Related papers: Observational Constraints on Red and Blue Helium B…

We use high-precision photometry of red-giant-branch (RGB) stars in 57 Galactic globular clusters (GCs), mostly from the `Hubble Space Telescope (HST) UV Legacy Survey of Galactic globular clusters', to identify and characterize their…

We re-examine a deep {\it Hubble Space Telescope} pencil-beam search for red dwarfs, stars just massive enough to burn Hydrogen. The authors of this search (Bahcall, Flynn, Gould \& Kirhakos 1994) found that red dwarfs make up less than 6\%…

We have used ESO telescopes at La Silla and the Hubble Space Telescope (HST) in order to obtain accurate B,V,I CCD photometry for the stars located within 200" (~= 2 half-mass radii, r_h = 1.71') from the center of the cluster NGC 6101.…

We model, via Monte Carlo simulations, the distribution of observed U-B, B-V, V-I galaxy colors in the range 1.75<z<5 caused by variations in the line-of-sight opacity due to neutral hydrogen (HI). We also include HI internal to the source…

(abridged) We investigate biases in cluster ages and [Fe/H] estimated from the (V-K)-(V-I) diagram, arising from inconsistent Horizontal Branch morphology, metal mixture, treatment of core convection between observed clusters and the…

We discuss a 175 deg^2 spectroscopic survey for blue horizontal branch (BHB) stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and find that the 2MASS…

Several independent lines of reasoning suggest that many of the very faint (B > 24) blue galaxies are low-mass objects that experienced a short epoch of star formation at redshifts 0.5 < z < 1 and have since faded into low luminosity, low…

We conduct a series of comparisons between spectroscopic and photometric observations of globular clusters and stellar models to examine their predictive power. Data from medium-to-high resolution spectroscopic surveys of lithium allow us…

Through the relationship between dispersion measures (DM) and redshifts, fast radio bursts (FRBs) are considered to be very promising cosmological probes. In this paper, we attempted to use the DM-z relationship of FRBs to study the helium…

We study the evolution of the galaxy population up to z\sim3 as a function of its colour properties. In particular, luminosity functions and luminosity densities have been derived as a function of redshift for the blue/late and red/early…

We present the results of infrared observations of Abell 1689 which was observed with ISOCAM, at 6.7\mic and 15\mic, and ISOPHOT at 200\mic. The cluster galaxies detected above a sensitivity limit of 0.15 mJy in the 6.7\mic band, whose…

We have incorporated the latest release of the Padova models into the evolutionary synthesis code Starburst99. The Padova tracks were extended to include the full asymptotic giant branch (AGB) evolution until the final thermal pulse over…

Stellar population models to predict the H Balmer and HeI lines in absorption are presented. Models are computed for burst and continuous star formation. It is found that the Balmer and HeI line profiles are sensitive to the age, except…

Supernova (SN) cosmology is based on the assumption that the corrected luminosity of SN Ia would not evolve with redshift. Recently, our age dating of stellar populations in early-type host galaxies (ETGs) from high-quality spectra has…

We studied the Na-O anti-correlation from moderately high resolution spectra for 35 stars on the blue HB (BHB), one RR Lyrae, and 55 stars are on the red HB (RHB) of NGC1851. We also derived abundances for He and N in BHB stars, and Ba and…

The colours of the galaxy class known as Extremely Red Objects (EROs; R-K>5) are considered to be consistent with two distinct galaxy populations at high redshift: evolved ellipticals or young dusty starbursts. In this paper the properties…

One crucial piece of information to study the origin of multiple stellar populations in globular clusters, is the range of initial helium abundances $\Delta{Y}$ amongst the sub-populations hosted by each cluster. These estimates are…

I review aspects of the evolution of horizontal branch (HB) stars. I start by discussing current topics in the study of HB stellar evolution, including a brief review of the main determinants of the structure of low-mass core helium burning…

We present HR Diagrams for the massive star populations in M31 and M33 including several different types of emission-line stars: the confirmed Luminous Blue Variables (LBVs), candidate LBVs, B[e] supergiants and the warm hypergiants. We…

We explore the effects of mergers on the evolution of massive early-type galaxies by modeling the evolution of their stellar populations in a hierarchical context. We investigate how a realistic red sequence population set up by z~1 evolves…