381 research outputs found
Gaia FGK Benchmark Stars: Effective temperatures and surface gravities
Large Galactic stellar surveys and new generations of stellar atmosphere
models and spectral line formation computations need to be subjected to careful
calibration and validation and to benchmark tests. We focus on cool stars and
aim at establishing a sample of 34 Gaia FGK Benchmark Stars with a range of
different metallicities. The goal was to determine the effective temperature
and the surface gravity independently from spectroscopy and atmospheric models
as far as possible. Fundamental determinations of Teff and logg were obtained
in a systematic way from a compilation of angular diameter measurements and
bolometric fluxes, and from a homogeneous mass determination based on stellar
evolution models. The derived parameters were compared to recent spectroscopic
and photometric determinations and to gravity estimates based on seismic data.
Most of the adopted diameter measurements have formal uncertainties around 1%,
which translate into uncertainties in effective temperature of 0.5%. The
measurements of bolometric flux seem to be accurate to 5% or better, which
contributes about 1% or less to the uncertainties in effective temperature. The
comparisons of parameter determinations with the literature show in general
good agreements with a few exceptions, most notably for the coolest stars and
for metal-poor stars. The sample consists of 29 FGK-type stars and 5 M giants.
Among the FGK stars, 21 have reliable parameters suitable for testing,
validation, or calibration purposes. For four stars, future adjustments of the
fundamental Teff are required, and for five stars the logg determination needs
to be improved. Future extensions of the sample of Gaia FGK Benchmark Stars are
required to fill gaps in parameter space, and we include a list of suggested
candidates.Comment: Accepted by A&A; 34 pages (printer format), 14 tables, 13 figures;
language correcte
VLT Observations of Turnoff stars in the Globular Cluster NGC 6397
VLT-UVES high resolution spectra of seven turnoff stars in the metal-poor
globular cluster NGC 6397 have been obtained. Atmospheric parameters and
abundances of several elements (Li, Na, Mg, Ca, Sc, Ti, Cr, Fe, Ni, Zn and Ba)
were derived for program stars. The mean iron abundance is [Fe/H] = -2.02, with
no star-to-star variation. The mean abundances of the alpha-elements (Ca, Ti)
and of the iron-peak elements (Sc, Cr, Ni) are consistent with abundances
derived for field stars of similar metallicity. Magnesium is also almost solar,
consistent with the values found by Idiart & Th\'evenin (2000) when non-LTE
effects (NLTE hereafter) are taken into account. The sodium abundance derived
for five stars is essentially solar, but one object (A447) is clearly Na
deficient. These results are compatible with the expected abundance range
estimated from the stochastic evolutionary halo model by Argast et al. (2000)
when at the epoch of [Fe/H] -2 the interstellar medium is supposed to
become well-mixed.Comment: to appear in A&
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
A new system for fast and quantitative analysis of heterologous gene expression in plants
Large-scale analysis of transcription factor–cis-acting element interactions in plants, or the dissection of complex transcriptional regulatory mechanisms, requires rapid, robust and reliable systems for the quantification of gene expression.Here, we describe a new system for transient expression analysis of transcription factors, which takes advantage of the fast and easy production and transfection of Physcomitrella patens protoplasts, coupled to flow cytometry quantification of a fluorescent protein (green fluorescent protein). Two small-sized and high-copy Gateway® vectors were specifically designed, although standard binary vectors can also be employed. As a proof of concept, the regulation of BANYULS (BAN), a key structural gene involved in proanthocyanidin biosynthesis in Arabidopsis thaliana seeds, was used. In P. patens, BAN expression is activated by a complex composed of three proteins (TT2/AtMYB123, TT8/bHLH042 and TTG1), and is inhibited by MYBL2, a transcriptional repressor, as in Arabidopsis. Using this approach, two new regulatory sequences that are necessary and sufficient for specific BAN expression in proanthocyanidin-accumulating cells were identified. This one hybrid-like plant system was successfully employed to quantitatively assess the transcriptional activity of four regulatory proteins, and to identify their target recognition sites on the BAN promoter
H-dibaryons and Primordial Nucleosynthesis
The apparent discrepancy between abundances of light nuclides predicted by
the standard Big-Bang and observational data is explained, by assuming the
presence of metastable H dibaryons at the nucleosynthesis era. These dibaryons
could be formed out of a small fraction of strange quarks at the moment of the
confinement transition. For a primordial deuterium abundance of the order of 3
10^{-5}, the measured differences in the 4He abundances requires a relative
abundance of H dibaryons of the order of n_H/n_B = 0.07, decaying in a
timescale of the order of 10^5 s.Comment: Latex, 5 pages, to appear in PR
Grown-up stars physics with MATISSE
MATISSE represents a great opportunity to image the environment around
massive and evolved stars. This will allow one to put constraints on the
circumstellar structure, on the mass ejection of dust and its reorganization ,
and on the dust-nature and formation processes. MATISSE measurements will often
be pivotal for the understanding of large multiwavelength datasets on the same
targets collected through many high-angular resolution facilities at ESO like
sub-millimeter interferometry (ALMA), near-infrared adaptive optics (NACO,
SPHERE), interferometry (PIONIER, GRAVITY), spectroscopy (CRIRES), and
mid-infrared imaging (VISIR). Among main sequence and evolved stars, several
cases of interest have been identified that we describe in this paper.Comment: SPIE, Jun 2016, Edimbourgh, Franc
HD 203608, a quiet asteroseismic target in the old galactic disk
A short observing run with the spectrometer Harps at the ESO 3.6-m telescope
was conducted in order to continue exploring the asteroseismic properties of F
type stars. In fact, Doppler observations of F type on the main sequence are
demanding and remain currently limited to a single case (HD 49933). Comparison
with photometric results obtained with the CoRoT mission on similar stars will
be possible with an enhanced set of observations. We selected the 4th magnitude
F8V star HD 203608, in order to investigate the oscillating properties of a
low-metallicity star of the old galactic disk. A 5-night asteroseismic
observation program has been conducted in August 2006 with Harps. Spectra were
reduced with the on-line data reduction software provided by the instrument. A
new statistical approach has been developed for extracting the significant
peaks in the Fourier domain. The oscillation spectrum shows a significant
excess power in the frequency range [1.5, 3.0 mHz]. It exhibits a large spacing
about 120.4 Hz at 2.5 mHz. Variations of the large spacing with frequency
are clearly identified, which require an adapted asymptotic development. The
modes identification is based on the unambiguous signature of 15 modes with
and 1. This observation shows the potential diagnostic of
asteroseismic constraints. Including them in the stellar modeling enhances
significantly the precision on the physical parameters of \cible, resulting in
a much more precise position in the HR diagram. The age of the star is now
determined in the range Gyr.Comment: 9 pages, submitted to A&
Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
We have determined the angular diameters of two metal-poor stars, HD 122563
and Gmb 1830, using CHARA and Palomar Testbed Interferometer observations. For
the giant star HD 122563, we derive an angular diameter theta_3D = 0.940 +-
0.011 milliarcseconds (mas) using limb-darkening from 3D convection simulations
and for the dwarf star Gmb 1830 (HD 103095) we obtain a 1D limb-darkened
angular diameter theta_1D = 0.679 +- 0.007 mas. Coupling the angular diameters
with photometry yields effective temperatures with precisions better than 55 K
(Teff = 4598 +- 41 K and 4818 +- 54 K --- for the giant and the dwarf star,
respectively). Including their distances results in very well-determined
luminosities and radii (L = 230 +- 6 L_sun, R = 23.9 +- 1.9 R_sun and L = 0.213
+- 0.002 L_sun, R = 0.664 +- 0.015 R_sun, respectively). We used the CESAM2k
stellar structure and evolution code in order to produce models that fit the
observational data. We found values of the mixing-length parameter alpha (which
describes 1D convection) that depend on the mass of the star. The masses were
determined from the models with precisions of <3% and with the well-measured
radii excellent constraints on the surface gravity are obtained (log g = 1.60
+- 0.04, 4.59 +- 0.02, respectively). The very small errors on both log g and
Teff provide stringent constraints for spectroscopic analyses given the
sensitivity of abundances to both of these values. The precise determination of
Teff for the two stars brings into question the photometric scales for
metal-poor stars.Comment: accepted A&A, 8 dbl-column pages, incl. 7 tables and 4 figure
An investigation of the close environment of beta Cep with the VEGA/CHARA interferometer
High-precision interferometric measurements of pulsating stars help to
characterize their close environment. In 1974, a close companion was discovered
around the pulsating star beta Cep using the speckle interferometry technique
and features at the limit of resolution (20 milli-arcsecond or mas) of the
instrument were mentioned that may be due to circumstellar material. Beta Cep
has a magnetic field that might be responsible for a spherical shell or
ring-like structure around the star as described by the MHD models. Using the
visible recombiner VEGA installed on the CHARA long-baseline interferometer at
Mt. Wilson, we aim to determine the angular diameter of beta Cep and resolve
its close environment with a spatial resolution up to 1 mas level. Medium
spectral resolution (R=6000) observations of beta Cep were secured with the
VEGA instrument over the years 2008 and 2009. These observations were performed
with the S1S2 (30m) and W1W2 (100m) baselines of the array. We investigated
several models to reproduce our observations. A large-scale structure of a few
mas is clearly detected around the star with a typical flux relative
contribution of 0.23 +- 0.02. Our best model is a co-rotational geometrical
thin ring around the star as predicted by magnetically-confined wind shock
models. The ring inner diameter is 8.2 +- 0.8 mas and the width is 0.6 +- 0.7
mas. The orientation of the rotation axis on the plane of the sky is PA = 60 +-
1 deg, while the best fit of the mean angular diameter of beta Cep gives UD[V]
= 0.22 +- 0.05 mas. Our data are compatible with the predicted position of the
close companion of beta Cep. These results bring additional constraints on the
fundamental parameters and on the future MHD and asteroseismological models of
the star.Comment: Paper accepted for publication in A&A (in press
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