Related papers: Evolutionary changes in the periods of galactic RR…

We present a study of the evolution of late-type field dwarfs over the last ~ 1.9 Gyr, based on HST ACS observations carried out as part of the GEMS survey. This study is amongst the first to probe the evolution of dwarfs over such a large…

During this last decade our knowledge of the evolutionary properties of stars has significantly improved. This result has been achieved thanks to our improved understanding of the physical behavior of stellar matter in the thermal regimes…

Observations in the Hubble Deep Fields have been used to study the evolution of galaxy morphology over time. The majority of galaxies with z < 1 are seen to be disk like, whereas most objects with z > 2 appear to be either chaotic or…

The eleventh part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 16836 RR Lyr stars detected in the OGLE fields toward the Galactic bulge. The total sample is composed of 11756 RR Lyr stars pulsating in the fundamental mode…

The properties of RR Lyrae variables make them excellent probes of the formation and evolution of a stellar population. The mere presence of such stars necessitates an age greater than ~10 Gyr while their periods and amplitudes can be used…

Open and globular star clusters have served as benchmarks for the study of stellar evolution due to their supposed nature as simple stellar populations of the same age and metallicity. After a brief review of some of the pioneering work…

We have constructed a family of simple models for spiral galaxy evolution to allow us to investigate observational trends in star formation history with galaxy parameters. The models are used to generate broad band colours from which ages…

In an effort to obtain further observational evidences for secular evolution processes in galaxies, as well as observational constraints to current theoretical models of secular evolution, we have used BVRI and Ks images of a sample of 18…

With the help of linear pulsation models we briefly discuss the peculiar period ratios characteristic for modulated double-mode RR Lyrae stars.

The present article is written in the wake of a recently published study of the relation between the light curves of Long Period Variables and their evolution along the Asymptotic Giant Branch (AGB). It introduces a pair of new parameters…

We report the serendipitous discovery of two RR Lyrae stars exhibiting significant s-process element enrichment, a rare class previously represented solely by TY Gruis. Our goal is to characterise these objects chemically and dynamically,…

I review recent observational progress concerning the evolution of the morphological distribution of galaxies in the rich cluster environment and in the faint field population. By coupling HST imagery with ground-based spectroscopic…

This paper presents an extensive overview of known and proposed RR Lyrae stars in binaries. The aim is to revise and extend the list with new Galactic field systems. We utilized maxima timings for eleven RRab type stars with suspicious…

Multiple systems play an important role in the evolution of star clusters. First we discuss several formation mechanisms which depend on the presence of binaries, either primordial or of dynamical origin. Hierarchical configurations are…

We collected over 6000 high-resolution spectra of four dozen field RR Lyrae (RRL) variables pulsating either in the fundamental (39 RRab) or in the first overtone (9 RRc) mode. We measured radial velocities (RVs) of four strong metallic and…

We report here on two types of cyclic variations that can be observed in the periods of RR Lyr stars, i.e., the Blazhko and the light-time effects. The former has been investigated by studying the amplitude variations recorded in RR Lyr…

The impact of new stellar evolution models with rotation on the predictions of population synthesis models is discussed. Massive rotating stars have larger convective cores than their non-rotating counterparts, and their outer layers are…

We have derived CNO abundances in 12 RR Lyrae stars. Four stars show [C/Fe] near 0.0 and two stars show [C/Fe] = 0.52 and 0.65. Red giant branch stars, which are known to be the predecessors of RR Lyrae stars, generally show a deficiency of…

We present the discovery of a new, peculiar form of double-periodic pulsation in RR Lyrae stars. In four, long-period ($P>0.6$ d) stars observed by the Optical Gravitational Lensing Experiment, and classified as fundamental mode pulsators…

The third part of the OGLE-III Catalog of Variable Stars comprises 24906 RR Lyr stars in the Large Magellanic Cloud (LMC). This sample consists of 17693 fundamental-mode (RRab), 4958 first-overtone (RRc), 986 double-mode (RRd) and 1269…