, R.;
Spite, M.; Spite, F.
2005NuPhA.758..217C Altcode:
Recently Cayrel et al. [Cayrel, R., Depagne, E., Spite, M. et al. 2004,
AfeA 416, 1117] have derived the abundances of several a and Fe-peak
elements for a sample of very metal poor giants ([Fe/H] from -4.0
to -3.0 dex) thus allowing us to test chemical evolution models in a
metallicity range never reached before. Moreover, the small spread in
the [el/Fe] ratios in the metallicity range from [Fe/H]=-4.0 up to -3.0
dex [Cayrel, R., Depagne, E., Spite, M. et al. 2004, AfeA 416, 1117]
is a clear sign that the halo of the Milky Way was well mixed even
in the earliest phases of its evolution. We computed the evolution of
the abundances of O, Mg, Si, Ca, K, Ti, Sc, Ni, Mn, Co, Fe and Zn in
the Milky Way. We made use of the most widely adopted nucleosynthesis
calculations and compared the model results with observational data
with the aim of imposing constraints upon stellar yields.
---------------------------------------------------------
Title: Astrophysics: Two's company
Authors: Cayrel, Roger
2005Natur.434..838C Altcode:
The matter from which the first stars formed was that left behind by
the Big Bang. Stars containing extremely small amounts of heavy elements
such as iron provide clues to the chemical composition of this matter.
---------------------------------------------------------
Title: First stars VI - Abundances of C, N, O, Li, and mixing in
extremely metal-poor giants. Galactic evolution of the light elements
Authors: Spite, M.; Cayrel, R.; Plez, B.; Hill, V.; Spite, F.; Depagne,
E.; François, P.; Bonifacio, P.; Barbuy, B.; Beers, T.; Andersen,
J.; Molaro, P.; Nordström, B.; Primas, F.
2005A&A...430..655S Altcode: 2004astro.ph..9536S
We have investigated the poorly-understood origin of nitrogen in the
early Galaxy by determining N abundances from the NH band at 336
nm in 35 extremely metal-poor halo giants, with carbon and oxygen
abundances from Cayrel et al. (\cite{CDS04}, A&A, 416, 1117),
using high-quality ESO VLT/UVES spectra (30 of our 35 stars are in the
range -4.1 < [Fe/H] < -2.7 and 22 stars have [Fe/H] < -3.0). N
abundances derived both from the NH band and from the CN band at 389
nm for 10 stars correlate well, but show a systematic difference
of 0.4 dex, which we attribute to uncertainties in the physical
parameters of the NH band (line positions, gf values, dissociation
energy, etc.). Because any dredge-up of CNO processed material to the
surface may complicate the interpretation of CNO abundances in giants,
we have also measured the surface abundance of lithium in our stars
as a diagnostic of such mixing. Our sample shows a clear dichotomy
between two groups of stars. The first group shows evidence of C to
N conversion through CN cycling and strong Li dilution, a signature
of mixing; these stars are generally more evolved and located on the
upper Red Giant Branch (RGB) or Horizontal Branch (HB). The second
group has [N/Fe] < 0.5, shows no evidence for C to N conversion,
and Li is only moderately diluted; these stars belong to the lower
RGB and we conclude that their C and N abundances are very close to
those of the gas from which they formed in the early Galaxy, they are
called “unmixed stars”. The [O/Fe] and [(C+N)/Fe] ratios are the
same in the two groups, confirming that the differences between them
are caused by dredge-up of CN-processed material in the first group,
with negligible contributions from the O-N cycle. The “unmixed”
stars reflect the abundances in the early Galaxy: the [C/Fe] ratio is
constant (about +0.2 dex) and the [C/Mg] ratio is close to solar at
low metallicity, favouring a high C production by massive zero-metal
supernovae. The [N/Fe] and [N/Mg] ratios scatter widely. Their mean
values in each metallicity bin decrease with increasing metallicity,
but this trend could be a statistical effect. The larger values of these
ratios define a flat upper plateau ([N/Mg] = 0.0, [N/Fe] = +0.1), which
could reflect higher values within a wide range of yields of zero-metal
SNe II. Alternatively, by analogy with the DLAs, the lower abundances
([N/Mg] = -1.1, [N/Fe] = -0.7) could reflect generally low yields from
the first SNe II, the other stars being N enhanced by winds of massive
Asymptotic Giant Branch (AGB) stars. Since all the stars show clear
[α/Fe] enhancements, they were formed before any significant enrichment
of the Galactic gas by SNe Ia, and their composition should reflect
the yields of the first SNe II. However, if massive AGB stars or AGB
supernovae evolved more rapidly than SNe Ia and contaminated the ISM,
our stars would also reflect the yields of these AGB stars. At present
it cannot be decided whether primary N is produced primarily in SNe
II or in massive AGB stars, or in both. The stellar N abundances and
[N/O] ratios are compatible with those found in Damped Lyman-α (DLA)
systems. They extend the well-known DLA “plateau” at [N/O] ≈ -0.8 to
lower metallicities, albeit with more scatter; no star is found below
the putative “low [N/α] plateau” at [N/O] ≈ -1.55 in DLAs. <P
/>Based on observations obtained with the ESO VLT under ESO programme
ID 165.N-0276(A). This work has made use of the SIMBAD database.
---------------------------------------------------------
Title: CS 29497-030: lead in the early Galaxy
Authors: Sivarani, T.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Spite,
M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.;
Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F.
2005HiA....13R.589S Altcode:
We present the abundance analysis of the star CS29497-030 which
displays a low metallicity ([Fe/H]=-2.8) and a large enhancement of the
neutron capture elements. The Pb overabundance with respect to iron
([Pb/Fe]=3.5) is the highest to-date among the s-process enhanced
very metal poor stars. The abundance analysis provides also a large
overabundance of carbon ([C/Fe]=+2.38) nitrogen ([N/Fe]=+1.88) and
oxygen ([O/Fe]=+1.67). These abundances result from the analysis of high
resolution and high S/N spectra obtained using the UVES spectrograph
on the 8.2m VLT-Kueyen telescope in the course of the Large Programme
165.N-0276 P.I. R. Cayrel. The origin of neutron capture elements
at low metallicity has for twenty years been thought to be from the
r-process only. The occurence of several stars of very low metallicity
which exhibit a large overabundance of s-process elements and lead
overabundance with respect to the heavy neutron capture elements(e.g
Ba La Ce Nd) seems to point unmistakably to an s-process origin. This
suggests that the s-process was operating at early times in the Galaxy
at least locally.
---------------------------------------------------------
Title: Lithium abundances in extremely metal-poor stars
Authors: Bonifacio, P.; Molaro, P.; Sivarani, T.; Spite, M.; Spite,
F.; Cayrel, R.; François, P.; Hill, V.; Plez, B.; Beers, T. C.;
Andersen, J.; Barbuy, B.; Depagne, E.; Nordström, B.; Primas, F.
2005HiA....13..581B Altcode:
In the course of the ESO Large Programme ""First Stars"" we have
observed with the UVES spectrograph at the 8.2m Kueyen-VLT telescope
more than thirty stars which were classified as Turn-Off based on
medium resolution spectra. Effective temperatures for these stars were
derived by fitting the ings of the H-alpha lines. The constant lithium
abundance found in metal-poor stars is generally understood to have
been produced primordially. If this is the case it provides a measure
of the baryonic density which may be compared to the valued recently
measured from the fluctuations of the cosmic microwave background
by the WMAP experiment. Howevere this may not be the case if the Li
observed on the surface of these stars has been increased by Galactic
production or decreased by atmospheric phenomena such effects could
be highlighted by the existence of variations with metallicity and/or
effective temperature of the Li abundance. In this poster we report on
the measurement of lithium abundances in this unique homogeneous sample
of extremely metal poor stars which provides important information on
the Li content of the early Galaxy.
---------------------------------------------------------
Title: Lithium abundances in extremely metal-poor unevolved stars
Authors: Bonifacio, P.; Molaro, P.; Sivarani, T.; Cayrel, R.; Spite,
M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.;
Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F.
2005IAUS..228...35B Altcode:
We have studied the lithium abundance in 18 extremely metal-poor
main-sequence turnoff stars as a function of [Fe/H] and T<SUB>eff</SUB>,
using high-quality VLT/UVES spectra. The sample covers the range
-3.3≤ [{Fe}/{H}]≤ -2.5, with half of the stars below [Fe/H] =
-3.0. T<SUB>eff</SUB> is determined from Hα line profiles as well as
from B-V, V-K, J-H and J-K colours. The behaviour of A(Li) as a function
of metallicity is markedly different when different temperature scales
are adopted. However, even when applying standard depletion corrections,
it is a robust result that the Li abundance in extremely metal poor
dwarfs is far below the prediction of standard big bang nucleosynthesis
using a baryonic density consistent with the WMAP data.
---------------------------------------------------------
Title: A Tribute to Monique and François Spite
Authors: Cayrel, R.
2005IAUS..228....3C Altcode:
This contribution retraces the scientific careers of Monique and
François. It highlights the impressive contributions that they have
brought to astrophysics, from the discovery of the lithium plateau
in subdwarfs the second year of operation of the Canada-France-Hawaii
telescope, to the exceptional contribution of Monique to the ESO VLT
Large Programme "First Stars", passing by several other findings which
have marked our knowledge of the nuclear evolution of our Galaxy and
of the Magellanic Clouds.
---------------------------------------------------------
Title: Heavy elements in a sample of extremely metal-poor giants
Authors: François, P.; Depagne, E.; Cayrel, R.; Hill, V.; Spite, F.;
Spite, M.; Plez, B.; Barbuy, B.; Beers, T.; Bonifacio, P.; Andersen,
J.; Primas, F.; Sivarani, T.; Nordström, B.; Molaro, P.
2005HiA....13R.583F Altcode:
The abundances of the neutron capture elements (Sr Ba La Ce Eu
[Truncated.]
---------------------------------------------------------
Title: Abundances in extremely metal-poor stars. Comparison of the
trends of abundance ratios in giants and turnoff stars
Authors: Spite, Monique; Bonifacio, Piercarlo; Cayrel, Roger; Hill,
Vanessa; François, Patrick; Spite, François; Plez, Bertrand;
Depagne, Eric; Barbuy, Beatriz; Molaro, Paolo; Beers, Timothy;
Andersen, Johannes; Nordström, Birgitta; Primas, Francesca
2005IAUS..228..185S Altcode:
As part of a study of the detailed abundance patterns in extremely
metal-poor stars, we have compared our samples of giants and dwarfs with
two samples of dwarfs measured by different teams. For most elements the
abundances are in good agreement, but for C, Na, and Al we show that
the atmospheric abundances are different in dwarfs and in giants. For
C the difference could be explained by "atmospheric effects" or by
the influence of the first dredge-up, but for Na and Al deep mixing
inside the stars must be invoked. Until now, such deep mixing has not
been observed in metal-poor field stars. An excess scatter in [Mg/Fe]
in giants remains unexplained.
---------------------------------------------------------
Title: Oxygen abundance and convection
Authors: van't Veer, C.; Cayrel, R.
2005HiA....13..152V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evolution of the abundances of the light elements C, Mg,
Al in the amosphere of extremely metal-poor stars ( [Fe/H] ⪉ -3)
Authors: Spite, M.; Cayrel, R.; Spite, F.; Hill, V.; Francois, P.;
Plez, B.; Depagne, E.
2005EAS....17..353S Altcode:
We present briefly some results of the ESO Large Program “First Stars"
where it is shown that the abundance ratios of some light elements in
the atmospheres of the extremely metal poor stars varies when the star
evolves. This could be explained by a mixing with deep layers but such
a mixing is not predicted by the theory.
---------------------------------------------------------
Title: Abundance of nitrogen in the early Galaxy from the NH band
at 336nm
Authors: Spite, M.; Plez, B.; Hill, V.; Spite, F.; Cayrel, R.;
François, P.; Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T.;
Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F.
2005HiA....13..590S Altcode:
In the frame of the ESO Large Program ""First Stars"" spectra of about
40 extremely metal-poor giants ([Fe/H]<-2.7) have been obtained with
UVES at the VLT in the range 330-900 nm. The behaviour of nitrogen
at low metallicity is up to now badly known. We present here a first
estimation of the nitrogen abundance in these extremely metal-poor
stars from a synthesis of the spectrum in the region of the NH band
between 336 and 337nm. The trend of [N/Fe] but also of [C+N/Fe] versus
metallicity are presented and discussed.
---------------------------------------------------------
Title: Constraints on early galactic enrichment from a large sample
of extremely metal-poor stars observed with VLT+UVES
Authors: Hill, V.; Cayrel, R.; Spite, M.; Plez, B.; Spite, F.;
François, P.; Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T.;
Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F.
2005HiA....13Q.584H Altcode:
Constraints on Early Galactic Enrichement from a large sample of
Extremely Metal Poor Stars <P />I will present the overall results from
an large effort conducted at ESO-VLT+UVES to measure abundances in a
sample of extremely metal-poor stars (EMPS) from high-resolution and
high signal to noise spectra. More than 70 EMPS with [Fe/H]<-2.7
were observed equally distributed between turnoff and giants stars
and very precise abundance ratios could be derived thanks to the high
quality of the data. Among the results those of specific interest are
lithium measurements in unevolved EMPS the much debated abundance of
oxygen in the early galaxy (we present [OI] line measurements down to
[O/Fe]=-3.5) and the trends of alpha elements iron group elements and
Zinc. The scatter around these trends will also be discussed taking
advantage of the small observationnal error-bars of this dataset. The
implications on the early Galactic enrichement will be rewiewed while
more specific topics covered by this large effort (and large team)
will be adressed in devoted posters.
---------------------------------------------------------
Title: General discussion III: Chemistry and self-pollution mechanisms
Authors: Cayrel, R.
2005HiA....13..157C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New analysis of the two carbon-rich stars CS 22948-27 and CS
29497-34: Binarity and neutron capture elements
Authors: Barbuy, B.; Spite, M.; Spite, F.; Hill, V.; Cayrel, R.;
Plez, B.; Petitjean, P.
2005A&A...429.1031B Altcode: 2004astro.ph..9213B
We have carried out a new determination of abundances in the very
metal-poor CH/CN strong stars CS 22948-27 and CS 29497-34, using
high-resolution spectra obtained with the HARPS spectrograph at
the 3.6 m telescope of ESO, La Silla, that covers the range λλ
4000-6900 Å at a resolution of R = 100 000. Both stars are found to
be long period binaries. It is confirmed that the abundance patterns
show an enhancement of the α-elements (like Mg, Ca), of the proton
capture elements (like Na and Al) and a strong enrichment in “r”
and “s” process elements, where the s-enrichment is probably due
to a mass transfer episode from a companion in its AGB phase. The
possible origins of the abundance pattern and especially of the
strong enhancement of both “s” and “r” elements are discussed. <P
/>Observations collected at the European Southern Observatory (ESO),
ESO Programme 72.A-0244 (PI Petitjean), and including data obtained
from the ESO/ST-ECF Science Archive Facility.
---------------------------------------------------------
Title: Lead abundance in the uranium star CS 31082-001
Authors: Plez, B.; Hill, V.; Cayrel, R.; Spite, M.; Barbuy, B.; Beers,
T. C.; Bonifacio, P.; Primas, F.; Nordström, B.
2004A&A...428L...9P Altcode: 2004astro.ph.10628P
In a previous paper we were able to measure the abundance of
uranium and thorium in the very-metal poor halo giant BPS <ASTROBJ>CS
31082-001</ASTROBJ>, but only obtained an upper limit for the abundance
of lead (Pb). We have got from ESO 17 h of additional exposure on
this star in order to secure a detection of the minimum amount of
lead expected to be present in <ASTROBJ>CS 31082-001</ASTROBJ>,
the amount arising from the decay of the original content of Th and
U in the star. We report here this successful detection. We find
an LTE abundance log(Pb/H)+12=-0.55 ± 0.15 dex, one dex below the
upper limits given by other authors for the similar stars <ASTROBJ>CS
22892-052</ASTROBJ> and <ASTROBJ>BD +17°3248</ASTROBJ>, also enhanced
in r-process elements. From the observed present abundances of Th
and U in the star, the expected amount of Pb produced by the decay of
<SUP>232</SUP>Th, and <SUP>238</SUP>U alone, over 12-15 Gyr is -0.73±
0.17 dex. The decay of <SUP>235</SUP>U is more difficult to estimate,
but is probably slightly below the contribution of <SUP>238</SUP>U,
making the contribution of the 3 actinides only slightly below, or even
equal to, the measured abundance. The contribution from the decay of
<SUP>234</SUP>U has was not included, for lack of published data. In
this sense our determination is a lower limit to the contribution of
actinides to lead production. We comment this result, and we note that
if a NLTE analysis, not yet possible, doubles our observed abundance,
the decay of the 3 actinides will still represent 50 per cent of the
total lead, a proportion higher than the values considered so far
in the literature. <P />Based on observations obtained with the Very
Large Telescope of the European Southern Observatory at Paranal, Chile.
---------------------------------------------------------
Title: The First Stars: What We Know and Do Not Know
Authors: Cayrel, R.; Spite, M.
2004Msngr.118...55C Altcode:
The H and K survey of Beers, Preston & Shectman has been the
mine of extremely metal-poor stars during the last decade of the
XXth century. The VLT-UVES combination has allowed us to study the
chemical composition of the brightest members of this population, fossil
component of events which have occured either during the formation of
the galaxy, or earlier in smaller systems having eventually merged
into our beautiful milky way. We report here what has been derived
from a VLT large programme devoted to these objects, as well as on
other questions relevant to the first stars.
---------------------------------------------------------
Title: The evolution of the Milky Way from its earliest phases:
Constraints on stellar nucleosynthesis
Authors: François, P.; Matteucci, F.; Cayrel, R.; Spite, M.; Spite,
F.; Chiappini, C.
2004A&A...421..613F Altcode: 2004astro.ph..1499F
We computed the evolution of the abundances of O, Mg, Si, Ca, K, Ti, Sc,
Ni, Mn, Co, Fe and Zn in the Milky Way. We made use of the most widely
adopted nucleosynthesis calculations and compared the model results with
observational data with the aim of imposing constraints upon stellar
yields. To best fit the data in the solar neighborhood, when adopting
the Woosley & Weaver (1995, ApJS, 101, 181) yields for massive stars
and the Iwamoto et al. (\cite{Iwamoto99}, ApJS, 125, 439) ones for type
Ia SNe, it is required that: i) the Mg yields should be increased in
stars with masses from 11 to 20 M<SUB>⊙</SUB> and decreased in masses
larger than 20 M<SUB>⊙</SUB>. The Mg yield should be also increased in
SNe Ia. ii) The Si yields should be slightly increased in stars above
40 M<SUB>⊙</SUB>, whereas those of Ti should be increased between
11 and 20 M<SUB>⊙</SUB> and above 30 M<SUB>⊙</SUB>. iii) The Cr
and Mn yields should be increased in stars with masses in the range
11-20 M<SUB>⊙</SUB>; iv) the Co yields in SNe Ia should be larger and
smaller in stars in the range 11-20 M<SUB>⊙</SUB>; v) the Ni yield
from type Ia SNe should be decreased; vi) the Zn yield from type Ia
SNe should be increased. vii) The yields of O (metallicity dependent
SN models), Ca, Fe, Ni, and Zn (the solar abundance case) in massive
stars from Woosley & Weaver (\cite{Woosley95}) are the best to fit
the abundance patterns of these elements since they do not need any
changes. We also adopted the yields by Nomoto et al. (\cite{Nomoto97},
Nucl. Phys. A, 621, 467) and Limongi & Chieffi (\cite{Limongi03},
ApJ, 592, 404) for massive stars and discuss the corrections required
in these yields in order to fit the observations. Finally, the small
spread in the [el/Fe] ratios in the metallicity range from [Fe/H]
= -4.0 up to -3.0 dex (Cayrel et al. \cite{Cayrel03}, A&A, 416,
1117) is a clear sign that the halo of the Milky Way was well mixed
even in the earliest phases of its evolution.
---------------------------------------------------------
Title: First stars V - Abundance patterns from C to Zn and supernova
yields in the early Galaxy
Authors: Cayrel, R.; Depagne, E.; Spite, M.; Hill, V.; Spite, F.;
François, P.; Plez, B.; Beers, T.; Primas, F.; Andersen, J.; Barbuy,
B.; Bonifacio, P.; Molaro, P.; Nordström, B.
2004A&A...416.1117C Altcode: 2003astro.ph.11082C
In the framework of the ESO Large Programme “First Stars”, very
high-quality spectra of some 70 very metal-poor dwarfs and giants
were obtained with the ESO VLT and UVES spectrograph. These stars are
likely to have descended from the first generation(s) of stars formed
after the Big Bang, and their detailed composition provides constraints
on issues such as the nature of the first supernovae, the efficiency
of mixing processes in the early Galaxy, the formation and evolution
of the halo of the Galaxy, and the possible sources of reionization
of the Universe. This paper presents the abundance analysis of an
homogeneous sample of 35 giants selected from the HK survey of Beers
et al. (\cite{BPS92}, \cite{Be99}), emphasizing stars of extremely low
metallicity: 30 of our 35 stars are in the range -4.1 <[Fe/H]<
-2.7, and 22 stars have [Fe/H] < -3.0. Our new VLT/UVES spectra, at a
resolving power of R∼45 000 and with signal-to-noise ratios of 100-200
per pixel over the wavelength range 330-1000 nm, are greatly superior
to those of the classic studies of McWilliam et al. (\cite{MPS95})
and Ryan et al. (\cite{RNB96}). <P />The immediate objective of the
work is to determine precise, comprehensive, and homogeneous element
abundances for this large sample of the most metal-poor giants presently
known. In the analysis we combine the spectral line modeling code
“Turbospectrum” with OSMARCS model atmospheres, which treat continuum
scattering correctly and thus allow proper interpretation of the blue
regions of the spectra, where scattering becomes important relative to
continuous absorption (λ < 400 nm). We obtain detailed information
on the trends of elemental abundance ratios and the star-to-star scatter
around those trends, enabling us to separate the relative contributions
of cosmic scatter and observational/analysis errors. <P />Abundances
of 17 elements from C to Zn have been measured in all stars, including
K and Zn, which have not previously been detected in stars with [Fe/H]
< -3.0. Among the key results, we discuss the oxygen abundance (from
the forbidden [OI] line), the different and sometimes complex trends
of the abundance ratios with metallicity, the very tight relationship
between the abundances of certain elements (e.g., Fe and Cr), and the
high [Zn/Fe] ratio in the most metal-poor stars. Within the error bars,
the trends of the abundance ratios with metallicity are consistent with
those found in earlier literature, but in many cases the scatter around
the average trends is much smaller than found in earlier studies, which
were limited to lower-quality spectra. We find that the cosmic scatter
in several element ratios may be as low as 0.05 dex. <P />The evolution
of the abundance trends and scatter with declining metallicity provides
strong constraints on the yields of the first supernovae and their
mixing into the early ISM. The abundance ratios found in our sample do
not match the predicted yields from pair-instability hypernovae, but
are consistent with element production by supernovae with progenitor
masses up to 100 M<SUB>⊙</SUB>. Moreover, the composition of the
ejecta that have enriched the matter <P />Based on observations
obtained in the frame of the ESO programme ID 165.N-0276(A). <P
/>Full Tables 3 and 8 are available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/1117 This work has
made use of the SIMBAD database.
---------------------------------------------------------
Title: Oxygen abundance and convection
Authors: Van't Veer, C.; Cayrel, R.
2004MmSAI..75..310V Altcode:
The triplet IR lines of O I near 777 nm are computed with the Kurucz's
code, modified to accept several convection models. The program has
been run with the MLT algorithm, with l/H = 1.25 and 0.5, and with
the Canuto-Mazzitelli and Canuto-Goldman-Mazzitelli approaches, on
a metal-poor turnoff-star model atmosphere with Teff=6200 K, log g =
4.3, [Fe/H]= -1.5. The results show that the differences in equivalent
widths for the 4 cases do not exceed 2 per cent (0.3 mA). The convection
treatment is therefore not an issue for the oxygen abundance derived
from the permitted lines.
---------------------------------------------------------
Title: General Discussion III: Chemistry and Self-Pollution
Mechanisms
Authors: Cayrel, R.
2004MmSAI..75..385C Altcode:
Round table 3 was devoted to the origin of chemical anomalies found in a
significant fraction of stars in GCs, but not in field metal-poor stars
of similar metallicity. Formerly a hot topic was if such anomalies,
studied only in giant stars, bright enough to allow reliable abundance
determinations, were generated in the course of the evolution of the
star, or inherited at the birth of the star. The ESO Large Program led
by R. Gratton has demonstrated, without ambiguity, that the most famous
of these “anomalies”, the O-Na anticorrelation, was already present
in turn-off (TO) stars, therefore already there at the birth of the
star. <P />This does not preclude that some modifications occur along
the red giant branch, as described for example already in Charbonnel
(1994), but those are well identified and do not include the O-Na
anticorrelation, but affect mostly <SUP>12</SUP>C,<SUP>13</SUP>C,
<SUP>14</SUP>N and Li.* More recently, models including rotation in
the evolution ( see for example talks by Charbonnel and Weiss at JD 4)
have been produced. The most promising process for explaining the O-Na
anticorrelation is the hot-bottom-burning process (HBB) in TP-AGBs,
Ventura et al. (2001). The problem remaining is the transfer of the
processed matter to an unevolved star. Here, several routes exist, and
so far no consensus has been reached on those which are dominant. <P
/>Roundtable 3 was expected to supply a live discussion between the
proponents of the various ideas emitted on this subject. Unfortunately,
in the time allotted, the only thing which appeared possible was to
suggest tests for evaluating the coherence of the various proposals,
against the widest set of observational constraints. For example,
the HBB produces an enrichment in helium, potentially affecting
the isochrones. Very accurate observations could try to detect this
side-effect. Transfer of mass from an AGB to an unevolved companion
is an efficient way of pollution. But it is then expected that the
remaining binary shows a variable radial velocity (unless the pair has
been disrupted afterwards...). At the other extreme, the mass loss of
AGBs may have been large enough to have produced a second generation
in a GC ( see F. D'Antona contribution). But let us leave their role
to our participants...
---------------------------------------------------------
Title: The Age of the First Nucleosynthesis in the Galaxy
Authors: Cayrel, R.; Hill, V.; Spite, M.; Spite, F.; François, P.;
Depagne, E.; Nordström, B.; Andersen, J.; Plez, B.; Barbuy, B.;
Beers, T.; Bonifacio, P.; Molaro, P.; Primas, F.
2004oee..sympE...9C Altcode:
The observation of extremely metal-poor stars makes possible to obtain
the epoch of formation of the first elements produced by massive
supernovae, or hypernovae. The classical way of obtaining stellar ages
(isochrone fitting) is unfortunately not applicable at present, as the
distances of these stars are not known with enough accuracy. Dating by
decay of radio-elements is another path, which has been renewed by the
observation of uranium in the yellow giant CS 31082-001. We discuss
the prospects opened by this discovery, and recent theoretical works
triggered by this new opportunity.
---------------------------------------------------------
Title: Trends of Abundance in Extremely Metal-poor Giants Observed
at the VLT
Authors: Spite, M.; Depagne, E.; Cayrel, R.; Hill, V.; François,
P.; Spite, F.; Nordström, B.; Andersen, J.; Plez, B.; Barbuy, B.;
Beers, T.; Bonifacio, P.; Molaro, P.; Primas, F.
2004oee..sympE..54S Altcode:
We present here the first abundance trends from C to Zn deduced from
the observation of 33 extremely metal-poor stars selected in the HK
survey of Beers et al. (1992). The trends of the abundance ratios of the
different elements like [Mg/Fe], [Cr/Fe] are not very different from
the trends deduced from the observations of McWilliam et al.(1995),
but for several important elements (like Mg, Cr) the spread is much
smaller. For almost all the elements the spread increases when the
metallicity decreases, this is particularly evident for the trend of
[Mn/Fe] versus [Fe/H]. <P />The elements heavier than Zn will be
discussed later.
---------------------------------------------------------
Title: First stars IV. CS 29497-030: Evidence for operation of the
s-process at very low metallicity
Authors: Sivarani, T.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Spite,
M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.;
Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F.
2004A&A...413.1073S Altcode: 2003astro.ph.10291S
We present an abundance analysis of the very metal-poor, carbon-enhanced
star CS 29497-030. Our results indicate that this unusually hot turnoff
star (T<SUB>eff</SUB> = 6650 K, log g = 3.5) has a metallicity [Fe/H]
= -2.8, and exhibits large overabundances of carbon ([C/Fe] = +2.38),
nitrogen ([N/Fe] = +1.88), and oxygen ([O/Fe] = +1.67). This star
also exhibits a large enhancement in its neutron-capture elements;
the pattern follows that expected to arise from the s-process. In
particular, the Pb abundance is found to be very high with respect
to iron ([Pb/Fe] = +3.5), and also with respect to the second peak
s-process elements (e.g., Ba, La, Ce, Nd), which fits into the newly
introduced classification of lead (Pb) stars. The known spectroscopic
binary status of this star, along with the observed s-process abundance
pattern, suggest that it has accreted matter from a companion, which
formerly was an Asymptotic Giant-Branch (AGB) star. In a preliminary
analysis, we have also identified broad absorption lines of metallic
species that suggest a large axial rotational velocity for this star,
which may be the result of spin-up associated with the accretion
of material from its previous AGB companion. In addition, this star
is clearly depleted in the light element Li. When considered along
with its rather high inferred temperature, these observations are
consistent with the expected properties of a very low metallicity
halo blue straggler. <P />Based on observations made with the
ESO Very Large Telescope at Paranal Observatory, Chile (program ID
165.N-0276(A)). <P />Table \ref{tab6} is only available in electronic
form at http://www.edpsciences.org
---------------------------------------------------------
Title: VizieR Online Data Catalog: Abundances in the early Galaxy
(Cayrel+, 2004)
Authors: Cayrel, R.; Depagne, E.; Spite, M.; Hill, V.; Spite, F.;
Francois, P.; Plez, B.; Beers, T.; Primas, F.; Andersen, J.; Barbuy,
B.; Bonifacio, P.; Molaro, P.; Nordstrom, B.
2003yCat..34161117C Altcode:
The observations were performed during several runs from April 2000
to November 2001 with the VLT-UT2 and the high-resolution spectrograph
UVES. <P />(3 data files).
---------------------------------------------------------
Title: First Stars. III. A detailed elemental abundance study of
four extremely metal-poor giant stars
Authors: François, P.; Depagne, E.; Hill, V.; Spite, M.; Spite,
F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.;
Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F.
2003A&A...403.1105F Altcode:
This paper reports detailed abundance analyses for four extremely
metal-poor (XMP) giant stars with [Fe/H]<-3.8, based on
high-resolution, high-S/N spectra from the ESO VLT (Kueyen/UVES) and
LTE model atmosphere calculations. The derived [alpha /Fe] ratios in
our sample exhibit a small dispersion, confirming previous findings in
the literature, i.e. a constant overabundance of the alpha -elements
with a very small (if any) dependence on [Fe/H]. In particular, the
very small scatter we determine for [Si/Fe] suggests that this element
shows a constant overabundance at very low metallicity, a conclusion
which could not have been derived from the widely scattered [Si/Fe]
values reported in the literature for less metal-poor stars. For the
iron-peak elements, our precise abundances for the four XMP stars in our
sample confirm the decreasing trend of Cr and Mn with decreasing [Fe/H],
as well as the increasing trend for Co and the absence of any trend for
Sc and Ni. In contrast to the significant spread of the ratios [Sr/Fe]
and [Ba/Fe], we find [Sr/Ba] in our sample to be roughly solar, with
a much lower dispersion than previously found for stars in the range
-3.5 < [Fe/H] < -2.5. <P />Based on observations made with the ESO
Very Large Telescope at Paranal Observatory, Chile (Large Programme ID
165.N-0276(A)). <P />The complete version of Table 5 is only available
in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.125.5) or via http:/ /cdsweb.u-strasbg.fr/cgi-bin/qcat?J
/A+A/403/1105
---------------------------------------------------------
Title: A grid of synthetic spectra and indices Fe5270, Fe5335, Mgb
and Mg<SUB>2</SUB> as a function of stellar parameters and [alpha/Fe]
Authors: Barbuy, B.; Perrin, M. -N.; Katz, D.; Coelho, P.; Cayrel,
R.; Spite, M.; Van't Veer-Menneret, C.
2003A&A...404..661B Altcode:
We have computed a grid of synthetic spectra in the wavelength range
lambda lambda 4600-5600 Å using revised model atmospheres, for a
range of atmospheric parameters and values of [alpha -elements/Fe] =
0.0 and +0.4. The Lick indices Fe5270, Fe5335, Mgb and Mg<SUB>2</SUB>
are measured on the grid spectra for FWHM = 2 to 8.3 Å. Relations
between the indices Fe5270, Fe5335 and Mg<SUB>2</SUB> and the stellar
parameters effective temperature T<SUB>eff</SUB>, log ; g, [Fe/H] and
[alpha /Fe], valid in the range 4000 <= T<SUB>eff</SUB> <= 7000 K,
are presented. These fitting functions are given for FWHM = 3.5 and 8.3
Å. The indices were also measured for a list of 97 reference stars with
well-known stellar parameters observed at ESO and OHP, and these are
compared to the computed indices. Finally, a comparison of the indices
measured on the observed spectra and those derived from the fitting
functions based on synthetic spectra is presented. <P />Observations
collected at the European Southern Observatory (ESO), La Silla, Chile
and at the Observatoire de Haute Provence (OHP), St-Michel, France. <P
/>All Tables of Appendices A and B are only available in electronic
form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/404/661
---------------------------------------------------------
Title: Oxygen Abundance in the Template Halo Giant HD 122563
Authors: Barbuy, Beatriz; Meléndez, Jorge; Spite, Monique; Spite,
François; Depagne, Eric; Hill, Vanessa; Cayrel, Roger; Bonifacio,
Piercarlo; Damineli, Augusto; Torres, Carlos A. O.
2003ApJ...588.1072B Altcode:
HD 122563 is a well-known bright (V=6.2) halo giant of low metallicity
([Fe/H]~-2.7). We have observed HD 122563 for infrared OH lines at
1.5-1.7 μm in the H band with the NIRSPEC high-resolution spectrograph
at the 10 m Keck Telescope. Optical spectra were obtained with the
UVES spectrograph at the 8 m VLT UT2 telescope at ESO (Paranal)
and the FEROS spectrograph at ESO (La Silla). Based on the optical
high-resolution data, a detailed analysis has been carried out, and
data on the forbidden [O I] 6300 Å line, unblended by telluric or sky
lines, was obtained with the FEROS spectrograph. Signal-to-noise ratios
of 200-400 were obtained at resolutions of 37,000 in the H band and
45,000 in the optical. For the analysis we have adopted a photometric
effective temperature T<SUB>eff</SUB>=4600 K. Two values for the gravity
were adopted: a value deduced from ionization equilibrium, logg=1.1,
with corresponding metallicity [Fe/H]=-2.8 and microturbulence velocity
v<SUB>t</SUB>=2.0 km s<SUP>-1</SUP>; and logg=1.5, derived from the
Hipparcos parallax, implying [Fe/H]=-2.71 and v<SUB>t</SUB>=2.0 km
s<SUP>-1</SUP>. The forbidden [O I] 6300 Å and the permitted O I 7771
Å lines give O/Fe ratios essentially insensitive to model parameter
variations, whereas the oxygen abundances from OH lines are sensitive
to gravity, giving [O/Fe]=+0.9 and +0.7, respectively, for logg=1.1
and 1.5. We derive the following oxygen abundances: for model 1,
[O/Fe]=+0.6, +1.1, and +0.9; and for model 2, [O/Fe]=+0.6, +1.1, and
+0.7, based on the [O I] 6300 Å, O I 7771 Å, and IR OH 1.6 μm lines,
respectively. The different oxygen abundance indicators give different
oxygen abundances, illustrating the problem of oxygen abundance
derivation in metal-poor giants. This is important because the age of
globular clusters and the production of Li, Be, and B from spallation
of C, N, and O atoms in the early Galaxy depend on the oxygen abundance
adopted for the metal-poor stars. <P />Observations carried out with the
Keck Telescope, Mauna Kea, Hawaii, within the Gemini-Keck agreement,
the Very Large Telescope at the European Southern Observatory (ESO),
Paranal, Chile, and the 1.5 m ESO telescope at ESO, La Silla, Chile.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Extremely metal-poor giants
equivalent widths (Francois+, 2003)
Authors: Francois, P.; Depagne, E.; Hill, V.; Spite, M.; Spite,
F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.;
Bonifacio, P.; Molaro, P.; Nordstroem, F.; Primas, B.
2003yCat..34031105F Altcode:
The observations were carried out during several observing runs in 2000
and 2001 using the VLT-Kueyen telescope and UVES spectrograph. The log
of the observations and spectrograph settings can be found in Table
1. <P />(1 data file).
---------------------------------------------------------
Title: VizieR Online Data Catalog: Fe5270, Fe5335, Mgb and
Mg<SUB>2</SUB> synthetic indices (Barbuy+,
Authors: Barbuy, B.; Perrin, M. -N.; Katz, D.; Coelho, P.; Cayrel,
R.; Spite, M.; van't Veer Menneret, C.
2003yCat..34040661B Altcode:
We have computed a grid of synthetic spectra in the wavelength
range λλ4600-5600Å using revised model atmospheres, for a range
of atmospheric parameters and values of [alpha-elements/Fe]=0.0
and +0.4. The Lick indices Fe5270, Fe5335, Mgb and Mg<SUB>2</SUB>
are measured on the grid spectra, for FWHM=2 to 8.3Å. Relations
between the indices Fe5270, Fe5335 and Mg<SUB>2</SUB> and stellar
parameters effective temperature T<SUB>eff</SUB>, logg, [Fe/H] and
[alpha/Fe], valid in the range 4000K>=T<SUB>eff</SUB>>=7000K,
are presented. These fitting functions are given for FWHM=3.5 and
8.3Å. The indices were also measured for a list of 97 reference stars
with well-known stellar parameters observed at ESO and OHP, and these
are compared to the computed indices. Finally, a comparison of the
indices measured on the observed spectra and those derived from the
fitting functions based on synthetic spectra is presented. <P />(11
data files).
---------------------------------------------------------
Title: Abundance Ratios in a Large Sample of Emps with VLT+UVES
Authors: Hill, Vanessa; Cayrel, Roger; Spite, Monique; Bonifacio,
Piercarlo; Eric, Depagne; Patrick, François; Timothy, Beers C.;
Johannes, Andersen; Beatriz, Barbuy; Birgitta, Nordström
2003IAUJD..15E..13H Altcode:
Constraints on Early Galactic Enrichement from a large sample of
Extremely Metal Poor Stars <P />I will present the overall results from
an large effort conducted at ESO-VLT+UVES to measure abundances in a
sample of extremely metal-poor stars (EMPS) from high-resolution and
high signal to noise spectra. More than 70 EMPS with [Fe/H]<-2.7
were observed equally distributed between turnoff and giants stars
and very precise abundance ratios could be derived thanks to the high
quality of the data. Among the results those of specific interest are
lithium measurements in unevolved EMPS the much debated abundance of
oxygen in the early galaxy (we present [OI] line measurements down to
[O/Fe]=-3.5) and the trends of alpha elements iron group elements and
Zinc. The scatter around these trends will also be discussed taking
advantage of the small observationnal error-bars of this dataset. The
implications on the early Galactic enrichement will be rewiewed while
more specific topics covered by this large effort (and large team)
will be adressed in devoted posters.
---------------------------------------------------------
Title: CS29497-030: Lead in the Early Galaxy
Authors: Sivarani, Thirupathi; Bonifacio, Piercarlo; Molaro, Paolo;
Cayrel, Roger; Spite, Monique; Spite, Francois; Plez, Bertrand;
Andersen, Johannes; Barbuy, Beatriz; Beers, Timothy C.
2003IAUJD..15E..41S Altcode:
We present the abundance analysis of the star CS29497-030 which
displays a low metallicity ([Fe/H]=-2.8) and a large enhancement of the
neutron capture elements. The Pb overabundance with respect to iron
([Pb/Fe]=3.5) is the highest to-date among the s-process enhanced
very metal poor stars. The abundance analysis provides also a large
overabundance of carbon ([C/Fe]=+2.38) nitrogen ([N/Fe]=+1.88) and
oxygen ([O/Fe]=+1.67). These abundances result from the analysis of high
resolution and high S/N spectra obtained using the UVES spectrograph
on the 8.2m VLT-Kueyen telescope in the course of the Large Programme
165.N-0276 P.I. R. Cayrel. The origin of neutron capture elements
at low metallicity has for twenty years been thought to be from the
r-process only. The occurence of several stars of very low metallicity
which exhibit a large overabundance of s-process elements and lead
overabundance with respect to the heavy neutron capture elements(e.g
Ba La Ce Nd) seems to point unmistakably to an s-process origin. This
suggests that the s-process was operating at early times in the Galaxy
at least locally.
---------------------------------------------------------
Title: Nitrogen Abundance in Extremely Metal-Poor Giants
Authors: Spite, Monique; Cayrel, Roger; Plez, Bertrand; Hill, Vanessa;
Barbuy, Beatriz; Depagne, Eric; Francois, Patrick; Primas, Francesca;
Spite, Francois; Bonifacio, Piercarlo
2003IAUJD..15E..42S Altcode:
In the frame of the ESO Large Program ""First Stars"" spectra of about
40 extremely metal-poor giants ([Fe/H]<-2.7) have been obtained with
UVES at the VLT in the range 330-900 nm. The behaviour of nitrogen
at low metallicity is up to now badly known. We present here a first
estimation of the nitrogen abundance in these extremely metal-poor
stars from a synthesis of the spectrum in the region of the NH band
between 336 and 337nm. The trend of [N/Fe] but also of [C+N/Fe] versus
metallicity are presented and discussed.
---------------------------------------------------------
Title: Lithium Abundances in Extremely Metal Poor Stars
Authors: Bonifacio, Piercarlo; Molaro, Paolo; Sivarani, Thirupathi;
Spite, Monique; Spite, Francois; Cayrel, Roger; Francois, Francois;
Hill, Vanessa; Plez, Bertrand; Beers, Timotrhy C.
2003IAUJD..15E..39B Altcode:
In the course of the ESO Large Programme ""First Stars"" we have
observed with the UVES spectrograph at the 8.2m Kueyen-VLT telescope
more than thirty stars which were classified as Turn-Off based on
medium resolution spectra. Effective temperatures for these stars were
derived by fitting the ings of the H-alpha lines. The constant lithium
abundance found in metal-poor stars is generally understood to have
been produced primordially. If this is the case it provides a measure
of the baryonic density which may be compared to the valued recently
measured from the fluctuations of the cosmic microwave background
by the WMAP experiment. Howevere this may not be the case if the Li
observed on the surface of these stars has been increased by Galactic
production or decreased by atmospheric phenomena such effects could
be highlighted by the existence of variations with metallicity and/or
effective temperature of the Li abundance. In this poster we report on
the measurement of lithium abundances in this unique homogeneous sample
of extremely metal poor stars which provides important information on
the Li content of the early Galaxy.
---------------------------------------------------------
Title: Neutron-Capture Elements in Extremely Metal-Poor Giants
Authors: Francois, Patrick; Hill, Vanessa; Cayrel, Roger; Spite,
Monique; Spite, Francois; Depagne, Eric; Primas, Francesca; Bonifacio,
Piercarlo; Plez, Bertrand; Beers, Tim C.
2003IAUJD..15E..44F Altcode:
The abundances of the neutron capture elements (Sr Ba LaCe Eu...) in
a sample of more than 30 extremely metal-poor giants ([Fe/H]<-2.7)
observed at the VLT with the high resolution spectrograph UVES. The
S/N ratio of the spectra is high and it is generally possible to
measure very weak lines (W>=1mA). The trends of the ratios [Sr/Fe]
[Ba/Fe]... with metallicity are shown and the scatters compared to the
scatter observed for iron-peak elements. Consequences for the formation
of these elements and the the galactic evolution are discussed.
---------------------------------------------------------
Title: Heavy Elements in a Sample of Extremely Metal-Poor Giants
Authors: Francois, Patrick; Depagne, Eric; Cayrel, Roger; Hill,
Vanessa; Spite, Francois; Spite, Monique; Plez, Bertrand; Barbuy,
Beatriz; Beers, Tim; Bonifacio, Piercarlo
2003IAUJD..15E..55F Altcode:
The abundances of the neutron capture elements (Sr Ba La Ce Eu
---------------------------------------------------------
Title: Elemental abundances of metal poor carbon rich lead star:
CS29497-030
Authors: Sivarani, T.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Spite,
M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.;
Depagne, E.; Hill, V.; Francois, P.; Nordstrom, B.; Primas, F.
2002astro.ph.12406S Altcode:
We present here the abundance analysis of a metal poor carbon rich lead
star, CS29497-030. High resolution and high signal to noise spectra
were obtained using the UVES spectrograph on the 8.2m VLT-Kueyen
telescope. The observations were made as a part of the Large Programme
165.N-0276, P.I. R. Cayrel. Abundance analysis was done using the
latest version of the MARCS model atmospheres (Plez et. al. 1992)
and the turbospectrum spectrum synthesis code. We have derived Teff =
6650K from the FeI lines. Visible and infrared broad band colours using
the Alonso et al. (1996) calibration, gives similar temperatures. A
log g value of 3.5 was obtained from the ionisation equilibrium of
FeI and FeII, we remark that this gravity also satisfies the MgI/MgII,
TiI/TiII and MnI/MnII equilibria, within errors. The abundance analysis
indicates a metallicity, [Fe/H] = --2.7. A large overabundance of
carbon ([C/Fe]=2.7) was found. We have also found large enhancement
in the s-process elements and in particular lead shows an extremely
high abundance of [Pb/Fe]=3.5, which makes this the star with the
highest Pb/Fe ratio, up to date. The Pb/Ba ratio is found to be high
([Pb/Ba]=1.2) and the same s true for other second-peak s-process
elements(e.g La, Ce, Nd). The star is a known spectroscopic binary with
a period of 346 days (Preston & Sneden 2000). The abundance pattern
suggests that CS 29497-30 has accreted matter from its companion,
when it was in the AGB phase.
---------------------------------------------------------
Title: The Old Star CS 31082-001, the Age of the Universe, and the
Nature of the r-process
Authors: Cayrel, Roger
2002hst..prop.9359C Altcode: 2002hst..prop.5712C
We propose to observe the newly discovered r-process-element enhanced
star, CS 31082-001 {Fe/H -2.9}, in order to determine abundances of the
heaviest stable elements, using absorption lines that are only reachable
in the near UV. This star is the only halo star for which a uranium
detection has been reported, and for which the U/Th chronometer has
been used to specify an age limit. In order to improve the accuracy
of the age determination from U/Th we require abundance estimates
of the daughter nuclides -Pb & Bi- for which only upper limits
have been obtained from ground-based observations. Such estimates
will provide crucial constraints on the initial production ratio of
U/Th, resulting in a more strict lower limit on the age of this star's
progenitor, hence on the age of the Universe. Measurements of 3rd-peak
neutron-capture elements, such as Pt, Os, Ir, and Au, all with lines
in the 2400-3100 Angstrom range, will expand our knowledge of element
synthesis in the early Galaxy. Our recent ESO-VLT data indicate that the
neutron-capture elements in this star exhibit different enhancements as
compared with the previously known “ r-process star” CS 22892-052,
an apparent anomaly that must be resolved. CS 31082-001 is the ideal
HST target in its class - it is 4-times brighter than CS 22892-052,
and less affected by molecular line blending. Consequently, these HST
data will become the reference in all future studies of similar stars.
---------------------------------------------------------
Title: First Stars. II. Elemental abundances in the extremely
metal-poor star CS 22949--037. A diagnostic of early massive
supernovae
Authors: Depagne, E.; Hill, V.; Spite, M.; Spite, F.; Plez, B.; Beers,
T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.; Bonifacio, P.; François,
P.; Nordström, B.; Primas, F.
2002A&A...390..187D Altcode: 2002astro.ph..5232D
CS 22949-037 is one of the most metal-poor giants known ([Fe/H]~-4.0),
and it exhibits large overabundances of carbon and nitrogen (Norris
et al.). Using VLT-UVES spectra of unprecedented quality, regarding
resolution and S/N ratio, covering a wide wavelength range (from lambda
= 350 to 900 nm), we have determined abundances for 21 elements in
this star over a wide range of atomic mass. The major new discovery
is an exceptionally large oxygen enhancement, [O/Fe] = 1.97+/-0.1,
as measured from the [O I] line at 630.0 nm. We find an enhancement of
[N/Fe] of 2.56+/- 0.2, and a milder one of [C/Fe] = 1.17+/-0.1, similar
to those already reported in the literature. This implies Z<SUB>star
</SUB>=0.01 Z<SUB>sun</SUB>. We also find carbon isotopic ratios
<SUP>12</SUP>C/<SUP>13</SUP>C =4+/-2.0 and <SUP>13</SUP>C/<SUP>14</SUP>N
=0.03 <SUP>+0.035</SUP><SUB>-0.015</SUB>, close to the equilibrium
value of the CN cycle. Lithium is not detected. Na is strongly
enhanced ([Na/Fe] = +2.1 +/- 0.2), while S and K are not detected. The
silicon-burning elements Cr and Mn are underabundant, while Co and
Zn are overabundant ([Zn/Fe]=+0.7). Zn is measured for the first
time in such an extremely metal-poor star. The abundances of the
neutron-capture elements Sr, Y, and Ba are strongly decreasing with
the atomic number of the element: [Sr/Fe] ~ +0.3, [Y/Fe] ~ -0.1, and
[Ba/Fe] ~ -0.6. Among possible progenitors of CS 22949-037, we discuss
the pair-instability supernovae. Such very massive objects indeed
produce large amounts of oxygen, and have been found to be possible
sources of primary nitrogen. However, the predicted odd/even effect
is too large, and the predicted Zn abundance much too low. Other
scenarios are also discussed. In particular, the yields of a recent
model (Z35Z) from Heger and Woosley are shown to be in fair agreement
with the observations. The only discrepant prediction is the very
low abundance of nitrogen, possibly curable by taking into account
other effects such as rotationally induced mixing. Alternatively,
the absence of lithium in our star, and the values of the isotopic
ratios <SUP>12</SUP>C/<SUP>13</SUP>C and <SUP>13</SUP>C/<SUP>14</SUP>N
close to the equilibrium value of the CN cycle, suggest that the CNO
abundances now observed might have been altered by nuclear processing
in the star itself. A 30-40 M<SUB>sun</SUB> supernova, with fallback,
seems the most likely progenitor for CS 22949-037. Based on observations
made with the ESO Very Large Telescope at Paranal Observatory, Chile
(programme ID 165.N-0276(A)).
---------------------------------------------------------
Title: The "First Stars" project - preliminary results for the
giant stars
Authors: Spite, M.; Cayrel, R.; Depagne, E.; Hill, V.; François,
P.; Plez, B.; Spite, F.
2002sf2a.conf..511S Altcode:
A general view of the status of the ESO LP "Galaxy Formation, Early
Nucleosynthesis, and the First Stars" will be given.A new step has
been the obtention of 48 orbits of the HST for studying the lines
of the r-process elements only accessible from space. Several giant
stars are presenting pattern never observed before, confirming the
variability of the yields in the early Galaxy.
---------------------------------------------------------
Title: First stars. I. The extreme r-element rich, iron-poor halo
giant CS 31082-001. Implications for the r-process site(s) and
radioactive cosmochronology
Authors: Hill, V.; Plez, B.; Cayrel, R.; Beers, T. C.; Nordström,
B.; Andersen, J.; Spite, M.; Spite, F.; Barbuy, B.; Bonifacio, P.;
Depagne, E.; François, P.; Primas, F.
2002A&A...387..560H Altcode: 2002astro.ph..3462H
We present a high-resolution (R= 75 000, S/N ~ 500) spectroscopic
analysis of the bright (V= 11.7), extreme halo giant CS 31082-001
([Fe/H] = -2.9), obtained in an ESO-VLT Large Programme dedicated to
very metal-poor stars. We find CS 31082-001 to be extremely rich in
r-process elements, comparable in this respect only to the similarly
metal-poor, but carbon-enriched, giant CS 22892-052. As a result
of the extreme overabundance of the heaviest r-process elements,
and negligible blending from CH and CN molecular lines, a reliable
measurement is obtained of the U II line at 386 nm, for the first time
in a halo star, along with numerous lines of Th II, as well as lines
of 25 other r-process elements. Abundance estimates for a total of 43
elements (44 counting Hydrogen) are reported in CS 31082-001, almost
half of the entire periodic table. The main atmospheric parameters of
CS 31082-001 are as follows: T<SUB>eff</SUB> = 4825 +/- 50 K, log g=
1.5 +/- 0.3 (cgs), [Fe/H] = -2.9 +/- 0.1 (in LTE), and microturbulence
1.8 +/- 0.2 km s<SUP>-1</SUP>. Carbon and nitrogen are not significantly
enhanced relative to iron. As usual in giant stars, Li is depleted
by dilution (log (Li/H) = 0.85). The alpha -elements show the usual
enhancements with respect to iron, with [O/Fe] = 0.6+/- 0.2 (from
[O I] 6300 Å), [Mg/Fe] = 0.45 +/- 0.16, [Si/Fe] = 0.24 +/- 0.1, and
[Ca/Fe] = 0.41 +/- 0.08, while [Al/Fe] is near -0.5. The r-process
elements show unusual patterns: among the lightest elements (Z ~ 40),
Sr and Zr follow the Solar r-element distribution, but Ag is down
by 0.8 dex. All elements with 56 <= Z <= 72 follow the Solar
r-element pattern, reduced by about 1.25 dex. Accordingly, the [r/Fe]
enhancement is about +1.7 dex (a factor of 50), very similar to that
of CS 22892-052. Pb, in contrast, seems to be below the shifted Solar
r-process distribution, possibly indicating an error in the latter,
while thorium is more enhanced than the lighter nuclides. In CS
31082-001, log(Th/Eu) is -0.22 +/- 0.07, higher than in the Solar
System (-0.46) or in CS 22892-052 (-0.66). If CS 31082-001 and CS
22892-052 have similar ages, as expected for two extreme halo stars,
this implies that the production ratios were different by about 0.4 dex
for the two objects. Conversely, if the Th/Eu production ratio were
universal, an age of 15 Gyr for CS 22892-052 would imply a negative
age for CS 31082-001. Thus, while a universal production ratio for
the r-process elements seems to hold in the interval 56 <= Z <=
72, it breaks down in the actinide region. When available, the U/Th
is thus preferable to Th/Eu for radioactive dating, for two reasons:
(i) because of its faster decay rate and smaller sensitivity to
observational errors, and (ii) because the inital production ratio
of the neighboring nuclides <SUP>238</SUP>U and <SUP>232</SUP>Th is
more robustly predicted than the <SUP>151</SUP>Eu/<SUP>232</SUP>Th
ratio. Our current best estimate for the age of CS 31082-001 is 14.0+/-
2.4 Gyr. However, the computed actinide production ratios should be
verified by observations of daughter elements such as Pb and Bi in
the same star, which are independent of the subsequent history of star
formation and nucelosynthesis in the Galaxy. Based on observations of
program 165.N-0276(A) obtained with the Very Large Telescope of the
European Southern Observatory at Paranal, Chile.
---------------------------------------------------------
Title: Determination of Fundamental Parameters
Authors: Cayrel, R.
2002ASPC..274..133C Altcode: 2002ohds.conf..133C
No abstract at ADS
---------------------------------------------------------
Title: Foreword (Organizations and strategies in astronomy III)
Authors: Cayrel, Roger
2002ASSL..280D...7C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic influence of temperature inhomogeneities
Authors: Cayrel, Roger; Steffen, Matthias
2002HiA....12..423C Altcode:
The effect of temperature inhomogeneities on the formation of two
oxygen lines and one Fe II line has been investigated based on 2-D
radiation hydrodynamics simulations of convection in the atmospheres
of metal-poor stars. It was expected that the IR O I triplet lines
would be enhanced by the temperature inhomogeneities, more than the
forbidden [O I] line or Fe II lines. The actual computations done on
two snapshots under the assumption of LTE have not confirmed this
expectation, instead suggesting that the main difference between
"classical" and "dynamical" atmospheres of metal-poor dwarfs is the
significantly cooler mean temperature of the dynamical upper photosphere
(τ<SUB>Ross</SUB><~0.01).
---------------------------------------------------------
Title: Determination of [O/Fe] in BD +23 3130 from ESO VLT-UVES
observations
Authors: Cayrel, R.; Andersen, J.; Barbuy, B.; Beers, T. C.; Bonifacio,
P.; François, P.; Hill, V.; Molaro, P.; Nordström, B.; Plez, B.;
Primas, F.; Spite, F.; Spite, M.
2001NewAR..45..533C Altcode:
We report a new determination of [O/Fe], the relative logarithmic
abundance of O/Fe with respect to the Sun, for the very metal-poor
star BD+23 3130 ([Fe/H]=-2.6). The value was derived from the
forbidden line [O I] at 630 nm and from six weak Fe II lines, with
a S/N ratio substantially larger than those obtained before, thanks
to the efficiency of the VLT-UVES instrument at Paranal. We obtain
[O/Fe]=0.71±0.25, a value 0.36 dex higher than the value obtained
from the same lines by Fulbright and Kraft [AJ 118 (1999) 527], but
0.46 lower than the one derived by Israelian et al. [ApJ 507 (1998)
805] from the UV OH bands.
---------------------------------------------------------
Title: R-process pattern in the Very-Metal-Poor Halo Star CS 31082-001
Authors: Hill, Vanessa; Plez, Bertrand; Cayrel, Roger; Beers,
Timothy C.
2001sf2a.conf..205H Altcode:
CS 31082-001 was discovered to be very strongly r-process-enhanced,
leading to the first <SUP>238</SUP> abundance measurement in an old
star (Cayrel et al. 2001). Together with the observed <SUP>232</SUP>
abundance, this observation provides the opportunity to use both
radioactive species for dating the progenitor to this star. However, age
computations all rely on the hypothesis that the r-process pattern in
this star is solar (as was indeed observed in the other famous r-process
enhanced very metal poor star CS22892-052). This hypothesis is tested
here by presenting the preliminary analysis of over 20 abundances of
neutron-capture elements in the range Z=38 to Z=82.
---------------------------------------------------------
Title: First measurement of the uranium/thorium ratio in a very old
star: implications for the age of the Galaxy
Authors: Cayrel, Roger
2001sf2a.conf..173C Altcode:
In the frame of an ESO Large Programme devoted to the study of the most
primitive stars in our Galaxy ([Fe/H] < -2.8) we have been able to
measure for the first time the abundance of uranium in a star. Now,
the couple U/Th seems the best radioactive chronometer for dating the
oldest stars of the Galaxy.
---------------------------------------------------------
Title: Measurement of stellar age from uranium decay
Authors: Cayrel, R.; Hill, V.; Beers, T. C.; Barbuy, B.; Spite, M.;
Spite, F.; Plez, B.; Andersen, J.; Bonifacio, P.; François, P.;
Molaro, P.; Nordström, B.; Primas, F.
2001Natur.409..691C Altcode: 2001astro.ph..4357C
The ages of the oldest stars in the Galaxy indicate when star formation
began, and provide a minimum age for the Universe. Radioactive dating
of meteoritic material and stars relies on comparing the present
abundance ratios of radioactive and stable nuclear species to the
theoretically predicted ratios of their production. The radioisotope
<SUP>232</SUP>Th (half-life 14Gyr) has been used to date Galactic
stars, but it decays by only a factor of two over the lifetime of the
Universe. <SUP>238</SUP>U (half-life 4.5Gyr) is in principle a more
precise age indicator, but even its strongest spectral line, from
singly ionized uranium at a wavelength of 385.957nm, has previously
not been detected in stars. Here we report a measurement of this line
in the very metal-poor star CS31082-001<SUP>8</SUP>, a star which
is strongly overabundant in its heavy elements. The derived uranium
abundance, log(U/H) = -13.7 +/- 0.14 +/- 0.12 yields an age of 12.5
+/- 3Gyr, though this is still model dependent. The observation of
this cosmochronometer gives the most direct age determination of the
Galaxy. Also, with improved theoretical and laboratory data, it will
provide a highly precise lower limit to the age of the Universe.
---------------------------------------------------------
Title: First Measurement of the Uranium/Thorium Ratio in a Very Old
Star: Implications for the Age of the Galaxy
Authors: Cayrel, R.; Spite, M.; Spite, F.; Hill, V.; Primas, F.;
François, P.; Beers, T. C.; Plez, B.; Barbuy, B.; Andersen, J.;
Nordström, B.; Molaro, P.; Bonifacio, P.
2001ASPC..245..244C Altcode: 2001aats.conf..244C; 2001astro.ph..4448C
During an ESO-VLT large program devoted to high-resolution spectroscopy
of extremely metal-poor stars selected from the H&K survey of Beers
and colleagues, a [Fe/H] giant star was found to be as enriched in
neutron-capture r-process elements as CS 22892-052, but with a much
reduced masking by molecular lines. This allowed the detection and
the measurement of the uranium line at 3859 A, for the first time in
an extremely old star. Making use of the short 238U decay time (4.47
Gyr) we obtained a radioactive dating of the formation of U and Th in
of this star, born in the early days of the Galaxy.
---------------------------------------------------------
Title: R-Process Pattern in the Very-Metal-Poor Halo Star CS 31802-001
Authors: Hill, Vanessa; Plez, Bertrand; Cayrel, Roger; Beers,
Timothy C.
2001ASPC..245..316H Altcode: 2001aats.conf..316H; 2001astro.ph..4172H
The very-metal-poor halo star CS31082-001 was discovered to be
very strongly r-process-enhanced during the course of a VLT+UVES
high-resolution follow-up of metal-poor stars identified in the
HK survey of Beers and colleagues. Both the strong n-capture
element enhancement and the low carbon and nitrogen content of
the star (reducing the CN molecular band contamination) led to
the first $^{238}$U abundance measurement in a stellar spectrum
(Cayrel et al. 2001), and the opportunity to use both radioactive
species $^{238}$U and $^{232}$Th for dating the progenitor to this
star. However, age computations all rely on the hypothesis that the
r-process pattern is solar, as this was indeed observed in the other
famous r-process-enhanced very metal poor stars CS22892-052 (Sneden
et al. 1996, 2000) and in HD115444 (Westin et al. 2000). Here, we
investigate whether this hypothesis is verified also for CS31082-001,
using a preliminary analysis of over 20 abundances of n-capture elements
in the range Z=38 to Z=92.
---------------------------------------------------------
Title: Li/h Measurements in Stars
Authors: Cayrel, R.; Spite, F.; Spite, M.
2001coev.conf...85C Altcode:
The abundance of Li in stars is still the object of intense
activity. New results are available on several type of stars. Abundances
have been measured in many extremely young or even pre-main sequence
stars, and these data rule out important pre-main sequence depletion
of <SUP>7</SUP>Li. The status of Li-rich giants and AGB or post AGB
stars has been somewhat clarified, but the discovery of an extremely
lithiumrich bright red giant in M3 located in the HR diagram among
other lithium normal giants remains a challenge. Finally the case of
metal-poor stars has been actively further investigated. A significant
amount of <SUP>6</SUP>Li is now measured in 6 stars, and there is
now general agreement on a very low level of scatter of Li abundance
on the Spite plateau. The connection between the measured abundance
of <SUP>7</SUP>Li on the Spite plateau and its cosmological abundance
remains a subject of intensive research. An upper limit of the depletion
of <SUP>7</SUP>Li of the order of 0.3 dex is suggested by the amount of
<SUP>6</SUP>Li present in the post-turnoff very metal-poor halo stars.
---------------------------------------------------------
Title: Element abundance ratios in an extremely metal-poor binary
star: CS 22873-139
Authors: Spite, M.; Depagne, E.; Nordström, B.; Hill, V.; Cayrel,
R.; Spite, F.; Beers, T. C.
2000A&A...360.1077S Altcode:
High-resolution spectra of the extremely metal-poor double-lined
spectroscopic binary star BPS CS 22873-139 have been analyzed to
determine the metallicity and abundance ratios for a number of
elements. From the analysis of the collected radial velocities, new
orbital elements are derived as well as an improved mass ratio. In spite
of its extreme metal deficiency, [Fe/H]= -3.4, the abundance ratios
of CS 22873-139 are not similar to those of a typical Population II
star. In particular, the α-elements are not enhanced relative to iron,
and the strontium abundance is very low. The abundance pattern of CS
22873-139 is compared to the patterns exhibited by other metal-poor
stars which exhibit also very low strontium abundances. There is a large
spread of elemental abundance ratios among these stars, suggesting
that low strontium abundance may be associated with a variety of
nucleosynthesis histories. The abundance ratios of CS 22873-139 are,
surprisingly, very similar to those found in a common proper-motion
pair HD 134439, HD 134440, even though the metallicity of this system
is almost two dex higher, [Fe/H] = -1.7. The ratios are compared to
those of another very metal-poor binary star BPS CS 22876-032. The
unusual abundance pattern of CS 22873-139 is discussed (by comparison
to the predicted yields of zero-metal SN II and hypernovae). The lithium
doublet at 6707 Å is not detected in CS 22873-139, but an abundance of
lithium consistent with the Spite plateau cannot be excluded, based on
the present data. Based on observations made at the European Southern
Observatory, La Silla, Chile
---------------------------------------------------------
Title: CHCN Very Metal-Poor Stars: Are These the Missing Pop III ?
Authors: Hill, Vanessa; Barbuy, Beatriz; Spite, François; Spite,
Monique; Cayrel, Roger; Nordström, Birgitta; Beers, Timothy C.
2000fist.conf...62H Altcode:
We have carried out a new analysis of two of the most extreme CH/CN
very metal poor giants (originally discovered as part of the ongoing
Beers Preston & Shectman HK survey [2]) with high resolution
spectroscopy to determine the precise chemical composition of these
objects, paying special attention to the heavy s and r neutron-capture
elements. The results of this study are presented and discussed in terms
of the possible origins for these objects: mass-transfer from a binary
companion or intrinsic evolutionary stage of evolved Pop III stars?
---------------------------------------------------------
Title: The (log T<SUB>eff</SUB>, M<SUB>bol</SUB> diagram of metal-poor
stars with Hipparcos parallaxes : comparison with theoretical
isochromes using NLTE iron abundances
Authors: Cayrel, R.; Perrin, M. -N.; Lebreton, Y.; Baglin, A.;
Fernandes, J.
2000LIACo..35..459C Altcode: 2000ghgc.conf..459C
No abstract at ADS
---------------------------------------------------------
Title: Effects of Photospheric Temperature Inhomogeneities on Lithium
abundance Determinations (2D) (Invited Paper)
Authors: Cayrel, R.; Steffen, M.
2000IAUS..198..437C Altcode: 2000astro.ph..3075C
Based on detailed 2D radiation hydrodynamics (RHD) simulations, we have
investigated the effects of photospheric temperature inhomogeneities
induced by convection on spectroscopic determinations of the lithium
abundance. Computations have been performed both for the solar case
and for a metal-poor dwarf. NLTE effects are taken into account,
using a five-level atomic model for LiI. Comparisons are presented
with traditional 1D models having the same effective temperature and
gravity. The net result is that, while LTE results differ dramatically
between 1D and 2D models, especially in the metal-poor case, this
does not remain true when NLTE effects are included: 1D/2D differences
in the inferred NLTE Li abundance are always well below 0.1 dex. The
present computations still assume LTE in the continuum. New computations
removing this assumption are planned for the near future.
---------------------------------------------------------
Title: Lithium Depletion in a [Fe/H]= -3.4 star?
Authors: Spite, M.; Spite, F.; Cayrel, R.; Hill, V.; Depagne, E.;
Nordström, B.; Beers, T. C.
2000IAUS..198..356S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Les premieres etoiles.
Authors: Cayrel, R.
2000CR4.....1..363C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Influence of temperature inhomogeneities on oxygen abundance
determination
Authors: Cayrel, R.; et al.
2000IAUJD...8E...4C Altcode:
The influence of temperature inhomogeneities on abundances derived from
the [O I] line and from the O I IR triplet lines will be studied with
the help of 2-D hydrodynamical models computed at the Astrophysical
Institute of Potsdam by M. Steffen and collaborators.
---------------------------------------------------------
Title: Preliminary Abundance Ratios in an Extremely Metal Poor
Binary Star
Authors: Nordström, Birgitta; Depagne, Eric; Spite, Monique; Spite,
François; Hill, Vanessa; Cayrel, Roger; Beers, Timothy C.
2000fist.conf...64N Altcode:
The orbital elements of CS 22873-139 have been revisited and preliminary
abundance ratios in this extremely metal poor binary star with [Fe/H]
≈ -3.6 are given.
---------------------------------------------------------
Title: Heavy-element abundances in the CH/CN-strong very metal-poor
stars CS 22948-27 and CS 29497-34
Authors: Hill, V.; Barbuy, B.; Spite, M.; Spite, F.; Cayrel, R.;
Plez, B.; Beers, T. C.; Nordström, B.; Nissen, P. E.
2000A&A...353..557H Altcode:
We have carried out a new analysis of the very metal-poor CH/CN
strong stars CS 22948-27 and CS 29497-34. In particular, the effective
temperatures were recomputed by comparing newly obtained photometric
data to colours derived from model atmospheres computed especially
for these stars. Metallicities of [Fe/H] = -2.45 and -2.90 are found,
respectively, for CS 22948-27 and CS 29497-34. The abundances of
heavy elements have been derived from newly obtained high-resolution
spectroscopy in the blue spectral region, together with previously
obtained spectra in the red, resulting in a total wavelength coverage
of lambda lambda 4000-8200 Ä. We find that the abundance patterns
of our stars reflect enrichment by the r-process (as indicated by a
high Eu abundance), as well as by the s-process, which could be due
to a mass transfer episode from a companion crossing the AGB phase,
although no clear evidence for binarity is indicated in the spectra
obtained to date. Observations collected at the European Southern
Observatory (ESO), La Silla, Chile.
---------------------------------------------------------
Title: The HIPPARCOS HR diagram of nearby stars in the metallicity
range: -1.0 < [Fe/H] < 0.3. A new constraint on the theory of
stellar interiors and model atmospheres
Authors: Lebreton, Y.; Perrin, M. -N.; Cayrel, R.; Baglin, A.;
Fernandes, J.
1999A&A...350..587L Altcode: 1999astro.ph..8277L
The Hipparcos mission has provided very high quality parallaxes of a
sample of a hundred nearby disk stars, of spectral types F to K. In
parallel, bolometric fluxes, effective temperatures, and accurate
Fe/H ratios of many of these stars became available through infrared
photometry and detailed spectroscopic analyses. These new accurate data
allow to build the Hertzsprung-Russell diagram of stars of the solar
neighbourhood with the smallest error bars ever obtained. We analyse
these observations by means of theoretical stellar models, computed
with the most recent input physics. We first examine the positions
of the objects versus standard theoretical isochrones, corresponding
to their chemical composition and age. For these isochrones we have
first assumed that the helium content was varying in locksteps with
metallicity. The comparison becomes age-independent in the lower part
of the HR diagram, where evolutionary effects are negligible. We show
that for the unevolved stars, the agreement between real stars and
models is fairly satisfactory for stars with metallicity within +/-
0.3 dex of the solar metallicity, but that a conflict exists for stars
with metallicity less than [Fe/H] = -0.5. This conflict cannot be
resolved by decreasing the helium abundance: values of this abundance
below the primordial abundance would be required. On the basis of
recent works, we show that the addition of two processes not included
in standard models can help solving the above discrepancy. These are
(i) correcting the LTE iron abundances using a non-LTE approach and
(ii) including microscopic diffusion of He and heavier elements in the
stellar interior. The case of the binary star mu Cas is particularly
useful to support this conclusion as its mass is also known from
its orbit. After inclusion of the two effects, mu Cas A falls on
its expected isochrone, within the error bars corresponding to its
mass. All stars with -0.3 < [Fe/H] < 0.3 are located between the
helium-scaled isochrones corresponding to these metallicities. However
five of them are not located exactly where they are expected to
be for their metallicity. This may reflect a helium content lower
than the metallicity-scaled value. But not necessarily, as a possible
sedimentation of the elements might complicate the determination of the
helium content. The age of main sequence solar composition stars covers
a large range, and the effects of sedimentation are time dependent.
---------------------------------------------------------
Title: Abundances in Very Metal-Poor Stars
Authors: Spite, M.; Spite, F.; Cayrel, R.; Hill, V.; Nordström, B.;
Barbuy, B.; Beers, T.; Nissen, P. E.
1999Ap&SS.265..141S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: In Situ Study of the Thick Disk. Preliminary Results
Authors: Katz, D.; Cayrel, R.; Coupry, M. -F.; Perrin, M. -N.; van't
Veer, C.; Soubiran, C.; Barbuy, B.; Bienaymé, O.; Friel, E.
1999Ap&SS.265..221K Altcode:
We report the advancement of our chemical and kinematical study of
thethick disk. The methods used to derive the stellar parameters
arediscussed and the preliminary results presented.
---------------------------------------------------------
Title: Lithium-6: evolution from Big Bang to present
Authors: Vangioni-Flam, Elisabeth; Cassé, Michel; Cayrel, Roger;
Audouze, Jean; Spite, Monique; Spite, François
1999NewA....4..245V Altcode: 1998astro.ph.11327V
The primordial abundances of deuterium, <SUP>4</SUP>He, and
<SUP>7</SUP>Li are crucial to the determination of the baryon density
of the Universe in the framework of standard Big Bang nucleosynthesis
(BBN). <SUP>6</SUP>Li is only produced in tiny quantities and it
is generally not considered to be a cosmological probe. However,
recent major observational advances have produced an estimate of the
<SUP>6</SUP>Li/ <SUP>7</SUP>Li ratio in a few very old stars in the
galactic halo which impacts the question whether or not the lithium
isotopes are depleted in the outer layers of halo stars, through proton
induced reactions at the base of (or below) the convective zone. Here,
we use (i) an empirical relation, independent of any evolutionary
model, to set an upper limit on the <SUP>6</SUP>Li rise compatible
with the very existence of the Spite's plateau (i.e. the flat lithium
abundance measured in very old stars of the halo of our Galaxy of
different iron content) and (ii) a well founded evolutionary model of
light elements based on spallation production ( Vangioni-Flam et al.,
1997; Vangioni-Flam et al., 1998). Indeed, <SUP>6</SUP>Li is a pure
product of spallation through the major production reactions, fast
oxygen and alphas interacting on interstellar H, He (especially in the
early Galaxy). The rapid nuclei are both synthesized and accelerated by
SN II. In this context, the <SUP>6</SUP>Li evolution should go in step
with that of beryllium and boron, recently observed by the Keck and HST
telescopes. <SUP>6</SUP>Li adds a new constraint on the early spallation
in the Galaxy. In particular, if confirmed, the <SUP>6</SUP>Li/
<SUP>9</SUP>Be ratio observed in two halo stars (HD 84937, BD +26°3578
= HD 338529) gives strong boundary conditions on the composition and
the spectrum of the rapid particles involved. Both methods converge
to show that <SUP>6</SUP>Li is essentially intact in halo stars,
and a fortiori <SUP>7</SUP>Li, which is more tightly bound. Moreover,
extrapolating empirical and theoretical evolutionary curves to the very
low metallicities, we can define a range of the <SUP>6</SUP>Li abundance
in the very early Galaxy consistent with Big Bang nucleosynthesis
(5.6×10 <SUP>-14</SUP> to 3×10 <SUP>-13</SUP>). Following the
evolution at increasing metallicity, we explain the abundance in the
solar system within a factor of about 2. The whole evolution from
Big Bang to present is reasonably reproduced, which demonstrates the
general consistency of the present analysis of <SUP>6</SUP>Li. The
baryonic density derived from both lithium isotopes is between 1.5 to
3.5% of the critical one, in good agreement with the determination
based on independent analyses. Consequently, thanks to these new
data and theoretical developments, we show that <SUP>6</SUP>Li can be
used to establish stellar <SUP>7</SUP>Li abundances as a valid tracer
due to the fact that it allows to reinforce the Spite's plateau as a
primordial test of BBN; on the other hand, its early evolution can be
used to corroborate the calculated BBN abundances. In the framework
of this work, a pregalactic α+ α process producing <SUP>6</SUP>Li
is not necessary. Finally, thanks to <SUP>6</SUP>Li, the physics of
spallative production of light elements should be more easily mastered
when more data will become available.
---------------------------------------------------------
Title: A Grid of Metal-Poor Model Stellar Atmospheres for Stars Born
in the Early Galaxy
Authors: van't Veer-Menneret, C.; Katz, D.; Cayrel, R.; Soubiran, C.
1999Ap&SS.265..257V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Survival of 6Li, and 7Li, in Metal-Poor Stars
Authors: Cayrel, R.; Lebreton, Y.; Morel, P.
1999Ap&SS.265...87C Altcode: 1999astro.ph..2068C
The relationship between the depletions of <SUP>6</SUP>Li and
<SUP>7</SUP>Li is studied for two models of lithium burning, below the
convective zone. The parametersof the depletion models are submitted
to the constraint that the slope ofthe <SUP>7</SUP>Li theoretical
depletion curve agrees with the slope of theobserved depletion curve,
for cool subdwarfs. Other less restrictive modelsare also considered.In
all cases, a <SUP>6</SUP>Li depletion less than 0.5 dex implies a
<SUP>7</SUP>Lidepletion less than 0.1 dex. With the constraint on the
slope of the<SUP>7</SUP>Li curve, the depletion of <SUP>7</SUP>Li for
the same depletion of <SUP>6</SUP>Li is below 0.05 dex.
---------------------------------------------------------
Title: New high S/N observations of the (6Li) /(7) Li blend in HD
84937 and two other metal-poor stars
Authors: Cayrel, R.; Spite, M.; Spite, F.; Vangioni-Flam, E.; Cassé,
M.; Audouze, J.
1999A&A...343..923C Altcode: 1999astro.ph..1205C
High signal to noise ratio spectra have been obtained with the GECKO
spectrograph at CFHT, at a spectral resolution of 100 000, for three
metal-poor stars in order to obtain more accurate abundances of the
very fragile element (6) Li. For two newly observed stars, <ASTROBJ>BD
+42 2667</ASTROBJ> and <ASTROBJ>BD +36 2165</ASTROBJ> it appears that
the first may have a detectable amount of (6) Li, whereas no (6) Li is
found in the second one. The S/N ratio of only a few hundreds obtained
for these two faint stars preclude however a firm conclusion. For
the third star, the well known object <ASTROBJ>HD84937</ASTROBJ>,
a very high S/N of 650 per pixel (over 1000 per resolved spectral
element) was obtained, yielding greatly improved accuracy over previous
determinations. A value of (6) Li / (7) Li = 0.052 +/- 0.019 (one sigma)
is obtained. We also conclude that the no- (6) Li assumption is ruled
out at the 95 per cent level, even in the most permissive case, when
a variation of all the other free parameters (wavelength zero-point,
continuum location, macroturbulent broadening, abundance of (7) Li) is
allowed. The possibility that the (6) Li feature is an artifact due to
a once suspected binarity of <ASTROBJ>HD 84937</ASTROBJ> is discussed,
with the conclusion that this assumption is ruled out by the extant
data on the radial velocity of the object. The (6) Li abundance is
compared with recent models of formation of the light elements Li,
Be and B. This comparison shows that (6) Li is either undepleted,
or only moderately depleted in <ASTROBJ>HD 84937</ASTROBJ>, from its
initial value. Under the assumption that the atmospheric depletion of
(6) Li and (7) Li in stars is by slow mixing with hot layers (underneath
the convective zone), in which these elements can burn, we conclude that
the depletion of (7) Li by this mechanism in <ASTROBJ>HD 84937</ASTROBJ>
is less than 0.1 dex. This new upper limit to the efficiency of the
depletion of (7) Li by slow mixing burning, in a star located on the
Spite plateau, leads to a more secure estimation of the primordial
abundance of (7) Li. However, the effect of temperature inhomogeneities
in the convective zone, on the derived abundance of lithium still
remains to be accurately determined. Based on observations made at
the Canada-France-Hawaii Telescope and at Observatoire de Haute Provence
---------------------------------------------------------
Title: Concluding Remarks: Observations
Authors: Cayrel, R.
1999ASPC..171..261C Altcode: 1999lcrr.conf..261C
No abstract at ADS
---------------------------------------------------------
Title: Calibration of Photometric Absolute Magnitudes for Subdwarfs
with Hipparcos
Authors: Meillon, L.; Crifo, F.; Cayrel, R.; Perrin, M. -N.; Gómez,
A. E.
1999ASPC..167..284M Altcode: 1999hcds.conf..284M
In order to obtain better photometric distances for high-velocity
stars in the Carney et al. (1994) sample, we have undertaken a
calibration of photometric absolute magnitudes. From the intersection
between this sample and the Hipparcos catalogue (770 common
stars), we keep only single stars with the most reliable parallaxes
(σ<SUB>π</SUB>/π)<SUB>HIP</SUB> <= 0.15). Metallicities, colours
and absolute magnitudes of these stars are used with VandenBerg et
al. (1998) isochrones in a colour-magnitude diagram. This set of
isochrones allows us to derive photometric absolute magnitudes for
the highest velocity stars. This photometric parallax calibration
is discussed.
---------------------------------------------------------
Title: New Grids of Synthetic Spectra for Abundance Derivation and
Population Synthesis
Authors: Barbuy, B.; Perrin, M. -N.; Cayrel, R.; Katz, D.; van't Veer,
C.; Schiavon, R. P.
1999IAUS..192..365B Altcode:
We have built a new grid of synthetic spectra in the wavelength range
lambdalambda 4600-5600 Angstroms for [alpha-elements/Fe] = 0.0 and
+0.4. This grid is used in combination with an observed spectra library
of reference stars in order to derive stellar parameters from low to
medium resolution spectra of faint stars. The basis of the method was
described in Cayrel et al. (1991, A&A 247, 108) and Meliani et
al. (1995, A&A, 300, 349). For the calculation of this new grid
already available, the set of atomic and molecular constants were
revised and model atmospheres with overshooting parameter appropriate
to reproduce the Hβ line wings (suitable to indicate temperatures)
were employed. The method is applied to Galactic halo faint stars, bulge
stars and Magellanic Cloud stars. It would be suitable also to analyse
stars in other nearby galaxies. A computation of a high-resolution grid
of spectra in the range lambdalambda 3800-7000 Angstroms, to be used
in the context of echelle spectrographs (and also at low resolution),
as well as a full grid in the range lambdalambda 3800-10200 Angstroms,
to be further used in conjunction with evolutionary population synthesis
models are also underway.
---------------------------------------------------------
Title: A Grid of Metal-Poor Model Stellar Atmospheres for Stars Born
in the Early Galaxy
Authors: van't Veer-Menneret, C.; Katz, D.; Cayrel, R.; Soubiran, C.
1999gecd.conf..257V Altcode:
We give a brief description of the automation, on UNIX stations, of the
exploitation of the KURUCZ' codes for stellar atmosphere computations,
allowing to get rapidly, in a serial mode, grids of models and of
corresponding fluxes, Balmer lines profiles(BLP), spectra and Bolometric
Correction for the Hipparcos bande Hp(BCHp). We will expose the methods
used to get reliable fundamental stellar atmospheric parameters using
high resolution and high S/N spectra. We will stress the use of BLP
properties to be pure effective temperature criteria while being
atmosphere structure indicators. Confrontation and discussion will
follow upon the results obtained for some stars of the galactic halo
and thick disk.
---------------------------------------------------------
Title: Abundances in Very Metal-Poor Stars
Authors: Spite, M.; Spite, F.; Cayrel, R.; Hill, V.; Nordström, B.;
Barbuy, B.; Beers, T.; Nissen, P. E.
1999gecd.conf..141S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Survival of <SUP>6</SUP>Li, and <SUP>7</SUP>Li, in Metal-Poor
Stars
Authors: Cayrel, R.; Lebreton, Y.; Morel, P.
1999gecd.conf...87C Altcode:
The most robust fossil-elements from the Big Bang are 4He and 7Li. The
early abundance of 4He is mostly determined from extragalactic sources,
whereas the early abundance of 7Li is determined from halo stars. The
question of knowing if this abundance has been altered or not by
nuclear burning in the star itself has been controversial for many
years now. New determinations of 6Li in a small number of halo stars
permit to discuss this crucial point with stronger constraints.
---------------------------------------------------------
Title: In Situ Study of the Thick Disk. Preliminary Results
Authors: Katz, D.; Cayrel, R.; Coupry, M. -F.; Perrin, M. -N.; van't
Veer, C.; Soubiran, C.; Barbuy, B.; Bienaymé, O.; Friel, E.
1999gecd.conf..221K Altcode:
When people focus on the problem of the formation of the Galaxy, many
questions arise. Is the Galaxy born from a single collapsing cloud
or from many interacting ones? Did the halo form before the disk or
not? Is the thick disk the progenitor of the thin disk? Many models
try to answer these questions, playing with the physical processes at
the origin of the different structures: free fall, infall, dissipative
collapse, secular diffusion of stars, dynamical friction, accretion of
galactic fragments, interactions between sub-structures. These formation
scenarios are making predictions on the "observables" characterizing
the halo, the thick and the thin disk: age, kinematic, abundance of
the various elements, density profile. These "observables" are the keys
to discriminate between the various models. We have observed a sample
of 500 stars in two fields: one in the direction of the north galactic
pole (near M3), the other in the direction of the galactic center at b =
47<SUP>circ</SUP> (near M5). The sample includes stars with magnitude up
to 17, in order to reach distances where each population is dominating
(around z = 2 kpc for the thick disk and z = 5 kpc for the halo). All
the stars have been studied photometrically, spectroscopically and
by the way of proper motion surveys, leading to the knowledge of:
effective temperature, surface gravity, metallicity, radial velocity,
proper motions, V, B, I magnitudes, distance, U, V, W velocities. This
sample of stars will be use to address various questions concerning
the thick disk: density profile, scale height, metallicity gradient,
kinematic properties, age, continuity with the halo or with the thin
disk and we will expose how the data put constraints on the galaxy
formation scenarios.
---------------------------------------------------------
Title: On-line determination of stellar atmospheric parameters
T<SUB>eff</SUB>, log g, [Fe/H] from ELODIE echelle spectra. II. The
library of F5 to K7 stars
Authors: Soubiran, C.; Katz, D.; Cayrel, R.
1998A&AS..133..221S Altcode: 1998astro.ph..6234S
A library of 211 echelle spectra taken with ELODIE at the Observatoire
de Haute-Provence is presented. It provides a set of spectroscopic
standards covering the full range of gravities and metallicities
in the effective temperature interval [4000 K, 6300 K]. The spectra
are straightened, wavelength calibrated, cleaned of cosmic ray hits,
bad pixels and telluric lines. They cover the spectral range [440 nm,
680 nm] with an instrumental resolution of 42000. For each star, basic
data were compiled from the Hipparcos catalogue and the Hipparcos
Input Catalogue. Radial velocities with a precision better than 100
m s<SUP>-1</SUP> are given. Atmospheric parameters (T<SUB>eff</SUB>,
log g, [Fe/H]) from the literature are discussed. Because of scattered
determinations in the bibliography, even for the most well-known
stars, these parameters were adjusted by an iterative process which
takes account of common or different spectral features between the
standards, using our homogeneous set of spectra. Revised values of
effective temperature, gravity and metallicity are proposed. They
are still consistent with the literature, and also lead to the
self-consistency of the library, in the sense that similar spectra
have similar atmospheric parameters. This adjustment was performed
by using step by step a method based on the least square comparison
of carefully prepared spectra, which was originally developed for the
on-line estimation of the atmospheric parameters of faint field stars
(companion paper in the main journal). Based on observations made on
the 193 cm telescope at Observatoire de Haute-Provence, France. The
library of spectra and corresponding data are only available in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5), or via http://cdsweb.u-strasbg.fr/Abstract.html
---------------------------------------------------------
Title: On-line determination of stellar atmospheric parameters T_eff,
log g, [Fe/H] from ELODIE echelle spectra. I. The method
Authors: Katz, D.; Soubiran, C.; Cayrel, R.; Adda, M.; Cautain, R.
1998A&A...338..151K Altcode: 1998astro.ph..6232K
We present a method estimating the atmospheric parameters
T<SUB>eff</SUB>, log g, [Fe/H] for stars observed, even at low signal
to noise ratio, with the echelle spectrograph ELODIE on the 193cm
telescope at Observatoire de Haute-Provence. The method relies on the
least-square comparison of the spectrum of a target star to a library
of 211 spectra of reference stars for which the atmospheric parameters
are well known and which were observed with the same instrument. In
order to obtain a meaningful comparison between target and reference
spectra, all features which are not intrinsic to the objects must be
removed. This treatment involves the correction of the blaze efficiency
for each order, cosmic rays hits and telluric line removal, convolution
of the spectra to a common spectral resolution, wavelength scale and
flux level adjustment. The library available at the present time covers
the effective temperature range [4000K, 6300K], the metallicity range
[-2.9, +0.35] and the gravities of both unevolved and evolved stars
existing at these temperatures and metallicities. Tests performed with
the actual library allow us to estimate the internal accuracy to be
86 K, 0.28 dex and 0.16 dex for T<SUB>eff</SUB>, log g, [Fe/H] for a
target star with S/N = 100 and 102 K, 0.29 dex and 0.17 dex at S/N =
10. This accuracy will improve in the future as the number of reference
stars in the library will increase. The software (named TGMET) has been
installed at Observatoire de Haute-Provence for the on-line analysis of
the high-resolution spectra of ELODIE, which was originally conceived
for accurate radial velocity measurements. based on observations made
on the 193cm telescope at Observatoire de Haute-Provence, France
---------------------------------------------------------
Title: VizieR Online Data Catalog: Library of ELODIE spectra (F5-K7
stars) (Soubiran+ 1998)
Authors: Soubiran, C.; Katz, D.; Cayrel, R.
1998yCat..41330221S Altcode:
A library of 211 echelle spectra taken with ELODIE at the Observatoire
de Haute-Provence is proposed. It provides a set of spectroscopic
standards covering the full range of gravities and metallicities
in the effective temperature interval [4000K, 6300K]. The spectra
are straightened, wavelength calibrated, cleaned of cosmic ray hits,
bad pixels and telluric lines. They cover the spectral range [440nm,
680nm] with an instrumental resolution of 42000. For each star, basic
data were compiled from the Hipparcos catalogue (Cat. <I/239>)
and the Hipparcos Input Catalogue (Cat. <I/196>) (Table 1). Radial
velocities with a precision better than 100m/s are given. Atmospheric
parameters Teff, logg, [Fe/H] from the literature are discussed. Because
of scattered determinations in the bibliography, even for the most
well-known stars, these parameters were adjusted by an iterative process
which takes account of common or different spectral features between
the standards, using our homogeneous set of spectra. Revised values of
effective temperature, gravity and metallicity are proposed in Table
1. They are still consistent with the literature, and also lead to the
self-consistency of the library, in the sense that similar spectra
have similar atmospheric parameters. This adjustment was performed
by using step by step a method based on the least square comparison
of carefully prepared spectra, which was originally developed for the
on-line estimation of the atmospheric parameters of faint field stars
(Katz et al., 1998A&A...338..151K. Paper I.). <P />(3 data files).
---------------------------------------------------------
Title: Lithium Abundances in Low-Z Stars
Authors: Cayrel, R.
1998SSRv...84..145C Altcode:
An historical view of the discovery and subsequent studies of lithium
in low-Z stars is presented. The determination of the lithium abundance
in extremely low-Z stars, found in the vast Beers, Preston and Shectman
survey, is reviewed. The problem of the exact connection between the
lithium abundance found in the photospheres of low-Z stars and the
true cosmological abundance of lithium is discussed, and identified
as the most important problem to be solved in the coming years.
---------------------------------------------------------
Title: Abundances of Metal-Poor Stars and the Formation of the Halo
Authors: Cayrel, R.
1998HiA....11...62C Altcode:
The origin of the elements in the early Galaxy has been thought to be
fairly well understood as primordial matter polluted by ejectae of type
II supernovae. Some recent observational results have led to reconsider
in more detail this statement. As a result, it is confirmed in some
respects, but curiously, when the same metallicity can be found both
in the halo and in the thick disk, the stars contaminated by SN Ia
ejecta are more the halo stars than the thick disk stars.
---------------------------------------------------------
Title: Lithium Abundances in Low-Z Stars
Authors: Cayrel, R.
1998pnge.conf..145C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Most Metal-Poor Stars
Authors: Cayrel, Roger
1998semi.conf..197C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Helium, [Fe/H] Abundances and the HR (log T<SUB>eff</SUB>,
M<SUB>bol</SUB>) Diagram with HIPPARCOS Data of the Four Nearest
Open Clusters: Hyades, Coma Berenices, The Pleiades and Praesepe
Authors: Cayrel de Strobel, G.; Cayrel, R.; Lebreton, Y.
1998HiA....11..565C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The HR Diagram for Late-Type Nearby Stars as a Function of
Helium and Metallicity
Authors: Lebreton, Y.; Perrin, M. -N.; Fernandes, J.; Cayrel, R.;
Cayrel de Strobel, G.; Baglin, A.
1997ESASP.402..379L Altcode: 1997hipp.conf..379L
Recent theoretical stellar models are used to discuss the helium
abundance of a number of low-mass stars for which the position in
the Hertzsprung-Russell diagram and the metallicity are known with
high accuracy. Hipparcos has provided very high quality parallaxes
of a sample of a hundred disk stars, of type F to K, located in the
solar neighbourhood. Among these stars we have carefully selected
those for which detailed spectroscopic analysis has provided effective
temperature and [Fe/H] ratio with a high accuracy. We have calculated
evolved stellar models and their associated isochrones in a large
range of mass, for several values of the metallicity and of the helium
abundance and we took into account an alpha-element enrichment in the
metal-deficient stars. The input physics is recent and appropriate to
the considered stellar mass range. We discuss the position in the H-R
diagram of those stars which can be considered as non-evolved. Once
the physics of the models has been fixed, this position only depends
on metallicity and helium abundance. We find that the thickness of
the observational main sequence is of about 0.25 magnitude, for stars
spanning a metallicity range from [Fe/H] = -1 to +0.2, while theoretical
stellar models predict a width of about 0.45 magnitude. The position in
the H-R diagram of stars of solar metallicity or close to it is well
accounted for by theoretical stellar models. Problems arise with the
moderately metal deficient stars which lie quite close to the stars
of solar metallicity and very far from the theoretical isochrones
corresponding to their expected chemical composition. To reconcile
theory and observations very low values of the helium abundance, well
below the primordial helium abundance, would be needed. We briefly
discuss the possible reasons of this discrepancy: improvements to
bring to the physics of the models, inaccuracies of observations.
---------------------------------------------------------
Title: The HR Diagram in the Plane log(T_(eff)), M_bol of Pop. II
Stars with HIPPARCOS Parallaxes
Authors: Cayrel, R.; Lebreton, Y.; Perrin, M. -N.; Turon, C.
1997ESASP.402..219C Altcode: 1997hipp.conf..219C
An HR diagram in the plane (log(T_(eff), M_bol) is presented for
population II subdwarfs and subgiants having Hipparcos parallaxes known
with an accuracy better than 15 per cent. The effective temperatures and
the apparent bolometric magnitudes have been taken from measurements
made by Alonso et al. (1996), by the IRFM method for the effective
temperatures, and direct integration of the fluxes for the bolometric
fluxes. This has allowed to bypass the use of bolometric corrections,
and the resulting errors. The resulting diagram is interpreted with
two sets of isochrones computed with OPAL opacities enhanced in
alpha-elements, updated equations of state, a helium abundance close
to the primordial value, and a mixing length to pressure scale height
ratio calibrated on the Sun. For the first time it has been possible
to check the validity of theoretical models for metal-poor stars
against accurate observations, and to derive the age of halo stars
independently of any globular cluster data.
---------------------------------------------------------
Title: The Bolometric Correction m_(bol) - HP
Authors: Cayrel, R.; Castelli, F.; Katz, D.; van't Veer, C.; Gomez,
A.; Perrin, M. -N.
1997ESASP.402..433C Altcode: 1997hipp.conf..433C
By the use of model atmospheres fluxes computed with Kurucz's ATLAS9
code, we have investigated the behaviour of the computed bolometric
correction of the Hipparcos Hp band, namely BCHp=m_bol-Hp, with
the basic physical parameters effective temperature, gravity and
metallicity. The theoretical relations of BCHp versus effective
temperature(T_(eff)) are compared to empirical ones.
---------------------------------------------------------
Title: a Kinematical and Chemical Probe of the Galaxy
Authors: Soubiran, C.; Cayrel, R.; Perrin, M. N.; Bienayme, O.; Friel,
E.; Coupry, M. F.
1997ASSL..212..219S Altcode: 1997wfs..conf..219S
No abstract at ADS
---------------------------------------------------------
Title: Helium, [Fe/H] Abundances and the HR (logTeff, Mbol) Diagram
with HIPPARCOS Data of the four Nearest Open Clusters: Ursa Major,
Hyades, Coma Berenices and the Pleiades
Authors: Cayrel de Strobel, G.; Cayrel, R.; Lebreton, Y.
1997IAUJD..14E..34C Altcode:
Here for the first time not only we discuss the metal abundance of
F,G, and K stars in the four nearest open clusters, but we give an
estimate of the value of their He abundance also. The study of the He
abundance is now possible thanks to Hipparcos which has permitted,
in improving the values of the individual distances of the cluster
stars, to derive the four observational main sequences in the HR
(logTeff,Mbol) diagram with god precision.The four main sequences have
been interpretd with theoretical internal structure models constituing
the ZAMSes. The position of these ZAMSes in the (logTeff,Mbol) diagram
depends upon two free parameters only: the He-abundance, Y, and the
metal abundance abundance, Z. In comparing the observational main
sequences with theoretical ZAMSes and having previously determined
the effective temperature and the metallicity of the consituing stars
with the help of high resolution, high S/N detailed analyses, it is
now possible to determine the only missing parameter of the clusters:
their He-abundance.
---------------------------------------------------------
Title: The Most Metal-Poor Stars
Authors: Cayrel, Roger
1997seim.proc..197C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analysis of two CH/CN-strong very metal-poor stars.
Authors: Barbuy, B.; Cayrel, R.; Spite, M.; Beers, T. C.; Spite, F.;
Nordstroem, B.; Nissen, P. E.
1997A&A...317L..63B Altcode:
Two very metal-deficient stars, BPS CS 22948-27 and BPS CS 29497-34,
recently identified in the HK objective-prism/interference-filter
survey of Beers and collaborators, which exhibit, at low resolution,
strong CH and CN bands and metallicities [Fe/H]~-3 , have been observed
at high spectral resolution and high S/N at the NTT at ESO with the
EMMI echelle spectrograph. A preliminary analysis of these spectra
shows that these objects are very unusual. The high-resolution work
confirms the very low metallicity of these stars and indicates: (i)
effective temperatures T_eff_~4000K and surface gravities logg~0.0
to 1.5; (ii) a very large overabundance of carbon and nitrogen, by
~2dex with respect to iron; (iii) a similar overabundance of a few
neutron-capture elements, in particular Ba, La and Nd, also by ~2dex;
(iv) a low isotopic ratio ^12^C/^13^C; (v) a variable radial velocity
for one of the stars (CS 22948-27). These findings suggest that the
two stars are extreme cases of CH stars. The spectra are considerably
richer in molecular bands than the spectrum of the remarkable star
CS-22892-52, identified in the same survey and studied by Sneden et
al.. The determination of the ratio of s-process to r-process elements
in these two stars must await observations in the blue spectral region.
---------------------------------------------------------
Title: On the use of CA I triplet lines as luminosity indicators.
Authors: Cayrel, R.; Faurobert-Scholl, M.; Feautrier, N.; Spielfieldel,
A.; Thevenin, F.
1996A&A...312..549C Altcode:
Many strong lines formed in stellar atmospheres are well known to
be dominated by pressure broadening, therefore their wings are a
precious help for determining the surface gravities of dwarf or
subgiant stars. In this paper, we explore the possibility for using
the wings of the Ca I triplet lines 6102, 6122, 6162A for which recent
theoretical computations of the damping are available. A NLTE code for
radiative transfer was used to check these new computations against
the integrated Solar Spectrum. We report here that (i) there is a
spectacular improvement in the fit of the computed profile with the
observed one when the new quantum mechanical computations are used
instead of the classical Unsoeld's expression of the Van der Waals
damping constant (ii) the departures from LTE in the computation of
the wings of these lines are negligible, and this justifies the use
of LTE computations for the determination of the surface gravities of
G type stars, by this method.
---------------------------------------------------------
Title: The first generations of stars
Authors: Cayrel, R.
1996A&ARv...7..217C Altcode:
Up to a decade ago, searches for population III stars (i.e. with
strictly the chemical composition left by the Big Bang) had led to
the results that (1) no such star had been found, (2) stars with
metallicities significantly below [Fe/H] = -2.5 were exceedingly
rare. Thanks to a major survey, undertaken by Beers, Preston and
Shectman 18 years ago, covering about 7500 square degrees in the
sky, and down to magnitude B =16.0, the situation has drastically
changed. The observational limit towards the lowest metallicities
is now about [Fe/H] = -4, i.e. 4 dex below the solar metallicity
Z<SUB>solar</SUB> = 0.02, (a level of pollution by supernova ejecta of
only a few ppm), and over 100 stars are known with metallicities [Fe/H]
in the range -4 to -3. The study of this sample, and of a few stars
found more serendipitously, has allowed a number of new conclusions: (i)
The cosmological element <SUP>7</SUP>Li stays constant (prolongation
of the Spite's plateau) down to the lowest metallicities, a great
observational gift to the hot Big Bang cosmology (ii) All heavier
elements show a roughly linear increase with the abundance of O (or
even Fe if the metallicity is below [Fe/H] = -1), including the other
light elements, Be and B. This last point has led to a reappraisal of
the current view that they were produced by spallation of interstellar
nuclei by galactic cosmic rays, because the rise of those elements
with metallicity should then have been more quadratic than linear. An
alternative new perspective is that these elements are produced by
spallation of the primary nuclei ejected by SNe ii against protons of
the interstellar medium. (iii) The ratio of the alpha elements (O, Si,
Mg,...) to iron also stays constant down to the lowest metallicities,
at about 3 times the solar value. (iv) Significant deviations to
a lockstep variation of the various elements within the iron-peak
start to appear below [Fe/H] = -2.5. The strongest are a decrease of
[Cr/Fe] and an increase of [Co/Fe] when [Fe/H] decreases from -2.5
to -4.0. These trends are not explained by the current status of
explosive nucleosynthesis. (v) A great scatter of the abundances of
the neutron capture elements relative to iron appears at very low
metallicities. Similar scatter is seen for [Al/Fe]. A remarkable star
with [Fe/H] = -3.1, CS 22892-052, has been found, with a superb spectrum
of the r-elements, involving over-abundances of those with respect
to iron by factors ranging between 10 and 50. (vi) The kinematics of
the very metal-poor stars is similar to that of other halo stars,
with a complete lack of systemic rotation in an inertial frame, if
not a small amount of counter-rotation in the Galaxy. Evidence exists
that the velocity ellipsoid is radially elongated for stars within
10 kpc from the galactic center, whereas it is more spherical or even
radially contracted at 20 kpc from the galactic center. (vii) The low
metallicity stars were likely formed at an early cosmological epoch
(z > 5 if H<SUB>0~</SUB> 65 km/s), before the Galaxy had developed
a disk. The new views concerning the sizes of the Lyα clouds open
the possibility that the low-metallicity Lyα systems are large halos
having the right metallicity for being protogalaxies, just forming early
stellar generations. (viii) One may wonder why, if more than 100 stars
are known with metallicities between [Fe/H] = -4 to -3 no pop. III has
been found, or even not one star near [Fe/H] = -5. Different kinds of
explanations have been proposed, with none conclusive at present. Either
we have already observed a pop. III star, but its pristine Big Bang
composition has been corrupted by a small amount of interstellar matter
accreted during its 10 Gyr of orbiting in an already-enriched gas,
or the collective process of star formation has polluted the medium
before it has produced the low-mass stars we can still observe now,
or, simpler, pop. III stars exist, but are sufficiently rare that we
have not yet observed a volume large enough to have found one.
---------------------------------------------------------
Title: HIPPARCOS et les sondages profonds.
Authors: Cayrel, R.
1996udh..conf..143C Altcode:
Les sondages profonds concernent des objets à des distances trop
élevées pour e^tre directement accessibles à HIPPARCOS. Cependant
HIPPARCOS permettra de calibrer les distances photométriques pout les
objets représentés dans un voisinage solaire étendu, disons jusqu'à
50 parsecs, et d'améliorer ainsi considérablement la détermination
des distances des étoiles rencontrées dans les sondages profonds,
pénétrant le disque épais in situ et le halo.
---------------------------------------------------------
Title: Contribution to the study of the visual binary ζ Herculis:
a detailed analysis of ζ Herculis A.
Authors: Chmielewski, Y.; Cayrel de Strobel, G.; Cayrel, R.; Lebreton,
Y.; Spite, M.
1995A&A...299..809C Altcode:
This research is a contribution to the study of the physical structure
and the state of evolution of the binary system ζ Herculis ( ζ
Her). This double star has a period of 34.49 years, which is half as
short as that of the system of α Centauri. In order to determine with
very great precision the fundamental parameters of the atmosphere of
the primary component ζ Her A, a new detailed spectroscopic analysis,
based on high resolution and high signal/noise spectra, has been
carried out for this star. The duplicity of the observed star has
been taken into account in as detailed a way as possible. The present
analysis attributes to the star a higher effective temperature than
that found in previous detailed analyses, and a solar metallicity. The
new results are used to rediscuss the age and the masses of the system,
with the help of internal structure models.
---------------------------------------------------------
Title: Quelques remarques sur Elodie.
Authors: Cayrel, R.
1995LOHP...14....8C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Distribution spatiale, cinématique et métallicité des
populations stellaires de la Galaxie.
Authors: Soubiran, C.; Cayrel, R.
1995LOHP...14....2S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar population study in the galactic direction (l=~0deg,
b=~45deg).
Authors: Perrin, M. -N.; Friel, E. D.; Bienayme, O.; Cayrel, R.;
Barbuy, B.; Boulon, J.
1995A&A...298..107P Altcode:
Quantitative medium resolution spectroscopic observations have been
performed on a sample of stars in a field of 9.6 square degrees in the
galactic direction (l=~0deg, b=~45deg), for which proper motions and
photographic photometry have been recently obtained. Radial velocities,
effective temperatures, surface gravities and metallicities have been
derived, leading to a complete set of kinematic and astrophysical
parameters for 28 stars, with apparent V magnitudes near 14.25 and
B-V in the range 0.93-1.03, to allow a safe discrimination between
dwarfs and giants from the Mg I green triplet. The main finding of
these observations is the very low proportion of population II giants
in this direction, about 5 to 10 times less than the predictions of
current galactic models. A discussion of this result in connection
with similar works available in the literature is presented.
---------------------------------------------------------
Title: Lithium in metal deficient binaries.
Authors: Spite, M.; Fleming, T.; Cayrel, R.; Pasquini, L.; Spite, F.
1995MmSAI..66..337S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A New Sample of Thick Disk and Halo Stars
Authors: Soubiran, C.; Perrin, M. N.; Cayrel, R.; Chereul, E.
1995IAUS..164..386S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nucleosynthesis in the First Galactic Stars
Authors: Andersen, J.; Nordström, B.; Beers, T. C.; Cayrel, R.;
Spite, F.; Spite, M.; Nissen, P. E.; Barbuy, B.
1995svlt.conf...75A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The effective temperature determination
Authors: Cayrel, R.
1995HiA....10..395C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Detailed Analysis of Stars in the Galactic Bulge with the VLT
Authors: Cayrel, R.; Nissen, P. E.
1995svlt.conf..171C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A case study of the quadruple system ξ Ursae Majoris: its
activity and lithium depletion.
Authors: Cayrel de Strobel, G.; Cayrel, R.; Friel, E.; Zahn, J. -P.;
Bentolila, C.
1994A&A...291..505C Altcode:
The quadruple system ξ UMa is an interesting test case for the
numerous problems encountered when studying the evolutionary status,
chromospheric activity and lithium depletion of solar-type stars. We
have carried out a detailed analysis of the major components A and B
of ξ UMa from high resolution, high signal-to-noise CFHT spectra. We
determine accurate temperatures for each of the principal components,
neither disturbed by their invisible, much less massive companion,
and find that the two differ in temperature by 300 K, one being
somewhat hotter than the Sun, the other cooler. The metal abundances
derived from iron and a few other elements are identical for the two
stars, and the system is moderately metal-deficient, by a factor of
two with respect to the Sun. We concur with previous studies that
lithium is fairly abundant in A whereas it is below detection in B:
we measured log N(Li)=2.33 in A and place a more stringent upper
limit log N(Li)<0.8 for B. We discuss this unusual combination of
lithium abundances and the position of the stars in the HR diagram
in the light of the complex binary nature of the two components, and
of current theories of stellar evolution and of lithium depletion. We
suggest that B has kept a high level of activity because its rotation
is tidally locked with the orbital motion, and that it has therefore
lost about ten times more matter than a single star of the same mass,
which explains its strong lithium depletion.
---------------------------------------------------------
Title: Incorporating the atmosphere in stellar structure models:
the solar case
Authors: Morel, P.; van't Veer, C.; Provost, J.; Berthomieu, G.;
Castelli, F.; Cayrel, R.; Goupil, M. J.; Lebreton, Y.
1994A&A...286...91M Altcode:
The diffusion limit of the transfer equation used in the calculations
of stellar interior models is only valid at large Rosseland optical
depth. From atmosphere models obtained with ATLAS 9 (Kurucz), it is
shown here that the diffusion limit of the transfer equation becomes
valid only at Rosseland optical depths τ_R_ >~ 10 that is at a
location well inside the Sun's convective zone. For the calculations
of stellar evolution, the atmosphere is built from T(τ) laws that are
derived either from theory or from full atmosphere computations; such a
T(τ) law depends upon effective temperature and gravity, therefore on
the evolutionary state of the model. Hence, in general, when following
the evolution of a star, various T(τ) laws need to be introduced. In
the case of the Sun, however, we show here that the atmosphere can be
restored with the use of only one T(τ) law. Particular efforts have
been made to include physics as consistent as possible in both the
model atmosphere from which one derives T(τ) laws and the internal
structure calculations which use them; as a result, we can rebuild
the atmosphere in stellar models with an accuracy of about +/- 0.5%
for the sound speed and the pressure. Remaining discrepancies are of
small effect on solar calibrated models. For the solar oscillations,
such small discrepancies generate frequency differences no larger than
2μHz for low degrees modes to about 10μHz for modes of large degrees
around 400.
---------------------------------------------------------
Title: Stellar atmospheric parameters for F-G-K stars from
low-resolution data: method and application to a sample of proper
motion stars
Authors: Cuisinier, F.; Buser, R.; Acker, A.; Cayrel, R.; Jasniewicz,
G.; Fresneau, A.
1994A&A...285..943C Altcode:
We develop a general method which allows us to derive fundamental
stellar parameters (T_eff_, [M/H]) of F, G, and K dwarfs from
low-resolution spectra covering the wavelength range 370-780 nm and
using three different grids of model atmosphere flux distributions. Two
extreme cases are explored: (1) broad-band synthetic color indices,
which exploit a large fraction of the available wavelength range, but at
highly degraded spectral resolution, and (2) synthetic spectrum fitting,
which takes full advantage of the available resolution in the data,
but which is limited to a relatively narrow wavelength interval. We
show that, while in either case the initial model-derived parameter
values differ systematically from published results obtained via
high-resolution spectroscopy these spectroscopic data can be used to
properly calibrate the models. Thus, as an application, we were able to
derive abundances for 40 proper motion stars, selected from Fresneau
(1990). Within the systematic biases that could exist, the derived
metallicity distribution is bimodal, one mode centered on [M/H] =
0.0dex (thin disk) and the other on [M/H] = -0.6dex (thick disk),
biased towards the thick disk. Furthermore, three low metallicity
stars and a super metal-rich one have been discovered.
---------------------------------------------------------
Title: Restoration of the atmosphere in solar models
Authors: Morel, P.; van't Veer, C.; Berthomieu, G.; Cayrel, R.;
Castelli, F.; Goupil, M. J.; Lebreton, Y.; Provost, J.
1993ASPC...40...57M Altcode: 1993IAUCo.137...57M; 1993ist..proc...57M
No abstract at ADS
---------------------------------------------------------
Title: The first stars in the Galaxy.
Authors: Cayrel, R.
1993oee..conf..465C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Early populations of stars
Authors: Cayrel, R.
1993flus.conf..171C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lithium in Population II Stars
Authors: Spite, F.; Spite, M.; Cayrel, R.; Huille, S.
1992IAUS..149..490S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Parameters in the Basel Field SA 141
Authors: Perrin, M. -N.; Cayrel, R.; Barbuy, B.; Buser, R.
1992IAUS..149Q.513P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: From spectrophotometry to fundamental parameters, effective
temperature, gravity and metallicity.
Authors: Cayrel, R.
1992ctap.conf..655C Altcode:
The practical problem of deriving the fundamental parameters,
effective temperature, gravity and metallicity from spectrophotometric
observations is considered. A methodology is established, and
experiments with synthetic spectra are performed. The respective merits
of spectroscopy, spectrophotometry and photometry are compared, with
and without interstellar reddening. Examples are taken in the field
of G stars, for which a full span of metallicity exists in the Galaxy.
---------------------------------------------------------
Title: Trouble in the Magellanic Clouds - First results from the
Key Programme on coordinated investigations of selected regions in
the Magellanic Clouds
Authors: de Boer, K. S.; Spite, F.; Francois, P.; Cayrel, R.; Spite,
M.; Baschek, B.; Koeppen, J.; Wolf, B.; Stahl, O.; Juettner, A.;
Seggeweiss, W.; Bomans, D. J.; Grebel, E. K.; Geyer, E. H.; Richtler,
T.; Vallenari, A.; Koornneef, J.; Israel, F. P.; Molaro, P.; Monai,
S.; Vladilo, G.; D'Odorico, S.; Leisy, R.; Dennefeld, M.; Ferlet,
R.; Vidal-Madjar, A.; Stasinska, G.; Azzopardi, M.; Meyssonnier, N.;
Muratorio, G.; Rebeirot, E.; Lequeux, J.
1991Msngr..66...14D Altcode: 1991Mgr....66...14D
Results of coordinated subprojects on selected regions in Magellanic
Clouds performed in the framework of the Key Program are briefly
reviewed. The subprojects include spectroscopic survey with EFOSC
(Marseille, Paris, Uppsala), CCD photometry of small field within
the regions (Bonn), IRAC photometry of small fields within the
regions (Baltimore, Leiden), stellar spectroscopy for studying
element abundances in the hot and cool stars (Heidelberg and Meudon,
respectively), the interstellar absorption lines (Trieste, Paris),
and the spectra of emission nebulae (Paris).
---------------------------------------------------------
Title: A grid of synthetic spectra for the determination of
effective temperature, gravity and metallicity of F,G and K
stars. II. Application to 41 stellar spectra taken in the Basel
field of SA 141.
Authors: Cayrel, R.; Perrin, M. -N.; Buser, R.; Barbuy, B.; Coupry,
M. -F.
1991A&A...247..122C Altcode:
A grid of synthetic spectra is used to derive the atmospheric parameters
temperature T<SUB>eff</SUB>, gravity log g and metallicity [M/H],
besides the radial velocity, from low-resolution spectra of 41 stars
in the Basel field SA 141 in the direction of the south galactic pole
(l = 245°.0, b = -85°.8). <P />The metallicity distribution as a
function of distance from the galactic plane is obtained and discussed.
---------------------------------------------------------
Title: A grid of synthetic spectra for the determination of effective
temperature, gravity and metallicity of F,G and K stars.I. Description
of the method.
Authors: Cayrel, R.; Perrin, M. -N.; Barbuy, B.; Buser, R.
1991A&A...247..108C Altcode:
The computation of a grid of synthetic spectra in the wavelength
region λλ4780-5300 Å is described. <P />With the use of this grid,
a method is developed for deriving the stellar parameters temperature,
gravity and metallicity from a low-resolution spectrum. <P />The use
of the grid is tested for 20 reference stars, in two ways. The stellar
parameters for these 20 stars are derived (1) directly from the grid,
(2) using the synthetic grid in conjunction with the observed spectrum
of another reference star. <P />A best fit is obtained by the second
method, i.e., by using the grid in combination with a number of standard
stars, in this way establishing corrections to the parameters obtained
exclusively from the grid.
---------------------------------------------------------
Title: The earliest observable stellar generation.
Authors: Cayrel, R.
1991pgrp.work..155C Altcode:
The observation of the oldest stars gives evidence on events which took
place at epochs as early as z ≅ 5 to 10. This evidence is summarized
and possible interpretations are discussed. One of them is that the
old population II is of extragalactic origin and was accreted by the
Galaxy when it became an isolated system.
---------------------------------------------------------
Title: The Fm-Am Stars: Observed Anomalies
Authors: Cayrel, R.; Burkhart, C.; van't Veer, C.
1991IAUS..145...99C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Derivation of stellar parameters using a grid of synthetic
spectra.
Authors: Barbuy, B.; Perrin, M. -N.; Cayrel, R.
1990RMxAA..21..406B Altcode:
A grid of synthetic spectra is built, for a set of stellar parameters,
in the spectral region λλ4780 - 5300 Å. Spectrophotometric indices
in this region are chosen and measured in the synthetic spectra;
these theoretical indices are directly compared to those measured
in the observed spectra, in order to obtain the stellar parameters
temperature, gravity and metallicity.
---------------------------------------------------------
Title: The construction of the Canada-France-Hawaii Telescope
Authors: Cayrel, R.
1990JRASC..84....3C Altcode:
The history of the construction of the Canada-France-Hawaii Telescope
(CFHT) between 1974 and 1979 is examined. Consideration is given to
the beginnings of the CFHT program, site selection, the administrative
aspects of the program, and the roles of the participating countries in
the development and construction of the telescope. The configuration of
the CFHT is illustrated and the process of reassembling the telescope
at Mauna Kea, Hawaii is described. The development of the telescope's
mirror, control system, dome, and mechanical structure is reviewed.
---------------------------------------------------------
Title: A review of IMF theories
Authors: Cayrel, R.
1990ASSL..162..343C Altcode: 1990ppfs.work..343C
An overview is presented of theories of the initial mass function (IMF),
starting from those essentially based on stochastic arguments to those
involving more physics. Consideration is given to the scheme of Auluck
and Kothari (1960, 1965), hierarchical theories, the predicted IMF,
coalescence theories, DiFazio's theory (1986), fragmentation from
sheets and filaments (bimodal star formation), and the criteria for
determining stellar masses. The following concepts are proposed as being
the most likely to survive: the general statistical arguments supporting
log-normal laws, or power laws; the opacity-limited fragmentation
concept; and the concept that the IMF is not a pure product of cloud
fragmentation processes but also depends on internal properties of
the object itself.
---------------------------------------------------------
Title: A thorough spectroscopic study of the very nearby triple
system : 36 Ophiuchi.
Authors: Cayrel de Strobel, G.; Perrin, M. N.; Cayrel, R.; Lebreton, Y.
1989A&A...225..369C Altcode:
The three K-star components of the 36 Ophiuchi system have
been analyzed in detail on high resolution, high S/N ESO Reticon
spectra. The atmospheric parameters of the stars (effective temperature,
spectroscopic gravity, microturbulence, metal abundances, and degree
of chromospheric activity) have been determined. The position of
the observational ZAMS built up by the three stars has been compared
with theoretical ZAMS. The agreement between the iron abundances is
excellent for the three components. A discussion of the masses of the
components is also given.
---------------------------------------------------------
Title: Strong lithium in the very nearby K-dwarf HD 17925.
Authors: Cayrel de Strobel, G.; Cayrel, R.
1989A&A...218L...9C Altcode:
On a Reticon spectrum centered at 6714 A, taken with the 1.4 m coude
auxiliary telescope and with the coude echelle spectrograph of ESO,
it was found that the cool K2V star, HD 17925 has a very strong lithium
line. This strong lithium line in such a cool star (5090 K) indicates
that HD 17925 must be very yound. Even in the comparatively young
Hyades, lithium is already totally depleted in stars with effective
temperatures around 5000 K. It is proposed that the star comes from
the Scorpio-Centaurus complex where it was formed only a few million
years ago.
---------------------------------------------------------
Title: La vie et l'œuvre de Bengt Strömgren (1908 - 4 July 1987)
Authors: Cayrel, R.
1989CRASG...6..609C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Learning about young globular clusters.
Authors: Cayrel, R.; Tarrab, I.; Richtler, T.
1988Msngr..54...29C Altcode: 1988Mgr....54...29C
Even after many decades of intensive investigation globular clusters
still fascinate astronomers. Galactic globular clusters are "fossils"
of the epoch of galaxy formation and sampies of a very early, but
still reachable stellar generation. The situation is different in
the Magellanic Clouds where globular-cluster- like objects with a
wide variety of ages can be found. We see globular clusters which,
judged by their stellar content, cannot be much older than 107
yr. Their integrated light is dominated by a slightly evolved upper
main sequence. Therefore, they have often been referred to as "blue
globular clusters". the question why such clusters are found in the
Magellanic Clouds (and perhaps in some other galaxies like M33 and
NGC 2403) and not in the Milky Way is certainly of significance for
the general understanding of galaxy evolution (see lAU Symp. 126 for
more information).
---------------------------------------------------------
Title: Observations on cosmic abundances of <SUP>4</SUP>He
and <SUP>7</SUP>Li, comparison with primordial nucleosynthesis
predictions.
Authors: Cayrel, Roger
1988ESASP.283...69C Altcode: 1988ssfp.rept...69C; 1988ssfp.conf...69C
Observations of He-4 in metal poor galaxies and of Li-7 in galactic
subdwarfs were used to derive constraints on the initial abundances of
the elements. An initial abundance of He-4 of 0.23 to 0.24 by mass,
and an initial abundance of 10 to the minus 10th power by number of
atoms for Li-7, with respect to hydrogen are obtained. These abundances
are compatible with a hot big bang having a nucleons/photons ratio
of about 2 to 5 times 10 to the minus 10th power, assuming 3 families
of particles.
---------------------------------------------------------
Title: Globular clusters and primordial composition.
Authors: Cayrel, Roger
1988IAUS..126..431C Altcode:
The primordial chemical composition and the abundance of the primordial
elements in globular clusters, specifically in population II, are
reviewed. Timetables of the big bang and of important events during
the nucleosynthesis period are presented, and the predicted primordial
abundances in the big bang are examined. The abundances of He-3 and
He-4, D, and Li; the metallicity of clusters; and the abundance ratios
in globular-cluster stars are discussed.
---------------------------------------------------------
Title: Data Analysis
Authors: Cayrel, R.
1988IAUS..132..345C Altcode:
The relationship between the r.m.s. photometric accuracy on the data
points of a stellar spectrum and the final accuracy on abundances and
physical parameters derived from these data is discussed.
---------------------------------------------------------
Title: The Iron Abundances, [Fe/H] in the Four Nearest Open Clusters :
Pleiades, Ursa Major Stream, Coma Berenices and Hyades
Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B.
1988IAUS..132..449C Altcode:
Iron abundances, [Fe/H] have been studied in G and K dwarfs of the
four nearest clusters. With the exception of the Pleiades stars which
are all fainter than the 10th magnitude, the observational material
consists of high resolution, high S/N spectra. The Hyades is the only
cluster with a significative overmetallicity with respect to the sun.
---------------------------------------------------------
Title: A new interpretation of the metallicity histogram of globular
clusters.
Authors: Cayrel, R.
1987JApA....8..153C Altcode:
A new interpretation is given to the low metallicity peak of the
bimodal metallicity histogram of galactic globular clusters. It is
proposed that these globular clusters are primordial, i.e., formed
out of big-bang matter. Their nonvanishing metallicity is attributed
to pollution by supermassive stars like R 136a. The first stellar
generation is formed out of the 'dirty' primordial matter.
---------------------------------------------------------
Title: First results of a spectroscopic search for gravitational
mirages.
Authors: Reboul, H.; Vanderriest, C.; Fringant, A. M.; Cayrel, R.
1987A&A...177..337R Altcode:
The first results of a systematic search for gravitational mirages
among close pairs of blue objects are presented and some representative
cases are discussed. The spectroscopic study of 15 candidates did not
yield new gravitational mirages but revealed about 40 percent of the
extragalactic physical systems including a large proportion of quasars,
active galaxies, and H II regions.
---------------------------------------------------------
Title: Star formation from primordial matter.
Authors: Cayrel, R.
1987SRToh...7..207C Altcode:
The gravitational collapse of a primordial cloud does differ
of the gravitational collapse of normal interstellar clouds,
mostly because radiative cooling processes and opacity are very
different. Fragmentation is of course affected by this. In the seventies
it was believed that fragmentation could be inhibited below one or
several solar masses in a zero-metal environment, leading to a first
stellar generation with no low-mass stars. However the problem appears
more complex now, and recent work on the subject, both theoretical
and observational, are surveyed.
---------------------------------------------------------
Title: Projets scientifiques pour un grand télescope.
Authors: Cayrel, R.
1987JAF....29...27C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The early chemical evolution of the halo and population III.
Authors: Cayrel, R.
1987ESOC...27..627C Altcode: 1987sedo.work..627C
It is noted that there is no clear bottom of metallicity in the
Galaxy. Even though a number of stars with metallicities below 0.001
Z-solar have been found, no star with zero metallicity has been
found. No unbiased metallicity histogram covering the range 0-0.1
Z-solar exists for the field halo population. It is suggested that the
scarcity of very metal-poor stars may be the result of self-pollution
in formation regions of stars orginating from the gravitational collapse
of primordial clouds.
---------------------------------------------------------
Title: Star formation from primordial matter
Authors: Cayrel, Roger
1987cega.proc...41C Altcode:
The topic of the star formation from primordial matter is examined
theoretically. Consideration is given to the questions of the
fragmentation limit in the primordial clouds, the mass-function of
fragments as a function of metallicity, the internal structure and
evolution of zero-metal stars, and the nucleosynthesis in the primordial
galaxy. The conclusions drawn from the theoretical considerations
suggest that the formatiom of stars from primordial matter must have
occurred, although no direct observational evidence has been jet found.
---------------------------------------------------------
Title: High resolution analysis of a star in the young SMC globular
cluster NGC 330.
Authors: Spite, M.; Cayrel, R.; François, P.; Richtler, T.; Spite, F.
1986A&A...168..197S Altcode:
The analysis of CASPEC spectra of the supergiant star A7 in the
young cluster NGC 330 (Small Magellanic Cloud) shows that the star
has a metellacity much smaller than the metallicity of the few field
supergiants of the SMC which have been analyzed. The metallicity of
the star is similar to that found in typical globular clusters of
the Galaxy, but does not deviate significantly from that of some H II
regions of the SMC. The distribution of the individual abundances of
the elements is definitely nonsolar, and is similar to the distribution
found in the typical globular clusters of the Galaxy. The abundances
of heavy elements (rare earths) and in particular of Europium, is
enhanced relative to the typical globular clusters of the Galaxy;
such anomaly is known in two halo field giants of the Galaxy, HD
115444 and DH 110184. The resonance line of lithium is observable,
and hence the star suffered only a small mass loss.
---------------------------------------------------------
Title: And if population III were population II?
Authors: Cayrel, R.
1986A&A...168...81C Altcode:
Based on the assumption that the first stellar generation was formed
out of massive primordial clouds, it is shown that the mean metallicity
of the low-mass stars of the first stellar generation is expected to
have a value similar to that of population II. Population II stars are
interpreted as former members of large associations of which globular
clusters are also remnants. The proposed scenario is consistent with the
lack of success of finding metal-free low mass stars, the invariance
of the metallicity histogram of the spherically distributed globular
clusters with galactocentric distance, the paucity of G dwarfs with
intermediate metallicity, and the O/Fe ratio difference in population
II and in the disk population.
---------------------------------------------------------
Title: The first stars.
Authors: Barbuy, B.; Cayrel, R.; Silk, J.
1986Rech...17.1060B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Steps towards the abundance scale. I. The abundance of heavy
elements in the Hyades cluster.
Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B.
1985A&A...146..249C Altcode:
An analysis is conducted of high S/N ratio coude spectra for 12
Hyades dwarfs, together with solar spectra for comparison, in order
to obtain accurate abundances for iron and other metals in the
Hyades. Temperatures relative to the sun are derived from H-alpha
wing profiles or broadband colors, and cluster stars are selected to
bracket the solar temperature. Equivalent widths of metal lines are
obtained by means of a profile fitting technique that accounts for
blends, and many of the measured lines are noted to be sufficiently
weak for uncertainties in microturbulence to be insignificant. The
resulting iron abundances are anomalously low for two Hyades dwarfs,
evidently due to high levels of chromospheric activity. Abundances
are also obtained for 10 other elements.
---------------------------------------------------------
Title: The lithium abundance of Hyades main-sequence stars.
Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B.; Dappen, W.
1984ApJ...283..205C Altcode:
From high-quality Reticon spectra of Hyades G and K dwarfs, their
lithium abundance is found to decline much more rapidly with decreasing
temperature than heretofore realized. Previous observations of the 6707
Li I doublet for the cooler dwarfs have probably been contaminated by
blends. However, the new lithium-temperature relation still does not
agree with simple models of lithium burning in the convective zone,
either with or without overshooting. Models have therefore to include
other mechanisms for lithium depletion.
---------------------------------------------------------
Title: Spectroscopic evidence for starspots in the G dwarf HD1835.
Authors: Campbell, B.; Cayrel, R.
1984ApJ...283L..17C Altcode:
High signal-to-noise ratio spectra of HD 1835 (G2 V) reveal very weak
lines of titanium oxide and calcium hydride. The authors show that
these are unlikely to come from an M dwarf companion. The molecular
lines probably originate in starspot umbrae, which cover about 3%
of the stellar surface.
---------------------------------------------------------
Title: A Random Walk Approach to the Problem of Turbulent Diffusion
and Lithium Destruction in Main-Sequence Stars
Authors: Cayrel, R.
1984IAUS..105..533C Altcode:
The author describes a way of computing the evolution of the lithium
content in the convective zone of a main sequence star, using a random
walk model for the mixing instead of the differential equation for
diffusion. The advantage of this approach is that the finite scale
of turbulent eddies can be taken into account. The burning rate of
lithium increases so fast with temperature that it cannot be taken for
granted that the free path of turbulent motions is small compared to
the scale-height of the burning rate.
---------------------------------------------------------
Title: An Observational Test on Stellar Interior Mixing - the Lithium
Depletion in Twelve Hyades Dwarfs
Authors: Cayrel, R.; Cayrel, G.; Campbell, B.; Dappen, W.
1984IAUS..105..537C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Knowledge acquired during the site testing for the
Canada-France-Hawaii Telescope.
Authors: Cayrel, R.
1984ESOC...18...45C Altcode: 1984stfl.work...45C
The present discussion is mainly concerned with a wind-tunnel
experiment which was conducted in connection with the task to select
one out of three possible places on the summit of Mauna Kea for the
'Canada-France-Hawaii Telescope'. The considered 3.5-m telescope
involved originally a purely French project, and, in a testing campaign,
only French sites were initially considered. Details regarding this
campaign are discussed, taking into account standard meteorological
observations, seeing measurements, and photometric measurements. It was
found, however, that the contemplated French sites could not provide
the outstanding observational possibilities existing in certain foreign
locations. After an extension of the search to prospective sites outside
of France, it was eventually decided to locate the telescope on Mauna
Kea in Hawaii. For the selection of a specific site, wind and turbulence
conditions had to be considered. The informnation needed was obtained in
tests in which a mock-up of the summit area was placed in a wind tunnel.
---------------------------------------------------------
Title: Steps towards the abundance scale I - the nearest open
clusters.
Authors: Cayrel, R.; Cayrel, G.; Campbell, B.
1983PASP...95S.587C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The galactic globular cluster system : helium content versus
metallicity.
Authors: Caputo, F.; Cayrel, R.; Cayrel de Strobel, G.
1983A&A...123..135C Altcode:
Theoretical constraints have been derived from recent stellar model
computations and these have been compared with some observational
parameters of galactic globular clusters. The objective was to obtain
information on the helium versus metallicity relationship for these
very old systems. The first result is that the disagreement between
the Y-[Fe/H] relations derived by different authors with different
methods can be resolved when the "canonical" frame is abandoned and
the CNO content as well as the He-core masses is allowed to vary with
[Fe/H]. Under these hypotheses the authors derive a unique Y-[Fe/H]
relation whose actual slope depends on the value of the coefficient a =
[CNO/Fe]/[Fe/H]. The implication of varying a is analyzed, particulary
as concerns the ratio ΔY/ΔZ. It is found that acceptable values of
the ratio ΔY/ΔZ may be attained when a = -0.5 to -0.6.
---------------------------------------------------------
Title: Evidence of high chromospheric activity in Hyades dwarfs from
spectroscopic observations.
Authors: Cayrel, R.; de Strobel, G. Cayrel; Campbell, B.; Mein, N.;
Mein, P.; Dumont, S.
1983A&A...123...89C Altcode:
The Hα Balmer line and the infrared Ca II triplet have been observed
in two solar type dwarfs of the Hyades at the Coudé Spectrograph
of the Canada-France-Hawaii Telescope. Noticeable differences appear
in the cores of the lines between the stellar spectra and the solar
spectrum (moonlight). These differences are ascribed to a more active
chromosphere in the relatively young Hyades stars. Non-LTE computations
show that the average disk of one of the Hyades dwarf is similar to
a very bright element of the solar chromospheric network.
---------------------------------------------------------
Title: Book-Review - High Spectral Resolution in Astrophysics
Authors: Cayrel, R.; Felenbok, P.; Notni, P.
1983AN....304..196C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Search for population II giants up to 50 kiloparsecs from
the sun.
Authors: Cayrel, R.; Boulon, J.
1983MmSAI..54...95C Altcode:
The results of an effort to segregate giants from dwarf stars cataloged
in the RGU photometric survey performed by Becker (1965) are reported. A
narrow-band filter centered on the MgI green triplet and the MgH green
that yields a magnitude depressgd for dwarfs by 0.2 to 0.3 mag with
respect to the giant stars were selected. The metal deficiency effect
was computed within a factor of 100 for the equivalent width of the
green line, with the finding that the metal deficiency decreases the
equivalent width of the triplet by a factor of two. Therefore, giants
within 100 kpc of the sun can be studied, and thereby the asymptotic
density decrease of the galactic halo. A larger data base on the field
halo giants can eventually permit derivation of radial velocities and
improved estimations of the mass of the Galaxy.
---------------------------------------------------------
Title: Le télescope Canada-France-Hawaii.
Authors: Cayrel, R.
1982LAstr..96..227C Altcode:
The features, performance, and discoveries of the Canada-France-Hawaii
3.6m telescope located on Mauna Kea are described. The choice of design
around 4 m was constrained by financial considerations, which are
asserted to increase significantly in building larger instruments. The
fused silicon primary lens resists thermal deformation and is capable of
concentrating 50 percent of the received luminescence into a diameter
of less than 0.2 arcsec. The telescope moves on a horseshoe track
10 m in diameter and has an axis of declination starting from 1/3 of
the cradle. Computer controls automatically align the instrument and
compensate for thermal changes in the structure. The objective also
includes an f/8 secondary lens and an f/35 oscillating Cassegrain lens
for IR viewing. Control of the microclimate which forms in the cupola
is discussed.
---------------------------------------------------------
Title: Book-Review - High Spectral Resolution in Astrophysics -
Applications to the Spatial Telescope
Authors: Cayrel, R.; Felenbok, P.; Griffin, R. F.
1982Obs...102..155C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Haute resolution spectrale en astrophysique: applications au
Telescope Spatial. Deuxième Colloque National du Conseil Français
du Telescope Spatial, Orsay, March 10 - 12 1981.
Authors: Cayrel, R.; Felenbok, P.
1982hrse.book.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Steps towards the abundance scale. I. The abundance of iron
in the Hyades.
Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B.
1981BAAS...13..926C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Les problèmes de l'Astrophysique dont l'étude nécessite
une haute résolution spectrale
Authors: Cayrel, R.
1981hrse.conf....7C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Haute resolution spectrale en astrophysique applications au
telescope spatial
Authors: Cayrel, Roger; Felenbok, Paul
1981hrse.conf.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Etoiles de la branche horizontale.
Authors: Cayrel, R.
1981ebds.conf...24C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Canada-France Telescope
Authors: Cayrel, R.
1980Msngr..21....1C Altcode:
The 3.6 m telescope of the Canada-France-Hawaii Corporation on the
summit of Mauna Kea, on one of the Hawaiian islands, was put into
operation last March. This nice instrument, located on what seems to be
one of the best possible sites in the world, is presented to the readers
of the Messenger by Dr. Roger Cayrel, director of the Corporation.
---------------------------------------------------------
Title: Small-Scale Versus Large-Scale Motions in the Solar Atmosphere
Derived from a Non-Lte Calculation of Multiplet 38 OF Tii
Authors: Cayrel, R.; Dumont, S.; Martin, P.
1980LNP...114..298C Altcode: 1980IAUCo..51..298C; 1980sttu.coll..298C
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Bibliographical Star Index
Authors: Cayrel, R.; Jung, J.; Kirchner, S.; Lahmek, R.; Ochsenbein,
F.; Spite, F.; Valbousquet, A.
1980AN....301...99C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Identification and Protection of Existing and Potential
Observatory Sites
Authors: Cayrel, R.
1979IAUTA..17a.215C Altcode: 1979IAUT...17..215C
No abstract at ADS
---------------------------------------------------------
Title: Fine structure of the H-R diagram for 138 stars in the solar
neighbourhood.
Authors: Perrin, M. -N.; Hejlesen, P. M.; Cayrel de Strobel, G.;
Cayrel, R.
1977A&A....54..779P Altcode:
The evolution of a large number of stars in the solar neighborhood
was studied on the basis of H-R diagrams converted to log T(eff),
M(bol). Effective temperatures were based on reliable model-atmosphere
computations, and reasonably accurate absolute bolometric magnitudes
were obtained from absolute magnitudes of stars having well determined
parallaxes and requiring small bolometric corrections. A special
metal index was also evaluated for each star, in order to account for
variation of metal content from star to star. The observational log
T(eff), M(bol) diagrams are discussed in relation to the theoretical
evolutionary and isochrone grids of Hejlesen (1975). The masses of
the stars in the sample are estimated, and the ages of evolved stars
are also estimated. A metal content versus age relation for disk stars
is given.
---------------------------------------------------------
Title: Split of the Fe curve of growth as a function of atmospheric
pressure.
Authors: Cayrel, G.; Cayrel, R.; Foy, R.
1977A&A....54..797C Altcode:
The intrinsic dispersion of the iron curve of growth is discussed for
a subdwarf (Groombridge 1830), a dwarf (the sun), and a G 9 III giant
(Epsilon Virginis). It is shown that this dispersion, which results
in a splitting of the curve of growth, is due to a large scatter
in the individual collisional damping constants of the lines. This
scatter is largely greater than that predicted by the Van der Waals
formula. The intrinsic dispersion of the curve of growth becomes larger
with increasing atmospheric density of the star, and the point at which
the intrinsic dispersion begins shifts for a dense subdwarf from the
first turnoff up to the end of the plateau for a bright giant. If one
does not take into account this phenomenon, systematic errors in the
abundance determination occur, chiefly if no or only a few weak lines
have been measured in a star. These errors may be as large as 0.30
dex and can alter the gravity determination.
---------------------------------------------------------
Title: Stellar atmospheres as indicator and factor of stellar
evolution. Joint discussion at the XVIth General Assembly of the
I.A.U., Grenoble, 1976.
Authors: Cayrel, R.; Pagel, B. E. J.
1977HiA.....4B..99C Altcode: 1977HiA.....4...99C
No abstract at ADS
---------------------------------------------------------
Title: Stellar atmospheres as indicator and factor of stellar
evolution
Authors: Cayrel, R.; Pagel, B. E. J.
1977saif.conf.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observational evidence for atmospheric physical characteristics
relevant to stellar evolution.
Authors: Cayrel, R.; Cayrel, G.
1977saif.conf..105C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Editor's concluding remarks
Authors: Cayrel, R.
1976pmas.conf..477C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theory of stellar atmospheres (Théorie des atmosphères
stellaires).
Authors: Cayrel, R.; Mihalas, D.
1976IAUTA..16b.189C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Physique des mouvements dans les atmospheres stellaires
Authors: Cayrel, R.; Steinberg, M.
1976pmas.conf.....C Altcode: 1976QB809.P48......
No abstract at ADS
---------------------------------------------------------
Title: Colors and ionization equilibria in K dwarfs.
Authors: Perrin, M. N.; Cayrel de Strobel, G.; Cayrel, R.
1975A&A....39...97P Altcode:
Summary. The strong discrepancy found by Oinas for K-dwarfs between
the actual ionization ratio and its expected value derived from normal
gravities and temperatures obtained by deblanketed scans has been
reinvestigated for six stars of his program. It has not been found
significant. Even in Oinas' analysis, if one eliminates entirely the
sun as comparison star and one carries out an absolute curve of growth
analysis, the discrepancy vanishes. In three other late-type stars
not analysed by Oinas, the phenomenon was also not found to exist
at an appreciable degree. Therefore it does not seem necessary any
longer to look for a new continuous absorber to be introduced in the
opacities of K stars in the 5000-10800 A spectral range. Key words:
stellar atmospheres ionization equilibrium K-dwarfs
---------------------------------------------------------
Title: The Bibliographical Star Index
Authors: Cayrel, R.; Jung, J.; Valbousquet, A.
1974BICDS...6...24C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Bibliographical star index 1950-1976
Authors: Cayrel, R.; Jung, J.; Valbousquet, A.
1974bsi..book.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Contribution to the study of supermetallicity in late-type
giants.
Authors: Blanc-Vaziaga, M. -J.; Cayrel, G.; Cayrel, R.
1973ApJ...180..871B Altcode:
This research is a detailed analysis of Aur and Leo, two of the best
examples of "super- metal-rich" (SMR) stars found by Spinrad and Taylor
by a scanner technique. They have been analyzed on high-dispersion
spectrograms taken at the 100-inch Mount Wilson coude' telescope (6.8
A mm-1) for Aur and at the coude' focus of the 60-inch ESO telescope in
Chile (12 A mm-1) for Leo. The star E Vir has been used as a comparison
star. Particular care has been taken only to compare spectrograms taken
with the same instrumentation. The spectra have been interpreted with
theoretical line computations using a grid of model atmospheres. The
models have been calculated on the assumption of LTE, hydrostatic
equilibrium, and radiative equilibrium. Convective transport in the
convective zone has been taken into account. Line blanketing has been
included using a statistical model of line absorption. The detailed
analysis of Aur versus e Vir has not revealed any peculiarity other than
a marginal deficiency of Aur in barium. With respect to the Sun, Aur has
a mild overabundance of Na, as does E Vir; and a possible overabundance
in Mg, Si, and Ca is just at the limit of significance. The analysis
of Leo versus either E Vir or the Sun shows an overabundance in Na,
Ca, Mn, and Cu and a deficiency in Ba. Iron and most other metals do
not show any significant overabundance, even allowing for a rather
larger uncertainty in the effective temperatures. The conclusion
reached about "supermetallicity" is that the word "super-metal-rich"
should be avoided, being misleading for stars which have a normal solar
iron/hydrogen ratio. Supermetallicity appears to be highly selective,
and limited to just a few elements. Subject headings:abundances,
stellar - atmospheres, stellar - late-type stars - line profiles -
stars, individual
---------------------------------------------------------
Title: Age from spectroscopic properties. Concluding remarks.
Authors: Cayrel, R.
1973stag.conf...59C Altcode: 1973IAUCo..17...59C
No abstract at ADS
---------------------------------------------------------
Title: Projets d'instrumentation pour le télescope de 3.60 m de
l'I.N.A.G.
Authors: Cayrel, R.
1972ailt.conf...91C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Les spectrographes et l'électronographie.
Authors: Combes, M.; Felenbok, P.; Picat, J. P.; Fort, B.; Cayrel, R.
1972ailt.conf..444C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Concluding Remarks
Authors: Cayrel, R.
1972ade..coll...59C Altcode: 1972IAUCo..17...59C
No abstract at ADS
---------------------------------------------------------
Title: Project de télescope de l'I.N.A.G.
Authors: Cayrel, R.; Belly, P. Y.
1971cltd.conf...59C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Abundance of Helium in Stellar Atmospheres
Authors: Cayrel, R.
1971HiA.....2..254C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Abundance of helium in stellar atmospheres.
Authors: Cayrel, R.
1971heun.conf..254C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: La composition chimique des étoiles
Authors: Cayrel, R.
1970pfa..conf..126C Altcode: 1969pfa..conf..126C
No abstract at ADS
---------------------------------------------------------
Title: Comparison of Synthetic Spectra with Real Spectra
Authors: Cayrel, R.
1969tons.conf..237C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Location of a Few Subdwarfs in the Theoretical H-R Diagram
and the Helium Content of Population II
Authors: Cayrel, Roger
1968ApJ...151..997C Altcode:
It is shown that photometric systems in which the line blocking is
small enough to be accurately de- termined, like the GRI colors of
Stebbins and Whitford, the vby colors of Stromgren, or the VRIJK
colors of Johnson offer a more reliable way to obtain the effective
temperature of subdwarfs than the UB V system. From the available
data on these different systems, it is established that the main
sequence of extreme subdwarfs, late enough to be unevolved, is below
the main sequence of non-metal-poor stars by an amount of 0.7 ± 0.3
mag. The conclusion that extreme subdwarfs have a normal helium-to-
hydrogen ratio seems unavoidable. Mild subdwarfs do not show any clear
segregation from Population I, except perhaps /L Cassiopeiae. It is
suggested that the smaller effect which should be observed for those
stars is nearly cancelled by a residual evolution effect
---------------------------------------------------------
Title: Abundance Determinations from Stellar Spectra
Authors: Cayrel, R.; Cayrel de Strobel, G.
1966ARA&A...4....1C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non-LTE Effects on Abundance Determination
Authors: Cayrel, R.
1965SAOSR.174..453C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Propriétés cinématiques et composition des étoiles
Authors: Cayrel, R.; Kovalevsky, J.
1964LAstr..78..437C Altcode: 1964LAstr..78..437K
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Results on the Effect of Blanketing on T(τ)
Authors: Cayrel, R.
1964SAOSR.167..139C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Temperature of Radiative Equilibrium in a Layer of
Optically Thin Gas in the Radiation Field of the Solar Photosphere
Authors: Cayrel, R.
1964SAOSR.167..169C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Les étoiles T Tauri
Authors: Cayrel, R.
1963LAstr..77..229C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Predicted fluxes and line intensities in late-type model
atmospheres
Authors: Cayrel, R.; Jugaku, Jun
1963AnAp...26..495C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Detailed Analysis of the Spectrum of Epsilon Virginis.
Authors: Cayrel, Giusa; Cayrel, Roger
1963ApJ...137..431C Altcode:
Lines in the spectral range X 4500-6700 A have been identified on
tracings of the spectrum of E Virginis (G8 III). Three plates had a
dispersion of 1 A/mm and five plates a dispersion of 2 8 A/mm. The
equivalent widths of 1400 lines have been measured From the width of
weak, unblended lines either a macroturbulence 3 6 + 1 km/sec, or a
rotation, V sin i = 4 8 * 1 3 km/sec, can be derived The profile of
the lines are not known with sufficient accuracy to favor one of these
two extreme interpretations microturbulence of from 2 to 3 km/sec
is derived from the curves of growth; there is a tendency to obtain
a higher value for ionized lines than for neutral lines A detailed
analysis of the atmosphere has been performed, leading to the values:
T,j = 49400 K * 1500; log g = 2 7 * 0 2; and log A = log A0 + 0 2
(probable errors) There is a good agreement between the spectroscopic
gravity and the value obtained from reasonable values of the mass
and radius of the star The chemical composition of the atmosphere
agrees with the solar composition within the probable error, except
perhaps for Na No systematic enrichment in heavy-element abundance
can be detected between the birth of the sun and that of E Virginis,
about 10' years ago Higher accuracy is needed, both in equivalent
width measurements and in the physical basis of the theory, to reveal
any difference that might be less than a factor of 2
---------------------------------------------------------
Title: L'abondance des métaux dans les vieilles étoiles de
population I
Authors: Cayrel, Roger.
1963NoPar...1...61C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sur quelques questions de la théorie des atmosphères
stellaires. - II. Nouvelles formules d'approximation pour le calcul
de l'intensité du rayonnement et du flux
Authors: Cayrel, R.
1960AnAp...23..245C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sur quelques questions de la théorie des atmosphères
stellaires. - I. Détermination de la gravité
Authors: Cayrel, R.
1960AnAp...23..233C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Model Atmospheres and Conventional Curve of Growth Analysis.
Authors: Cayrel, Roger
1960AJ.....65R.486C Altcode:
Possible systematic differences between abundances derived from the
conventional curve of growth analysis and from detailed model atmosphere
computations have been investigated. They have been found to be small,
usually less than the sum of the errors arising from observational
inaccuracy and incorrect assumptions in the theory. The main advantage
of using models seems, therefore, to be confined to the use of more
observational data to determine the physical parameters, temperature and
gravity. Color, Balmer jump, and profiles of the Balmer lines are such
examples. In addition, the use of models removes the uncertainty in the
connection between the excitation and ionization temperatures. Supported
by U.S. Air Force Office of Scientific Research under contract.
---------------------------------------------------------
Title: Zur Frage der Druckverbreiterung der solaren Balmerlinien. Mit
4 Textabbildungen
Authors: Cayrel, R.; Traving, G.
1960ZA.....50..239C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Grands et petits télescopes
Authors: Cayrel, R.
1958LAstr..72..247C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations et etudes theorique du spectre de XI Persei.
Authors: Cayrel, R.
1958SAnAp....f...1C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations et Étude Théorique du Spectre de Zeta Per
Authors: Cayrel, Roger
1958SAnAp...6....5C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations et étude théorique du spectre de ζ Per Title:
Observations et étude théorique du spectre de ζ Per Title:
Observations and theoretical study of the spectrum of ζ Per;
Authors: Cayrel, Roger
1957PhDT........43C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: La polarisation de la lumiere par des poussieres de graphite
et la polarisation interstellaire
Authors: Schatzman, E.; Cayrel, R.
1955LIACo...6..601S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sur la polarisation interstellaire par des particules de
graphite
Authors: Cayrel, R.; Schatzman, E.
1954AnAp...17..555C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sur une cause d'erreur en spectrophotométrie
Authors: Cayrel, Roger
1953AnAp...16..129C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Relation largeur equivalente-profondeur centrale pour des raies
d'absorption. Formulation analityque de la relation et comparaison
avec l'observation
Authors: Cayrel, R.; Taffara, S.
1953MmSAI..24..265C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Effects secondaires renforçant une cause d'erreur en
spectrophotométrie
Authors: Cayrel, Roger
1953AnAp...16..466C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Contributions à l'étude de l'équilibre radiatif
Authors: Cayrel, Roger
1951AnAp...14....1C Altcode:
No abstract at ADS
