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F. Cuisinier

Publications and source records attributed to F. Cuisinier.

17 recordsLinked to original sources
arXiv2009

A VLT VIMOS study of the anomalous BCD Mrk 996: mapping the ionised gas kinematics and abundances

A study of the blue compact dwarf (BCD) galaxy Mrk 996 based on high resolution optical VLT VIMOS integral field unit spectroscopy is presented. Mrk 996 displays multi-component line emission, with most line profiles consisting of a narrow, central Gaussian with an underlying broad component. The broad HI Balmer component splits into two separate broad components inside a 1".5 radius from the nucleus; these are attributed to a two-armed mini-spiral. The rotation curve of Mrk 996 derived from the Hαnarrow component yields a total mass of 5x10^8 Msol within a radius of 3 kpc. The high excitation energy, high critical density [O III] 4363 and [N II] 5755 lines are only detected from the inner region and exist purely in broad component form, implying unusual excitation conditions. Surface brightness, radial velocity, and FWHM maps for several emission components are presented. A separate physical analysis of the broad and narrow emission line regions is undertaken. We derive an upper limit of 10,000 K for the electron temperature of the narrow line gas, together with an electron density of 170 cm^-3, typical of normal H II regions. For the broad line component, we estimate a temperature of 11,000 K and an electron density of 10^7 cm^-3. The broad line emission regions show a N/H enrichment factor of ~20 relative to the narrow line regions, but no He/H, O/H, S/H, or Ar/H enrichment is inferred. The dominant line excitation mechanism is photoionisation by the ~3000 WR stars and ~150,000 O-type stars estimated to be present in the core. This is indeed a peculiar BCD, with extremely dense zones of gas in the core, through which stellar outflows and possible shock fronts permeate contributing to the excitation of the broad line emission. [Abridged]

astro-ph.GA↗
arXiv2009

Planetary nebulae in the direction of the Galactic bulge: On nebulae with emission-line central stars

We present a homogeneous set of spectroscopic measurements secured with 4-meter class telescopes for a sample of 90 planetary nebulae (PNe) located in the direction of the Galactic bulge. We derive their plasma parameters and chemical abundances. For half of the objects this is done for the first time. We discuss the accuracy of these data and compare it with other recently published samples. We analyze various properties of PNe with emission-line central stars in the Galactic bulge. Investigating the spectra we found that 7 of those PNe are ionized by Wolf-Rayet ([WR]) type stars of the very late (VL) spectral class [WC 11] and 8 by weak emission-line (WEL) stars. From the analysis we conclude that the PN central stars of WEL, VL and remaining [WR] types form three, evolutionary unconnected forms of enhanced mass-loss among central stars of PNe. [WR] PNe seem to be intrinsically brighter than other PNe. Overall, we find no statistically significant evidence that the chemical composition of PNe with emission-line central stars is different from that of the remaining Galactic bulge PNe.

astro-ph.SR↗
arXiv2006

A Spectroscopic Study of the Near-IR [SIII] Lines in a Sample of HII Galaxies: chemical abundances

A detailed spectroscopic study, from lambda 3700 A to 1 um, was performed for a sample of 34 HII galaxies in order to derive fundamental parameters for their HII regions and ionizing sources, as well as gaseous metal abundances. All the spectra included the nebular [SIII]9069,9532 A lines, given their importance in the derivation of the S/H abundance and relevant ionization diagnostics. A systematic method was followed to correct the near-IR [SIII] line fluxes for the effects of the atmospheric transmission.A comparative analysis of the predictions of the empirical abundance indicators R23 and S23 has been performed. The relative hardness of their ionizing sources was studied using the eta parameter, and exploring the role played by metallicity. For 22 galaxies of the sample a direct value of te[SIII] was derived, along with their ionic and total S/H abundances. Their ionic and total O/H abundances were derived using direct determinations of te[OIII].For the rest of the objects, the total S/H abundance was derived using S23. The abundance range covered by our sample goes from 1/20 solar up to solar metallicity. The mean S/O ratio derived is log (S/O)=-1.68+/-0.20 dex, 1 sigma below the solar S/O value. The S/O abundance ratio shows no significant trend with O/H over the range of abundance covered in this work, in agreement with previous findings.There is a trend for HII galaxies with lower gaseous metallicity to present harder ionizing spectra. We compared the distribution of the ionic ratios O+/O++ vs. S+/S++ derived for our sample with the predictions of a grid of photoionization models performed for different stellar effective temperatures. This analysis indicates that a large fraction of galaxies in our sample seem to be ionized by extremely hard spectra.

astro-ph↗
arXiv2006

On the geometrical evolution of the ionized gas in HII galaxies

In this paper, we investigate the behaviour of the number of Lyman continuum ionizing photons as compared to the actual number of hydrogen recombinations in HII galaxies. We evaluate the number of ionizing photons from the population synthesis of spectra observed in the visible, extrapolating the spectra to the extreme ultraviolet (EUV), beyond the Lyman limit. We check for possible systematic deviations of the predicted ionizing spectra in the EUV by comparing the ratio of the predicted number of ionizing photons to the number of recombinations, as measured in H$β$, ${\rm Δ\log Q(H^0)}$, with the metallicity. We find that, as far as the number of ionizing photons is concerned, no systematic tendency can be detected. The ${\rm Hβ}$ equivalent width can be understood as a nebular age indicator, decreasing with age, although the observed ${\rm Hβ}$ equivalent width can also be affected by the contribution to the continuum by the accumulation of previous, non-ionizing stellar populations. We attribute the increase of ${\rm Δ\log Q(H^0)}$ with the age of the burst to the fact that more and more ionizing photons escape the nebulae when the nebulae get older, because of their increasing, expansion-induced subfragmentation.

astro-ph↗
arXiv2004

Stellar Populations in HII Galaxies

We analyse the stellar content of a large number of HII galaxies from the continua and absorption features of their spectra using population synthesis methods, in order to gain information about the star formation histories of these objects. We find that all galaxies of our sample contain an old stellar population (>= 1 Gyr) that dominates the stellar mass, and in a majority of these we also found evidence for an intermediate-age population >= 50 Myr apart from the presently bursting, ionizing young generation <= 10^7 yrs

astro-ph↗
arXiv2001

A standard stellar library for evolutionary synthesis. III. Metallicity calibration

We extend the colour calibration of the widely used BaSeL standard stellar library (Lejeune, Cuisinier, & Buser 1997, 1998) to non-solar metallicities, down to [Fe/H] ~ -2.0 dex. Surprisingly, we find that at the present epoch it is virtually impossible to establish a unique calibration of UBVRIJHKL colours in terms of stellar metallicity [Fe/H] which is consistent simultaneously with both colour-temperature relations and colour-absolute magnitude diagrams (CMDs) based on observed globular cluster photometry data and on published, currently popular standard stellar evolutionary tracks and isochrones. The problem appears to be related to the long-standing incompleteness in our understanding of convection in late-type stellar evolution, but is also due to a serious lack of relevant observational calibration data that would help resolve, or at least further significant progress towards resolving this issue. In view of the most important applications of the BaSeL library, we here propose two different metallicity calibration versions: (1) the "WLBC 99" library, which consistently matches empirical colour-temperature relations and which, therefore, should make an ideal tool for the study of individual stars; and (2), the "PADOVA 2000" library, which provides isochrones from the Padova 2000 grid (Girardi et al., 2000) that successfully reproduce Galactic globular-cluster colour-absolute magnitude diagrams and which thus should prove particularly useful for studies of collective phenomena in stellar populations in clusters and galaxies.

astro-ph↗
arXiv2001

The BaSeL library as a basic tool to provide fundamental stellar parameters of future space missions: COROT and GAIA

COROT and GAIA are two future major space missions directly connected to most of the stellar astrophysic questions, from stellar physics to evolution of galaxies. We describe a project for the preparation of these two missions by using the possibilities of the ``BaSeL'' models, a library of theoretical stellar energy distributions, to provide automatically the fundamental stellar parameters of the candidate stars. We present the results already obtained for the stars of the COROT main programme.

astro-ph↗
arXiv2001

Atmospheric parameters for non-interacting eclipsing binaries: preliminary results from synthetic photometry

Double-lined spectroscopic binaries which are also eclipsing provide the most accurate stellar data, and are consequently of first importance to improve stellar evolution modelling. While the mass and radius of each component of detached eclipsing binaries (EBs) can be accurately known, their temperature Teff and chemical composition ([Fe/H]) are still uncertain. To contribute to overcome these difficulties, we present metallicity-dependent Teff determinations of 11 EBs (22 individual stars) from Stromgren synthetic photometry. Inconsistencies suggesting new photometric observations are discussed. Moreover, by exploring the best chi^2-fits to the photometric data, we have re-derived their reddening.

astro-ph↗
arXiv2001

Preparation of the COROT space mission: fundamental stellar parameters determinations from photometric and spectroscopic analyses for COROT potential target candidates

We present a sample of 9 nearby F-type stars with detailed spectroscopic analyses to investigate the Basel Stellar Library (BaSeL) in two photometric systems simultaneously, UBV Johnson and uvby Stromgren. The sample corresponds to potential targets of the central seismology programme of the COROT space experiment, which have been recently observed at Observatoire de Haute-Provence (OHP, France). The atmospheric parameters Teff, [Fe/H], and log g obtained from the BaSeL models are compared with spectroscopic determinations as well as with results of other photometric calibrations. Moreover, new rotational velocity determinations are also derived from the spectroscopic analysis and compared with previous results compiled in the SIMBAD database. All the methods presented give consistent solutions, and the agreement between Templogg and BaSeL for the hottest stars of the sample could be especially useful in view of the well known difficulty of spectroscopic determinations for fast rotating stars. Finally, we present current and future developments of the BaSeL models for a systematic application to all the COROT targets. (Abridged)

astro-ph↗
arXiv2001

The Galactic Bulge: The Stellar and Planetary Nebulae Populations

We compare abundances patterns in the Bulge for elements observed in stars and in planetary nebulae. Some alpha elements, like Mg and Ti, are overabundant respect to Fe, and others are not, like He, O, Si, S, Ar, Ca. The first ones favor a quick evolution of the Galactic Bulge, and the seconds a much slower one.

astro-ph↗
arXiv2000

Exploration of the BaSeL stellar library for 9 F-type stars COROT potential targets

The Basel Stellar Library (BaSeL models) is constituted of the merging of various synthetic stellar spectra libraries, with the purpose of giving the most comprehensive coverage of stellar parameters. It has been corrected for systematic deviations detected in respect to UBVRIJHKLM photometry at solar metallicity, and can then be considered as the state-of-the-art knowledge of the broad band content of stellar spectra. In this paper, we consider a sample of 9 F-type stars with detailed spectroscopic analysis to investigate the Basel Stellar Library in two photometric systems simultaneously, Johnson (B-V, U-B) and Stromgren (b-y, m_1, and c_1). The sample corresponds to potential targets of the central seismology programme of the COROT space experiment, which have been recently observed at OHP. The atmospheric parameters T_eff, [Fe/H], and log g obtained from the BaSeL models are compared with spectroscopic determinations as well as with results of other photometric calibrations. For a careful interpretation of the BaSeL solutions, we computed confidence regions around the best $χ$^2-estimates and projected them on T_eff-[Fe/H], T_eff-log g, and log g-[Fe/H] diagrams. (Abridged)

astro-ph↗
arXiv2000

Stars and Planetary Nebulae in the Galactic Bulge

We compare the populations of Red Giant stars and Planetary Nebulae in the Galactic Bulge, in the light of recent determinations of their abundances patterns. We find both populations to be compatible. From the planetary nebulae, we find evidences that the Bulge did not form stars recently. The whole abundances pattern remains however puzzling, some elements favoring a quick evolution of the Galactic Bulge (Mg and Ti), and others a much slower one (He, O, Si, S, Ar and Ca).

astro-ph↗
arXiv1999

Observations of planetary nebulae in the Galactic Bulge

High quality spectrophotometric observations of 30 Planetary Nebulae in the Galactic Bulge have been made. Accurate reddenings, plasma parameters, and abundances of He,O,N,S,Ar,Cl are derived. We find the abundances of O,S,Ar in the Planetary Nebulae in the Galactic Bulge to be comparable with the abundances of the Planetary Nebulae in the Disk, high abundances being maybe slightly more frequent in the Bulge. The distribution of the N/O ratio does not present in the Galactic Bulge Planetary Nebulae the extension to high values that it presents in the Disk Planetary Nebulae. We interpret this as a signature of the greater age of Bulge Planetary Nebulae. We thus find the Bulge Planetary Nebulae to be an old population, slightly more metal-rich than the Disk Planetary Nebulae. The population of the Bulge Planetary Nebulae shows hence the same characteristics than the Bulge stellar population.

astro-ph↗
arXiv1997

A standard stellar library for evolutionary synthesis: II. The M dwarf extension

A standard library of theoretical stellar spectra intended for multiple synthetic photometry applications including spectral evolutionary synthesis is presented. The grid includes M dwarf model spectra, hence complementing the first library version established in Paper I (Lejeune, Cuisinier & Buser 1997). It covers wide ranges of fundamental parameters: Teff : 50,000 K to 2000 K, log g : 5.5 to -1.02, and [M/H] : +1.0 to -5.0. A correction procedure is also applied to the theoretical spectra in order to provide color-calibrated flux distributions over a large domain of effective temperatures. For this purpose, empirical Teff-color calibrations are constructed between 11500 K and 2000 K, and semi-empirical calibrations for non-solar abundances ([M/H] = -3.5 to +1.0) are established. Model colors and bolometric corrections for both the original and the corrected spectra, synthesized in the UBVRcIcJHKLL'M system, are given for the full range of stellar parameters. We find that the corrected spectra provide a more realistic representation of empirical stellar colors, though the method employed is not completely adapted to the lowest temperature models. In particular the original differential colors of the grid implied by metallicity and/or luminosity changes are not preserved below 2500 K. Limitations of the correction method used are also discussed.

astro-ph↗
arXiv1997

A standard stellar library for evolutionary synthesis: I. Calibration of theoretical spectra

A comprehensive hybrid library of synthetic stellar spectra based on three original grids of model atmosphere spectra by Kurucz (1995), Fluks et al. (1994), and Bessell et al. (1989, 1991) is presented. The combined library is intended for multiple-purpose synthetic photometry applications and is constructed in order (i) to cover the largest possible ranges in Teff, log g, and [M/H]), (ii) to provide flux spectra with useful resolution on the uniform grid of wavelengths, and (iii) to provide realistic synthetic broad-band colors for the largest possible parameter and wavelength ranges. For each value of the effective temperature and for each wavelength, we calculate the correction function that must be applied to a (theoretical) solar-abundance model flux spectrum which yields synthetic UBVRIJHKL colors matching the (empirical) color-temperature calibrations derived from observations. The calibration algorithm is designed to preserve the original differential grid properties implied by metallicity and/or luminosity changes in the new library. The corresponding color calibration is described in some detail.

astro-ph↗
arXiv1995

COMPARATIVE STUDY OF A [WC 6] NUCLEUS WITH OTHER EMISSION-LINES NUCLEI OF PLANETARY NEBULAE

The central star (CSPN) of the planetary nebula M 1-25 (PN G 4.9+4.9) is classified as a [WC 6] star, the only CSPN of this subclass known at this time. A comparison with the other emission-lines CSPN (the [WC]-class and the 'weak emission-lines stars' or {\em wels}-class) shows that (1) the characteristics of this [WC 6] star fit well inside the main properties of the other [WC] CSPN ; (2) the [WC] CSPN seem to evolve from the [WC 8-11] (latter) to [WC 2-4] (earlier) subclasses, say from dense nebulae with cool stars to more extended nebulae with hot nuclei, as for other CSPN ; (3) on the two-colour IRAS diagram,the [WC] and the {\em wels} CSPN form two different groups : the progenitors of the [WC]-type CSPN seem to be Carbon stars evolving along post-AGB tracks, whereas the {\em wels} CSPN seem to be related to OH/IR stars, some of them having possibly experienced a late helium-flash.

astro-ph↗