The Antlia dwarf galaxy, recently found to be a possible local Group member, is analyzed using VI photometry. The galaxy is resolved into a large number of stars and although the galaxy is intrinsically faint and of low surface brightness, its stellar populations reveal characteristics more typical of faint star-forming dIrs rather than dEs. Significant star formation is currently going on in the central part of Antlia although little or no tar formation is taking place in the outer regions. This indicates a two-component (core-halo) morphology which appears to be common, lot only in large spirals (disk-halo), but in dwarf galaxies as well. The SFR averaged over the lifetime of the galaxy is estimated to be <(psi)over bar>/A similar to 2-4 x 10(-10) M-. yr(-1) pc(-2) while the more recent star formation, averaged over the last 1 Gyr is much higher (<(psi)over bar>(1Gyr)/A similar to 3 - 9 x 10(-10) M-. yr(-1) pc(-2) for the central region). The total mass locked into stars and stellar remnants is estimated to be M(star)similar to 2-4 x 10(6) M-.. Its distance, estimated from the TRGB, is 1.32+/-0.06 Mpc, which places Antlia just beyond the Local Group, and makes it a close companion of the dwarf galaxy NGC 3109 (Delta r greater than or similar to 30 kpc), although it is not clear whether they are gravitationally bound. (C) 1997 American Astronomical Society.

The Antlia dwarf galaxy, recently found to be a possible local Group member, is analyzed using VI photometry. The galaxy is resolved into a large number of stars and although the galaxy is intrinsically faint and of low surface brightness, its stellar populations reveal characteristics more typical of faint star-forming dIrs rather than dEs. Significant star formation is currently going on in the central part of Antlia although little or no tar formation is taking place in the outer regions. This indicates a two-component (core-halo) morphology which appears to be common, lot only in large spirals (disk-halo), but in dwarf galaxies as well. The SFR averaged over the lifetime of the galaxy is estimated to be <(psi)over bar>/A similar to 2-4 x 10(-10) M-. yr(-1) pc(-2) while the more recent star formation, averaged over the last 1 Gyr is much higher (<(psi)over bar>(1Gyr)/A similar to 3 - 9 x 10(-10) M-. yr(-1) pc(-2) for the central region). The total mass locked into stars and stellar remnants is estimated to be M(star)similar to 2-4 x 10(6) M-.. Its distance, estimated from the TRGB, is 1.32+/-0.06 Mpc, which places Antlia just beyond the Local Group, and makes it a close companion of the dwarf galaxy NGC 3109 (Delta r greater than or similar to 30 kpc), although it is not clear whether they are gravitationally bound. (C) 1997 American Astronomical Society.

The study of gradients in the stellar populations of dwarf galaxies will give us necessary information to construct detailed models of their formation and evolution. We find clear traces of these gradients, in the sense of stars being older for larger galactocentric distances, in two interesting nearby dwarfs: Phoenix and Leo I.

The study of gradients in the stellar populations of dwarf galaxies will give us necessary information to construct detailed models of their formation and evolution. We find clear traces of these gradients, in the sense of stars being older for larger galactocentric distances, in two interesting nearby dwarfs: Phoenix and Leo I.

We present observations of the now Local Group galaxy candidates Cassiopeia dSph, Pegasus dSph = And VI and Camelopadalis A. Our deep color-magnitude diagrams show that the first two galaxies are certainly Local Group members, and likely dSph galaxies at a distance similar to that of the Andromeda galaxy. Cam A seems to be a star-forming galaxy situated considerably further away.

We present observations of the now Local Group galaxy candidates Cassiopeia dSph, Pegasus dSph = And VI and Camelopadalis A. Our deep color-magnitude diagrams show that the first two galaxies are certainly Local Group members, and likely dSph galaxies at a distance similar to that of the Andromeda galaxy. Cam A seems to be a star-forming galaxy situated considerably further away.

We present the results of a search for variable stars in the Local Group dwarf galaxy Phoenix. Nineteen Cepheids, six candidate long-period variables, one candidate eclipsing binary, and a large number of candidate RR Lyrae stars have been identified. Periods and light curves have been obtained for all the Cepheid variables. Their distribution in the period-luminosity diagram reveals that both anomalous Cepheids (ACs) and short-period classical Cepheids (s-pCC's) are found in our sample. This is the first time that both types of variable stars are identified in the same system even though they likely coexist, but have gone unnoticed so far, in other low-metallicity galaxies such as Leo A and Sextans A. We argue that the conditions for the existence of both types of variable stars in the same galaxy are a low metallicity at all ages and the presence of both young and intermediate-age ( or old, depending on the nature of AC) stars. The RR Lyrae candidates trace, together with the well-developed horizontal branch, the existence of an important old population in Phoenix. The different spatial distributions of s-pCC's, ACs, and RR Lyrae variables in the Phoenix field are consistent with the stellar population gradients found in Phoenix, in the sense that the younger population is concentrated in the central part of the galaxy. The gradients in the distribution of the young population within the central part of Phoenix, which seem to indicate a propagation of the recent star formation, are also reflected in the spatial distribution of the s-pCC's.

We present the results of a search for variable stars in the Local Group dwarf galaxy Phoenix. Nineteen Cepheids, six candidate long-period variables, one candidate eclipsing binary, and a large number of candidate RR Lyrae stars have been identified. Periods and light curves have been obtained for all the Cepheid variables. Their distribution in the period-luminosity diagram reveals that both anomalous Cepheids (ACs) and short-period classical Cepheids (s-pCC's) are found in our sample. This is the first time that both types of variable stars are identified in the same system even though they likely coexist, but have gone unnoticed so far, in other low-metallicity galaxies such as Leo A and Sextans A. We argue that the conditions for the existence of both types of variable stars in the same galaxy are a low metallicity at all ages and the presence of both young and intermediate-age ( or old, depending on the nature of AC) stars. The RR Lyrae candidates trace, together with the well-developed horizontal branch, the existence of an important old population in Phoenix. The different spatial distributions of s-pCC's, ACs, and RR Lyrae variables in the Phoenix field are consistent with the stellar population gradients found in Phoenix, in the sense that the younger population is concentrated in the central part of the galaxy. The gradients in the distribution of the young population within the central part of Phoenix, which seem to indicate a propagation of the recent star formation, are also reflected in the spatial distribution of the s-pCC's.

Fifty years ago, GE Hutchinson defined the ecological niche as a hypervolume in n-dimensional space with environmental variables as axes. Ecologists have recently developed renewed interest in the concept, and technological advances now allow us to use stable isotope analyses to quantify these niche dimensions. Analogously, we define the isotopic niche as an area (in delta-space) with isotopic values (delta-values) as coordinates. To make isotopic measurements comparable to other niche formulations, we propose transforming delta-space to p-space, where axes represent relative proportions of isotopically distinct resources incorporated into an animal's tissues. We illustrate the isotopic niche with two examples: the application of historic ecology to conservation biology and ontogenetic niche shifts. Sustaining renewed interest in the niche requires novel methods to measure the variables that define it. Stable isotope analyses are a natural, perhaps crucial, tool in contemporary studies of the ecological niche.

Fifty years ago, GE Hutchinson defined the ecological niche as a hypervolume in n-dimensional space with environmental variables as axes. Ecologists have recently developed renewed interest in the concept, and technological advances now allow us to use stable isotope analyses to quantify these niche dimensions. Analogously, we define the isotopic niche as an area (in delta-space) with isotopic values (delta-values) as coordinates. To make isotopic measurements comparable to other niche formulations, we propose transforming delta-space to p-space, where axes represent relative proportions of isotopically distinct resources incorporated into an animal's tissues. We illustrate the isotopic niche with two examples: the application of historic ecology to conservation biology and ontogenetic niche shifts. Sustaining renewed interest in the niche requires novel methods to measure the variables that define it. Stable isotope analyses are a natural, perhaps crucial, tool in contemporary studies of the ecological niche.