83 research outputs found
The photospheric solar oxygen project: IV. 3D-NLTE investigation of the 777 nm triplet lines
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. We carry out an
independent redetermination of the solar oxygen abundance by investigating the
center-to-limb variation of the OI IR triplet lines at 777 nm in different sets
of spectra with the help of detailed synthetic line profiles based on 3D
hydrodynamical CO5BOLD model atmospheres and 3D non-LTE line formation
calculations with NLTETD. The idea is to simultaneously derive the oxygen
abundance,A(O), and the scaling factor SH that describes the cross-sections for
inelastic collisions with neutral hydrogen relative the classical Drawin
formula. The best fit of the center-to-limb variation of the triplet lines
achieved with the CO5BOLD 3D solar model is clearly of superior quality
compared to the line profile fits obtained with standard 1D model atmospheres.
Our best estimate of the 3D non-LTE solar oxygen abundance is A(O) = 8.76 +/-
0.02, with the scaling factor SH in the range between 1.2 and 1.8. 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 -independent microturbulence.Comment: 25 pages, 17 figures, 7 tables (Accepted for publication in A&A
De Novo Duplication in the CHD7 Gene Associated With Severe CHARGE Syndrome.
CHARGE syndrome is an autosomal dominant developmental disorder associated with a constellation of traits involving almost every organ and sensory system, in particular congenital anomalies, including choanal atresia and malformations of the heart, inner ear, and retina. Variants in CHD7 have been shown to cause CHARGE syndrome. Here, we report the identification of a novel de novo p.Asp2119_Pro2120ins6 duplication variant in a conserved region of CHD7 in a severely affected boy presenting with 3 and 5 of the CHARGE cardinal major and minor signs, respectively, combined with congenital umbilical hernia, congenital hernia at the linea alba, mildly hypoplastic inferior vermis, slight dilatation of the lateral ventricles, prominent metopic ridge, and hypoglycemic episodes
Abundance of zirconium in the globular cluster 47 Tuc: a possible Zr-Na correlation?
We determined abundances of Na and Zr in the atmospheres of 237 RGB stars in
Galactic globular cluster (GGC) 47 Tuc (NGC 104), with a primary objective of
investigating possible differences between the abundances of Zr in the first
generation (1P) and second generation (2P) stars. For the abundance analysis,
we used archival UVES/GIRAFFE spectra obtained during three different observing
programmes. Abundances were determined from two Na I and three Zr I lines,
using 1D hydrostatic ATLAS model atmospheres. The target stars for the
abundance analysis were limited to those with 4200
4800 K. This is the largest sample of GGC stars in which Na and Zr abundances
have been studied so far. While our mean [Na/Fe] and [Zr/Fe] ratios agree well
with those determined in the earlier studies, we find a weak but statistically
significant correlation in the plane. A
comparison of the mean [Zr/Fe] abundance ratios in the 1P and 2P stars suggests
a small but statistically significant Zr over-abundance in the 2P stars,
dex. Also, our analysis shows
that stars enriched in both Zr and Na are more centrally concentrated. However,
we find no correlation between their distance from the cluster centre and their
full spatial velocity. While there may be some influence of CN line blends on
the determined Zr abundances, it seems very unlikely that the detected Zr-Na
correlation, for the slightly higher Zr abundances in the 2P stars, would be
caused by the CN blending alone. The obtained results indicate that, in 47 Tuc,
some amount of Zr should have been synthesised by the same polluters that
enriched 2P stars with the light elements. Unfortunately, our data alone do not
allow us to distinguish which of the two scenarios, or whether or not a
combination of both, could have operated in this GGC
Can we trust elemental abundances derived in late-type giants with the classical 1D stellar atmosphere models?
We compare the abundances of various chemical species as derived with 3D
hydrodynamical and classical 1D stellar atmosphere codes in a late-type giant
characterized by T_eff=3640K, log g = 1.0, [M/H] = 0.0. For this particular set
of atmospheric parameters the 3D-1D abundance differences are generally small
for neutral atoms and molecules but they may reach up to 0.3-0.4 dex in case of
ions. The 3D-1D differences generally become increasingly more negative at
higher excitation potentials and are typically largest in the optical
wavelength range. Their sign can be both positive and negative, and depends on
the excitation potential and wavelength of a given spectral line. While our
results obtained with this particular late-type giant model suggest that 1D
stellar atmosphere models may be safe to use with neutral atoms and molecules,
care should be taken if they are exploited with ions.Comment: Poster presented at the IAU Symposium 265 "Chemical Abundances in the
Universe: Connecting First Stars to Planets", Rio de Janeiro, 10-14 August
2009; 2 pages, 1 figur
Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tuc
We aim to determine abundances of Li, O and Na in a sample of of 110 turn-off
(TO) stars, in order to study the evolution of light elements in this cluster
and to put our results in perspective with observations of other globular and
open clusters, as well as with field stars. We use medium resolution spectra
obtained with the GIRAFFE spectrograph at the ESO 8.2m Kueyen VLT telescope and
use state of the art 1D model atmospheres and NLTE line transfer to determine
the abundances. We also employ CO5BOLD hydrodynamical simulations to assess the
impact of stellar granulation on the line formation and inferred abundances.
Our results confirm the existence of Na-O abundance anti-correlation and hint
towards a possible Li-O anti-correlation in the TO stars of 47 Tuc. We find no
convincing evidence supporting the existence of Li-Na correlation. The obtained
3D NLTE mean lithium abundance in a sample of 94 TO stars where Li lines were
detected reliably,
dex, appears to be significantly lower than what is observed in other globular
clusters. At the same time, star-to-star spread in Li abundance is also larger
than seen in other clusters. The highest Li abundance observed in 47 Tuc is
about 0.1 dex lower than the lowest Li abundance observed among the un-depleted
stars of the metal-poor open cluster NGC 2243. The lithium abundances in 47
Tuc, when put into context with observations in other clusters and field stars,
suggest that stars that are more metal-rich than [FeH] \sim -1.0 experience
significant lithium depletion during their lifetime on the main sequence, while
the more metal-poor stars do not. Rather strikingly, our results suggest that
initial lithium abundance with which the star was created may only depend on
its age (the younger the star, the higher its Li content) and not on its
metallicity.Comment: 24 pages, 13 figures; discussion and conclusions expanded. Accepted
for publication in A&
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The solar photospheric silicon abundance according to CO5BOLD: Investigating line broadening, magnetic fields, and model effects
Context. In this work, we present a photospheric solar silicon abundance derived using CO5BOLD model atmospheres and the LINFOR3D spectral synthesis code. Previous works have differed in their choice of a spectral line sample and model atmosphere as well as their treatment of observational material, and the solar silicon abundance has undergone a downward revision in recent years. We additionally show the effects of the chosen line sample, broadening due to velocity fields, collisional broadening, model spatial resolution, and magnetic fields. Aims. Our main aim is to derive the photospheric solar silicon abundance using updated oscillator strengths and to mitigate model shortcomings such as over-broadening of synthetic spectra. We also aim to investigate the effects of different line samples, fitting configurations, and magnetic fields on the fitted abundance and broadening values. Methods. CO5BOLD model atmospheres for the Sun were used in conjunction with the LINFOR3D spectral synthesis code to generate model spectra, which were then fit to observations in the Hamburg solar atlas. We took pixel-to-pixel signal correlations into account by means of a correlated noise model. The choice of line sample is crucial to determining abundances, and we present a sample of 11 carefully selected lines (from an initial choice of 39 lines) in both the optical and infrared, which has been made possible with newly determined oscillator strengths for the majority of these lines. Our final sample includes seven optical Si i lines, three infrared Si i lines, and one optical Si ii line. Results. We derived a photospheric solar silicon abundance of log ϵSi = 7.57 ± 0.04, including a - 0.01 dex correction from Non-Local Thermodynamic Equilibrium (NLTE) effects. Combining this with meteoritic abundances and previously determined photospheric abundances results in a metal mass fraction Z/X = 0.0220 ± 0.0020. We found a tendency of obtaining overly broad synthetic lines. We mitigated the impact of this by devising a de-broadening procedure. The over-broadening of synthetic lines does not substantially affect the abundance determined in the end. It is primarily the line selection that affects the final fitted abundance
Barium abundance in red giants of NGC 6752. Non-local thermodynamic equilibrium and three-dimensional effects
(Abridged) Aims: We study the effects related to departures from non-local
thermodynamic equilibrium (NLTE) and homogeneity in the atmospheres of red
giant stars in Galactic globular cluster NGC 6752, to assess their influence on
the formation of Ba II lines. Methods: One-dimensional (1D) local thermodynamic
equilibrium (LTE) and 1D NLTE barium abundances were derived using classical 1D
ATLAS stellar model atmospheres. The three-dimensional (3D) LTE abundances were
obtained for 8 red giants on the lower RGB, by adjusting their 1D LTE
abundances using 3D-1D abundance corrections, i.e., the differences between the
abundances obtained from the same spectral line using the 3D hydrodynamical
(CO5BOLD) and classical 1D (LHD) stellar model atmospheres. Results: The mean
1D barium-to-iron abundance ratios derived for 20 giants are _{1D
NLTE} = 0.05 \pm0.06 (stat.) \pm0.08 (sys.). The 3D-1D abundance correction
obtained for 8 giants is small (~+0.05 dex), thus leads to only minor
adjustment when applied to the mean 1D NLTE barium-to-iron abundance ratio for
the 20 giants, _{3D+NLTE} = 0.10 \pm0.06(stat.) \pm0.10(sys.). The
intrinsic abundance spread between the individual cluster stars is small and
can be explained in terms of uncertainties in the abundance determinations.
Conclusions: Deviations from LTE play an important role in the formation of
barium lines in the atmospheres of red giants studied here. The role of 3D
hydrodynamical effects should not be dismissed either, even if the obtained
3D-1D abundance corrections are small. This result is a consequence of subtle
fine-tuning of individual contributions from horizontal temperature
fluctuations and differences between the average temperature profiles in the 3D
and 1D model atmospheres: owing to the comparable size and opposite sign, their
contributions nearly cancel each other.Comment: Minor typos corrected. Accepted for publication in A&A (9 pages, 3
figures, 6 tables
Bolometric correction and spectral energy distribution of cool stars in Galactic clusters
We have investigated the relevant trend of the bolometric correction (BC) at
the cool-temperature regime of red giant stars and its possible dependence on
stellar metallicity. Our analysis relies on a wide sample of optical-infrared
spectroscopic observations, along the 3500A-2.5micron wavelength range, for a
grid of 92 red giant stars in five (3 globular + 2 open) Galactic clusters,
along the -2.2<[Fe/H]<+0.4 metallicity range. Bolometric magnitudes have been
found within an internal accuracy of a few percent. Making use of our new
database, we provide a set of fitting functions for the V and K BC vs. Teff and
broad-band colors, valid over the interval 3300K<Teff<5000K, especially suited
for Red Giants. No evident drift of both BC(V) and BC(K) with [Fe/H] is found.
Things may be different, however, for the B-band correction, given a clear
(B-V) vs. [Fe/H] correlation in place for our data, with metal-poor stars
displaying a "bluer" (B-V) with respect to the metal-rich sample, for fixed
Teff. Our empirical bolometric scale supports the conclusion that (a) BC(K)
from the most recent studies are reliable within <0.1 mag over the whole
color/temperature range considered in this paper, and (b) the same conclusion
apply to BC(V) only for stars warmer than ~3800K. At cooler temperatures the
agreement is less general, and MARCS models are the only ones providing a
satisfactory match to observations.Comment: 18 pages with 12 color figures and 12 tables. To appear in the MNRAS.
Full spectral catalog of stars available at
http://www.bo.astro.it/~eps/home.htm
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MINCE: I. Presentation of the project and of the first year sample
Context. In recent years, Galactic archaeology has become a particularly vibrant field of astronomy, with its main focus set on the oldest stars of our Galaxy. In most cases, these stars have been identified as the most metal-poor. However, the struggle to find these ancient fossils has produced an important bias in the observations - in particular, the intermediate metal-poor stars (-2.5 < [Fe/H] <-1.5) have been frequently overlooked. The missing information has consequences for the precise study of the chemical enrichment of our Galaxy, in particular for what concerns neutron capture elements and it will be only partially covered by future multi object spectroscopic surveys such as WEAVE and 4MOST. Aims. Measuring at Intermediate Metallicity Neutron Capture Elements (MINCE) is gathering the first high-quality spectra (high signal-to-noise ratio, S/N, and high resolution) for several hundreds of bright and metal-poor stars, mainly located in our Galactic halo. Methods. We compiled our selection mainly on the basis of Gaia data and determined the stellar atmospheres of our sample and the chemical abundances of each star. Results. In this paper, we present the first sample of 59 spectra of 46 stars. We measured the radial velocities and computed the Galactic orbits for all stars. We found that 8 stars belong to the thin disc, 15 to disrupted satellites, and the remaining cannot be associated to the mentioned structures, and we call them halo stars. For 33 of these stars, we provide abundances for the elements up to zinc. We also show the chemical evolution results for eleven chemical elements, based on recent models. Conclusions. Our observational strategy of using multiple telescopes and spectrographs to acquire high S/N and high-resolution spectra for intermediate-metallicity stars has proven to be very efficient, since the present sample was acquired over only about one year of observations. Finally, our target selection strategy, after an initial adjustment, proved satisfactory for our purposes
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