173 research outputs found
On the correlation of elemental abundances with kinematics among galactic disk stars
We have performed the detailed analysis of 174 high-resolution spectra of FGK
dwarfs obtained with the ELODIE echelle spectrograph at the Observatoire de
Haute-Provence. Abundances of Fe, Si and Ni have been determined from
equivalent widths under LTE approximation, whereas abundances of Mg have been
determined under NLTE approximation using equivalent widths of 4 lines and
profiles of 5 lines. Spatial velocities with an accuracy better than 1 km/s, as
well as orbits, have been computed for all stars. They have been used to define
2 subsamples kinematically representative of the thin disk and the thick disk
in order to highlight their respective properties. A transition occurs at
[Fe/H]=-0.3. Stars more metal-rich than this value have a flat distribution
with Zmax<1 kpc and sigma_W<20 km/s, and a narrow distribution of [alpha/Fe].
There exist stars in this metallicity regime which cannot belong to the thin
disk because of their excentric orbits, neither to the thick disk because of
their low scale height. Several thin disk stars are identified down to
[Fe/H]=-0.80. Their Mg enrichment is lower than thick disk stars with the same
metallicity. We confirm from a larger sample the results of Feltzing et al
(2003) and Bensby et al (2003) showing a decrease of [alpha/Fe] with [Fe/H] in
the thick disk interpreted as the signature of the SNIa which have
progressively enriched the ISM with iron. However our data suggest that the
star formation in the thick disk stopped when the enrichment was [Fe/H]=-0.30,
[Mg/Fe]=+0.20, [Si/Fe]=+0.17. A vertical gradient in [alpha/Fe] may exist in
the thick disk but should be confirmed with a larger sample. Finally we have
identified 2 new candidates of the HR1614 moving group.Comment: Accepted in A&A, 16 pages, 14 figure
Superflare G and K Stars and the Lithium abundance
We analyzed here the connection of superflares and the lithium abundance in G
and K stars based on Li abundance determinations conducted with the echelle
spectra of a full set of 280 stars obtained with the ELODIE spectrograph. For
high-active stars we show a definite correlation between and the
chromosphere activity. We show that sets of stars with high Li abundance and
having superflares possess common properties. It relates, firstly, to stars
with activity saturation. We consider the X-ray data for G, K, and M stars
separately, and show that transition from a saturation mode to solar-type
activity takes place at values of rotation periods 1.1, 3.3, and 7.2 days for
G2, K4 and M3 spectral types, respectively. We discuss bimodal distribution of
a number of G and K main-sequence stars versus an axial rotation and location
of superflare stars with respect to other Kepler stars. We conclude that
superflare G and K stars are mainly fast rotating young objects, but some of
them belong to stars with solar-type activity. At the same time, we found a
group of G stars with high Li content , but being
slower rotators with rotation periods > 10 days, which are characterized by low
chromospheric activity. This agrees with a large spread in Li abundances in
superflare stars. A mechanism leading to this effect is discussed.Comment: 6 pages, 8 figures. The 19th Cambridge Workshop on Cool Stars,
Stellar Systems, and the Su
Barium and Yttrium abundance in intermediate-age and old open clusters
Barium is a neutron capture element, that, in open clusters, is frequently
over-abundant with respect to the Iron. A clear explanation for this is still
missing. Additionally, its gradient across the Galactic disk is poorly
constrained. We measure the abundance of yttrium and barium using the synthetic
spectrum method from UVES high-resolution spectra of eight distant open
clusters, namely Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73, Berkeley 75,
NGC 6192, NGC 6404, and NGC 6583. The barium abundance was estimated using NLTE
approximation. We confirm that Barium is indeed over-abundant in most clusters,
especially young clusters. Finally, we investigated the trend of yttrium and
barium abundances as a function of distance in the Galaxy and ages. Several
scenarios for the barium over-abundance are then discussed.Comment: 9 pages, 10 figure
On the subject of the Ba overabundance in the open clusters stars
For eight distant open clusters, namely Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73, Berkeley 75, NGC 6192, NGC 6404, and NGC 6583, we determined the yttrium and barium abundances using the UVES, VLT spectra (ESO, Chile). The stars of one young cluster (Ruprecht 7) demonstrate significant barium overabundance( 3c0.55 dex) that can not be due to the determination error. We have considered the Ba abundance determination errors due to LTE approach, saturation of the lines, synthetic and observed barium line fitting, and the causes of the Ba overabundance associated with the Galactic disc enrichment or the origin of open clusters. Possible explanation for this overabundance can be the origin of n-capture elements enrichment of the clusters (galactic or extragalactic) or additional sources of the Ba production
The NLTE Barium Abundance in Dwarf Stars in the Metallicity Range of -1 < [Fe/H] < +0.3
We present the results of determination of the barium abundance considering
the non-LTE (NLTE) effects in 172 dwarf stars in the metallicity range of -1<
[Fe/H] <+0.3, assigned to different Galactic substructures by kinematic
criteria. We used a model of the Ba atom with 31 levels of Ba I and 101 levels
of Ba II. The atmosphere models for the investigated stars were computed using
the ATLAS9 code modified by new opacity distribution functions. The NLTE
profiles of the unblended Ba II (4554 A, 5853 A, 6496 A) were computed and then
compared to those observed. The line 6141 A was also used, but with an
allowance for its correlation with the iron line. The average barium abundances
in the thin and thick discs are 0.01 +/- 0.08 and -0.03 +/- 0.07, respectively.
The comparison to the calculations of the Galactic chemical evolution by
Serminato et al. (2009) was conducted. The trend obtained for the Ba abundance
versus [Fe/H] suggests a complex barium production process in the thin and
thick discs
Mn abundances in the stars of the Galactic disc with metallicities â1.0 < [Fe/H] < 0.3
In this work, we present and discuss the observations of the Mn abundances for 247 FGK dwarfs, located in the Galactic disc with metallicity â1 < [Fe/H] < +0.3. The observed stars belong to the substructures of the Galaxy thick and thin disks, and to the Hercules stream. The observations were conducted using the 1.93m telescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle-type spectrographs ELODIE and SOPHIE. The abundances were derived under the LTE approximation, with an average error for the [Mn/Fe] ratio of 0.10 dex. For most of the stars in the sample, Mn abundances are not available in the literature. We obtain an evolution of [Mn/Fe] ratio with the metallicity [Fe/H] consistent with previous data compilations. In particular, within the metallicity range covered by our stellar sample, the [Mn/Fe] ratio is increasing with the increase of metallicity. This due to the contribution to the Galactic chemical evolution of Mn and Fe from thermonuclear supernovae. We confirm the baseline scenario where most of the Mn in the Galactic disc and in the Sun is made by thermonuclear supernovae. In particular, the effective contribution from core-collapse supernovae to the Mn in the Solar system is about 10-20 per cent. However, present uncertainties affecting the production of Mn and Fe in thermonuclear supernovae are limiting the constraining power of the observed [Mn/Fe] trend in the Galactic discs on, e.g. the frequency of different thermonuclear supernovae populations. The different production of these two elements in different types of thermonuclear supernovae needs to be disentangled by the dependence of their relative production on the metallicity of the supernova progenito
Abundances of Cu and Zn in metal-poor stars: clues for Galaxy evolution
We present new observations of copper and zinc abundances in 90 metal-poor
stars, belonging to the metallicity range -3< [Fe/H] < -0.5. The present study
is based on high resolution spectroscopic measurements collected at the Haute
Provence Observatoire (R= 42000, S/N > 100). The trend of Cu and Zn abundances
as a function of the metallicity [Fe/H] is discussed and compared to that of
other heavy elements beyond iron. We also estimate spatial velocities and
galactic orbital parameters for our target stars in order to disentangle the
population of disk stars from that of halo stars using kinematic criteria. In
the absence of a firm a priori knowledge of the nucleosynthesis mechanisms
controlling Cu and Zn production, and of the relative stellar sites, we derive
constraints on these last from the trend of the observed ratios [Cu/Fe] and
[Zn/Fe] throughout the history of the Galaxy, as well as from a few well
established properties of basic nucleosynthesis processes in stars. We thus
confirm that the production of Cu and Zn requires a number of different sources
(neutron captures in massive stars, s-processing in low and intermediate mass
stars, explosive nucleosynthesis in various supernova types). We also attempt a
ranking of the relative roles played by different production mechanisms, and
verify these hints through a simple estimate of the galactic enrichment in Cu
and Zn. In agreement with suggestions presented earlier, we find evidence that
Type Ia Supernovae must play a relevant role, especially for the production of
Cu.Comment: Accepted for A&A, 27 pages, 14 figure
Spectroscopy of high proper motion stars in the ground--based UV
Based on high quality spectral data (spectral resolution R>60000) within the
wavelength range of 3550-5000 AA we determined main parameters (effective
temperature, surface gravity, microturbulent velocity, and chemical element
abundances including heavy metals from Sr to Dy) for 14 metal-deficient G-K
stars with large proper motions. The stars we studied have a wide range of
metallicity: [Fe/H]=-0.3 \div -2.9. Abundances of Mg, Al, Sr and Ba were
calculated with non-LTE line-formation effects accounted for. Abundances both
of the radioactive element Th and r-process element Eu were determined using
synthetic spectrum calculations. We selected stars that belong to different
galactic populations according to the kinematical criterion and parameters
determined by us. We found that the studied stars with large proper motions
refer to different components of the Galaxy: thin, thick disks and halo. The
chemical composition of the star BD+80 245 located far from the galactic plane
agrees with its belonging to the accreted halo. For the giant HD115444 we
obtained [Fe/H]=-2.91, underabundance of Mn, overabundance of heavy metals from
Ba to Dy, and, especially high excess of the r-process element Europium:
[Eu/Fe]=+1.26. Contrary to its chemical composition typical for halo stars,
HD115444 belongs to the disc population according to its kinematic parameters.Comment: 16 pages, 4 figures, 5 tables, "UV Universe-2010 (2nd NUVA Symposium)
conference
The Galactic thick and thin disks: differences in evolution
Recent observations demonstrate that the thin and thick disks of the Galaxy
have different chemical abundance trends and evolution timescales. The relative
abundances of -elements in the thick Galactic disk are increased
relative to the thin disk. Our goal is to investigate the cause of such
differences in thick and thin disk abundances. We investigate the chemical
evolution of the Galactic disk in the framework of the open two-zone model with
gas inflow. The Galactic abundance trends for -elements (Mg, Si, O) and
Fe are predicted for the thin and thick Galactic disks. The star formation
histories of the thin and thick disks must have been different and the gas
infall must have been more intense during the thick disk evolution that the
thin disk evolution.Comment: 9 pages, 10 figures, A&A accepte
Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th
The study of the origin of heavy elements is one of the main goals of nuclear astrophysics. In this paper, we present new observational data for the heavy r-process elements gadolinium (Gd, Z= 64), dysprosium (Dy, Z= 66), and thorium (Th, Z= 90) in a sample of 276 Galactic disc stars (-1.0 < [Fe/H] < + 0.3). The stellar spectra have a high resolution of 42 000 and 75 000, and the signal-to-noise ratio higher than 100. The LTE abundances of Gd, Dy, and Th have been determined by comparing the observed and synthetic spectra for three Gd lines (149 stars), four Dy lines (152 stars), and the Th line at 4019.13 angstrom (170 stars). For about 70 per cent of the stars in our sample, Gd and Dy are measured for the first time, and Th for 95 per cent of the stars. Typical errors vary from 0.07 to 0.16 dex. This paper provides the first extended set of Th observations in the Milky Way disc. Together with europium (Eu, Z= 63) data from our previous studies, we have compared these new observations with nucleosynthesis predictions and Galactic Chemical Evolution simulations. We confirm that [Gd/Fe] and [Dy/Fe] show the same behaviour of Eu. We study with GCE simulations the evolution of [Th/Fe] in comparison with [Eu/Fe], showing that unlike Eu, either the Th production is metallicity dependent in case of a unique source of the r-process in the Galaxy, or the frequency of the Th-rich r-process source is decreasing with the increase in [Fe/H]
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