F. Cuisinier

Federal University of Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil

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Publications (60)79.58 Total impact

  • Pieter Westera, François Cuisinier, Didier Curty, Roland Buser
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    ABSTRACT: Dwarf irregular galaxies are usually low-metallicity objects, and show ongoing or very recent star formation, giving rise to their irregular appearance. Especially HII galaxies, a sub-category of dwarf irregulars showing unusually high star formation activity, are believed to be among the least evolved galaxies in existence today. Therefore, they are very interesting objects for studies of early galaxy evolution and of metallicity enrichment mechanisms.
    Proceedings of the International Astronomical Union 03/2013; 8(S292):254-254.
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    Pieter Westera, François Cuisinier, Didier Curty, Roland Buser
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    ABSTRACT: We examine the gas and stellar metallicities in a sample of HII galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of HII galaxy spectra to date. We eliminated all spectra with an insufficient signal-to-noise ratio, without strong emission lines, and without the [OII] lambda3727 {\AA} line, which is necessary for the determination of the gas metallicity. This excludes galaxies with redshift <~ 0.033. Our final sample contains ~700 spectra of HII galaxies. Through emission line strength calibrations and a detailed stellar population analysis employing evolutionary stellar synthesis methods, which we already used in previous works, we determined the metallicities of both the gas and the stellar content of these galaxies. We find that in HII galaxies up to stellar masses of 5\cdot10^9 M_sol, enrichment mechanisms do not vary with galactic mass, being the same for low- and high-mass galaxies on average. They do seem to present a greater variety at the high-mass end, though, indicating a more complex assembly history for high-mass galaxies. In around 23 per cent of our HII galaxies we find a metallicity decrease over the last few Gyr. Our results favour galaxy evolution models featuring constantly infalling low-metallicity clouds that retain part of the galactic winds. Above 5\cdot10^9 M_sol stellar mass, the retention of high metallicity gas by the galaxies' gravitational potential dominates.
    Monthly Notices of the Royal Astronomical Society 12/2011; 421(1). · 5.52 Impact Factor
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    Didier Curty, François C. Cuisinier, Carlos R. Rabaça
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    ABSTRACT: The wavelet transform acts to segregate objects in function of their size. We apply this method on images of galaxies to decompose them into coefficients representing only objects of the same size. The total fluxes of the wavelet coefficients describe the cumulative power spectrum of spatial frequencies. Based on this spectrum, we propose a new parameter to quantify the galaxy texture. As expected, it remains small and quite invariant for early-type galaxies, while it covers a large range and takes larger values for late-type galaxies. Combined with a second parameter, our determination of the texture is able to successfully separate galaxy types. By thresholding the wavelet coefficients, we detect luminous lumps. In irregular galaxies, their radial distribution seems to show a double peak. This could be the trace of a privileged radial distance of strong star formation regions.
    Proceedings of the International Astronomical Union 04/2010; 5(S262):317-318.
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    Pieter Westera, François Cuisinier, Carlos R. Rabaça
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    ABSTRACT: We examine the star forming phenomenon as it can be encountered in galaxies in the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of star forming galaxy spectra to date. After eliminating all spectra with an insufficient signal-to-noise ratio, without strong emission lines, and without the [OII] lambda3727 Å line, which is necessary for the determination of the gas metallicity (which excludes galaxies with redshift &lsim; 0.024-0.025), our sample contains ~6000 spectra of star forming galaxies. Through a detailed stellar population analysis employing evolutionary synthesis methods we determined the stellar composition of these galaxies, that is, the masses, ages and metallicities of their partial stellar populations. We find that most, possibly all, galaxies of our sample contain, apart from the presently bursting, ionising young generation (= 109 yrs) and intermediate (between 107 and 109 yrs) populations, whereas the old population dominates the stellar mass (but not the light). We also find that high (stellar) mass galaxies have higher gas metallicities and lower present star formation rates relative to their total (stellar) masses, than low mass galaxies, indicating a higher chemical evolution degree for high mass galaxies. Furthermore, we find that gas enrichment mechanisms in star forming galaxies do not vary with galactic mass, being the same for low- and high-mass galaxies on average. Gas enrichment mechanisms seem to present a greater variety at the high-mass end, though, indicating a more complex assembly history for high-mass galaxies.
    Proceedings of the International Astronomical Union 01/2010; 262:446-447.
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    ABSTRACT: ABSTRACTA 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) ∼ 110 km s−1] with an underlying broad component (FWHM ∼ 400 km s−1). The broad H i 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 ∼50 km s−1 from the systemic velocity of the galaxy. The rotation curve of Mrk 996 derived from the Hα narrow component yields a total mass of 5 × 108 M⊙ within a radius of 3 kpc. From the Hα luminosity we infer a global star formation rate of ∼2 M⊙ yr−1.The high excitation energy, high critical density [O iii]λ4363 and [N ii]λ5755 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, measured [O iii] and [Fe iii] diagnostic line ratios are consistent with a temperature of 11 000 K and an electron density of 107 cm−3. The broad line emission regions show N/H and N/O enrichment factors of ∼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⊙ (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 region's N/O ratio is now typical for the galaxy's metallicity. The narrow line component's N/O ratio peaks outside the core region, spatially correlating with ∼3-Myr-old stellar populations. The dominant line excitation mechanism is photoionization by the ∼3000 Wolf–Rayet 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.
    Monthly Notices of the Royal Astronomical Society 08/2009; 398(1):2 - 22. · 5.52 Impact Factor
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    ABSTRACT: We present Integral Field Unit GMOS-IFU data of the compact H II galaxy UM 408, obtained at the Gemini South telescope, in order to derive the spatial distribution of emission lines and line ratios, kinematics, plasma parameters, and oxygen abundances as well the integrated properties over an area of 3''×44 equivalent with ~750 pc × 1100 pc located in the central part of the galaxy. The starburst in this area is resolved into two giant regions of about 15 and 1'' (~375 and ~250 pc) diameter, respectively and separated 1.5-2'' (~500 pc). The extinction distribution concentrate its highest values close but not coincident with the maxima of Hα emission around each one of the detected regions. This indicates that the dust has been displaced from the exciting clusters by the action of their stellar winds. The ages of these two regions, estimated using Hβ equivalent widths, suggest that they are coeval events of ~5 Myr with stellar masses of ~104 M ☉. We have also used [O III]/Hβ and [S II]/Hα ratio maps to explore the excitation mechanisms in this galaxy. Comparing the data points with theoretical diagnostic models, we found that all of them are consistent with excitation by photoionization by massive stars. The Hα emission line was used to measure the radial velocity and velocity dispersion. The heliocentric radial velocity shows an apparent systemic motion where the east part of the galaxy is blueshifted, while the west part is redshifted, with a relative motion of ~10 km s–1. The velocity dispersion map shows supersonic values typical for extragalactic H II regions. We derived an integrated oxygen abundance of 12+log(O/H) = 7.87 summing over all spaxels in our field of view. An average value of 12+log(O/H) = 7.77 and a difference of Δ(O/H) = 0.47 between the minimum and maximum values (7.58 ± 0.06-8.05 ± 0.04) were found, considering all data points where the oxygen abundance was measured. The spatial distribution of oxygen abundance does not show any significant gradient across the galaxy. On the other hand, the bulk of data points are lying in a region of ±2σ dispersion (with σ = 0.1 dex) around the average value, confirming that this compact H II galaxy, like other previously studied dwarf irregular galaxies, is chemically homogeneous. Therefore, the new metals processed and injected by the current star formation episode are possibly not observed and reside in the hot gas phase, whereas the metals from previous events are well mixed and homogeneously distributed through the whole extent of the galaxy.
    The Astronomical Journal 05/2009; 137(6):5068. · 4.97 Impact Factor
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    ABSTRACT: Through the application of the wavelet technique to a planetary nebulae image, we are able to identify different scale sizes structures present in its wavelet coefficient decompositions. In a multiscale vision model, an object is defined as a hierarchical set of these structures. We can then use this model to independently reconstruct the different objects that compose the nebulae. The result is the separation and identification of superposed objects, some of them with very low surface brightness, what makes them, in general, very difficult to be seen in the original images due to the presence of noise. This allows us to make a more detailed analysis of brightness distribution in these sources. In this project, we use this method to perform a detailed morphological study of some planetary nebulae and to investigate whether one of them indeed shows internal temperature fluctuations. We have also conducted a series of tests concerning the reliability of the method and the confidence level of the objects detected. The wavelet code used in this project is called OV_WAV and was developed by the UFRJ's Astronomy Departament team.
    05/2009;
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    ABSTRACT: 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 H\alpha narrow 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] Comment: Accepted for publication in MNRAS main journal. Minor corrections made and additional discussion. 23 pages, 23 figures
    03/2009;
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    ABSTRACT: Through the application of the wavelet technique to a planetary nebulae image, we are able to identify different scale sizes structures present in its wavelet coefficient decompositions. In a multiscale vision model, an object is defined as a hierarchical set of these structures. We can then use this model to independently reconstruct the different objects that compose the nebulae. The result is the separation and identification of superposed objects, some of them with very low surface brightness, what makes them, in general, very difficult to be seen in the original images due to the presence of noise. This allows us to make a more detailed analysis of brightness distribution in these sources. In this project, we use this method to perform a detailed morphological study of some planetary nebulae and to investigate whether one of them indeed shows internal temperature fluctuations. We have also conducted a series of tests concerning the reliability of the method and the confidence level of the objects detected. The wavelet code used in this project is called OV_WAV and was developed by the UFRJ's Astronomy Departament team.
    XII Latin American IAU Regional Meeting; 10/2007
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    ABSTRACT: We present a detailed spectroscopic study of a sample of 34 star-forming dwarf galaxies, ranging from the blue to near-infrared (λ3700Å-1μm) (Kehrig et al. 2006). The metal enrichment in this kind of objects has been operating typically at low metallicity enviroments. The spectra were observed with the 1.52m telescope at La Silla/ESO. We derive fundamental parameters for HII regions and ionizing sources in our star-forming galaxies, as well as gaseous metal abundances. All the spectra include the nebular[SIII]λλ9069,9532Å lines, that are of crucial importance in the derivation of the S/H abundances, and relevant ionization diagnostics. We study the relative hardness of their ionizing sources using the η' parameter (Vílchez & Pagel 1988), and exploring the roles played by metallicity and age. The ionic and total O/H was also derived using direct determinations of the te[OIII]. The mean S/O ratio derived in this work is constant and slightly below the solar (S/O) value (see fig 1). The data presented here are consistent with the conclusion that S/O remains constant as O/H varies among the sample of HII galaxies. Variations in S/O along the whole O/H abundance range may be present, but the scatter in S/O (due mainly to observational errors) is still large to constrain them. The assumption that the S/O ratio remains constant for all abundances is still an open question and should be explored further (Pérez-Montero et al. 2006).
    Proceedings of the International Astronomical Union 07/2006; 2:315 - 315.
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    ABSTRACT: 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. Comment: 12 pages, 8 figures, accepted for publication in the A&A, minor gramatical corrections included
    Astronomy and Astrophysics 06/2006; · 5.08 Impact Factor
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    F. Cuisinier, P. Westera, E. Telles, R. Buser
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    ABSTRACT: 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$\beta$, ${\rm \Delta \log Q(H^0)}$, with the metallicity. We find that, as far as the number of ionizing photons is concerned, no systematic tendency can be detected. The ${\rm H\beta}$ equivalent width can be understood as a nebular age indicator, decreasing with age, although the observed ${\rm H\beta}$ 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 ${\rm \Delta \log Q(H^0)}$ 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. Comment: 14 pages, accepted in A&A
    Astronomy and Astrophysics 05/2006; · 5.08 Impact Factor
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    ABSTRACT: In this work, we investigate the recycling properties of the interestellar medium in HII galaxies from the analysis of the spatial variation of Oxygen abundance. The spatial variation of the abundance of this element should reflect the physical mechanisms involved in their recycling processes. We present the preliminary results for the galaxy UM 408, observed at the Gemini south observatory using GMOS-IFU spectroscopy. UM 408 is a compact and low metallicity galaxy without WR signature in their spectra. Maps of emission lines, continuum, EW(Hbeta ), Log [OIII]/Hbeta and T_e are derived and compared with the spatial distribution of 12+Log(O/H). We do not observe a significant gradient in the oxygen abundance, suggesting that the new metals formed in the current star formation episode are possibly not observed and reside in a hot gas phase, whereas the metals from previous events are well mixed and homogeneously distributed through the whole extent of the galaxy. Under this supposition an underlying old stellar population would be expected.
    01/2006;
  • P. Westera, F. Cuisinier, E. Telles, C. Kehrig
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    ABSTRACT: 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 (>=1Gyr) that dominates the stellar mass, and in a majority of these we also found evidence for an intermediate-age population >=50Myr apart from the presently bursting, ionizing young generation
    VizieR Online Data Catalog. 08/2005;
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    ABSTRACT: We present an analysis of narrowband images of planetary nebulae, obtained from the HST archive, by wavelet transform. This technique allows us to identify new substructures, present in all planetary nebulae of our sample at some level. In the case of one planetary nebula Hubble 4, we were even able to identify a new secondary pair of low ionization structures. We repport as well on the extension of our work to ground based photometry, through an analysis of images from the ``IAC catalogue of Galactic Planetary Nebulae'' (Manchado et al. 1996).
    Planetary Nebulae as Astronomical Tools (APN III); 06/2005
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    ABSTRACT: We have analysed long-slit spectrophotometric observations of a sample of 35 H II galaxies in the red (between 6000Å and 1 μm), including the nebular [S III] λλ9069,9532Å lines. For 6 of the 35 objects observed it has been possible to measure the auroral [S III] line at 6312Å. All of these galaxies were observed previously in the blue, and it has therefore been possible to derive two line temperatures directly: t([O III]) from the [O III] λ4363Å line and t([S III]) from the [S III] λ6312Å line. Both spectra, red and blue, were obtained on the 1.52m telescope with the Boller & Chivens spectrograph at La Silla, ESO. In this work, we present the physical conditions and chemical abundances of these 6 galaxies derived from the measured [S III]λ6312Å line, with particular emphasis on the S/H abundance. Despite the observed dispersion in the temperatures, the final result for the abundances is in accordance with the expected values for H II galaxies. In addition, we have added our observed H II galaxies to the empirical calibration of the metallicity parameter, S23 = ([S II]+[S III])/Hα (Pérez-Montero & Díaz 2003). This calibration presents two important advantages with respect to the R23 parameter, which is based on the optical oxygen lines: it remains single-valued up to abundances close to solar and is almost independent of the ionization parameters of the nebula.
    04/2005; 329:32P.
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    ABSTRACT: We have analysed long-slit spectrophotometric observations of a sample of 35 HII galaxies in the red (6000 Å -1µm), including the nebular [SIII] lines λλ9069, 9532Å. Given the uncertainties associated with the [SIII]λ6312Å line and the importance of S ++ (the dominant ion) in determining the S/H, it is clear that the observations of the strong near-IR [SIII] lines were needed. All these galaxies were observed previously in the blue wavelength range from which we could derive the O/H abundance using the T e [OIII] temperature.
    01/2005;
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    P. Westera, F. Cuisinier, E. Telles, C. Kehrig
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    ABSTRACT: 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 Comment: 23 pages, 14 Encapsulated Postscript figures, accepted for publication in A&A
    Proceedings of the International Astronomical Union 05/2004;
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    Carolina Kehrig, Eduardo Telles, François Cuisinier
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    ABSTRACT: We present the results of a spectrophotometric study of star forming regions in HII galaxies. In particular, we find that, besides their `blobbiness', HII galaxies are quite homogenous in their chemical properties, though we do see important fluctuations in some physical properties (e.g. extinction).
    Proceedings of the International Astronomical Union 01/2004; 222:183-184.
  • C. Kehrig, E. Telles, F. Cuisinier
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    ABSTRACT: Galáxias HII são galáxias anãs de baixa luminosidade que apresentam alta taxa de formação estelar. Seus espectros são dominados por intensas linhas de emissão devido à fotoionização pela presença de um grande número de estrelas do tipo O e B. Nós apresentamos um catálogo espectrofotométrico de 111 galáxias HII observadas no telescópio 1.52m do ESO com o espectrógrafo Boller & Chivens. Determinamos propriedades estatísticas da amostra e derivamos condições físicas (temperatura eletrônica, densidade eletrônica) e abundâncias químicas. Para algumas galáxias, fomos também capazes de resolver espacialmente regiões de formação estelar individuais e determinar propriedades espectroscópicas para estas regiões separadamente, o que nos permitiu avaliar as flutuações das condições físico-químicas dentro das galáxias HII. Em particular, vimos que apesar das galáxias HII apresentarem formação estelar espalhada ao longo do corpo da galáxia, são objetos quimicamente homogêneos. A fim de estudar a evolução temporal dos objetos durante o tempo de vida das estrelas ionizantes construimos também alguns diagramas relacionando razões de linhas de emissão com a largura equivalente de Hb (EW(Hb)). Para interpretar tais diagramas utilizamos modelos de fotoionização para populações estelares integradas. Concluímos que as galáxias HII não correspondem a simples idéia de um burst instantâneo envolvido por um gás opaco aos fótons ionizantes e com densidade constante. As relações observadas entre razões de linhas e EW(Hb) podem ser melhor compreendidas se as galáxias HII apresentarem populações estelares mais velhas, que contribuem para o contínuo óptico observado.
    Bulletin of the Astronomical Society of Brazil. 08/2003;