F. Cuisinier

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

We present 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), respectively. The combined library has been intended for multiple-purpose synthetic photometry applications and was constructed according to the precepts adopted by Buser & Kurucz (1992): (i) to cover the largest possible ranges in stellar parameters (Te ,l og g ,a nd (M=H)); (ii) to provide flux spectra with useful resolution on the uniform grid of wave- lengths adopted by Kurucz (1995); and (iii) to provide synthetic broad{band colors which are highly realistic for the largest possible parameter and wavelength ranges. Because the most astrophysically relevant step consists in establishing a realistic library, the corresponding color calibration is described in some detail. Basically, for each value of the eective temperature and for each wavelength, we calculate the correction function that must be applied to a (theoretical) solar{abundance model flux spectrum in order for this to yield synthetic UBVRIJHKL colors matching the (empirical) color{temperature calibrations derived from observations. In this way, the most important systematic dierences existing between the original model spectra and the observations can indeed be eliminated. On the other hand, synthetic UBV and Washington ultravio- let excesses(U B) and(C M) and(C T1) obtained from the original giant and dwarf model spectra are in excel- lent accord with empirical metal{abundance calibrations (Lejeune & Buser 1996). Therefore, the calibration algo- rithm is designed in such a way as to preserve the original dierential grid properties implied by metallicity and/or luminosity changes in the new library, if the above cor- rection function for a solar{abundance model of a given eective temperature is also applied to models of the same temperature but dierent chemical compositions (M=H) and/or surface gravities logg. Send oprint requests to :R. Buser While the new library constitutes a rst{order approx- imation to the program set out above, it will be allowed to develop toward the more ambitious goal of matching the full requirements imposed on a standard library .M ajor input for renement and completion is expected from the extensive tests now being made in population and evolu- tionary synthesis studies of the integrated light of globular clusters (Lejeune 1997) and galaxies (Bruzual et al. 1997).

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

Aims. We present a homogeneous set of spectroscopic measurements secured with 4-m class telescopes for a sample of 90 planetary nebulae (PNe) located in the direction of the Galactic bulge. Methods. 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. Results. 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.

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

A study of the blue compact dwarf (BCD) galaxy Mrk 996 based on high-resolution optical Very Large Telescope Visible Multi-Object Spectrograph integral field unit spectroscopy is presented. Mrk 996 displays multicomponent line emission, with most line profiles consisting of a narrow, central Gaussian [full width at half-maximum (FWHM) similar to 110 km s(-1)] with an underlying broad component (FWHM similar to 400 km s(-1)). The broad HI Balmer component splits into two separate broad components inside a 1.5-arcsec radius from the nucleus; these are attributed to a two-armed minispiral. This spiral-like nucleus rotates in the same sense as the extended narrow line ionized gas but is offset by similar to 50 km s(-1) from the systemic velocity of the galaxy. The rotation curve of Mrk 996 derived from the H alpha narrow component yields a total mass of 5 x 10(8) M-circle dot within a radius of 3 kpc. From the H alpha luminosity we infer a global star formation rate of similar to 2 M-circle dot yr(-1).The high excitation energy, high critical density [O III] lambda 4363 and [N II] lambda 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 000K 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, measured [O III] and [Fe III] diagnostic line ratios are consistent with a temperature of 11 000K and an electron density of 107 cm(-3). The broad line emission regions show N/H and N/O enrichment factors of similar to 20 relative to the narrow line regions, but no He/H, O/H, S/H or Ar/H enrichment is inferred. Previous studies indicated that Mrk 996 showed anomalously high N/O ratios compared with BCDs of a similar metallicity. Our multicomponent analysis yields a revised metallicity of >= 0.5 Z(circle dot) (12 + log O/H = 8.37) for both the narrow and broad gas components, significantly higher than previous studies. As a result the narrow line regions N/O ratio is now typical for the galaxys metallicity. The narrow line components N/O ratio peaks outside the core region, spatially correlating with similar to 3-Myr-old stellar populations. The dominant line excitation mechanism is photoionization by the similar to 3000 Wolf-Rayet stars and similar to 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.

A spectroscopic study of the near-IR [SIII] lines in a sample of HII galaxies: chemical abundances

Aims. A detailed spectroscopic study covering the blue to near-infrared wavelength range (λ3700 A–1µm) 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]λλ9069,9532 A lines, given their importance in the derivation of the S/H abundance and relevant ionization diagnostics. Methods. 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 S 23 was performed for our sample galaxies. The relative hardness of their ionizing sources was studied using the η � parameter and exploring the role played by metallicity. Results. For 22 galaxies of the sample, a value of the electron temperature 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 the S 23 calibration. The abundance range covered by our sample goes from 1/20 solar up to solar metallicity. Six galaxies present 12+log (O/H) < 7.8 dex. The mean S/O ratio derived in this work is log (S/O) = −1.68 ± 0.20 dex, 1σ 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 three different stellar effective temperatures. This analysis indicates that a large fraction of galaxies in our sample seem to be ionized by extremely hard spectra, in line with recent suggestions for extra ionizing sources in HII galaxies.

Exploration of the BaSeL stellar library for 9 F-type stars COROT potential targets - Comparisons of fundamental stellar parameter determinations

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, m1 ,a ndc1). 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 Te, (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 condence regions around the best 2 -estimates and projected them on Te-(Fe/H), Te-log g ,a nd logg-(Fe/H) diagrams. We rst derive the 3 atmospheric parameters from the full photometric information available (Johnson and Stromgren data). The BaSeL library has only been calibrated for broad band UBVRIJHKLM photometry, and it presents therefore intrinsic limitations in respect to other photometric systems, especially with dierent bandwidth. Thus, using this combination (Johnson and Stromgren), BaSeL temperatures are systematically lower (130 K), and the discrepancy for the gravity and the metallicity can be quite large in comparison to the other methods. To disentangle these unexpected discrepancies, we xed the temperatures at their spectroscopic values and studied the relative influence of each colour index in the log g-(Fe/H) diagrams. We nd inconsistent results between Stromgren and Johnson synthetic colours. While the Johnson colours give impressively good log g-(Fe/H) solutions, the combination of the m1 and c1 Stromgren synthetic indices does not provide reliable results. This is not, of course, due to any intrinsic superiority of the UBV over the Stromgren system, but to the properties of the BaSeL models. Finally, in order to simultaneously and accurately determine the stellar parameters Te, (Fe/H) and log g, we suggest to use the combination of the synthetic BaSeL indices B V , U B and b y rather than B V , U B, b y, m1 and c1.

New Spectroscopic Data and Classification of Southern [WC] Stars*

New spectroscopic data of a sample of 10 southern [WC] stars are presented and described. Equivalent widths of carbon line transitions (C II λ4267, C III λ5696, and C IV λλ5801, 5812) are used to revise the classification of the seven late-type [WCL] stars of the sample. For them, our spectra allowed us to employ a quantitative system. We have confirmed the previous classification for three of the objects, but for three others, we have encountered different subtypes. Because of the weakness of the oxygen lines, it was not possible to suggest subtypes for the three [WCE] stars.

On the geometrical evolution of the ionized gas in HII galaxies

Aims. 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. Methods. 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 ,

Towards a Complete Library of Stellar Spectra for Evolutionary Synthesis

{\Delta \log Q\rm (H^0)}

Planetary Nebulae and Wavelet Transform

, with the metallicity. We find that, as far as the number of ionizing photons is concerned, no systematic tendency can be detected.
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Testing Evolutionary Models of Dwarf Irregular Galaxies through Gas and Stellar Metallicity Determinations in HII Galaxies

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