Calcium Triplet Synthesis

We present theoretical equivalent widths for the sum of the two strongest lines of the Calcium Triplet, CaT index, in the near-IR, using evolutionary techniques and the most recent models and observational data for this feature in individual stars. We compute the CaT index for Single Stellar Populations (instantaneous burst, standard Salpeter-type IMF) at four metallicities, Z=0.004, 0.008, 0.02 (solar) and 0.05, and ranging in age from very young bursts of star formation (few Myr) to old stellar populations, up to 17 gyr, representative of globular clusters, elliptical galaxies and bulges of spirals. The interpretation of the observed equivalent widths of CaT in different stellar systems is discussed. Composite-population models are also computed as a tool to interpret the CaT detections in star-forming regions, in order to disantangle between the component due to Red Supergiants stars, RSG, and the underlying, older, population. CaT is found to be an excellent metallicity-indicator for populations older than 1 Gyr, practically independent of the age. We discuss its application to remove the age- metallicity degeneracy, characteristic of all studies of galaxy evolution based on the usual integrated indices (both broad band colors and narrow band indices). The application of the models computed here to the analysis of a sample of elliptical galaxies will be discussed in a forthcoming paper (Gorgas et al. 1998).Comment: 17 pages, 7 figures, to be published in A&

Reconstructing the Topology on Monoids and Polymorphism Clones of the Rationals

We show how to reconstruct the topology on the monoid of endomorphisms of the rational numbers under the strict or reflexive order relation, and the polymorphism clone of the rational numbers under the reflexive relation. In addition we show how automatic homeomorphicity results can be lifted to polymorphism clones generated by monoids

Multiwavelength study of the starburst galaxy NGC7714. I: Ultraviolet-Optical spectroscopy

We have studied the physical conditions in the central 300 pc of the proto-typical starburst galaxy NGC 7714. Our analysis is based on ultraviolet spectroscopy with the HST+GHRS and ground-based optical observations.The data are interpreted using evolutionary models optimized for young starburst regions. The massive stellar population is derived in a self-consistent way using the continuum and stellar absorption lines in the ultraviolet and the nebular emission line optical spectrum. The central starburst has an age of about 4.5 Myr, with little evidence for an age spread. Wolf-Rayet features at the ultraviolet indicates a stellar population of $\sim$ 2000 Wolf-Rayet stars. The overall properties of the newly formed stars are quite similar to those derived, e.g., in 30 Doradus. A standard Salpeter IMF is consistent with all observational constraints. We find evidence for spatial structure within the central 300 pc sampled. Therefore it is unlikely that the nucleus of NGC 7714 hosts a single star cluster exceeding the properties of other known clusters. Contrary to previous suggestions, we find no evidence for a nuclear supernova rate that would significantly exceed the total disk-integrated rate. About one supernova event per century is predicted.Comment: 19 pages, 9 figures in a tar file. Accepted for publication in ApJ, 1999, March, issue 51

The evolution of H{\sc ii} galaxies: Testing the bursting scenario through the use of self-consistent models

We have computed a series of realistic and self-consistent models of the emitted spectra of H{\sc ii} galaxies. Our models combine different codes of chemical evolution, evolutionary population synthesis and photoionization. The emitted spectrum of H{\sc ii} galaxies is reproduced by means of the photoionization code CLOUDY, using as ionizing spectrum the spectral energy distribution of the modelled H{\sc ii} galaxy, which in turn is calculated according to a Star Formation History (SFH) and a metallicity evolution given by a chemical evolution model that follows the abundances of 15 different elements. The contribution of emission lines to the broad-band colours is explicitly taken into account. The results of our code are compared with photometric and spectroscopic data of H{\sc ii} galaxies. Our technique reproduces observed diagnostic diagrams, abundances, equivalent width-colour and equivalent width-metallicity relations for local H{\sc ii} galaxies.Comment: 13 figures and 2 tables, accepted for publication in MNRAS Main Journa

AVOCADO: A Virtual Observatory Census to Address Dwarfs Origins

Dwarf galaxies are by far the most abundant of all galaxy types, yet their properties are still poorly understood -especially due to the observational challenge that their intrinsic faintness represents. AVOCADO aims at establishing firm conclusions on their formation and evolution by constructing a homogeneous, multiwavelength dataset for a statistically significant sample of several thousand nearby dwarfs (-18 < Mi < -14). Using public data and Virtual Observatory tools, we have built GALEX+SDSS+2MASS spectral energy distributions that are fitted by a library of single stellar population models. Star formation rates, stellar masses, ages and metallicities are further complemented with structural parameters that can be used to classify them morphologically. This unique dataset, coupled with a detailed characterization of each dwar's environment, allows for a fully comprehensive investigation of their origins and to track the (potential) evolutionary paths between the different dwarf types.Comment: 4 pages, 1 figure. To appear in the proceedings of IAU Symposium 277, "Tracing the Ancestry of Galaxies on the Land of our Ancestors", Carignan, Freeman, and Combes, ed