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.

The Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey obtained approximate to 240,000 moderate-resolution (R similar to 1800) spectra from 3900 angstrom to 9000 angstrom of fainter Milky Way stars (14.0 < g < 20.3) of a wide variety of spectral types, both main-sequence and evolved objects, with the goal of studying the kinematics and populations of our Galaxy and its halo. The spectra are clustered in 212 regions spaced over three quarters of the sky. Radial velocity accuracies for stars are sigma(RV) similar to 4 km s(-1) at g < 18, degrading to s(RV) similar to 15 km s(-1) at g similar to 20. For stars with signal-to-noise ratio > 10 per resolution element, stellar atmospheric parameters are estimated, including metallicity, surface gravity, and effective temperature. SEGUE obtained 3500 deg(2) of additional ugriz imaging (primarily at low Galactic latitudes) providing precise multicolor photometry (sigma(g, r, i) similar to 2%), (sigma(u, z) similar to 3%) and astrometry (approximate to 0 ''.1) for spectroscopic target selection. The stellar spectra, imaging data, and derived parameter catalogs for this survey are publicly available as part of Sloan Digital Sky Survey Data Release 7.

The Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey obtained approximate to 240,000 moderate-resolution (R similar to 1800) spectra from 3900 angstrom to 9000 angstrom of fainter Milky Way stars (14.0 < g < 20.3) of a wide variety of spectral types, both main-sequence and evolved objects, with the goal of studying the kinematics and populations of our Galaxy and its halo. The spectra are clustered in 212 regions spaced over three quarters of the sky. Radial velocity accuracies for stars are sigma(RV) similar to 4 km s(-1) at g < 18, degrading to s(RV) similar to 15 km s(-1) at g similar to 20. For stars with signal-to-noise ratio > 10 per resolution element, stellar atmospheric parameters are estimated, including metallicity, surface gravity, and effective temperature. SEGUE obtained 3500 deg(2) of additional ugriz imaging (primarily at low Galactic latitudes) providing precise multicolor photometry (sigma(g, r, i) similar to 2%), (sigma(u, z) similar to 3%) and astrometry (approximate to 0 ''.1) for spectroscopic target selection. The stellar spectra, imaging data, and derived parameter catalogs for this survey are publicly available as part of Sloan Digital Sky Survey Data Release 7.