The physical conditions and chemical abundances were determined for M2-29 and BB-1 from optical spectrophotometric data and from available IUE material (Table 1). M2-29 has the lowest O/H ratio in PNe and it belongs to the Ar and S rich type IV PN group while BB-1 is very C, N, and Ne rich being Ar and S poor. Comparing with all known PNe of type IV it is found that C/N/O/Ne/Ar do not vary in lockstep, but C, N, O and Ne appear enriched in Ar poor objects (Table 2). C and N are expected to be enriched by the central star, however the anomalous O/Ne/Ar behavior is not understood unless O and Ne are also enriched by the progenitor star. The paper in full will appear in P.A.S.P. 1991.

It has been suggested that most of the primeval galactic globular clusters have been dissociated by encounters with molecular clouds, and by tidal effects in the vicinity of the galactic center; their stellar remnants would move preserving some memory of their original kinematical parameters and might resemble the well-known population I moving clusters. However it has been shown, by direct numerical integration, that a significant fraction of the halo stars have chaotic orbits and many others reach high z-values; hence the usual criterium of identifying group members by the similarity of their V-velocities breaks down. Instead, we use the constancy of the integrals of motion, i.e. the total energy and the z- component of the angular momentum, as well as the metallicity [Fe/H], as the identifying parameters for group membership of a given star. From the analysis of the metallicities and the integrals of motion of 206 halo stars, we have been able to identify several halo moving groups.

Spectral energy distribution for a sample of starburst galaxies has been synthesized. The proposed sample contains galaxies whose optical light is mainly dominated by an early type galaxy population. A low excitation nebular spectrum is superimposed whose strength in the Halfa emssion line suggests the presence of very massive stars responsible of the observed ionization.

A survey for carbon stars in the Small Magellanic Cloud (SMC) has been carried out with the triplet camera at the prime focus of the ESO 3.6 m telescope using a Grism giving a dispersion of 2200 A/mm. 13 circular fields of 0.78 sq. degrees each, partially overlapping, cover the main body of the SMC (Rebeirot et al. 1987).

We report here an observational study on the IR properties of members of the rich clusters of galaxies: Abell 194, Perseus and Hercules. Following the precepts described in previous papers concerning the manifold of the early-type galaxies from IR photometry for the Coma (Recillas-Cruz et al. 1990) and Virgo (Recillas-Cruz et al. 1991) cluster members; interstellar reddening and redshift corrections for Abell 194, Perseus and Hercules were estimated. Interstellar reddening corrections for Abell 194 and Hercules galaxy members were found to be small, except for Perseus cluster galaxies where extinction values are somewhat larger. IR redshift K-corrections were estimated from linear relations with z for (J-H), (H-K) and K (Persson et al. 1979). Corrected magnitudes and colors were then used to construct (J-H) vs. (H-K) diagrams for elliptical and S0 galaxies and color-magnitude diagrams (J-H), (H-K), (J-K), (B-K) and (V-K) vs. K.

Extensive Montecarlo simulations of populations of post-Asymptotic Giant Branch (P-AGB) stars have been constructed. The time evolution of luminosity and effective temperature for any stellar mass has been approximated by suitable analytical approximations based on the P-AGB evolutionary tracks of Paczyński (1971, Acta Astron. 21, 417) and Schönberner (1983, A&A 79, 108). By constructing synthetic HR diagrams for P-AGB stars we explore the effects of various assumptions, such as the IMF, the initial mass-final mass relation, the AGB to PN transition time, etc. We have also investigated how the uncertainties in the various assumptions and observational errors in luminosity and temperature propagate into the inferred mass distribution of the P-AGB stars. As an example of the possible applications, we show in the Figure the mass distributions of two P-AGB populations, which differ only on the effective temperatures. We have assumed a systematic error in the observed temperature, such as logTobs = 1.01 ·logTtrue + 0.01. Such an error is very small in comparison to usual Zanstra temperature uncertainties for Planetary Nebula Nuclei, yet the two distributions are remarkably different. The broken line represents the observed distribution. The mean mass are respectively < M/M⊙ >= 0.594 for the true distribution (i. e. using Ttrue), and < M/M⊙ >= 0.628 for the observed one (i. e. using Tobs). This simulation emphasizes the need for accurate temperatures in order to obtain useful mass distributions for P-AGB stars, when using an observed distribution of P-AGB stars in the HR diagram. Further applications and details will be included in a forthcoming paper (Stanghellini & Renzini, in preparation).

The detection of a strong resonance line of Li I at 6708å in the spectra of some apparently normal K giant stars, has roused what we can call the “K Giant Lithium Problem”. In fact, according to the standard stellar evolution theory this element must be strongly depleted in the atmospheres of these stars. No satisfactory explanation of this peculiarity has been given to the present time. Anyway, to understand the involved mechanisms it is important to obtain the best possible values of the corresponding Li abundances. Our method use the secondary Li line at 6104å which is very sensitive to abundances, specially when these are high. This is not the case of the strong and saturated resonance line. The weaker 6104 line is formed deeper in the stellar atmosphere than the resonance line, being less affected by non LTE effects. In this work we present partial results obtained with LTE theory (a general non LTE approach will be publish elsewhere) for the following stars: HD 787, HD 39853 and HD 19745. The first two are known bright K giant stars having respectively medium and high intensity 6104 lines. The last star is a member of a group of weak K giant stars recently discovered at the LNA (Brazil) in a search based on IRAS point sources. This star has the strongest 6104 line detected up to now in those kind of stars. The observations of the 6104 line were performed with the 1.4m Coude Auxiliary Telescope at ESO with a spectral resolution of 0.062å. Each program star was observed at least twice and the S/N ratios of the combined spectra exceed 200. Other spectral ranges were observed to determine the Fe, O, C and N abundances. With the main parameters (Teff, log g, V turb.) for stars: HD 787 (3970, 1.7, 1.7); HD 39853 (3900, 1.2, 1.0); HD 19745 (4990, 2.1, 1.7); we obtain the following LTE abundances for Li by means of the 6104 line only (in the scale log H=12): HD 787, logLi=2.20; HD 39853, logLi=2.90; HD 19745, logLi=4.08. Concerning these three objects, HD 39853 is the only high velocity object and HD 19745 is the only IRAS source. The main conclusion is that the richest Li star HD 19745 seems to have a Li abundance larger than that of the mean interstellar medium (logLi=3.30). The explanation of this fact constitute a challenge to the classical theory of evolution of these objects. In fact, this apparently low mass star has not sufficient core mass to generate an extra quantity of 3He which could explain a large 7Li enrichment, by means of the 7Be mechanism.

The ages of the galactic globular clusters belonging to the disk subsystem are still widely unknown. By considering the HB morphology Richtler et al. (1991) were led to the conjecture that some of the disk clusters may resemble the populous intermediate-age clusters in the Magellanic Clouds, but no main-sequence photometry was published at that time. We now present B,V photometry for the clusters NGC 6496, 6624, and 6637 (M69) which in all cases show the turn-off point and allow reliable age determinations.

New population synthesis models for starburst regions have been computed, with an emphasis on the W-R population and the output of ionizing photons.

If the grains in pre-collapsing clouds are due to the contribution of winds from previous generations of stars and supernovae ejecta, they already contain a fraction if not all, of the heavy elements. The far infrared spectrum of Bok globules, which are at relatively early contraction stages, has been attributed to dusty material.

An infrared scan of the Baade's Window (BW) is obtained. The cumulative K-counts function (hereafter CCF, which is the number of sources per square degree down to K = +13.5) is formed by combining 1.9m telescope scans with AAT scans. With the aid of a theoretical exponential disk model (e.g., Ruelas-Mayorga, A., Rev. Mex. Astr. Astrof. 22, 43, 1991) and observations at 1 = 20°, b = −5°, we decompose the observed CCF into disk-CCF and bulge-CCF components. The bulge CCF is steeper than the disk CCF in the range K = (+5.0,+11.0) showing a relative depletion of high mass stars with respect to the disk. The bulge CCF is compared with derived CCF's for the globular clusters 47 Tuc, M92, M3 and M13 and the open cluster M67. The similarity of the slope of the bulge-CCF to those of the globular clusters suggests that the stellar population of the bulge may be similar in age and perhaps also in metallicity characteristics of the stellar populations in globular clustes. Photometric studies of a bright-K subsample: 165 of the 578 sources found in BW down to K = +11.0 are made. Several sources with mild IR-excesses are found, and through spectroscopy, were confirmed to be Miras variables. The reddening E(J-K) = +0.27 agrees well with the value E(B-V) = +0.45 obtained by optical techniques. In a HR diagram most of the sources in our photometric subsample lie above the giant branch tips of ω Centauri, 47 Tuc and M92. If the giant branches (GB) of these clusters are extrapolated to higher K brightnesses, a sizeable fraction of our sample would lie between them. This also suggests that their metallicity may lie in the range between that of M92 and 47 Tuc. For those sources with redded J-K colours than the 47 Tuc GB, and with magnitudes brighter than K = +8.5, even higher metallicities are required.

The galaxy NGC 1313 is a late-type (almost Magellanic) barred spiral located midway between the Magellanic Clouds but at a distance of about 4.5 Mpc (de Vaucouleurs 1963). A comprehensive imaging and spectrophotometry program has been carried out in order to investigate the peculiar kinematics of NGC 1313 (Marcelin and Athanassoula 1982), as well as to study the relationships between the formation of massive stars and light element chemical abundances in spiral galaxies.

We present the results of a multi-wavelength observational study of actively star-forming dwarf galaxies (also known as Blue Compact Dwarfs). We combine optical, infrared and H-alpha imaging with optical spectroscopy and HI data in an attempt to better understand the stellar population make-up and star-formation histories of this type of galaxy. In particular, we address the long-standing ambiguity concerning the source of the near-infrared flux in BCDs. We find in nearly all cases that there is clear evidence for an older population of stars. However, the currently active starburst often contributes a large fraction of the total near-infrared flux in the form of nebular continuum emission and/or light from hot main sequence stars.

We have found evidence of a CNO/Fe excess in the integrated spectrum of 47 Tuc relative to a synthetic cluster built up of solar neighbourhood stellar spectra from Gunn & Stryker's library (GS, 1983). The 47 Tuc spectrum was synthesized between 3200 < λ < 9750å aided by the cluster color-magnitude diagram (Hesser et al. 1987) complemented with a low main sequence, which was simulated by a canonical initial mass function (IMF) of slope x = 2.8. If a flat IMF (Hesser et al. 1987) is attributed to stars earlier than M, then x ≍ 5 is necessary for lower masses. A similar synthesis procedure was previously applied to the Galactic open cluster M11 (Santos Jr. et al. 1990). The residuals from the spectral synthesis were analyzed between 3200 < λ < 5400å, where a blanketing stronger in 47 Tuc than in the solar model remained. This is the integrated version of blue/violet excesses found in 47 Tuc individual giants (Hesser et al. 1977). It is well known that 47 Tuc has lower [Fe/H] than the solar model, suggesting non-solar [CNO/Fe] as responsible for the blanketing. As the localized bands CN, C2 and CH are not enough to explain it, we have used 28 plausible diatomic molecular patterns (two examples are shown in Fig. 1) and a synthesis technique to suggest possible absorbers contributing to this blanketing. Fig. 2 presents the molecular model and the residuals shifted by a constant, where a NH localized band is clear. The CO molecule resulted the dominant distributed absorption (≍ 50% in flux of the total blanketing), followed by SiN (20%). Definite identifications of the absorbers need much higher resolution than that in GS's library (20-40å). On the other hand, the methods proved to be very efficient for analysing the 47 Tuc population by means of stellar synthesis and molecular synthesis.

Population synthesis is a powerful tool to study stellar populations where the analysis of the stellar content of a composite system is based on the results of breaking down into components (of a given base) the spectrum of the observed system. Such process constitutes an inverse problem which can have a multitude of possible or “acceptable” solutions. This degenerative character of the synthesis rises mainly from observable errors and from the base of components itself with respect to its internal consistency and its (in)capacity to fully embrace all the free parameters involved.

We analyze a deep CMD for the LMC cluster NGC1831, based on CTIO PFCCD frames. More than 4 magnitudes of main sequence (MS) are evident, as well as a prominent clump, and a few possible giant branch stars. We fit the MS to a series of models and Galactic clusters, and derive a distance of 18.3±0.1 and an age of 0.5±0.1 Gyr, for an abundance of about 2/3 solar ([Fe/H]~–0.23), based on the VandenBerg models (Vandenberg and Poll 1989). A fit to the empirical Pleiades MS, assuming an intrisic modulus of 5.6, gives a LMC modulus of 18.25-18.35, after an adjustment for the relative abundance difference of −0.2.

uvby – β photometry for 1149 high–velocity and metal–poor stars has been obtained and is being used to derive metallicities, distances, and ages for these stars. The distances have been combined with proper motions and radial velocities from the literature to calculate the stars' galactic space velocities. Our ultimate aim is to reach a better understanding of the early dynamical and chemical evolution of our Galaxy by studying the possible existence of correlations between metallicity, age, and kinematics for these stars. In particular, the V(rot), [Fe/H], Toomre energy, and W′,[Fe/H] diagrams are being used to analyze the kinematic characteristics of this sample. Two distinct, separate populations are very clearly seen, and there is also some evidence for additional stellar components. Our kinematic and metallicity data argue quite strongly for mostly uncoupled evolutions for the disk and halo populations of the Galaxy.

Using the uvby – β data of Schuster and Nissen (1988) to calculate photometric distances and using the galactic potentials of Allen and Martos (1986) and Allen and Santillán (1991), galactic orbits have been integrated for 615 halo and high-velocity disk stars. Correlations between orbital characteristics, metallicities, and ages are being studied. For the 206 halo stars of this sample, a particularly high percentage of the orbits (35-50%) show some chaotic behavior, due mainly to their low angular momenta which lead to small (< 1 Kpc) perigalactic distances. The newer potential of Allen and Santillán, which includes a spherical central bulge rather than a central mass point, gives the higher percentage of chaotic orbits. The effects of this chaos upon chemical gradients and upon the dynamical structure of the halo are being investigated.

A study of 67 E and S0 galaxies located mostly in the field and in groups reveals that at any given luminosity the UBV colors become systematically bluer as the amount of fine structure (ripples, jets of luminous matter, X-structure, and boxy isophotes) increases. Figure 1 shows the resulting correlations between the color residuals δ(U – B)e,0, δ(B – V)e,0 (calculated as deviations from the mean color–luminosity relations) and the fine structure parameter Σ. These correlations closely resemble correlations found earlier between CN, Mg2, and Hβ line strengths and the same parameter Σ in 36 ellipticals (Schweizer et al., Ap.J. Letters 364, L33, 1990). Both sets of correlations are most likely due to systematic variations in mean age, rather than mean metallicity, of the stellar populations in these early-type galaxies. We model the evolution of galaxies undergoing a major merger by convolving a single-burst model (Charlot & Bruzual, Ap.J. 367, 126, 1991) with a star formation rate that declines exponentially with a long time constant (6–10 Gyr) before the merger and with a short time constant (0.1–0.5 Gyr) afterwards. Some of the model parameters are determined from observations of two 1–2 Gyr old merger remnants. Comparisons between the observed UBV colors and the models suggest that the bluest E + S0 galaxies in our sample formed through mergers only a few billion years ago, which also explains their high amount of fine structure.

Different methods have been used to derive velocity dispersions of stellar populations in bulges of galaxies. In all cases, the spectrum of a K giant is used as template: the stellar spectrum convolved with the appropriate gaussian, the Fourier transform technique, or the cross-correlation technique (see Dalle Ore et al., 1991, for a review).