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We present a method for deriving the stellar fundamental parameters. It is based on a regularized sliced inverse regression (RSIR).We first tested it on noisy synthetic spectra of A, F, G, and K-type stars, and inverted simultaneously... more
We present a method for deriving the stellar fundamental parameters. It is based on a regularized sliced inverse regression (RSIR).We first tested it on noisy synthetic spectra of A, F, G, and K-type stars, and inverted simultaneously their atmospheric fundamental parameters: Teff., log g, [M/H] and v sin i. Different learning databases were calculated using a range of sampling in Teff., log g, v sin i, and [M/H]. Combined with a principal component analysis (PCA) nearest neighbors (NN) search, the size of the learning database is reduced. A Tikhonov regularization is applied, given the ill-conditioning of SIR. For all spectral types, decreasing the size of the learning database allowed us to reach internal accuracies better than PCA-based NN-search using larger learning databases. For each analyzed parameter, we have reached internal errors that are smaller than the sampling step of the parameter. We have also applied the technique to a sample of observed FGK and A stars. For a sel...
Context. Determination of high-precision abundances of late-type stars has been and always will be an important goal of spectroscopic studies, which requires accurate modeling of their stellar spectra with non-local thermodynamic... more
Context. Determination of high-precision abundances of late-type stars has been and always will be an important goal of spectroscopic studies, which requires accurate modeling of their stellar spectra with non-local thermodynamic equilibrium (NLTE) radiative transfer methods. This entails using up-to-date atomic data of the elements under study, which are still subject to large uncertainties. Aims. We investigate the role of hydrogen collisions in NLTE spectral line synthesis, and introduce a new general empirical recipe to determine inelastic charge transfer (CT) and bound-bound hydrogen collisional rates. This recipe is based on fitting the energy functional dependence of published quantum collisional rate coefficients of several neutral elements (BeI, Na I, Mg I, Al I, Si I and Ca I) using simple polynomial equations. Methods. We perform thorough NLTE abundance calculation tests using our method for four different atoms, Na, Mg, Al and Si, for a broad range of stellar parameters....
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Abundances of 18 chemical elements have been derived for 27 A/Am and 16 F stars members of the Pleiades and Coma Berenices open clusters. We have specifically computed, with the Montrèal code, a series of evolutionary models for two A... more
Abundances of 18 chemical elements have been derived for 27 A/Am and 16 F stars members of the Pleiades and Coma Berenices open clusters. We have specifically computed, with the Montrèal code, a series of evolutionary models for two A star members of these two clusters. None of the models reproduces entirely the overall shape of the abundance patterns. The
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ABSTRACT Abundances of 14 chemical elements have been derived for the two components of the double-lined AmFm spectroscopic binary o Leonis in order to set constraints on the main physical processes that lead to the Am star phenomenon.... more
ABSTRACT Abundances of 14 chemical elements have been derived for the two components of the double-lined AmFm spectroscopic binary o Leonis in order to set constraints on the main physical processes that lead to the Am star phenomenon. The tomographic image reconstruction and Fourier disentangling techniques were used in order to recover individual spectra from the composite spectra of the binary system observed in 9 nights using the SOPHIE spectrograph at the Observatoire de Haute Provence. Abundances have been derived by iteratively adjusting synthetic spectra to the normalized spectra of the two components by chi-squared minimization. The abundance determinations made in this paper clearly show that both components of the o Leonis binary system exhibit Am characteristics. Comparison with self-consistent evolutionary models including atomic diffusion and turbulence or mass loss shows a good agreement. This is in favor of the scenario in which element separation occurs relatively deep in the star.
ABSTRACT We show how the range of application of the principal component analysis-based inversion method of Paletou et al. (2015) can be extended to late-type stars data. Besides being an extension of its original application domain, for... more
ABSTRACT We show how the range of application of the principal component analysis-based inversion method of Paletou et al. (2015) can be extended to late-type stars data. Besides being an extension of its original application domain, for FGK stars, we also used synthetic spectra for our learning database. We discuss our results on effective temperatures against previous evaluations made available from Vizier and Simbad services at CDS.
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Abundance anomalies have been determined at the surface of many field and open cluster A and F dwarfs. These abundance anomalies are most likely caused by microscopic diffusion at work within the stable envelopes of A stars. However... more
Abundance anomalies have been determined at the surface of many field and open cluster A and F dwarfs. These abundance anomalies are most likely caused by microscopic diffusion at work within the stable envelopes of A stars. However diffusion can be counteracted by several other mixing processes such as convection, rotational mixing and mass loss. We present a short review of the surface abundance patterns of A/F stars in the Pleiades (100 Myr), Coma Berenices (450 Myr) and Hyades (650 Myr) open clusters. Real star-to-star variations of the abundances were found for several chemical elements in the A dwarfs in these clusters. The derived abundances are then compared to evolutionary models from the Montreal group. These comparisons strongly suggest the occurence of hydrodynamical processes at play within the radiative zones of these stars and hindering the effects of microscopic diffusion (mixing processes/mass loss). In the frame of Gaia mission, simulations are presented that predi...
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In table 11, we present the magnitudes values for Gaia, Johnson-Cousins, Hipparcos, Tycho and Sloan bands. These magnitude are derived for the BaSeL3.1 sample stars with four absorption values (0,1,3,5). Table 12 displays the bolometric... more
In table 11, we present the magnitudes values for Gaia, Johnson-Cousins, Hipparcos, Tycho and Sloan bands. These magnitude are derived for the BaSeL3.1 sample stars with four absorption values (0,1,3,5). Table 12 displays the bolometric correction un G, BP and RP for the BaSeL3.1 stars. Table 13 represents the computed ratios for interstellar absorption in different bands. (3 data files).
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Abundances of 18 chemical elements have been derived for 27 A/Am and 16 F stars members of the Pleiades and Coma Berenices open clusters. We have specifically computed, with the Montr\'eal code, a series of evolutionary models for two... more
Abundances of 18 chemical elements have been derived for 27 A/Am and 16 F stars members of the Pleiades and Coma Berenices open clusters. We have specifically computed, with the Montr\'eal code, a series of evolutionary models for two A stars members of these two clusters. None of the models reproduces entirely the overall shape of the abundances patterns. The
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In table 5 and 6, we present the abundances of 15 chemical elements in 16 A and 26 F stars members of the Hyades open cluster. These abundances are relative to hydrogen and to the sun. The abundances derived for procyon are also included.... more
In table 5 and 6, we present the abundances of 15 chemical elements in 16 A and 26 F stars members of the Hyades open cluster. These abundances are relative to hydrogen and to the sun. The abundances derived for procyon are also included. The absolute parameters for the observed stars as the luminosity, effective temperature, mass and fractional age (fraction of time spent on the Main Sequence) are displayed in table 7. Table 8 collects the abundances derived for each transition for each studied element in all A and F stars including Procyon (F5V) which served as control star for the spectral synthesis. In this table, the absolute values are represented (log(X/H)+12) and the wavelengths are in Angstrom. (4 data files).
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Abundances of Fe, Ti, Cr, Mg and He have been determined for 10 stars (5 B, 3 A, 1 F dwarfs and 1 chemically peculiar giant B8IIIp with apparent velocities ranging from 15 to 130 km.s-1) of the Alpha Persei open cluster (log age=7.40... more
Abundances of Fe, Ti, Cr, Mg and He have been determined for 10 stars (5 B, 3 A, 1 F dwarfs and 1 chemically peculiar giant B8IIIp with apparent velocities ranging from 15 to 130 km.s-1) of the Alpha Persei open cluster (log age=7.40 yrs). The method consists in adjusting grids of synthetic spectra calculated with SYNSPEC48 code (Hubeny & Lanz 1992) in the region of 4450-4600 Å and Kurucz's ATLAS9 model atmospheres. A correlation may exist between [Fe/H] and the effective temperature. Further observations of a much larger sample of B, A and F stars in this cluster are foreseen in the near future.