478 research outputs found
A large sample of calibration stars for Gaia: log g from Kepler and CoRoT
Asteroseismic data can be used to determine surface gravities with precisions
of < 0.05 dex by using the global seismic quantities Deltanu and nu_max along
with Teff and [Fe/H]. Surface gravity is also one of the four stellar
properties to be derived by automatic analyses for 1 billion stars from Gaia
data (workpackage GSP_Phot). We explore seismic data from MS F, G, K stars
(solar-like stars) observed by Kepler as a potential calibration source for
methods that Gaia will use for object characterisation (log g). We calculate
log g for bright nearby stars for which radii and masses are known, and using
their global seismic quantities in a grid-based method, we determine an
asteroseismic log g to within 0.01 dex of the direct calculation, thus
validating the accuracy of our method. We find that errors in Teff and mainly
[Fe/H] can cause systematic errors of 0.02 dex. We then apply our method to a
list of 40 stars to deliver precise values of surface gravity, i.e. sigma <
0.02 dex, and we find agreement with recent literature values. Finally, we
explore the precision we expect in a sample of 400+ Kepler stars which have
their global seismic quantities measured. We find a mean uncertainty
(precision) on the order of <0.02 dex in log g over the full explored range 3.8
< log g < 4.6, with the mean value varying only with stellar magnitude (0.01 -
0.02 dex). We study sources of systematic errors in log g and find possible
biases on the order of 0.04 dex, independent of log g and magnitude, which
accounts for errors in the Teff and [Fe/H] measurements, as well as from using
a different grid-based method. We conclude that Kepler stars provide a wealth
of reliable information that can help to calibrate methods that Gaia will use,
in particular, for source characterisation with GSP_Phot where excellent
precision (small uncertainties) and accuracy in log g is obtained from seismic
data.Comment: Accepted MNRAS, 15 pages (10 figures and 3 tables), v2=some rewording
of two sentence
On the galactic chemical evolution of sulfur
Sulfur abundances have been determined for ten stars to resolve a debate in
the literature on the Galactic chemical evolution of sulfur in the halo phase
of the Milky Way. Our analysis is based on observations of the S I lines at
9212.9, 9228.1, and 9237.5 A for stars for which the S abundance was obtained
previously from much weaker S I lines at 8694.0 and 8694.6 A. In contrast to
the previous results showing [S/Fe] to rise steadily with decreasing [Fe/H],
our results show that [S/Fe] is approximately constant for metal-poor stars
([Fe/H] < -1) at [S/Fe] = +0.3. Thus, sulfur behaves in a similar way to the
other alpha elements, with an approximately constant [S/Fe] for metallicities
lower than [Fe/H] = -1. We suggest that the reason for the earlier claims of a
rise of [S/Fe] is partly due to the use of the weak S I 8694.0 and 8694.6 A
lines and partly uncertainties in the determination of the metallicity when
using Fe I lines. The S I 9212.9, 9228.1, and 9237.5 A lines are preferred for
an abundance analysis of sulfur for metal-poor stars.Comment: Accepted by A&A, 12 pages. Full article with figures in A&
On the metallicity distribution of classical Cepheids in the Galactic inner disk
We present homogeneous and accurate iron abundances for almost four dozen
(47) of Galactic Cepheids using high-spectral resolution (R40,000) high
signal-to-noise ratio (S/N 100) optical spectra collected with UVES at
VLT. A significant fraction of the sample (32) is located in the inner disk (RG
6.9 kpc) and for half of them we provide new iron abundances. Current
findings indicate a steady increase in iron abundance when approaching the
innermost regions of the thin disk. The metallicity is super-solar and ranges
from 0.2 dex for RG 6.5 kpc to 0.4 dex for RG 5.5 kpc. Moreover,
we do not find evidence of correlation between iron abundance and distance from
the Galactic plane. We collected similar data available in the literature and
ended up with a sample of 420 Cepheids. Current data suggest that the mean
metallicity and the metallicity dispersion in the four quadrants of the
Galactic disk attain similar values. The first-second quadrants show a more
extended metal-poor tail, while the third-fourth quadrants show a more extended
metal-rich tail, but the bulk of the sample is at solar iron abundance.
Finally, we found a significant difference between the iron abundance of
Cepheids located close to the edge of the inner disk ([Fe/H]0.4) and
young stars located either along the Galactic bar or in the nuclear bulge
([Fe/H]0). Thus suggesting that the above regions have had different
chemical enrichment histories. The same outcome applies to the metallicity
gradient of the Galactic bulge, since mounting empirical evidence indicates
that the mean metallicity increases when moving from the outer to the inner
bulge regions.Comment: 10 pages, 5 figures; Corrected typos, corrected Table
Lagrange formalism of memory circuit elements: classical and quantum formulations
The general Lagrange-Euler formalism for the three memory circuit elements,
namely, memristive, memcapacitive, and meminductive systems, is introduced. In
addition, {\it mutual meminductance}, i.e. mutual inductance with a state
depending on the past evolution of the system, is defined. The Lagrange-Euler
formalism for a general circuit network, the related work-energy theorem, and
the generalized Joule's first law are also obtained. Examples of this formalism
applied to specific circuits are provided, and the corresponding Hamiltonian
and its quantization for the case of non-dissipative elements are discussed.
The notion of {\it memory quanta}, the quantum excitations of the memory
degrees of freedom, is presented. Specific examples are used to show that the
coupling between these quanta and the well-known charge quanta can lead to a
splitting of degenerate levels and to other experimentally observable quantum
effects
A grid of NLTE corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia
We investigate NLTE effects for magnesium and calcium in the atmospheres of
late-type giant and supergiant stars. The aim of this paper is to provide a
grid of NLTE/LTE equivalent width ratios W/W* of Mg and Ca lines for the
following range of stellar parameters: Teff in [3500, 5250] K, log g in [0.5,
2.0] dex and [Fe/H] in [-4.0, 0.5] dex. We use realistic model atoms with the
best physics available and taking into account the fine structure. The Mg and
Ca lines of interest are in optical and near IR ranges. A special interest
concerns the lines in the Gaia spectrograph (RVS) wavelength domain [8470,
8740] A. The NLTE corrections are provided as function of stellar parameters in
an electronic table as well as in a polynomial form for the Gaia/RVS lines.Comment: 27 pages, 19 figures and 11 tables. Also on-line data; MNRAS (2011)
000
The Carina Project VII: Towards the breaking of the age-metallicity degeneracy of red giant branch stars using the c_UBI index
We present an analysis of photometric and spectroscopic data of the Carina
dSph galaxy, testing a new approach similar to that used to disentangle
multiple populations in Galactic globular clusters (GCs). We show that a proper
colour combination is able to separate a significant fraction of the red giant
branch (RGB) of the two main Carina populations (the old one, \sim 12 Gyr, and
the intermediate-age one, 4-8 Gyr). In particular, the c_UBI=(U-B)-(B-I)
pseudo-colour allows us to follow the RGB of both populations along a relevant
portion of the RGB. We find that the oldest stars have more negative c_UBI
pseudo-colour than intermediate-age ones. We correlate the pseudo-colour of RGB
stars with their chemical properties, finding a significant trend between the
iron content and the c_UBI. Stars belonging to the old population are
systematically more metal poor ([Fe/H]=-2.32\pm0.08 dex) than the
intermediate-age ones ([Fe/H]=-1.82\pm0.03 dex). This gives solid evidence on
the chemical evolution history of this galaxy, and we have a new diagnostic
that can allow us to break the age-metallicity degeneracy of H-burning advanced
evolutionary phases. We compared the distribution of stars in the c_UBI plane
with theoretical isochrones, finding that no satisfactory agreement can be
reached with models developed in a theoretical framework based on standard
heavy element distributions. Finally, we discuss possible systematic
differences when compared with multiple populations in GCs.Comment: 11 pages, 11 figures, 1 table, accepted for publication in Ap
The Carina Project. X. On the kinematics of old and intermediate-age stellar populations
We present new radial velocity (RV) measurements of old (horizontal branch)
and intermediate-age (red clump) stellar tracers in the Carina dwarf
spheroidal. They are based on more than 2,200 low-resolution spectra collected
with VIMOS at VLT. The targets are faint (20<V<21.5 mag), but the accuracy at
the faintest limit is <9 kms-1. These data were complemented with RV
measurements either based on spectra collected with FORS2 and FLAMES/GIRAFFE at
VLT or available in the literature. We ended up with a sample of 2748 stars and
among them 1389 are candidate Carina stars. We found that the intermediate-age
stellar component shows a well defined rotational pattern around the minor
axis. The western and the eastern side of the galaxy differ by +5 and -4 km s-1
when compared with the main RV peak. The old stellar component is characterized
by a larger RV dispersion and does not show evidence of RV pattern. We compared
the observed RV distribution with N-body simulations for a former disky dwarf
galaxy orbiting a giant MilkyWay-like galaxy (Lokas et al. 2015). We rotated
the simulated galaxy by 60 degrees with respect to the major axis, we kept the
observer on orbital plane of the dwarf and extracted a sample of stars similar
to the observed one. Observed and predicted Vrot/{\sigma} ratios across the
central regions are in remarkable agreement. This evidence indicates that
Carina was a disky dwarf galaxy that experienced several strong tidal
interactions with the Milky Way. Owing to these interactions, Carina
transformed from a disky to a prolate spheroid and the rotational velocity
transformed into random motions.Comment: 21 pages, 16 figures, 4 tables. Accepted for publication in Ap
Complexity and robustness of the flavonoid transcriptional regulatory network revealed by comprehensive analyses of MYB-bHLH-WDR complexes and their targets in Arabidopsis seed.
In Arabidopsis thaliana, proanthocyanidins (PAs) accumulate in the innermost cell layer of the seed coat (i.e. endothelium, chalaza and micropyle). The expression of the biosynthetic genes involved relies on the transcriptional activity of R2R3-MYB and basic helix-loop-helix (bHLH) proteins which form ternary complexes (\u27MBW\u27) with TRANSPARENT TESTA GLABRA1 (TTG1) (WD repeat protein). The identification of the direct targets and the determination of the nature and spatio-temporal activity of these MBW complexes are essential steps towards a comprehensive understanding of the transcriptional mechanisms that control flavonoid biosynthesis. In this study, various molecular, genetic and biochemical approaches were used. Here, we have demonstrated that, of the 12 studied genes of the pathway, only dihydroflavonol-4-reductase (DFR), leucoanthocyanidin dioxygenase (LDOX), BANYULS (BAN), TRANSPARENT TESTA 19 (TT19), TT12 and H(+) -ATPase isoform 10 (AHA10) are direct targets of the MBW complexes. Interestingly, although the TT2-TT8-TTG1 complex plays the major role in developing seeds, three additional MBW complexes (i.e. MYB5-TT8-TTG1, TT2-EGL3-TTG1 and TT2-GL3-TTG1) were also shown to be involved, in a tissue-specific manner. Finally, a minimal promoter was identified for each of the target genes of the MBW complexes. Altogether, by answering fundamental questions and by demonstrating or invalidating previously made hypotheses, this study provides a new and comprehensive view of the transcriptional regulatory mechanisms controlling PA and anthocyanin biosynthesis in Arabidopsis
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