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The excess numbers of blue galaxies at faint magnitudes is a subject of much controversy. Recent Hubble Space Telescope results has revealed a plethora of galaxies with peculiar morphologies tentatively identified as the evolving population. We report the results of optical spectroscopy and near-infrared photometry of a sample of faint \HST galaxies from the Medium Deep Survey to ascertain the physical properties of the faint morphological populations. We find four principal results: Firstly that the population of objects classified as `peculiar' are intrinsically luminous in the optical ($M_B\sim -19$). Secondly these systems tend to be strong sources of [OII] line luminosity. Thirdly the optical-infrared colours of the faint population (a) confirm the presence of a population of compact blue galaxies and (b) show the stellar populations of Irregular/Peculiar galaxies encompass a wide range in age. Finally a surface-brightness comparison with the local galaxy sample of Frei et al shows that these objects are not of anomalously low surface brightness, rather we find that all morphological classes have evolved to a higher surface brightness at higher-redshifts ($z>0.3$)., 17 pages. 6 figures (embedded), MNRAS in press

Submitted by Aglair Aguiar (aglair@ct.ufrj.br) on 2018-12-06T16:30:59Z No. of bitstreams: 1 867659.pdf: 2970741 bytes, checksum: 960de20dc6f46888e985b67bb3437488 (MD5) Made available in DSpace on 2018-12-06T16:30:59Z (GMT). No. of bitstreams: 1 867659.pdf: 2970741 bytes, checksum: 960de20dc6f46888e985b67bb3437488 (MD5) Previous issue date: 2017-07 Análise da homogeneidade da distribuição de matéria no Universo, aqui chamada de homogeneidade observacional (HO) e a qual é feita na hipersuperfície tipo-nulo do cone de luz do passado. O tipo de análise da homogeneidade já conhecida é definida pelo Princípio Cosmológico, que chamamos de homogeneidade espacial (HE), a qual ocorre nas hipersuperfícies tipo-espacial do espaço-tempo. Realizamos este trabalho utilizando o modelo cosmológico de Einstein-de Sitter. Todas as discussões de homogeneidades foram feitas para quatro tipos de distâncias cosmológicas, que são: distância por área dA, distância por área galáctica dG, distância de luminosidade dL e distância por desvio para o vermelho dz. Simulamos vários tipos de contagens de fontes cosmológicas e, no caso de universo com homogeneidade espacial, usamos a contagem numérica prevista pelo modelo de Einstein-de Sitter (EdS, NEdS), pois assume o Princípio Cosmológico. Para simularmos o universo com homogeneidade observacional, usamos a contagem numérica proposta por Wertz (1970) e Pietronero (1987), para a distribuição de galáxias. A partir de duas funções de densidade numérica radiais definidas em Ribeiro (2005), que são a densidade diferencial γi e a densidade diferencial integral γi*, fizemos uma análise das homogeneidades espacial e observacional da distribuição de galáxias, esta última é definida pela constância de γi*. Foram apresentados gráficos mostrando o papel central da escolha da distância cosmológica na determinação das densidades. Pôde ser observado claramente que para caracterizar se a distribuição de galáxias em grande escala do Universo possui ou não HO, é necessário conhecer não somente a distribuição geral de massa-energia, a qual é determinada pela contagem Ni de fontes cosmológicas, mas também o volume geométrico que define densidade, que, por sua vez, depende da distância cosmológica. In this work we propose a second way of analysing the homogeneity of the matter distribution in the Universe, called here as observational homogeneity (OH), and which is carried out along the past light cone null type hypersurface. The usual type of homogeneity is given by the Cosmological Principle, called here as spatial homogeneity (SH), and which is defined along space-like hypersurfaces of the spacetime. In this work we adopted the Einstein-de Sitter cosmological model. All discussion regarding homogeneity were done by means of four cosmological distances, namely, the area distance dA, the galaxy area distance dG, the luminosity distance dL and the redshift distance dz. Simulations of various types of counting of cosmological sources were carried out and in the case of an universe model with SH we used the number counting obtained from the Einsteinde Sitter (EdS) model (NEdS), since it assumes the Cosmological Principle. In order to simulate an universe with OH, we adopted the number counts expression advanced by Wertz (1970) and Pietronero (1987) for the galaxy distribution. Starting from two radial density functions defined in Ribeiro (2005), namely the differential density γi and the integral differential density γ ∗ i , we carried out an analysis of spatial and observational homogeneities of the galaxy distribution, were the latter (OH) was defined by the constant value of γ ∗ i . Various plots were presented showing the central role played by the cosmological distance choice. It was also clearly observed that in order to characterize whether or not the large-scale galaxy distribution in the Universe has, or has not, OH, it is necessary to know not only the general mass-energy distribution, which is determined by the count Ni of cosmological sources, but also the geometrical volume which defines the density and, by itself, depends on the cosmological distance.

AL~3 (BH 261), previously classified as a faint open cluster candidate, is shown to be a new globular cluster in the Milky Way, by means of B, V and I Color-Magnitude Diagrams. The main feature of AL~3 is a prominent blue extended Horizontal Branch. Its Color-Magnitude Diagrams match those of the intermediate metallicity cluster M~5. The cluster is projected in a rich bulge field, also contaminated by the disk main sequence. The globular cluster is located in the Galactic bulge at a distance from the Sun d$_{\odot}$ = 6.0$\pm$0.5 kpc. The reddening is E(B-V)=0.36$\pm$0.03 and the metallicity is estimated to be [Fe/H] $\approx$ -1.3$\pm$0.25. AL~3 is probably one of the least massive globular clusters of the Galaxy., 6 figures. Astrophysical Journal Letters, in press

New CCD V I photometric data for 10 template open clusters with accurately determined fundamental parameters are presented. From the observed V versus V—I diagrams of the clusters, Ðducial sequences have been defined and transformed into the Mv versus (V—I) diagram by averaging sequences of template open clusters with similar ages. The resulting composite Mv versus (V—I)o diagram presents a homogeneous set of empirical isochrones in the age range between 5 Myr and 4 Gyr. These empirical isochrones show an overall very good agreement with those computed from stellar evolutionary models. Theoretical isochrones with moderate overshooting fit the observed main sequences better than the canonical ones for clusters older than 600 Myr. The present set of empirical isochrones will be useful for the study of faint reddened open clusters.

We performed N-body simulations of star cluster encounters with Hernquist's TREECODE in a CRAY YMP-2E computer under different initial conditions (relative positions and velocities, cluster sizes, masses and concentration degrees). The total number of particles per simulation ranged from 1024 to 20480. These models are compared with a series of isodensity maps of cluster pairs in the Magellanic Clouds. Evidence is found that during the interactions, transient morphological effects such as an expanded halo, isophotal deformation and isophotal twisting can occur as a result of tidal effects and dynamical friction. The simulations also show that different outcomes are possible depending on the initial parameters: (i) long-standing changes of concentration degree can occur after the collision; (ii) one member can disaggregate; or (iii) the pair can coalesce into a single cluster with a distinct structure compared with the original ones. These simulations can reproduce a wide range of morphological structures in observed cluster pairs.

In the recent years we have concentrated efforts to collect Colour-Magnitude Diagrams of the globular clusters projected in the central parts of the Galaxy. So far we were able to gather photometric data in the V, I and Gunn z bandpasses, for 16 out of the 17 known clusters in the central 5º radius, most of them severely reddened. Reddening, distance and metallicity are estimated from the horizontal and red giant branches. We study the resulting cluster spatial distribution and conclude that essentially no cluster is detected beyond the Galactic Center distance. The results favour a flattened bulge extending from the Galactic Center to 4.5 kpc from the Sun. The density distribution of the clusters follows the current models for bulge field stars.We estimate that missing clusters on the opposite side of the Galaxy bulge may amount ~15 clusters similar to those detected on our side. The projected distribution of clusters is asymmetrical, with higher absorption in the southern Galactic hemisphere. The metallicity distribution of our sample clusters results similar to that of bulge field stars. The present ground-based results coupled to main sequence data of two genuine bulge clusters using the Hubble Space Telescope, point to a scenario of an old flat bulge withcommonorigin for the stellar populations in both globular clusters and field.

We investigate two chemical abundance calibrations for the narrow-line region (NLR) of active galaxies in terms of three easily observable optical emission-line ratios, namely, [O III] λλ4959, 5007/Hβ; [N II] λλ6548, 6584/Hα; and [O II] λ3727/[O III] λλ4959, 5007. The calibrations are obtained from a grid of models on the assumption that the main process responsible for the production of these lines is photoionization by a "typical" active galactic nucleus continuum. The elemental abundances vary with oxygen, except nitrogen, which is assumed to be a product of secondary nucleosynthesis. The calibrations are calculated for the range 8.4≤12]log (O/H)≤9.4 and tested using NLR data for a sample of Seyfert galaxies and LINERs that have H II regions in the vicinity of the nucleus. The gaseous abundances of these H II regions have been determined in previous works, and the NLR abundances are obtained on the assumption that they can be extrapolated from those of the H II regions. The calibrations work very well for the Seyfert galaxies, yielding abundance values that agree with those obtained from the H II regions, and can thus be used for quick estimates of the chemical abundances of the NLRs. For the LINERs, the calibrations yield lower values than those derived from the corresponding H II regions, suggesting that the assumptions of the models do not apply for them and that there are di†erent physical processes at work in the NLR of the LINERs.

As part of a systematic study of the UV properties of galaxies in the IUE library,we present in this paper an analysis of nuclear stellar populations in spiral galaxies with radial velocity ≤ 5 000kms-ˡ. In this sample of 60 galaxies the IUE aperture probes a mean 1.0 kpc 2.1 kpc area. Prior to any comparison of galaxy spectra in the range covered by IUE (1200–3200 Å), wehave formed subsets according to the absolute magnitude and morphological type of the studied galaxies. In a second step, and within each subset, we have co-added the spectra, and hence the objects into groups of similar spectral properties in the UV, also taking into account their spectral properties in the visible/near infrared ranges. As a result, high signal-to-noise ratio templates have been obtained, and information on spectral features can now be extracted and interpreted. We distinguish 4 groups for Sa, 8 for Sb, and 4 for Sc galaxies. We have carried out population syntheses using as base elements: H II regions, integrated star clusters, and far-UV weak elliptical galaxies as representative of bulge stellar population. The variety ofUVspectral types found in the central regions of spiral galaxies can be readily explained by different mixtures of bulge, circumnuclear burst and disc populations. Across different morphological types, similar templates can also be found. This is due to compensation effects of bulge contribution with the disc and circumnuclear burst ones. Flux fractions derived from the population synthesis have been converted into mass contributions and inferences have been made on the star-formation histories. In the central kpc of the galaxies with strong UV flux, we find that the mass stored in the young components (t < 500 Myr) is typically ≈ 107Mʘ . We confirm that such star-formation enhancements occur preferentially in barred spirals. Internal reddening in the templates has been studied and inferences have been made on the corresponding reddening laws. We find cases where an SMC-like law applies and others where a faint λ2200 Å absorption feature occurs resembling the reddening law of the LMC. The interest of the IUE data set resides in its rather large entrance aperture which samples a large portion of nearby galaxies, and is therefore quite suitable for the interpretation of large redshift galaxies.

We present V and I photometry of two open clusters in the LMC down to V~26. The clusters were imaged with the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope (HST), as part of the Medium Deep Survey Key Project. Both are low-luminosity (MV~-3.5), low-mass (M~10³Mо) systems. The chance discovery of these two clusters in two parallel WFPC2 fields suggests a significant incompleteness in the LMC cluster census near the bar. One of the clusters is roughly elliptical and compact, with a steep light profile, a central surface brightness µV(0)~20.2 mag arcsec-², a half-light radius rhl~0.9 pc (total visual major diameter D~3 pc) and an estimated mass M~1500 Mо. From the colour magnitude diagram and isochrone fits we estimate its age as Τ~(2–5)x10 8 yr. Its mass function has a fitted slope of Г = ∆logØ (M)/ ∆logM =-1.8±0.7 in the range probed (0.9

We present V and I photometry, obtained with the Hubble Space Telescope, for ~ 15 800 stars in a field in the inner disc of the Large Magellanic Cloud. We confirm previous results indicating that an intense star formation event, probably corresponding to the formation of the LMC disc, occurred a few times 109 yr ago. We find a small but real difference between our field and one further out in the disc observed by Gallagher et al.: either star formation in the inner disc commenced slightly earlier, or the stars are slightly more metal-rich. We also find evidence for a later burst, around 1 Gyr ago, which may correspond to the formation of the LMC bar. About 5 per cent of the stars in our field are substantially older than either burst, and are probably members of an old disc or halo population with age ~ 12 Gyr.

The results of an optical monitoring campaign on the active nucleus in the luminous Seyfert 1 galaxy Fairall 9 are presented. This campaign was undertaken in parallel with ultraviolet spectroscopic monitoring with the IUE satellite which is described in a separate paper. The primary purpose of this program is to measure the response times (or "lags") of the emission lines to continuum variations and thus to extend the range in luminosity of active galactic nuclei (AGNs) for which such measurements have been made. The main conclusions of this work are as follows : 1. Continuum (at 5340 Å ) variations of amplitude ~12% are detected on timescales as short as ~20 days. These variations are much larger than the typical uncertainties in the measurements, which are of order ~2%. Over ~94 days, a factor of 2 change in the nuclear continuum was observed. 2. The optical continuum light curve resembles that of the UV continuum, showing two "events" of low-amplitude variations with a duration of ~70 days and with no measurable lag between the UV and optical continuum light curves. The UV data show a third larger amplitude event that occurred after the optical monitoring had terminated and unfortunately went unobserved in the optical. 3. The Hβ emission-line flux also underwent significant, low-amplitude (≥20%) variations. Crosscorrelation analysis reveals that Hβ lags behind the UV continuum by about 23 days, a value much smaller than what was previously suggested by earlier variability studies. However, this small lag is consistent with the lags for the UV lines during this campaign in the sense that the Hβ lag is approximately 50% larger than that of Lya λ1216, as it has been found for lower luminosity AGNs. 4. The Hβ difference profile produced by subtracting the low-state from the high-state data can be described as a two-component structure with blue and red components of similar width (~2500 km s-ˡ) and that appear to vary in phase.

We present V, I colour-magnitude diagrams of the globular cluster HP 1 obtained at the European Southern Observatory New Technology Telescope under exceptional seeing conditions. The cluster shows blue horizontal branch (HB) and red giant branch morphologies very similar to clusters of intermediate metallicity such as NGC 6752; we therefore estimate [Fe/H] ~~ - 1.5 for HP 1. The blue HB morphology is extended, which is not unusual for a post-core-collapse cluster. We derive a reddening of E (B - V) = 1.19 and a distance d̛ =6.85 kpc. HP 1 might be a halo cluster crossing the bulge or belong to the low-metallicity tail of the bulge.

Recent measurements of the Circinus galaxy with ISO by Moorwood et al. (1996) have confirmed the extremely high excitation of the emission-line spectrum in this active galaxy. Moorwood et al. modelled the spectrum in terms of photoionization of gas by a hard X-ray continuum plus a UV bump near 70 eV. We present new photoionization calculations which differ markedly in geometry and in the adopted spectrum of the ionizing radiation. In our model, all the zones of high excitation coexist within the internal structure of matter-bounded clouds of 1 pc thickness with a total cross section of 165 pc2. A strong UV bump is not required to explain the line ratios in this picture. Our calculations consider the effects of radiation pressure exerted by photoelectric absorption which become very important at the high ionization parameters required by the line ratios. We propose that the radiation pressure generates a strong density gradient within the photoionized structure and is responsible for accelerating the matter-bounded gas, explaining the systematic blueshift observed for the coronal lines.

We study the globular cluster Terzan 4 projected close to the Galactic center, by means of V, I and Gunn z Colour-Magnitude Diagrams. The images were obtained under exceptional seeing conditions (0.35" - 0.55") at the ESO New Technology Telescope equipped with SUSI. We derive a reddening of E(B-V) = 2.35 amd a distance from the Sun dΘ = 8.3 kpc for Terzan 4. From the similarity of the VI Colour-Magnitude Diagrams of Terzan 4 and M30, in particular the presence of a blue horizontal branch, it could be as metal-poor as [Fe/H] ≈ -2.0. It is therefore another blue horizontal branch globular cluster located close to the Galactic center.

We present V, I photometry of the loose star cluster NGC 6749, and for the first time colour-magnitude diagrams are provided. We confirm that it is a globular cluster and its blue horizontal branch indicates that it is metal-poor. We derive a reddening of E(B - V) = 1.39 ± 0.04 and a distance from the Sun d̛ = 7.3 ± 0.9 kpc (assuming a total-to-selective absorption R = 3.4). The cluster is projected very close to the Galactic plane, and the derived distance implies a Galactic coordinate Z ~~ - 300 pc. lt is thus a halo globular cluster located close to the disc plane. We also discuss the properties of 78 newly discovered long-period variable stars, of which 75 are Miras, projected within 1º of the cluster centre. The variables do not appear to be associated with the globular cluster. From their periods, most of them belong to the metal-rich disc or bulge stellar populations.

We report the first results of a color-magnitude diagram survey of 25 candidate old LMC clusters. For almost all of the sample, it was possible to reach the turnoff region, and in many clusters we have several magnitudes of the main sequence. Age estimates based on the magnitude difference $\delta T_1$ between the giant branch clump and the turnoff revealed that no new old clusters were found. The candidates turned out to be of intermediate age (1-3 Gyr) We show that the apparently old ages as inferred from integrated UBV colors can be explained by a combination of stochastic effects produced by bright stars and by photometric errors for faint clusters lying in crowded fields. The relatively metal poor candidates from the CaII triplet spectroscopy also turned out to be of intermediate age. This, combined with the fact that they lie far out in the disk, yields interesting constraints regarding the formation and evolution of the LMC disk. We also study the age distribution of intermediate age and old clusters This homogeneous set of accurate relative ages allows us to make an improved study of the history of cluster formation/destruction for ages $>1$Gyr. We confirm previous indications that there was apparently no cluster formation in the LMC during the period from 3-8 Gyr ago, and that there was a pronounced epoch of cluster formation beginning 3 Gyrs ago that peaked at about 1.5 Gyrs ago. Our results suggest that there are few, if any, genuine old clusters in the LMC left to be found., Comment: LaTeX, to be published in Nov. 1997 Astronomical Journal

We present for the rst time optical colour magnitude diagrams of the globular cluster Terzan 2, in the V, I colours. The horizontal branch is red. The red giant branch morphology can be fitted with that of 47 Tuc, but definitely not that of NGC 6553. We derive a reddening of E(B-V) = 1.54 and a distance dΘ = 7.7 kpc if R = 3.1, or 5.3 kpc if R = 3.6. Terzan 2 adds to the list of bulge metal-rich clusters now with reliable parameters.

O estudo da distribuição da extinção na direção da Pequena Nuvem de Magalhães (PNM) é feito atravéss da contagem de galáxias de ”fundo”, e espectroscopicamente pela comparação de espectros nucleares de uma amostra das mesmas com os de galáxias de referência de similar população estelar. O método de contagens é baseado em um novo catálogo realizado no presente trabalho, contendo 3037 galáxias estendendo-se até a magnitude limite B¼ 20 em 6 placas do ESO/SERC na região da PNM e seus arredores. O método espectroscópico foi aplicado a uma amostra de 16 galáxias na mesma região, assim como numa outra de 27 galáxias na direção da Grande Nuvem de Magalhães, para comparação. A deficiência de galáxias indicada pelo método de contagens sugere E(B-V)=0.35 nas partes centrais da PNM, e E(B-V)=0.15 a 6º do centro. Por outro lado o método espectroscópico indica que a PNM é basicamente transparente. Sugerem-se as seguintes explicações para esta diferença: (i) a deficiência de galáxias nas regiões centrais detectadas pelo método de contagens é signifivativamente afetada pela alta concentração de estrelas e objetos extendidos pertencentes à PNM; (ii) a amostra espectroscópica conteria tipicamente galáxias em zonas menos avermelhadas, o que indicaria que a absorção ocorre em nuvens de poeira com uma distribuição preferencialmente discreta. A aplicação do m´etodo espectroscópico na GNM também sugere a presença de nuvens de poeira discretas nas suas regiões centrais.

We use the radio axis as an indicator of the orientation of the obscuring torus in Seyfert galaxies and analyze the di†erence between the position angles of extended radio structures and host galaxy major axis of Seyfert 1 and Seyfert 2 galaxies. We find that Seyfert 1's are less likely to have extended radio structures along the host galaxy major axis while Seyfert 2's have these structures distributed in most directions. We also find a zone of avoidance in the distribution of position angles : both Seyfert 1's and Seyfert 2's seem to avoid close alignment between the radio axis and the host galaxy plane axis. These results are analyzed from the point of view of a model in which Seyfert 1's have their obscuring torus axis aligned preferentially along the host galaxy disk axis and Seyfert 2's have their torus axis lying at an intermediate angle between the galaxy disk and its axis.

We carried out V RI and Gunn z observations of the obscured globular cluster Liller 1. The cluster is so reddened (Av ≈ 9.0) that it is at the detection limit in V. The RGB in I vs. (I–z) shows a strong curvature. Recalling that the nearly solar metallicity globular clusters NGC 6553 and NGC 6528 present similar blanketing effects only in the visible bandpasses, we conclude that Liller 1 is considerably more metal-rich than these clusters. The CMD comparison of Liller 1 with the inner bulge field around it (located ≈ 5° from the nucleus), suggests that the cluster is as metallic as the most metallic fraction of this inner bulge population. Similarly deep I and z observations at ≈ 0.5° away from Liller 1, at the nominal position of Grindlay 1 do not reveal any cluster.

We study the metal-rich bulge globular cluster Terzan 5 by means of VI colour-magnitude diagrams, with images obtained under exceptional seeing conditions (0.34"–0.50"). Differential reddening is important across the cluster. We derive a reddening of E(B – V) = 2.49 and a distance from the Sun dΘ = 5.6kpc, closer than previous estimates. Based on the red giant branch curvature, we derive a metallicity somewhat higher than that of NGC 6553, probably solar.

We study optical spectra in high and low activity states of the faint, distant Seyfert 1 galaxy C16.16. A strong stellar population contribution to the continuum is observed, even in the high-state spectrum. The low-ionization emission lines show large equivalent widths. Narrow-line ratios are used to parameterize and investigate the physical conditions in the narrow-line region. Photoionization models with nitrogen depletion, ionization continuum typical of an active galactic nucleus (AGN), and an ionization parameter U = 10 -2.8 reproduce the observed narrow lines. The AGN continuum shows a strong variation, while the Balmer lines vary moderately. The Balmer lines have a broad and asymmetric component with double-peaked structure. Using the profiles of emission lines originated in a relativistic circular disk, we successfully fit the observed broad Hα profile. This disk component shows no variation in the observations. A variable, intermediate-width (~6000 km s-ˡ) Balmer component is also found. These two com­ ponents seem to arise by different processes.

Recent claims in the literature, that the rate of mass loss from red giant branch (RGB) stars in old, open clusters like M 67 and NGC 6791, increases with the metallicity above the value holding for Globular Clusters and predicted by the classical Reimers (1975) relation, are thoroughly scrutinized by means of the global fit of the color-magnitude diagram (CMD) of these clusters (M 67 in particular) to modern sets of theoretical isochrones. The above claim stems from recognizing that there is wide agreement in literature on the metallicity (nearly solar), age (about 5 Gyr), and distance modulus ((m – M)=9.55) of M 67, and from estimating the mass of its giant stars in the red clump to be about 0.7 MΘ . At the above age, the masses at the turn-off and near the tip of the RGB are about 1.2 MΘ and 1.3 MΘ, respectively. This means that in clusters with nearly solar metallicity, much more mass ought to be lost by the red giant stars than classically predicted. In this paper we show that in order to be able to derive the mass of the red stars in the clump from their position in the CMD, the color difference Δ(B – V) between the turnoff and the base of the RGB should be known with a precision smaller than δ[Δ(B – V)] = 0.01 mag and, at the same time, the distance modulus should be determined with a precision higher than 0.025 mag. The analysis of the problem clarifies in fact that in the global isochrone fitting technique, both the distance modulus and mass of the clump stars depend on the above color difference according to the relations ðMvto/ðΔ(B – V) ~- –9.2 and ð MHB/ðΔ(B – V) ~- –22 MΘ/mag. Therefore, an uncertainty in Δ(B – V) as small as δ[Δ(B – V)] = 0.01 mag implies an uncertainty in the distance modulus of δ(m – M) = 0.1 mag and, even more important, an uncertainty in the mass of the clump stars of 0.22 MΘ . Fits of the CMD of M 67 (and NGC 6791) are presented, in which the classical value of the mass for the stars in question is recovered. The claim that the rate of mass loss from RGB stars increases with the metallicity is not supported by the present day data for M 67. Finally, the claim that in NGC 6791 the metallicity higher than in M 67 is the cause of the occurrence of a few faint, blue stars, and in turn that mass loss plays the key role in generating stars that are potential candidates as sources of UV flux in elliptical galaxies and bulges, are also not supported by current data.

We study the UV turnup in early-type galaxies from coadded IUE spectra reaching an unprecedented signal to noise ratio. Some spectral groups resulted with strong or moderate UV turnup, while in others it is very weak or absent. We study the relationships of the UV turn up intensity with absolute magnitude, X-ray and Hα luminosities. Galaxies in the strong UV turnup groups are systematically bright, and have high X-ray and Hα luminosities; however, some other galaxies with the latter properties do not exhibit a significant UV turn up. The spectral groups with an important intermediate age component are far-UV weak. The contribution from an intermediate age population with varying strength might explain why some red stellar population early-type galaxies present the UV turn up while others do not. The available spectral groups have been further coadded into one with strong UV turnup and another one without it, and we analyse their difference. We compare the spectral slope of the isolated UV turnup with IUE spectra of various hot sources which had been proposed in previous studies to explain it. We conclude that only very hot stars like sdO and sdB subdwarfs, some nuclei of planetary nebulae or DO white dwarfs, have the proper slope to explain the UV turnup. The UV turnup as detected through the IUE aperture is not featureless: it presents absorptions similar to those observed in the galaxies with weak far-UV flux. These features appear to be the λ1400 Å and λ1600 Å ones, characteristic of moderately cool white dwarfs (DA 5), which indicates that these stars are dominant flux contributors between λ1300 - 2000 Å in the farUV weak groups.The cooling time of DA 5 stars together with the evolutionary time since they left the main sequence, imply that they evolved from low-mass stars possibly associated with the initial burst of star formation in early-type galaxies and/or merger events at intermediate ages. On the other hand, two possible scenari are discussed for the origin of the hot component which causes the UV turn up, one related to late stages of normal evolution of low-mass stars, and another related to past nuclear activity events and jets which might have blown away the atmospheres of red giants in the central parts of the galaxies, exposing the hot stellar cores and mimicking a spectral distribution like that of the hottest stars observed.

Shock induced star formation in a stellar density wave scenario produces an azimuthal gradient of ages across the spiral arms which has opposite signs on either side of the corotation resonance (CR). We present a method based on the Fourier analysis of azimuthal profiles, to locate the CR and determine the arm character (trailing or leading) in spiral galaxies. Basically, we compare the behavior of the phase angle of the two-armed spiral in blue and infrared colors which pick out respectively young and older disk stellar population. We illustrate the method using theoretical leading and trailing, spirals. We have also applied the method to the spiral galaxies NGC 7479, for which we confirm the reported leading arms, and NGC 1832. In these galaxies we find two and three CRs respectively., Comment: 9 pages, accepted for publication in ApJL, figures 4 and 6 avaliables at ftp://ftp.inaoep.mx/pub/salida/puerari, full paper also avaliable at http://www.inaoep.mx/~puerari

We analyse the nuclear stellar population and emission-line spectrum in the range λλ 3100-9700 Å of the infrared luminous merger galaxy NGC 6240. Two spectral extractions from CCD frames are studied: one corresponding to the double nucleus and the other from a light peak 4 arcsec east of the nucleus. The double nucleus is ∆E (B-V)~~ 0.30 mag more reddened and has a stronger interstellar Na I D absorption as compared to the eastern peak; otherwise the two extractions present similar spectral properties, in particular the dereddened continuum distribution and emission-line ratios. The population synthesis of the double nucleus, which has age and metallicity as free 'parameters and is based on spectral properties of a library of star clusters, indicates that the continuum flux fraction at 5870 Å owing to an old bulge/halo component is ~~ 7 5 per cent, that of intermediate-age components (1 to 5 Gyr) is ~~5 per cent, and that associated with young ones (50 to 500 Myr) is ~~ 20 per cent. Currently star-forming regions do not contribute more than 1-2 per cent to the continuum at 5870 Å, and this amount is contributed only if they are differentially reddened from the rest of the stellar components by ∆E (B - V)i > 1.00. The age distribution of the nuclear stellar population, when compared to that found in normal nuclei, sets constraints on the age of the dynamical interaction that led to the present merger; the synthesis suggests that the interaction has been operating for ~~ 1 Gyr. We derive an internal reddening affecting the nuclear stellar population of E(B-V)sp=0.48. The population-subtracted optical emission-line spectrum is typical of a shock-heated gas. We derive an internal reddening for the emitting gas clouds of E(B- V)g = 0.60. We conclude that in the central 2-3 kpc of NGC 6240 the old (bulge) and 1-Gyr to 50-Myr stellar components are homogeneously mixed, and they coexist with colliding gas clouds from the discs of the merging spirals. The continuum and line emission flux from currently star-forming regions is apparently blocked from the optical spectrum by dust absorption, and their absorbed photons from the ultraviolet to the optical appear to be the source of the strong emission observed with lRAS.

We have carried out spectrophotometry in the range 3600–9700Å of five globular clusters in NGC 5128 for which previous photometric studies suggested a high metal content. We compare the equivalent widths of a set of metallic features of the NGC 5128 clusters with those of well-studied Galactic and M31 globular clusters. This enables us to derive a reliable ranking and estimate of the metallicity for the NGC 5128 clusters. The reddening is obtained from the comparison of the continuum distribution of the observed clusters with those of reference clusters. The present spectroscopic study clarifies the question raised in the photometric studies about the NGC 5128 clusters metallicities. We conclude that, in the present NGC 5128 sample, no object has actually a metallicity higher than solar, unlike what happens in M31.

We have obtained long-slit spectroscopy of five active galaxies showing extended high excitation emission lines reaching distances of several kiloparsecs from the nuclei. Measurement of the fluxes of weak lines, such as [OIII]λ4363 and HeIIλ4686, requires careful subtraction of the contribution of the stellar population, and the procedure for this subtraction is discussed in detail. For each galaxy, we present emission-line ratios for the nucleus and the extended gas at the most distant locations for which the fluxes of the weaker high excitation lines can be measured with an uncertainty ≤30%. In a companion paper (Paper II), these line ratios are used in a reevaluation of photoionization models of extended gas in active galaxies.

Recent reliable measurements of the weak lines of [O III]λ4363, He IIλ4686 and [Ne V]λ3426 seen in emission in extended and nuclear regions of AGN (Storchi-Bergmann et al. 1996) are used to discriminate between different types of photoionization models. The sample comprises Seyferts and Narrow Line Radio Galaxies. A well known problem, the scatter and the extreme values of He II/Hβ encountered in the nuclei and extended regions, is solved in a similar fashion to Viegas & Prieto (1992) by considering two populations of ionized clouds: a matter-bounded (MB) component responsible for most of the He II emission, and an ionization-bounded (IB) component emitting low-to-intermediate excitation lines. A new sequence of photoionization calculations is thereby obtained by varying AM/I, which is defined as the solid angle ratio occupied by the MB component relative to the IB component. In various line ratio diagrams, the AM/I-sequence is compared to the traditional single component U-sequence in which one arbitrarily varies the relative intensity of the ionizing source. An original aspect of the new calculations is that the IB clouds are photoionized exclusively by the radiation which has filtered ('leaked') through the MB component. This situation could arise if, for example, the MB component is the low density 'halo' of a cloud, and the IB component the high density core. Such a filtered ionizing spectrum enlarges the range in He II/Hβ accessible to models without requiring changes in the spectral index of the ionizing source, which we fix at =–α1.3. The main success of the model is that it provides a natural explanation for the newly found correlations between both the [O II]/[Ne V] and [O II]/[0 III] ratio and the He II/Hβ ratio. On the other hand, the standard U-sequence cannot account for such correlations between the gaseous excitation and the He II/Hβ ratio. Furthermore, the so-called 'temperature problem' is solved with the AM/I-sequence provided the thickness and the ionization parameter (UMB>~(0.03) of the MB component are appropriately selected. Finally, the AM/I-sequence produces much stronger high excitation lines of [Ne V] and C IV λλ1549 than the U-sequence, in accordance with observations. The AM/I-sequence predicts a temperature difference of 5 000 K between the T OIII and T NII temperatures while for the U-sequence this difference is less than 1 000 K. To the extent that 'cooling flows' and LINERs share the same excitation mechanism as our IB component (i.e. photoionization by an absorbed ionizing continuum), we predict a value of He II/Hβ0.1.

We carried out spectrophotometry in the range 4000- 7000Å and V, I and Gunn z imaging of the initially thought to be globular cluster candidates in the direction of the Galactic bulge TJ 5 and TJ 23 (Terzan & Ju 1980) and the one reported by Bica (1994). The three objects turned out to be small nebulae in rich stellar fields. Diagnostic diagrams for emission line ratios indicate that TJ 5 and TJ 23 are planetary nebulae. The locus of the third object strongly suggests it to be a supernova remnant, with very strong [NII]λ6584 and strong [SII]λλ6717,31. The sizes o f the nebulae are d=28", 45" and 49", and the reddening derived from the Balmer decrement indicates E(B–V)=0.86, 1.81 and 0.19, respectively for TJ 5, TJ 23 and the supernova remnant.

An average integrated spectrum of the nearlysolar metallicity globular clusters NGC 6528, NGC 6553 and NGC 6440 is synthesized in the range 3500 < λ < 9750Å with a library of stellar spectra and constraints provided by the observed colour-magnitude diagram (CMD) of NGC 6553. In order to account for the CMD parts below the observational cutoff, we employ a power law mass function with slopes x =-0.5, 1.35 and 2.5. We conclude that the MS contribution amounts to ≈15% of the integrated light at 5870Å and this minor contribution makes the integrated spectrum basically insensitive to these x values. The dominant components are the Red Giant Branch and the Horizontal Branch with respectively ≈60% and ≈20% of the flux at λ5870Å. The residuais of the observed integrated spectrum with respect to the model suggest that [Fe/H] is slightly subsolar in these globular clusters, whereas [CNO/Fe] is slightly above the solar ratio.

We present the data and initial results from a combined HST/IUE/ground-based spectroscopic monitoring campaign on the Seyfert I galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once every 2 days for a period of 74 days beginning on 1993 March 14. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations (both eco imaging and aperture photometry), are reported for the period 1992 October-1993 September, although many of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution we describe the acquisition and reduction of ali of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies. During the HST portion of the monitoring campaign, the 1350 Å continuum flux is found to have varied by nearly a factor of 2. In other wave bands, the continuum shows nearly identical behavior, except that the amplitude of variability is larger at shorter wavelengths, and the continuum light curves appear to show more short­ timescale variability at shorter wavelengths. The broad emission lines also vary in flux, with amplitudes that are slightly smaller than the UV continuum variations and with a small time delay relative to the UV continuum. On the basis of simple time-series analysis of the UV and optical continuum and emission-line light curves, we find (1) that the ultraviolet and optical continuum variations are virtually simultaneous, with any lag between the 1350 Å continuum and the 5100 Å continuum amounting to less than about 1 day; (2) that the variations in the highest ionization lines observed, He II λ1640 and N v λ1240, lag behind the continuum variations by somewhat less than 2 days; and (3) that the velocity field of the C IV-emitting region is not dominated by radial motion. The results on the C IV velocity field are pretiminary and quite uncertain, but there are some weak indications that the emission-line wings (|Δv|≥ 3000 km s-ˡ) respond to continuum variations slightly more rapidly than does the core. The optical observations show that the variations in the broad Hβ line flux follow the continuum variations with time lag of around 2 weeks, about twice the lag for Lyα and C IV, as in our previous monitoring campaign on this same galaxy. However, the lags measured for Lyα, C IV, and Hβ are each slightly smaller than previous determmations. We confirm two trends reported eartier, namely, (1) that the UV /optical continuum becomes "harder" as it gets brighter and (2) that the highest ionization emission lines have the shortest lags, thus indicating radial ionization stratification of a broad-line region that spans over an order of magnitude range in radius.

Combined UV, optical, and near-IR spectral distributions of a sample of 48 southern star-forming and Seyfert 2 galaxies are presented. The optical and near-IR spectra were obtained using apertures matching those ofthe UV observations (1O" X 20") and in most cases correspond to the bulk of the gas and stellar population contribution from the whole galaxy. No such data set-taken with matched apertures and spanning such a large spectral range-exists in the literature today. The obtained spectral distributions are particularly useful as a comparison sample for spectroscopic surveys of more distant galaxies. Emission-line fluxes, continuum fluxes, and equivalent widths of absorption lines are measured from the spectra, and average values corresponding to the different activity types-blue compact dwarf, blue compact, starburst, Seyfert, and composite (starburst and Seyfert)-are presented and discussed.

We study the integrated spectral evolution in the blue-violet range of 97 blue star clusters in the Magellanic Clouds, from those associated with gas emission to those as old as a few hundred Myr. Some clusters are dominated by the flux of those massive stars that pass through evolutionary stages such as Wolf-Rayet, Luminous Blue Variable, Be, and supergiant stars of different temperatures. The relationships among spectral features such as absorption and emission lines, Balmer discontinuity and Balmer continuum are used to study the spectral evolution of the clusters. Finally, we sort into groups spectra of similar evolutionary stages, creating a template spectral library with possible applications in stellar population syntheses of star-forming galaxies and in the spectral simulation of bursts of star formation with different mean ages and durations.

In this paper we revise the relationship between ages and metallicities of LMC star clusters and their integrated UBV colors. The study stands on the catalog of UBV colors of the Large Magellanic Cloud (LMC) clusters by Bica et al. (1994; BCDSP) and the photometric models of single stellar populations (SSP) calculated by Bertelli et al. (1994). These photometric models nicely describe the color distribution of LMC clusters in the (U – B) vs. (B – V) plane together with the observed dispersion of the colors and the existence of a gap in a certain region of this diagram. In the case of blue clusters, most of the dispersion in the colors can be accounted for by the presence of stochastic effects on the mass distribution of stars, whereas for the red ones additional dispersion's of ~ 0.2 dex in metallicity and of ~ 0.05 mag in color excess are needed. From comparing the observed distribution of integrated colors in the (U – B) vs. (B – V) diagram with the theoretical models, it turns out that: 1) The data are consistent with the presence of a gap (period of quiescence) in the history of cluster formation. If the age-metallicity relation (AMR) for the LMC obeys the simple model of chemical evolution, the gap is well evident and corresponds to the age interval ~ 3 Gyr to (12- 15) Gyr. On the contrary, if the chemical enrichment has been much slower than in the simple model, so that intermediate age clusters are less metal rich, the gap is expected to occur over a much narrower color range and to be hidden by effects of color dispersion. 2) The bimodal distribution of B – V colors can be reproduced by a sequence of clusters almost evenly distributed in the logarithm of the age, whose metallicity is governed by a normal AMR. No need is found of the so-called phase transitions in the integrated colors of a cluster taking place at suitable ages (Renzini & Buzzoni 1986). 3) The gap noticed by BCDSP in the (U – B) vs. (B – V) plane can be explained by the particular direction along which cluster colors are dispersed in that part of the (U – B) vs. (B – V) diagram. Also in this case, no sudden changes in the integrated properties of clusters must be invoked. The results of this analysis are used to revise the empirical method proposed by Elson & Fall (1985, EF85) to attribute ages to LMC clusters according to their integrated UBV colors. We show that the EF85 method does not provide the correct relation between ages and colors for clusters of low metallicity and hence its inability to date the old clusters. We propose two modifications to the definition of the parameter 8 of EF85 such that the age sequence of red clusters is suitably described, and the intrinsic errors on ages caused by the heavy presence of various effects dispersing the colors are reduced to a minimum. The age sequence is calibrated on 24 template clusters for which ages were independently derived from recent color-magnitude diagrams (CMD). Finally, we attribute ages to all clusters present in BCDSP catalog, and derive the global age distribution function (ADF) for LMC clusters. The ADF presents new features that were not clear in previous analyses of UBV data, but were already suggested by a number of independent observational studies. The features in question are periods of enhanced cluster formation at ~100 Myr and 1 – 2 Gyr, and a gap in the cluster formation history between ~ 3 and (12 – 15) Gyr. The peaks observed in the distribution of B – V colors are found to be sensítíve to the presence of these periods of enhanced cluster formatíon and the lack of extremely red clusters caused by the age gap between íntermediate-age and old clusters.

In order to gain a better understanding of starburst and merger events, we have extended to dwarf galaxies our previous spectral simulations of burst evolution over 3 Gyr, superimposed on an old underlying stellar population. We have used a library of star cluster and galaxy integrated spectra in the 3700-9700 Å wavelength range. Two kinds of galaxy spectra representing the underlying red stellar populations have been considered: (i) an average spectrum of the central regions of NGC 3056 and 4476, for which previous population syntheses have shown a maximum metallicity of [Z/Z̛0 ]= -0.5, and (ii) a combination of globular cluster spectra in the range - 2≤s;[Z/Z̛] ≤ -1, which could represent the old stellar population in the transition between dwarf ellipticals and dwarf spheroidals. These spectra were combined with those of Large Magellanic Cloud (LMC) and Galactic disc star clusters in the 3-Myr to 3-Gyr age range, in order to simulate starburst events in dwarf galaxies and model the subsequent spectral evolution of the composite system. The star cluster spectra have been properly scaled to represent starburst-to-galaxy mass fractions of 1O, 1 and 0.1 per cent. The resulting models forma spectral atlas for comparisons with observa­ tions. Rest-frame BVRI magnitudes and the related colours have been derived from these models, as well as the equivalent widths for a set of metallic and Balmer features. The behaviour of these índices is analysed as a function of the burst age and strength. The results can be used to study the properties of star-forming events in galaxies.

We present narrow-band CCD images of the high-excitation Seyfert 2 galaxy ES0138-G01, centred on the emission tines [O III] λ5007, Hα+[N II] λλ6548, 6584 and adjacent continua. The continuum-subtracted [O III] image presents an elongated jet-like structure to the west of the nucleus which is only weakly visible in the Hα image, and which we conclude is ionized by the nuclear source. The ionization map shows high excitation at the nucleus and at the 'jet'. The continuum ratio map shows that this galaxy is very blue for its morphological type, consistent with the large contribution of a young stellar population up to 3 kpc from the nucleus. We also propose that ESO138 - GO1 is the hard X-ray source previously identified with the nearby galaxy NGC 6621.

We present evidence for a young stellar population component in the early-type member of the E+S galaxy pair AM 0327-285. This young population is consistent with the occurrence of cross-fueling in this interacting system. We used spectroscopy, optical imaging, IRAS data, and stellar population synthesis to study the stellar content in the early-type galaxy. We also attempted to date episodes of star formation in its nuclear region, from population synthesis and basic dynamical considerations. The dominant population is old and metal-rich ([Z/Z]Θ=0.3) while ~ 10% of the flux at 5870 Å arises from a superimposed young stellar population with age

With the aim of better understanding the physical processes that produce the continuous emission in active galactic nuclei (AGNs), a snapshot of the overall continuous energy distribution of NGC 3783, from γ-ray to radio wavelengths, has been obtained within the framework of the World Astronomy Days. The data collected in this campaign are from GRO, ROSAT, Voyager 2, IUE, HST, ESO, CTIO, SAAO and the VLA. Great care has been taken in disentangling the genuine AGN continuous emission from other contributions: depending on the waveband, the latter might be (i) unrelated contaminating sources in cases where the instrument field of view is large, (ii) components within which the AGN is embedded, such as the stellar bulge population which accounts for a significant fraction of the optical continuum, and free-bound and FeII blends which contribute to the ultraviolet flux. After correction for these other contributions, the continuous emission of the isolated AGN appears to be rather ftat (i.e., approximately equal energy per unit logarithmic frequency) from soft γ-ray to infrared wavelengths. At high energies (0.1 MeV to 0.1 keV), the AGN continuum can be fitted by a power law Fv ∝ v-α with a spectral index α ≈ 1. At longer wavelengths, two excesses above this power law ("bumps") appear: in the ultraviolet, the classical big blue bump, which can be interpreted as thermal emission from the accretion disc surrounding a massive black hoJe, and in the infrared a second bump which can be ascribed to thermal emission from dust in the vicinity of the AGN, heated by ultraviolet radiation from the central source. By fitting accretion-disc models to the observed AGN spectral energy distribution, we find values for the accretion disc innermost temperature, accretion rate, and black hole mass, with some differences that depend on whether or not we extrapolate the high-energy power law up to infrared wavelengths. A fit to the IR bump above the extended a = 1 power law suggests the presence of a dust component covering the region from a distance r ≈ 80 light days (hot grains at a temperature T ≈ 1500 K) to r ≈ 60 light years (cool grains at T ≈ 200 K). The total mass of dust is around 60 Mʘ.

We studied NGC 6522 colour magnitude diagrams using CCD photometry with BV filters. We have carefully estimated the reddening, which is criticai for Baade Window studies, obtaining E(B-V) = 0.55. We derive for this intermediate metallicity cluster, a distance of 6.2 kpc, slightly foreground to the bulk of the metal-rich bulge population. The CMD properties of the cluster core show an enhanced and extended blue horizontal branch, a characteristic in common with many other core collapsed globular clusters.

We have carried out U BV I and Gunn z CCD photometry and integrated spectroscopy in the range λλ3700-10 000 Å of NGC 6540, which was previously classified as an open cluster. The observations indicate that we are dealing with a globular cluster of metallicity [Fe/H] ≈ -1.0 with an extended blue horizontal branch but some stars are also present on the red side. We derive a reddening of E(B- V)= 0.60 ± 0.10 and a distance d = 3.5 kpc from the Sun. The cluster giant branch is very poorly populated like in some Palomar clusters; however it has a very concentrated nucleus. Bright giants, extended in the E-W direction, are outside the nucleus. Therefore the cluster has many characteristics in common with post core collapse clusters. A structural analysis by means of stellar isopleths reveals that the cluster is elongated in the N-S direction in the outer parts, whereas the inner contours are progressively twisted towards E-W.

This work undertakes the study of the galaxy NGC 4861, using imaging centered at the strong lines Hα, Hβ, [O III] λ5007 and nearby continua. Integrated, absolute fluxes of 28 H II regions, and the region known as the bright knot, have been measured showing correlations between the equivalent width of Hβ and the excitation index log([O III]/Hβ). An excitation gradient has been detected along the chain of H II regions extending northwards from the bright knot, which is unusual for irregular galaxies like NGC 4861. We suggest that this gradient is due to different stages of evolution, or ages, of the H II regions. The continuum fluxes of eight emissionless associations and lhe continuum colors of the companion galaxy IC 3961 have also been measured, and the presence of ionized gas cannot be detected. The age and mass of the stellar population and ionizing stars of the bright knot were subsequently estimated. lt was also verified that this region is the most important burst of star formation in NGC 4861.

We have carried out BVRI and Gunn z CCD photom­ etry for the globular cluster NGC6652 which had no previous colour magnitude study. This cluster, which is projected close to the bulge minor axis at ≈ 11° from the center, has a CMD morphology suggesting a moderately high metallicity of [Fe/H] ≈ -0.9. The Horizontal Branch is red with the possibility of a few members in the RR Lyrae gap. The cluster appears to have several blue stragglers. We derive a reddening of E(B-V) = 0.10 ± 0.02 and a distance of dʘ = 9.3Kpc. The turnoff is reached and we obtain ∆V(TO-HB) = 3.35±0.16 suggesting that it is slightly younger than the average age of Galactic globular clusters.

We discuss narrow band CCD imaging of NGC 4861 in continua at 4500 Å, 5300 Å and 6300 Å as well as in Hα, Hβ and [OIII] λ 5007Å lines. We find that the system exhibits a double nucleus structure anda counter-tail to the well-known NE chain of HII regions. The mean value of lines and continua frames for the main body brightness distribution ofNGC 4861 is R-2.04±0.35, comparable to the Hubble-Reynolds law R-². The three mentioned characteristics indicate that NGC 4861 might have undergone a merger process. The time elapsed from the beginning of the phenomenon is set to be smaller than three crossing times. New observations are proposed to confirm or reject the merger scenario for this peculiar galaxy.

We study integrated spectra of 37 star clusters in the range 3100-4200 Å. The sample includes Galactic globular and open clusters, as well as Magellanic Cloud clusters. Feature equivalent widths (W) and continuum distribution are analyzed as a function of age and metallicity. In particular we discuss the behaviour of the Balmer Jump and of the 4000 Å Break, which are measured by the same continuum ratio C3660 Å / C4020 Å. For ages t < 500 Myr the Balmer Jump is dominant over the 4000 Å Break and for t < 50 Myr it is an excellent age discriminator. The effects of blue Horizontal Branch morphology on globular cluster spectra are also discussed: they increase the Balmer line W, but do not dilute substantially the Near­ UV metallic features. The present data will provide a means to connect optical to UV integrated star cluster spectra, with im­ portant applications in stellar population analyses, in particular for distant galaxies at redshift up to 1.

The discovery of a previously uncatalogued extended object at a19so = 17h 21m 508 and 81950 = -24° 15' 44" is reported. The size (d 60") and appearance on the ESO R Atlas field 519 are similar to those of several reddened globular clusters found in the last two decades. This globular cluster candidate is projected on the bulge, at 1 = 1.411° and b = 6.393°. Within the region 20° vs 20° centered on the Galactic nucleus direction, the object is located in the quadrant least populated by known globular clusters.

The star formation history in the nucleus of late spiral galaxies is compared between a sample in a high galaxy density medium (HDS) and a control sample (CS) of isolated galaxies. We have observed 20 HDS and 18 CS galaxies from a larger list generated by the application of a group-finding algorithm to the SSRS survey. Using equivalent widths of absorption lines and the continuum distribution, we determined the nuclear stellar population types, from those dominated by old population to those containing star formation bursts of different ages and intensities. The HDS and CS stellar population type histograms are similar, suggesting that environmental influences, at least for the present sample, do not affect substantially the nuclear stellar population. However, the nuclear emission lines indicate that, in the BPT diagnostic diagrams, there is an excess of HDS galaxies located within or close to the AGN loci. For six HDS and two CS galaxies, it was possible to determine oxygen (0/H) and nitrogen (N/H) abundances. The samples present similar 0/H values, but in the CS galaxies the N/0 ratio is lower at equal galaxy luminosity.

We have observed Lyngå 7, previously catalogued as an open cluster, in B, V and I.The Colour Magnitude Diagrams (CMDs) show that it is old like a globular cluster, or an extremely old thick/old disk cluster. It has a red horizontal branch and the CMD morphology indicates that it is metal rich, intermediate between 47 Tuc and NGC 6553. We derive a reddening of E(B – V) = 0.72 and a distance of ≈ 6.7 kpc from the Sun. Its position in the Galaxy shows that it should belong to the metal-rich disk system of globular clusters, being close to its edge.

We present BVRI and Gunn z CCD photometry for the bulge metal-rich globular cluster Terzan 1. The RGB shows an anomalous shape and the HB is extremely red. lt is projected on a very metal-rich bulge population. We demonstrate that this cluster is strongly affected by blanketing in the B and V bands. From the I vs. (V – I) photometry, we obtained a reddening E(B – V) ≈ 1.67, in agreement with previous JHK photometry estimate. We conclude that this cluster has a very high metallicity, as revealed by an anomalous RGB morphology, in particular in the V vs. (B – V) diagram, and an excess blanketing of ∆ (V – I) ~ 0.8 – 0.9 relative to the Baade window population. These results should be considered in the modelisation of metal-rich atmospheres and analyses of metal-rich composite spectra and photometric indices.

We present B, V colour magnitude diagrams of the rich open cluster NGC 6603. A foreground reddening of E(B- V)f = 0.50 and an internal one of E(B- V)i = 0.29 were derived with the additional help of integrated spectra. The resulting age is 200±100Myr, and the distance is about 3.6 kpc. The surrounding field is also studied, appearing to be part of a star cloud which contains age components in the range 200 to 600 Myr or more. The cluster appears to be spatially associated with the star cloud, being part of its youngest component. The cluster and the star cloud location in the inner disk are in agreement with other studies showing an enhancement of star formation in this region.